Image summary: This is a photograph. The image depicts a surgical team consisting of several medical professionals wearing sterile gowns, caps, masks, and protective eyewear while performing a procedure on a patient in an operating room. The scene shows the surgeons focused on the surgical site, utilizing medical instruments and specialized equipment under bright overhead surgical lights. It can be inferred that the team is following strict aseptic protocols to maintain a sterile environment and is engaged in a complex medical intervention requiring coordinated teamwork.

The Genital (Reproductive) Systems

The Genital Systems and Homeostasis

The male and female genital organs work together to produce offspring. In addition, the female genital organs contribute to sustaining the growth of embryos and fetuses.

Humans produce offspring by a process called sexual reproduction in which haploid sperm produced by the testes of males fertilize the haploid secondary oocytes produced by the ovaries of females. As a result of fertilization, the resulting diploid cell is called a zygote and contains one set of chromosomes from each parent. Males and females have anatomically distinct genital organs that are designed to produce, nourish, and transport the haploid cells, facilitate fertilization and, in females, sustain the growth of the embryo and fetus.

28.1 Male Genital (Reproductive) System

Objectives

• Describe the location, structure, and functions of the organs of the male genital system.

• Discuss the process of spermatogenesis in the testes.

The male and female genital organs can be grouped by function. The gonads—testes in males and ovaries in females—produce gametes and secrete sex hormones. Various ducts then store and transport the gametes, and accessory male genital glands produce substances that protect the gametes.

Figure 28.1 Male Genital Organs and Surrounding Structures.

Genital organs are adapted for producing new individuals and passing on genetic material from one generation to the next. and facilitate their movement. Finally, supporting structures, such as the penis in males and the uterus in females, assist the delivery of gametes, and the uterus is also the site for the growth of the embryo and fetus during pregnancy.

The organs of the male genital system include the testes, a system of ducts (epididymis, ductus deferens, ejaculatory ducts, and urethra), accessory male genital glands (seminal glands, prostate, and bulbourethral glands), and several supporting structures, including the scrotum and the penis (Figure 28.1). The testes (male gonads) produce sperm and secrete hormones. The duct system transports and stores sperm, assists in their maturation, and conveys them to the exterior. Semen contains sperm plus the secretions provided by the accessory male genital glands.

Figure 28.1 summary: This figure is an anatomical diagram. It provides a sagittal cross-section of the male reproductive and urinary systems, labeling key internal and external structures including the urinary bladder, prostate, seminal glands, ductus deferens, testis, epididymis, and the various sections of the urethra and penis. The diagram illustrates the spatial relationship and connectivity between the organs responsible for urine excretion and sperm transport.

The supporting structures have various functions. The penis delivers sperm into the female genital tract and the scrotum supports the testes.

As noted in Chapter 26, urology urology is the study of the urinary system. Urologists also diagnose and treat

Functions of the Male Genital System

1. The testes produce sperm and the male sex hormone testosterone.

2. The ducts transport, store, and assist in maturation of sperm.

3. The accessory male genital glands secrete most of the liquid portion of semen.

4. The penis contains the urethra, a passageway for ejaculation of semen and excretion of urine.

The scrotum consists of loose skin and an underlying subcutaneous tissue and supports the testes.

Which muscles help regulate the temperature of the testes?

The seminiferous tubules contain two types of cells: spermatogonia, the sperm-forming cells, and nurse cells, which have several functions in supporting spermatogenesis (Figure 28.4). Spermatogonia (sper'-ma-to-Go-ne-a; -gonia = offspring; singular is spermatogonium) are stem cells that develop from primordial germ cells primordial = primitive or early form) and arise from the umbilical vesicle and enter the testes during the fifth week of development. In the embryonic testes, the primordial germ cells differentiate into spermatogonia, which remain dormant during childhood and actively begin producing sperm at puberty. Toward the lumen of the seminiferous tubule are layers of progressively more mature cells. In order of advancing maturity, these are primary spermatocytes, secondary spermatocytes, spermatids, and sperm. After a sperm, or spermatozoon (sper'-ma-to-Zo-on; zoom = life), has formed, it is released into the lumen of the seminiferous tubule. (The plural terms are sperm and spermatozoa.)

Figure 28.4 summary: This figure consists of a detailed anatomical diagram and a scanning electron micrograph. The images illustrate a transverse section of a seminiferous tubule, highlighting the structural organization and the process of spermatogenesis. The diagram identifies key components including the basement membrane, blood capillaries, interstitial endocrine cells, and nurse cells, while the micrograph provides a high-magnification view of the tubule's interior. The figures demonstrate the progression of spermatogenic cells from diploid spermatogonia located near the basement membrane, through primary and secondary spermatocytes and spermatids, eventually becoming haploid sperm that are released into the lumen of the seminiferous tubule. It can be inferred that the blood-testis barrier, formed by tight junctions, separates the developing germ cells from the surrounding vasculature to protect them, and that the spatial arrangement of cells reflects a maturation gradient from the outer periphery toward the central lumen.

Embedded among the spermatogonia in the seminiferous tubules are large nurse cells, also called sustentacular cells or Sertoli cells (sër-TÖ-lê), which extend from the basement membrane to the lumen of the tubule. Internal to the basement membrane and spermatogonia, tight junctions join neighboring nurse cells to one another. These junctions form an obstruction known as the blood-testis barrier because substances must first pass through the nurse cells before they can reach the developing sperm.

By isolating the developing gametes from the blood, the blood-testis barrier prevents an immune response against the surface antigens of the spermatogonia, which are recognized as “foreign” by the immune system. The blood-testis barrier does not include spermatogonia.

Nurse cells support and protect developing spermatogonia cells in several ways. They nourish spermatocytes, spermatids, and sperm; phagocytoze excess spermatid cytoplasm as development proceeds; and control the release of sperm into the lumen of the seminiferous tubule. They also produce fluid for

Figure 28.3 Internal and External Anatomy of a Testis.

The testes are the male gonads, which produce haploid sperm.

Figure 28.4 Microscopic anatomy of the seminiferous tubules and stages of sperm production (spermatogenesis). Arrows indicate the progression of cells from least mature to most mature. The (n) and (2n) refer to haploid and diploid numbers of chromosomes, respectively. sperm transport, secrete the hormone inhibin, and regulate the effects of testosterone and F.S.H (follicle-stimulating hormone).

In the spaces between adjacent seminiferous tubules are clusters of cells called interstitial endocrine cells or Leydig cells (Lî-dig) (Figure 28.4). These cells secrete testosterone, the most prevalent androgen. An androgen is a hormone that promotes the development of masculine characteristics. Testosterone also promotes a man's libido (sexual drive).

Figure 28.3 summary: This figure consists of anatomical diagrams and photographs showing different views of the testis. The content includes a detailed sagittal cross-section and a lateral view, labeling key structures such as the seminiferous tubules, rete testis, epididymis, ductus deferens, spermatic cord, and various protective layers like the tunica vaginalis and tunica albuginea. The figure illustrates the internal organization of the testis, showing how seminiferous tubules lead into straight tubules and the rete testis, which then connect to the efferent ductules and the epididymis for sperm transport. It concludes that the testis is a complex organ with a hierarchical system of ducts designed to produce and transport sperm toward the spermatic cord.

Clinical Connection

Cryptorchidism

The condition in which the testes do not descend into the scrotum is called cryptorchidism cryptorchidism; crypt-= hidden; orchid = testis); it occurs in about 3% of full-term infants and about 30% of premature infants. Untreated bilateral cryptorchidism results in sterility because the cells involved in the initial stages of spermatogenesis are destroyed by the higher temperature of the pelvic cavity. The chance of testicular cancer is 30 to 50 times greater in cryptorchid testes. The testes of about 80% of boys with cryptorchidism will descend spontaneously during the first year of life. When the testes remain undescended, the condition can be corrected surgically, ideally before 18 months of age.

Spermatogenesis Before you read this section, please review the topic of reproductive cell division in Chapter 3 in Section 3.7. Pay particular attention to Figures 3.33 and 3.34.

In humans, spermatogenesis takes 65 to 75 days. It begins with the spermatogonia, which contain the diploid (2n) number of chromosomes (Figure 28.5). Spermatogonia are stem Figure 28.5 Events in spermatogenesis. Diploid cells (2n) have 46 chromosomes; haploid cells (n) have 23 chromosomes. cells; when they undergo mitosis, some spermatogonia remain near the basement membrane of the seminiferous tubule in an undifferentiated state to serve as a reservoir of cells for future cell divisions and subsequent sperm production. The rest of the spermatogonia lose contact with the basement membrane, squeeze through the tight junctions of the blood-testis barrier, undergo developmental changes, and differentiate into primary spermatocytes spermatocytes. Primary spermatocytes, like spermatogonia, are diploid (2n); that is, they have 46 chromosomes.

Figure 28.5 summary: This figure is a biological process diagram. It illustrates the stages of spermatogenesis, starting from spermatogonia located near the basement membrane of the seminiferous tubule and progressing through mitosis and meiosis to produce mature sperm cells in the lumen. The process involves the differentiation of spermatogonia into primary spermatocytes, which then undergo meiosis I to become secondary spermatocytes and meiosis II to become spermatids, followed by spermiogenesis. The diagram indicates that the process results in a reduction of chromosomal content from diploid to haploid and culminates in the transformation of round spermatids into motile sperm cells.

Shortly after it forms, each primary spermatocyte replicates its D.N.A and then meiosis begins (Figure 28.5). In meiosis I, homologous pairs of chromosomes line up at the metaphase plate, and crossing-over occurs. Then, the meiotic spindle pulls one (duplicated) chromosome of each pair to an opposite pole of the dividing cell. The two cells formed by meiosis I are called secondary spermatocytes. Each secondary spermatocyte has 23 chromosomes, the haploid number (n). Each chromosome within a secondary spermatocyte, however, is made up of two chromatids (two copies of the D.N.A) still attached by a centromere. No replication of D.N.A occurs in the secondary spermatocytes.

In meiosis Two, the chromosomes line up in single file along the metaphase plate, and the two chromatids of each chromosome separate. The four haploid cells resulting from meiosis Two are called spermatids spermatids. A single primary spermatocyte therefore produces four spermatids with the haploid number (n) via two rounds of cell division (meiosis I and meiosis 2) with the haploid number (n) .

A unique process occurs during spermatogenesis. As sperm proliferate, they fail to complete cytoplasmic separation (cytokinesis). The cells remain in contact via cytoplasmic bridges through their entire development (see Figures 28.4 and 28.5). This pattern of development most likely accounts for the synchronized production of sperm in any given area of the seminiferous tubule. It may also have survival value in that half of the sperm contain an X chromosome and half contain a Y chromosome. The larger X chromosome may carry genes needed for spermatogenesis that are lacking on the smaller Y chromosome.

The final stage of spermatogenesis, spermiogenesis spermatogenesis, is the maturation of haploid spermatids into sperm. No cell division occurs in spermiogenesis; each spermatid becomes a single sperm. During this process, spherical spermatids transform into elongated, slender sperm.

An acrosome (described shortly) forms atop the nucleus, which condenses and elongates, a flagellum develops, and mitochondria multiply. Nurse cells dispose of the excess cytoplasm that sloughs off. Finally, sperm are released from their connections to nurse cells, an event known as spermiation (sper'-mê-ô-shun).

Sperm then enter the lumen of the seminiferous tubule. Fluid secreted by nurse cells pushes sperm along their way, toward the ducts of the testes. At this point, sperm are not yet able to swim.

Sperm Each day about 300 million sperm complete the process of spermatogenesis. A sperm is about 60 μm long and contains several structures that are highly adapted for reaching and penetrating a secondary oocyte (Figure 28.6). The major parts of a sperm are the head and the tail. The flattened, pointed head of the sperm is about 4 to 5 μm long. It contains a nucleus with 23 highly condensed chromosomes. Covering the anterior two-thirds of the nucleus is the acrosome acrosome; acro-= atop; -some = body), a caplike vesicle filled with enzymes that help a sperm to penetrate a secondary oocyte to bring about fertilization.

Figure 28.6 summary: This figure is an anatomical diagram. It illustrates the structure of a human sperm cell, labeling the primary regions as the head and the tail. Within the head, the acrosome and nucleus are identified. The tail section is further divided into the neck, the middle piece containing mitochondria, the principal piece, and the end piece. The detailed labeling indicates that the sperm is specialized for motility and fertilization, with the head containing genetic material and the tail providing the propulsion necessary to reach the egg.

Among the enzymes are hyaluronidase and proteases. The tail of a sperm is subdivided into four parts: neck, middle piece, principal piece, and end piece. The centrioles form the microtubules that comprise the remainder of the tail.

The neck is the constricted region just behind the head that contains centrioles. The middle piece contains mitochondria arranged in a spiral, which provide the energy (A.T.P) for locomotion of sperm to the site of fertilization and for sperm metabolism. The principal piece is the longest portion of the tail, and the end piece is the terminal, tapering portion of the tail. Once ejaculated, most sperm do not survive more than 48 hours within the female genital tract.

Hormonal Control of Testicular Function Although the initiating factors are unknown, at puberty certain hypothalamic neurosecretory cells increase their secretion of gonadotropin-releasing hormone (GnRH) gonadotropin. This hormone in turn stimulates gonadotrophic cells in the anterior pituitary to increase their secretion of the two gonadotropins, luteinizing hormone (L.H) luteinizing and follicle-stimulating hormone (F.S.H). Figure 28.7 shows the hormones and negative feedback loops that control secretion of testosterone and spermatogenesis.

Figure 28.7 summary: This figure is a biological pathway diagram. It illustrates the hormonal regulation of the male reproductive system, specifically the hypothalamic-pituitary-gonadal axis. The diagram shows the flow of signals from the hypothalamus and anterior pituitary gland to the testes, involving the release of gonadotropin-releasing hormone, follicle-stimulating hormone, and luteinizing hormone. It details how these hormones interact with specific cells in the testes to stimulate testosterone secretion and spermatogenesis, while also depicting the negative feedback loops where testosterone and inhibin inhibit the further release of their stimulating hormones. The diagram concludes by listing the physiological effects of testosterone and dihydrotestosterone on male development and characteristics. The figure demonstrates that male reproductive function is maintained through a complex balance of stimulatory hormones and inhibitory feedback mechanisms to ensure stable hormone levels and continuous sperm production.

L.H stimulates interstitial endocrine cells, which are located between seminiferous tubules, to secrete the hormone testosterone testosterone. This steroid hormone is synthesized from cholesterol in the testes and is the principal androgen. It is lipid-soluble and readily diffuses out of interstitial cells into the interstitial fluid and then into blood. Via negative feedback, testosterone suppresses secretion of L.H by anterior pituitary gonadotrophs and suppresses secretion of GnRH by hypothalamic neurosecretory cells. In some target cells, such as those Figure 28.7 Hormonal control of spermatogenesis and actions of testosterone and dihydrotestosterone (D.H.T). In response to stimulation by F.S.H and testosterone, nurse cells secrete androgen-binding protein (A.B.P). Dashed red lines indicate negative feedback inhibition. in the external genitals and prostate, the enzyme 5 alpha-reductase converts testosterone to another androgen called dihydrotestosterone (D.H.T) dihydrotestosterone.

F.S.H acts indirectly to stimulate spermatogenesis (Figure 28.7). F.S.H and testosterone act synergistically on the nurse cells to stimulate secretion of androgen-binding protein (A.B.P) into the lumen of the seminiferous tubules and into the interstitial fluid around the spermatogonia. A.B.P binds to testosterone, keeping its concentration high. Testosterone stimulates the final steps of spermatogenesis in the seminiferous tubules. Once the degree of spermatogenesis required for male reproductive functions has been achieved, nurse cells release inhibin, a protein hormone named for its role in inhibiting F.S.H secretion by the anterior pituitary (Figure 28.7). If spermatogenesis is proceeding too slowly, less inhibin is released, which permits more F.S.H secretion and an increased rate of spermatogenesis.

Testosterone and dihydrotestosterone both bind to the same androgen receptors, which are found within the nuclei of target cells. The hormone–receptor complex regulates gene expression, turning some genes on and others off. Because of these changes, the androgens produce several effects:

• Prenatal development. Before birth, testosterone stimulates the male pattern of development of genital system ducts and the descent of the testes. Dihydrotestosterone stimulates development of the external genitals (described in Section 28.6). Testosterone also is converted in the brain to estrogens (feminizing hormones), which may play a role in the development of certain regions of the brain in males.

• Development of male sexual characteristics. At puberty, testosterone and dihydrotestosterone bring about development and enlargement of the male sex organs and the development of masculine secondary sexual characteristics. Secondary sex characteristics are traits that distinguish males and females but do not have a direct role in reproduction. These include muscular and skeletal growth that results in wide shoulders and narrow hips; facial and chest hair (within hereditary limits) and more hair on other parts of the body; thickening of the skin; increased sebaceous gland secretion; and enlargement of the larynx and consequent deepening of the voice.

• Development of sexual function. Androgens contribute to male sexual behavior and spermatogenesis and to sex drive (libido) in both males and females. Recall that the suprarenal cortex is the main source of androgens in females.

• Stimulation of anabolism. Androgens are anabolic hormones; that is, they stimulate protein synthesis. This effect is obvious in the heavier muscle and bone mass of most men as compared to women.

A negative feedback system regulates testosterone production (Figure 28.8). When testosterone concentration in the blood increases to a certain level, it inhibits the release of GnRH by cells in the hypothalamus. As a result, there is less GnRH in the portal blood that flows from the hypothalamus to the anterior pituitary. Gonadotrophic cells in the anterior pituitary then release less L.H, so the concentration of L.H in systemic blood falls. With less stimulation by L.H, the interstitial endocrine cells in the testes secrete less testosterone, and there is a return to homeostasis. If the testosterone

Figure 28.8 summary: This figure is a flow chart illustrating a biological feedback loop. It describes the negative feedback mechanism regulating the blood level of testosterone, starting from a stimulus that increases testosterone levels, which then triggers receptors in the hypothalamus to decrease the secretion of GnRH. This input leads the control center in the anterior pituitary to reduce the output of luteinizing hormone, which subsequently signals the effectors in the testes to secrete less testosterone. The conclusion is that this process results in a decrease in blood testosterone levels, returning the system to homeostasis.

Figure 28.8 Negative Feedback Control of Blood Level of Testosterone.

Which Hormones Inhibit Secretion of F.S.H and L.H by the Anterior Pituitary?

concentration in the blood falls too low, however, GnRH is again released by the hypothalamus and stimulates secretion of L.H by the anterior pituitary. L.H in turn stimulates testosterone production by the testes.

1. Describe the function of the scrotum in protecting the testes from temperature fluctuations.

2. Describe the internal structure of a testis. Where are sperm produced? What are the functions of nurse cells and interstitial endocrine cells?

3. Describe the principal events of spermatogenesis.

4. Which part of a sperm contains enzymes that help the sperm fertilize a secondary oocyte?

5. What are the roles of F.S.H, L.H, testosterone, and inhibin in the male genital system? How is secretion of these hormones controlled?

Genital System Ducts in Males

Ducts of the Testis Pressure generated by the fluid secreted by nurse cells pushes sperm and fluid along the lumen of seminiferous tubules and then into a series of very short ducts called straight tubules (see Figure 28.3a). The straight tubules lead to a system of ducts in the testis called the retestis (RÉ-tê = network). From the retestis, sperm move into a series of coiled efferent ductules efferent in the epididymis that empty into a single tube called the duct of epididymis.

Epididymis The epididymis epididymis; epi-= above or over; -didymis = testis) is an organ about 4 centimeters (1.5 in.) long that curves along the superior and posterior border of each testis, having a comma shape in profile (see Figure 28.3a). The plural is epididymides epididymis. Each epididymis consists mostly of the tightly coiled duct of epididymis. The efferent ductules from the testis join the duct of epididymis at the larger, superior portion of the epididymis called the head of epididymis. The body of epididymis is the narrow midportion of the epididymis, and the tail is the smaller, inferior portion. At its distal end, the tail of the epididymis continues as the ductus deferens (discussed shortly).

The duct of epididymis would measure about 3 to 4 m (10 to 13 ft) in length if it were uncoiled. It is lined with pseudostratified columnar epithelium and encircled by layers of smooth muscle. The free surfaces of the columnar cells contain stereocilia stereocilia, which despite their name are long, branching microvilli (not cilia) that increase the surface area for the reabsorption of degenerated sperm. Connective tissue around the muscular layer attaches the loops of the duct of epididymis and carries blood vessels and nerves.

Functionally, the epididymis is the site of sperm maturation, the process by which sperm acquire motility and the ability to fertilize an ovum. This occurs over a period of about 14 days. The epididymis also helps propel sperm into the ductus deferens during sexual arousal by peristaltic contraction of its smooth muscle. In addition, the epididymis stores sperm, which remain viable here for up to several months. Any stored sperm that are not ejaculated by that time are eventually reabsorbed.

Ductus Deferens Within the tail of the epididymis, the duct of epididymis becomes less convoluted, and its diameter increases. Beyond this point, the duct is known as the ductus deferens or vas deferens deference (see Figure 28.3a). The ductus deferens, which is about 45 centimeters (18 in.) long, ascends along the posterior border of the epididymis through the spermatic cord and then enters the pelvic cavity. There it loops over the ureter and passes over the side and down the posterior surface of the urinary bladder (see Figure 28.1a). The dilated terminal portion of the ductus deferens is the ampulla ampulla = little jar; see Figure 28.9). The mucosa of the ductus deferens consists of pseudostratified columnar epithelium and lamina propria (areolar connective tissue). The muscular layer is composed of three layers of smooth muscle; the inner and outer layers are longitudinal, and the middle layer is circular.

Figure 28.9 summary: This figure consists of an anatomical illustration and a corresponding cadaveric photograph. The images display the male reproductive and urinary systems, highlighting organs such as the urinary bladder, prostate, seminal glands, and the various sections of the urethra and ductus deferens, as well as surrounding structures like the hip bone and pelvic muscles. The figure demonstrates the spatial arrangement and connectivity of the male internal genitalia, showing how the ductus deferens and seminal glands converge to form the ejaculatory ducts that pass through the prostate into the urethra. This illustrates the integrated pathway for transporting gametes and secretions from the reproductive glands to the external environment.

Functionally, the ductus deferens conveys sperm during sexual arousal from the epididymis toward the urethra by peristaltic contractions of its muscular layer. Like the epididymis, the ductus deferens also can store sperm for several months. Any stored sperm that are not ejaculated by that time are eventually reabsorbed.

Spermatic Cord The spermatic cord is a supporting structure of the male genital system that ascends out of the scrotum (see Figure 28.2). Each spermatic cord consists of a ductus deferens as it ascends through the scrotum, the testicular artery, veins that drain the testis and carry testosterone into circulation (the pampiniform plexus), autonomic nerves, lymphatic vessels, and the cremaster muscle. The spermatic cord and ilioinguinal nerve pass through the inguinal canal inguinal = groin), an oblique passageway in the anterior abdominal wall just superior and parallel to the medial half of the inguinal ligament. The canal, which is about 4 to 5 centimeters (about 2 in.) long, originates at the deep (abdominal) inguinal ring, a slitlike opening in the aponeurosis of the transversus abdominis muscle; the canal ends at the superficial (subcutaneous) inguinal ring (see Figure 28.2), a somewhat triangular opening in the aponeurosis of the external oblique muscle. In females, the round ligament of the uterus and ilioinguinal nerve pass through the inguinal canal.

Figure 28.2 summary: This is an anatomical diagram. The figure illustrates the internal structures of the male reproductive system, specifically detailing the contents of the inguinal canal, the composition of the spermatic cord, the anatomy of the scrotum, and a transverse section of the penis. It identifies various muscles, ligaments, vessels, nerves, and ducts, including the ductus deferens, testicular artery, and the various layers of fascia. The diagram demonstrates the complex arrangement of supportive tissues and the pathway of the spermatic cord from the superficial inguinal ring down to the testis. It concludes that the male reproductive anatomy involves multiple protective layers of muscle and fascia that secure and regulate the position of the testes and the structural integrity of the penis.

The term varicocele varicocele; varico-= varicose; -kele = hernia) refers to a swelling in the scrotum due to a dilation of the veins that drain the testes. It is usually more apparent when the person is standing and typically does not require treatment.

Ejaculatory Ducts Each ejaculatory duct ejaculatory; ejacul-= to expel) is about 2 centimeters (1 in.) long and is formed by the union of the duct from the seminal gland and the ampulla of the ductus deferens (Figure 28.9). The short ejaculatory ducts form just superior to the base (superior portion) of the prostate and pass inferiorly and anteriorly through the prostate. They terminate in the prostatic urethra, where they eject sperm and seminal gland secretions just before the release of semen from the urethra to the exterior.

Urethra In males, the urethra (ü-Re-thra) is the shared terminal duct of the genital and urinary systems; it serves as a passageway for both semen and urine. About 20 centimeters (8 in.) long, it passes through the prostate, the deep muscles of the perineum, and the penis, and is subdivided into three parts (see Figures 28.1 and 26.22). The prostatic urethra prostatic is 2 to 3 centimeters (1 in.) long and passes through the prostate. As this duct continues inferiorly, it passes through the deep muscles of the perineum, where it is known as the membranous urethra membranous. The membranous urethra is about 1 centimeters (0.5 in.)

Figure 28.9 Locations of Several Accessory Male Genital Glands. The Prostate, Urethra, and Penis Have Been Sectioned to Show Internal Details.

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Functions of Accessory Male Genital Gland Secretions

1. The seminal glands secrete seminal fluid, an alkaline, viscous fluid that helps neutralize acid in the female genital tract, provides fructose for A.T.P production by sperm, contributes to sperm motility and viability, and helps semen coagulate after ejaculation.

2. The prostate secretes prostatic fluid, a milky, slightly acidic fluid that contains enzymes that

break down clotting proteins from the seminal glands.

3. The bulbourethral glands secrete an alkaline fluid that neutralizes the acidic environment of the urethra and mucus that lubricates the lining of the urethra and the tip of the penis during sexual intercourse.

in length. As this duct passes through the corpus spongiosum of the penis, it is known as the spongy urethra, which is about 15 to 20 centimeters (6 to 8 in.) long. The spongy urethra ends at the external urethral orifice. The histology of the male urethra may be reviewed in Section 26.8.

Checkpoint

6. Which ducts transport sperm within the testes?

7. Describe the location, structure, and functions of the duct of epididymis, ductus deferens, and ejaculatory duct.

8. Give the locations of the three subdivisions of the male urethra.

9. Trace the course of sperm through the system of ducts from the seminiferous tubules to the urethra.

10. List the structures within the spermatic cord.

Accessory Male Genital Glands

The ducts of the male genital system store and transport sperm, but the accessory male genital glands secrete most of the liquid portion of semen. The accessory male genital glands include the seminal glands, the prostate, and the bulbourethral glands.

Seminal Glands The paired seminal glands or seminal vesicles are convoluted pouchlike structures, about 5 centimeters (2 in.) in length, lying posterior to the base of the urinary bladder and anterior to the rectum (Figure 28.9). Through the seminal gland ducts, the seminal glands secrete seminal fluid, an alkaline, viscous fluid that contains fructose (a monosaccharide sugar), prostaglandins, and clotting proteins that are different from those in blood. The alkaline nature of the seminal fluid helps to neutralize the acidic environment of the male urethra and female genital tract that otherwise would inactivate and kill sperm. The fructose is used for A.T.P production by sperm. Prostaglandins contribute to sperm motility and viability and may stimulate smooth muscle contractions within the female genital tract. The clotting proteins help semen coagulate after ejaculation.

It is thought that coagulation occurs in order to keep sperm from leaking from the vagina. Fluid secreted by the seminal glands normally constitutes about 60% of the volume of semen.

Prostate The prostate prostate; prostata = one who stands before) is a single, doughnut-shaped gland about the size of a golf ball. It measures about 4 centimeters (1.6 in.) from side to side, about 3 centimeters (1.2 in.) from top to bottom, and about 2 centimeters (0.8 in.) from front to back. It is inferior to the urinary bladder and surrounds the prostatic urethra (Figure 28.9). The prostate slowly increases in size from birth to puberty. It then expands rapidly until about age 30, after which time its size typically remains stable until about age 45, when further enlargement may occur, constricting the urethra and interfering with urine flow.

The prostate secretes prostatic fluid a milky, slightly acidic fluid (pH about 6.5) that contains several substances. Citric acid in prostatic fluid is used by sperm for A.T.P production via the Krebs cycle. Several proteolytic enzymes, such as prostate-specific antigen (P.S.A), pepsinogen, lysozyme, amylase, and hyaluronidase, eventually break down the clotting proteins from the seminal glands. The function of the acid phosphatase secreted by the prostate is unknown. Seminal plasmin in prostatic fluid is an antibiotic that can destroy bacteria. Seminal plasmin may help decrease the number of naturally occurring bacteria in semen and in the lower female genital tract. Secretions of the prostate enter the prostatic urethra through many prostatic ducts. Prostatic secretions make up about 25% of the volume of semen and contribute to sperm motility and viability.

Bulbourethral Glands The paired bulbourethral glands (bul'-bo-u-Re-thral), or Cowper's glands Cowpers, are about the size of peas. They are located inferior to the prostate on either side of the membranous urethra within the deep muscles of the perineum, and their ducts open into the spongy urethra (Figure 28.9). During sexual arousal, the bulbourethral glands secrete an alkaline fluid into the urethra that protects the passing sperm by neutralizing acids from urine in the urethra. They also secrete mucus that lubricates the end of the penis and the lining of the urethra, decreasing the number of sperm damaged during ejaculation. Some males release a drop or two of this mucus upon sexual arousal and erection. The fluid does not contain sperm.

Semen

Semen (= seed) is a mixture of sperm and seminal fluid, a liquid that consists of the secretions of the seminiferous tubules, seminal glands, prostate, and bulbourethral glands. The volume of semen in a typical ejaculation is 2.5 to 5 milliliters (mL), with 50 to 150 million sperm per mL. When the number falls below 20 million/mL, the male is likely to be infertile. A very large number of sperm is required for successful fertilization because only a tiny fraction ever reaches the secondary oocyte, whereas too many sperm without sufficient dilution from seminal fluid results in infertility because the sperm tails tangle and lose mobility.

Despite the slight acidity of prostatic fluid, semen still has a slightly alkaline pH of 7.2 to 7.7 due to the higher pH and larger volume of fluid from the seminal glands. The prostatic fluid gives semen a milky appearance, and fluids from the seminal glands and bulbourethral glands give it a sticky consistency. Seminal fluid provides sperm with a transportation medium, nutrients, and protection from the hostile acidic environment of the male's urethra and the female's vagina.

Once ejaculated, liquid semen coagulates within 5 minutes due to the presence of clotting proteins from the seminal glands. The functional role of semen coagulation is not known, but the proteins involved are different from those that cause blood coagulation. After about 10 to 20 minutes, semen reliquefies because prostate-specific antigen (P.S.A) and other proteolytic enzymes produced by the prostate break down the clot.

Abnormal or delayed liquefaction of clotted semen may cause complete or partial immobilization of sperm, thereby inhibiting their movement through the cervix of the uterus. After passing through the uterus and uterine tube, the sperm are affected by secretions of the uterine tube in a process called capacitation (see Section 28 point 2). The presence of blood in semen is called hemospermia hemospermia; hemo equals blood; -sperma equals seed). In most cases, it is caused by inflammation of the blood vessels lining the seminal glands; it is usually treated with antibiotics.

Penis

The penis (= tail) contains the part of the spongy urethra and is a passageway for the ejaculation of semen and the excretion of urine (Figure 28.10). It is cylindrical in shape and consists of a body, glans penis, and a root. The body of the penis is composed of three cylindrical masses of tissue, each surrounded by dense irregular connective tissue called the tunica albuginea (Figure 28.10). The two dorsolateral masses are called the corpora cavernosa penis (corpora = main bodies; cavernosa = hollow). The smaller midventral mass, the corpus spongiosum penis, contains the spongy urethra and keeps it open during ejaculation. Skin and a subcutaneous tissue enclose all three masses, which consist of erectile tissue. Erectile tissue is composed of numerous blood sinuses (vascular spaces) lined by endothelial cells and surrounded by smooth muscle and elastic connective tissue.

The distal end of the corpus spongiosum penis is a slightly enlarged, acorn-shaped region called the glans penis; its margin is the corona (ko-Ro-na). The distal urethra enlarges within the glans penis and forms a terminal slitlike opening, the external urethral orifice. Covering the glans in an uncircumcised penis is the loosely fitting prepuce prepuce, or foreskin. This can be removed in a surgical procedure called circumcision.

The root of the penis is the attached portion (proximal portion). It consists of the bulb of the penis, the expanded posterior continuation of the base of the corpus spongiosum penis, and the crura of the penis crura; singular is crus = resembling a leg), the two separated and tapered portions of the corpora cavernosa penis. The bulb of the penis is attached to the inferior surface of the deep muscles of the perineum and is enclosed by the bulbospongiosus muscle, a muscle that aids ejaculation. Each crus of the penis bends laterally away from the bulb of the penis to attach to the ischial and inferior pubic rami and is surrounded by the ischiocavernosus muscle (see Figure 11.13). The weight of the penis is supported by two ligaments that are continuous with the fascia of the penis. The fundiform ligament fundiform arises from the inferior part of the linea alba. The suspensory ligament of the penis arises from the pubic symphysis.

Upon sexual stimulation, parasympathetic fibers from the sacral portion of the spinal cord initiate and maintain an erection, the enlargement and stiffening of the penis. The parasympathetic fibers produce and release nitric oxide (no). The no causes smooth muscle in the walls of arterioles supplying erectile tissue to dilate (relax). This in turn causes large amounts of blood to enter the erectile tissue of the penis.

no also causes the smooth muscle within the erectile tissue to relax, resulting in widening of the blood sinuses. The combination of increased blood flow and widening of the blood sinuses results in an erection. Expansion of the blood sinuses also compresses the Figure 28.10 Internal structure of the penis and the mechanism of erection. The inset in (b) shows details of the skin and fasciae.

The penis contains the urethra, a common pathway for semen and urine.

Clinical Connection

Circumcision (= to cut around) is a surgical procedure in which part of or the entire prepuce (foreskin) is removed. It is usually performed just after delivery or several days after birth, and is done for social, cultural, religious, and (more rarely) medical reasons. Although most health-care professionals find no medical justification for circumcision, some feel that it has benefits, such as a lower risk of urinary tract infections, protection against penile cancer, and possibly a lower risk for sexually transmitted diseases. Indeed, studies in several African villages have found lower rates of H.I.V infection among circumcised men.

Figure 28.10 Continued veins that drain the penis; the slowing of blood outflow helps to maintain the erection. The insertion of the erect penis into the vagina is called heterosexual sexual intercourse or coitus (KÖ-i-tus). A major stimulus for erection is mechanical stimulation of the penis. Mechanoreceptors provide direct input to the erection-integrating center in the spinal cord.

Erotic sights, sounds, smells, and thoughts can also stimulate erection. This involves descending inputs from the brain (hypothalamus and limbic system) to the spinal cord. Negative stimuli (a bad mood, depression, anxiety, etcetera) can also inhibit erection through these descending pathways.

The term priapism priapism refers to a persistent and usually painful erection of the penis that does not involve sexual desire or excitement. The condition may last up to several hours and is accompanied by pain and tenderness. It results from abnormalities of blood vessels and nerves, usually in response to medication used to produce erections in males who otherwise cannot attain them. Other causes include a spinal cord disorder, leukemia, sickle-cell disease, or a pelvic tumor.

Ejaculation ejaculation, the powerful release of semen from the urethra to the exterior, is a sympathetic reflex coordinated by the lumbar portion of the spinal cord. As part of the reflex, the smooth muscle sphincter at the base of the urinary bladder closes, preventing urine from being expelled during ejaculation, and semen from entering the urinary bladder. Even before ejaculation occurs, peristaltic contractions in the epididymis, ductus deferens, seminal glands, ejaculatory ducts, and prostate propel semen into the spongy urethra.

Typically, this leads to emission emission, the discharge of a small volume of semen before ejaculation. Emission may also occur during sleep (nocturnal emission). The musculature of the penis (bulbospongiosus, ischiocavernosus, and superficial transverse perineal muscles), which is supplied by the pudendal nerves, also contracts at ejaculation (see Figure 11.13).

Once sexual stimulation of the penis has ended, the arterioles supplying the erectile tissue of the penis constrict and the smooth muscle within erectile tissue contracts, making the blood sinuses smaller. This relieves pressure on the veins supplying the penis and allows the blood to drain through them. Consequently, the penis returns to its flaccid (relaxed) state.

Clinical Connection

Premature Ejaculation

A premature ejaculation is ejaculation that occurs too early, for example, during foreplay or on or shortly after penetration. It is usually caused by anxiety, other psychological causes, or an unusually sensitive foreskin or glans penis. For most males, premature ejaculation can be overcome by various techniques (such as squeezing the penis between the glans penis and shaft as ejaculation approaches), behavioral therapy, or medication.

11. Briefly explain the locations and functions of the seminal glands, prostate, and bulbourethral glands.

12. What is semen? What is its function?

13. Explain the physiological processes involved in erection and ejaculation.

28.2 Female Genital (Reproductive) System

Objectives

- Describe the location, structure, and functions of the organs of the female genital system.

• Discuss the process of oogenesis in the ovaries.

The organs of the female genital system (Figure 28.11) include the ovaries (female gonads); the uterine tubes, or oviducts; the uterus; the vagina; and external organs, which are collectively called the vulva. The mammary glands are considered part of both the integumentary system and the female genital system. Gynecology gynecology; gyneco-= woman; -logy = study of) is the specialized branch of medicine concerned with the diagnosis and treatment of diseases of the female genital system.

Figure 28.11 summary: This figure is an anatomical diagram. It provides a sagittal cross-section of the female pelvic region, labeling key internal and external reproductive organs as well as surrounding structures. The diagram illustrates the spatial relationships between the uterus, ovaries, uterine tubes, vagina, and clitoris, and their proximity to the urinary bladder, rectum, and pelvic bone structures such as the pubic symphysis and sacrum. The illustration demonstrates that the uterus is positioned superior to the bladder and anterior to the rectum, with the vagina serving as the canal connecting the cervix to the external environment.

Ovaries

The ovaries (= egg receptacles), which are the female gonads, are paired glands that resemble unshelled almonds in size and shape; they are homologous to the testes. (Here homologous means that two organs have the same embryonic origin.) The ovaries produce gametes, secondary oocytes that develop into mature ova (eggs) after fertilization, and hormones, including progesterone and estrogens (the female sex hormones), inhibin, and relaxin.

The ovaries, one on either side of the uterus, descend to the brim of the superior portion of the pelvic cavity during the third month of development. A series of ligaments holds them in position (Figure 28.12). The broad ligament of the uterus, which is a fold of the parietal peritoneum, attaches to the ovaries by a double-layered fold of peritoneum called the mesovarium (mez'-ô-VÃ-rê-um). The ovarian ligament anchors the ovaries to the uterus, and the suspensory ligament attaches them to the pelvic wall. Each ovary contains a hilum (Hî-lum), the point of entrance and exit for blood vessels and nerves along which the mesovarium is attached.

Figure 28.12 summary: This is an anatomical diagram showing a transverse cross-section of the female pelvic region. The figure illustrates the spatial relationship between various internal organs and supporting structures, including the uterus, urinary bladder, ovaries, uterine tubes, and parts of the digestive system such as the cecum, appendix, ileum, and sigmoid colon. It also identifies several key ligaments and blood vessels that support and supply the pelvic organs. The arrangement shows that the urinary bladder is located most anteriorly, followed by the uterus, with the digestive organs positioned posteriorly and laterally. This layout demonstrates how the female reproductive organs are centrally located and supported by a complex network of ligaments, while being closely integrated with the urinary and gastrointestinal systems.

Histology of the Ovary Each ovary consists of the following parts (Figure 28.13):

Figure 28.13 summary: This figure consists of an anatomical diagram and a scanning electron micrograph. The diagram provides a detailed cross-section of an ovary in the coronal plane, labeling various structures including the ovarian mesothelium, tunica albuginea, ovarian cortex, and ovarian medulla. It illustrates the progression of follicle development from primordial and primary stages to secondary and tertiary ovarian follicles, as well as the subsequent stages of the ovarian cycle, such as the corpus hemorrhagicum, corpus luteum, degenerating corpus luteum, and corpus albicans. The accompanying micrograph provides a high-magnification view of the ovarian cortex, showing multiple ovarian follicles embedded within the tissue. Together, the images demonstrate the spatial organization of the ovary and the cyclical nature of follicular maturation and degeneration, highlighting the transition from immature follicles to the release of a secondary oocyte during ovulation and the eventual breakdown of the luteal structures.

• The ovarian mesothelium or surface epithelium is a layer of simple epithelium (low cuboidal or squamous) that covers the surface of the ovary.

• The tunica albuginea is a whitish capsule of dense irregular connective tissue located immediately deep to the ovarian mesothelium.

Figure 28.11 Female Genital Organs and Surrounding Structures.

The female genital organs include the ovaries, uterine tubes, uterus, vagina, vulva, and mammary glands.

Functions of the Female Genital System

1. The ovaries produce secondary oocytes and hormones, including progesterone and estrogens (female sex hormones), inhibin, and relaxin.

2. The uterine tubes transport a secondary oocyte to the uterus and normally are the sites where fertilization occurs.

3. The uterus is the site of implantation of a fertilized ovum, development of the fetus during pregnancy, and labor.

4. The vagina receives the penis during sexual intercourse and is a passageway for childbirth.

5. The mammary glands synthesize, secrete, and eject milk for nourishment of the newborn.

• The ovarian cortex is a region just deep to the tunica albuginea. It consists of ovarian follicles (described shortly) surrounded by dense irregular connective tissue that contains collagen fibers and fibroblast-like cells called stromal cells.

• The ovarian medulla is deep to the ovarian cortex. The border between the cortex and medulla is indistinct, but the medulla consists of more loosely arranged connective tissue and contains blood vessels, lymphatic vessels, and nerves.

• Ovarian follicles (folliculus = little bag) are in the cortex and consist of oocytes (Ö-ö-sits) in various stages of development, plus the cells surrounding them. Oocytes are immature ova (egg cells). When the surrounding cells form a single layer, they are called follicular cells follicular; later in development, when they form several layers, they are referred to as granulosa cells (gran'-u-LÖ-sa). The surrounding cells nourish the developing oocyte and begin to secrete estrogens as the ovarian follicle grows larger.

• A tertiary ovarian follicle, also called a vesicular or Graafian follicle Graafian is a large, fluid-filled ovarian follicle that is ready to rupture and expel its secondary oocyte, a process known as ovulation (ov'-û-LÃ-shun).

• A corpus luteum (= yellow body) contains the remnants of tertiary ovarian follicle after ovulation. The corpus luteum produces progesterone, estrogens, relaxin, and inhibin until it degenerates into fibrous scar tissue called the corpus albicans albicans = white body).

Image summary: This figure is an anatomical diagram. It displays a sagittal section of the female pelvic region, labeling various internal and external reproductive and excretory organs including the uterus, ovaries, bladder, rectum, and external genitalia. The labels indicate the spatial relationship between the urinary, reproductive, and digestive systems within the pelvic cavity.

Which structures in males are homologous to the ovaries, the clitoris, the paraurethral glands, and the greater vestibular glands?

Figure 28.12 Relative Positions of the Ovaries, the Uterus, and the Ligaments That Support Them.

Ligaments holding the ovaries in position are the mesovarium, the ovarian ligament, and the suspensory ligament.

Figure 28.13 Histology of the ovary. The arrows indicate the sequence of developmental stages that occur as part of the maturation of an ovum during the ovarian cycle.

The ovaries are the female gonads; they produce haploid oocytes.

Oogenesis and Follicular Development

formation of gametes in the ovaries is termed oogenesis oogenesis; oo-= egg). In contrast to spermatogenesis, which begins in males at puberty, oogenesis begins in females before they are even born. Oogenesis occurs in essentially the same manner as spermatogenesis; meiosis (see Chapter 3) takes place and the resulting germ cells undergo maturation.

During early fetal development, primordial (primitive) germ cells migrate from the umbilical vesicle to the ovaries. There, germ cells differentiate within the ovaries into oogonia (o-o-Go-ne-a; singular is oogonium). Oogonia are diploid (2n) stem cells that divide mitotically to produce millions of germ cells. Even before birth, most of these germ cells degenerate in a process known as atresia atresia. A few, however, develop into larger cells called primary oocytes that enter prophase of meiosis I during fetal development but do not complete that phase until after puberty. During this arrested stage of development, each primary oocyte is surrounded by a single layer of flat follicular cells, and the entire structure is called a primordial ovarian follicle (Figure 28.14a). The ovarian cortex surrounding the primordial follicles consists of collagen fibers and fibroblast-like stromal cells. At birth, approximately 200,000 to 2,000,000 primary oocytes remain in each ovary.

Of these, about 40,000 are still present at puberty, and around 400 will mature and ovulate during a woman's reproductive lifetime. The remainder of the primary oocytes undergo atresia.

Each month after puberty until menopause, gonadotropins (F.S.H and L.H) secreted by the anterior pituitary further stimulate the development of several primordial ovarian follicles, although only one will typically reach the maturity needed for ovulation. A few primordial ovarian follicles start to grow, developing into primary ovarian follicles (Figure 28.14b). Each primary ovarian follicle consists of a primary oocyte that is surrounded in a later stage of development by several layers of cuboidal and low-columnar cells called granulosa cells. The outermost granulosa cells rest on a basement membrane. As the primary ovarian follicle grows, it forms a clear glycoprotein layer called the zona pellucida pellucida between the primary oocyte and the granulosa cells. In addition, stromal cells surrounding the basement membrane begin to form an organized layer called the theca folliculi theca follicle.

With continuing maturation, a primary ovarian follicle develops into a secondary follicle (Figure 28.14c). In a secondary ovarian follicle, the theca differentiates into two layers:

Figure 28.14 Ovarian Follicles.

(1) the theca interna, a highly vascularized internal layer of cuboidal secretory cells that secrete androgens, and the theca externa, an outer layer of stromal cells and collagen fibers. In addition, the granulosa cells begin to secrete follicular fluid, which builds up in a cavity called the antrum in the center of the secondary ovarian follicle. The innermost layer of granulosa cells becomes firmly attached to the zona pellucida and is now called the corona radiata (corona = crown; radiata = radiating) (Figure 28.14c).

The secondary ovarian follicle eventually becomes larger, turning into a tertiary ovarian follicle (Figure 28.14d). While in this ovarian follicle, and just before ovulation, the diploid primary oocyte completes meiosis I, producing two haploid (n) cells of unequal size—each with 23 chromosomes (Figure 28.15). The smaller cell produced by meiosis I, called the first polar body, is essentially a packet of discarded nuclear material. The larger cell, known as the secondary oocyte, receives most of the cytoplasm. Once a secondary oocyte is formed, it begins meiosis Two but then stops in metaphase. The tertiary follicle soon ruptures and releases its secondary oocyte, a process known as ovulation.

At ovulation, the secondary oocyte is expelled into the pelvic cavity together with the first polar body and corona radiata. Normally these cells are swept into the uterine tube. If fertilization does not occur, the cells degenerate.

If sperm are present in the uterine tube and one penetrates the secondary oocyte, however, meiosis Two resumes. The secondary oocyte splits into two haploid cells, again of unequal size. The larger cell is the ovum (ootid), or mature egg; the smaller one is the second polar body. The nuclei of the sperm and the ovum then unite, forming a diploid zygote.

If the first polar body undergoes another division to produce two polar bodies, then the primary oocyte ultimately gives rise to three haploid polar bodies, which all degenerate, and a single haploid ovum. Thus, one primary oocyte gives rise to a single gamete (an ovum). By contrast, recall that in males one primary spermatocyte produces four gametes (sperm).

Figure 28.14 summary: This figure consists of a series of anatomical diagrams and light micrographs. The content illustrates the progressive stages of ovarian follicle development, moving from primordial and primary follicles to secondary and tertiary follicles, while also showing their arrangement within the ovarian cortex and a detailed view of a mature follicle. The sequence demonstrates that as a follicle matures, it increases in size and complexity, characterized by the proliferation of granulosa cells, the formation of the theca folliculi, and the eventual development of a fluid filled cavity called the antrum. It can be concluded that follicular maturation involves a systematic transition from a simple structure to a complex multicellular unit designed to support the primary oocyte.

Clinical Connection

Ovarian Cysts

Ovarian cysts are fluid-filled sacs in or on an ovary. Such cysts are relatively common, are usually noncancerous, and frequently disappear on their own. Cancerous cysts are more likely to occur in women over 40. Ovarian cysts may cause pain, pressure, a dull ache, or fullness in the abdomen; pain during sexual intercourse; delayed, painful, or irregular menstrual periods; abrupt onset of sharp pain in the lower abdomen; and/or vaginal bleeding. Most ovarian cysts require no treatment, but larger ones (more than 5 centimeters or 2 in.) may be removed surgically.

Figure 28.15 Oogenesis. Diploid cells (2n) have 46 chromosomes; haploid cells (n) have 23 chromosomes.

Q How does the age of a primary oocyte in a female compare with the age of a primary spermatocyte in a male?

Table 28.1 summarizes the events of oogenesis and follicular development.

16. Describe the principal events of oogenesis.

Uterine Tubes

Females have two uterine tubes, also called fallopian tubes or oviducts, that extend laterally from the uterus (Figure 28.16). The tubes, which measure about 10 centimeters (4 in.) long, lie within the folds of the broad ligaments of the uterus. They provide a route for sperm to reach an ovum and transport secondary oocytes and fertilized ova from the ovaries to the uterus. The funnel-shaped portion of each tube, called the infundibulum infundibulum, is close to the ovary but is open to the pelvic cavity.

It ends in a fringe of fingerlike projections called fimbriae fimbriae = fringe), one of which is attached to the lateral end of the ovary. From the infundibulum, the uterine tube extends medially and eventually inferiorly and attaches to the superior lateral angle of the uterus. The ampulla ampulla of the uterine tube is the widest, longest portion, making up about the lateral two-thirds of its length.

The isthmus isthmus of the uterine tube is the more medial, short, narrow, thick-walled portion that joins the uterus.

Histologically, the uterine tubes are composed of three layers: mucosa, muscular layer, and serosa. The mucosa consists of epithelium and lamina propria (areolar connective tissue). The epithelium contains ciliated simple columnar cells, which function as a “ciliary conveyor belt” to help move a fertilized ovum (or secondary oocyte) within the uterine tube toward the uterus, and nonciliated cells called peg cells, which have microvilli and secrete a fluid that provides nutrition for the ovum (Figure 28.17). The middle layer, the muscular layer, is composed of an inner, thick, circular ring of smooth muscle and an outer, thin region of longitudinal smooth muscle.

Figure 28.17 summary: This figure consists of a series of anatomical diagrams and micrographs. The first part is a schematic illustration of the female reproductive system showing the location of a transverse plane cut through the uterine tube. The second part is a light microscopy image of a transverse section of the uterine tube epithelium, and the third part is a scanning electron microscopy image providing a surface view of the same tissue. The micrographs detail the cellular composition of the uterine tube lining, identifying the lumen, the underlying lamina propria, and the epithelial layer. The epithelium is composed of ciliated simple columnar cells and nonciliated peg cells characterized by microvilli. From these images, it can be inferred that the uterine tube epithelium is specialized for both transport and secretion. The presence of numerous cilia suggests a mechanism for moving materials through the lumen, while the interspersed peg cells indicate a secretory function within the tube.

Peristaltic contractions of the muscular layer and the ciliary action of the mucosa help move the oocyte or fertilized ovum toward the uterus. The outer layer of the uterine tubes is a serous membrane, the serosa formed by the visceral peritoneum.

After ovulation, local currents are produced by movements of the fimbriae, which surround the surface of the ovary just before ovulation occurs. These currents sweep the ovulated secondary oocyte from the peritoneal cavity into the uterine tube. A sperm usually encounters and fertilizes a secondary oocyte in the ampulla of the uterine tube, although fertilization in the peritoneal cavity is not uncommon.

Fertilization can occur up to about 24 hours after ovulation. Some hours after fertilization, the nuclear materials of the haploid ovum and sperm unite. The diploid fertilized ovum is now called a zygote and begins to undergo cell divisions while moving toward the uterus.

It arrives in the uterus 6 to 7 days after ovulation. Unfertilized secondary oocytes disintegrate.

Uterus

The uterus (womb) serves as part of the pathway for sperm deposited in the vagina to reach the uterine tubes. It is also the site of implantation of a fertilized ovum, development of the fetus during pregnancy, and labor. During reproductive cycles when implantation does not occur, the uterus is the source of menstrual flow.

Anatomy of the Uterus Situated between the urinary bladder and the rectum, the uterus is the size and shape of an inverted pear (see Figure 28.16). In females who have never been pregnant, it is about 7.5 centimeters (3 in.) long, 5 centimeters (2 in.) wide, and 2.5 centimeters (1 in.) thick. The uterus is larger in females who have recently been pregnant, and smaller (atrophied) when sex hormone levels are low, as occurs after menopause.

Anatomical subdivisions of the uterus include (1) a dome-shaped portion superior to the uterine tubes called the fundus, (2) a tapering central portion called the body, and an inferior narrow portion called the cervix that opens into the vagina. Between the body of the uterus and the cervix is the isthmus, a constricted region about 1 centimeters (0.5 in.) long. The interior of the body of the uterus is called the uterine cavity, and the interior of the cervix is called the cervical canal. The cervical canal opens into the uterine cavity at the internal os (os = mouthlike opening) and into the vagina at the external os.

Chart 28.1 summary: This figure is a flow chart illustrating the biological processes of oogenesis and follicular development across different life stages. The diagram maps the progression from the fetal period through childhood and into the period from puberty to menopause, detailing the cellular transitions of the female gamete and the corresponding growth of the ovarian follicles. It tracks the development from the oogonium to the primary oocyte, and eventually to the secondary oocyte and ovum, while simultaneously showing the maturation of primordial follicles into primary, secondary, and tertiary ovarian follicles. The chart demonstrates that oogenesis begins before birth but is paused during childhood, resuming in a cyclical manner during the reproductive years. It concludes that the completion of meiosis is dependent on fertilization, which transforms the secondary oocyte into a mature ovum, while the byproduct polar bodies eventually degenerate.

Figure 28.16 Relationship of the Uterine Tubes to the Ovaries, Uterus, and Associated

structures. In the left side of the drawing, the uterine tube and uterus have been sectioned to show internal structures.

After ovulation, a secondary oocyte and its corona radiata move from the pelvic cavity into the infundibulum of the uterine tube. The uterus is the site of menstruation, implantation of a fertilized ovum, development of the fetus, and labor.

Normally, the body of the uterus projects anteriorly and superiorly over the urinary bladder in a position called anteflexion anteflexion; ante-= before). The cervix projects inferiorly and posteriorly and enters the anterior wall of the vagina at nearly a right angle (see Figure 28.11). Several ligaments that are either extensions of the parietal peritoneum or fibromuscular cords maintain the position of the uterus (see Figure 28.12). The paired broad ligaments are double folds of peritoneum attaching the uterus to either side of the pelvic cavity. The paired uterosacral ligaments (ü'-ter-ö-SÄ-kral), also peritoneal extensions, lie on either side of the rectum and connect the uterus to the sacrum.

The cardinal (lateral cervical) ligaments are located inferior to the bases of the broad ligaments and extend from the pelvic wall to the cervix and vagina. The round ligaments are bands of dense irregular connective tissue between the layers of the broad ligament; they extend from a point on the uterus just inferior to the uterine tubes to a portion of the labia majora of the external genitals. Although the ligaments normally maintain the anteflexed position of the uterus, they also allow the uterine body enough movement that the uterus may become malpositioned.

A posterior tilting of the uterus, called retroflexion retroflexion; retro-= backward or behind), is a harmless variation of the normal position of the uterus. There is often no cause for the condition, but it may occur after childbirth.

Clinical Connection

Uterine Prolapse

A condition called uterine prolapse (prolapse = falling down or downward displacement) may result from weakening of supporting ligaments and pelvic musculature associated with age or disease, traumatic vaginal delivery, chronic straining from coughing or difficult bowel movements, or pelvic tumors. The prolapse may be characterized as first degree (mild), in which the cervix remains within the vagina; second degree (marked), in which the cervix protrudes through the vagina to the exterior; and third degree (complete), in which the entire uterus is outside the vagina. Depending on the degree of prolapse, treatment may involve pelvic exercises, dieting if a patient is overweight, a stool softener to minimize straining during defecation, pessary therapy (placement of a rubber device around the uterine cervix that helps prop up the uterus), or surgery.

Figure 28.17 Histology of the Uterine Tube.

Peristaltic contractions of the muscular layer and ciliary action of the mucosa of the uterine tube help move the oocyte or fertilized ovum toward the uterus.

Histology of the Uterus Histologically, the uterus consists of three layers of tissue: perimetrium, myometrium, and endometrium (Figure 28.18). The outer layer—the perimetrium (per'-i-MÉ-trê-um; peri= around; metreum= uterus) or serosa—is part of the visceral peritoneum; it is composed of simple squamous epithelium and areolar connective tissue. Laterally, it becomes the broad ligament. Anteriorly, the peritoneum reflects off the uterus to cover the urinary bladder and forms a shallow pouch, the vesicouterine pouch (ves'-i-kô-Ü-ter-in; vesico-= bladder; see Figure 28.11). Posteriorly, it covers the rectum and forms a deep pouch between the uterus and rectum, the rectouterine pouch (rek-tô-Ü-ter-in; recto-= straight) or pouch of Douglas—the most inferior point in the pelvic cavity.

Figure 28.18 summary: This figure consists of a series of micrographs, including light microscopy images and a scanning electron microscopy image. The images display the histological structure of the uterine wall at different stages of the menstrual cycle. The sections identify the lumen of the uterus, the endometrium, and the myometrium. Within the endometrium, the compact layer, functional layer, and basal layer are distinguished. Specific features such as endometrial glands, ciliated simple columnar epithelium, and mucus secretions are highlighted in the detailed views. Comparing the transverse sections reveals that the endometrium undergoes structural changes between the second and third weeks of the menstrual cycle. The detailed views show that the functional layer is more developed during the secretory phase, characterized by prominent endometrial glands and the presence of mucus, which prepares the uterine lining for potential implantation.

The middle layer of the uterus is the muscular layer called the myometrium (myo-= muscle) and consists of three layers of smooth muscle fibers that are thickest in the fundus and thinnest in the cervix. The thicker middle layer is circular; the inner and outer layers are longitudinal or oblique. During labor and childbirth, coordinated contractions of the myometrium in response to oxytocin from the posterior pituitary help expel the fetus from the uterus.

The inner layer of the uterus is the mucosa, which is highly vascularized and referred to as the endometrium (endo=within). It has three layers: the compact layer of the endometrium, the functional layer of the endometrium, and the basal layer of the endometrium. The compact layer is the most superficial layer and is composed of ciliated simple columnar epithelium and nonciliated secretory columnar cells, a very thick endometrial stroma (lamina propria) composed of areolar connective tissue, and initial portions, of simple tubular uterine glands that develop as invaginations of the epithelium and extend through the other layers of the endometrium almost to the myometrium. The functional layer consists of a spongy endometrial stroma (lamina propria) composed of areolar connective tissue that is rich in ground substance and includes most of the length of the uterine glands. The functional layer and compact layer are sloughed off during menstruation in response to declining levels of progesterone from the ovaries.

The basal layer is also composed of an endometrial stroma (lamina propria) that is more highly cellular and includes the terminal ends of the uterine glands. The basal layer is permanent and contains stem cells that give rise to a new functional and compact layer after each menstruation.

Branches of the internal iliac artery called uterine arteries (Figure 28.19) supply blood to the uterus. Uterine arteries give off branches called arcuate arteries arcuate = shaped like a bow) that are arranged in a circular fashion in the myometrium. These arteries branch into radial arteries that penetrate deeply into the myometrium.

Figure 28.19 summary: This figure is an anatomical diagram. It illustrates the structural organization of the uterus and its associated blood supply, featuring a detailed inset that magnifies a portion of the uterine wall. The diagram identifies the primary layers of the uterus, including the parametrium, myometrium, and endometrium, and maps the vascular network from the main uterine arteries to the arcuate, radial, and spiral arterioles. The inset provides a closer view of the endometrium, distinguishing between the compact, functional, and basal layers, as well as the endometrial glands. The figure demonstrates that the uterine blood supply is hierarchical, branching from large arteries into smaller arterioles to provide targeted nourishment to the uterine tissues. It further indicates that the endometrium is a complex, layered structure designed to support functional changes, with specific vascularizations like spiral arterioles serving the functional layer.

Just before the branches enter the endometrium, they divide into two kinds of arterioles: Straight arterioles supply the basal layer with the materials needed to regenerate the compact and functional layers; spiral arterioles supply the functional layer and change markedly during the menstrual cycle. Blood leaving the uterus is drained by the uterine veins into the internal iliac veins. The extensive The three layers of the uterus from superficial to deep are the perimetrium (serosa), the myometrium, and the endometrium.

Q What structural features of the endometrium and myometrium contribute to their functions? blood supply of the uterus is essential to support regrowth of new compact and functional layers after menstruation, implantation of a fertilized ovum, and development of the placenta.

Cervical Mucus The secretory cells of the mucosa of the cervix produce a secretion called cervical mucus, a mixture of water, glycoproteins, lipids, enzymes, and inorganic salts. During their reproductive years, females secrete 20 to 60 mL of cervical mucus per day. Cervical mucus is more hospitable to sperm at or near the time of ovulation because it is then less viscous and more alkaline (pH 8.5). At other times, a more viscous mucus forms a cervical plug that physically impedes sperm penetration.

Cervical mucus supplements the energy needs of sperm, and both the cervix and cervical mucus protect sperm from phagocytes and the hostile environment of the vagina and uterus. Cervical mucus may also play a role in capacitation (ka-pas'-i-TÃ-shun)—a series of functional changes that sperm undergo in the female genital tract before they are able to fertilize a secondary oocyte. Capacitation causes the tail of a sperm to beat even more vigorously, and it prepares the plasma membrane of the sperm to fuse with the oocyte's plasma membrane.

Figure 28.19 Blood supply of the uterus. The inset shows histological details of the blood vessels of the endometrium.

Straight arterioles supply the materials needed for regeneration of the functional layer.

Clinical Connection

Hysterectomy

Hysterectomy hysterectomy; hyster-= uterus), the surgical removal of the uterus, is the most common gynecological operation. It may be indicated in conditions such as fibroids, which are noncancerous tumors composed of muscular and fibrous tissue; endometriosis; pelvic inflammatory disease; recurrent ovarian cysts; excessive uterine bleeding; and cancer of the cervix, uterus, Q What is the functional significance of the basal layer of the endometrium? or ovaries. In a partial (subtotal) hysterectomy, the body of the uterus is removed but the cervix is left in place. A complete hysterectomy is the removal of both the body and cervix of the uterus. A radical hysterectomy includes removal of the body and cervix of the uterus, uterine tubes, possibly the ovaries, the superior portion of the vagina, pelvic lymph nodes, and supporting structures, such as ligaments. A hysterectomy can be performed either through an incision in the abdominal wall or through the vagina.

Vagina

The vagina (= sheath) is a tubular, 10-cm (4-in.) long fibromuscular canal lined with mucous membrane that extends from the exterior of the body to the uterine cervix (see Figures 28.11 and 28.16). It is the receptacle for the penis during sexual intercourse, the outlet for the menstrual flow, and the passageway for childbirth. Situated between the urinary bladder and the rectum, the vagina is directed superiorly and posteriorly, where it attaches to the uterus. A recess called the fornix (= arch or vault) surrounds the vaginal attachment to the cervix. When properly inserted, a contraceptive diaphragm rests in the fornix, where it is held in place as it covers the cervix.

The mucosa of the vagina is continuous with that of the uterus (Figure 28.20a, b). Histologically, it consists of nonkeratinized stratified squamous epithelium and areolar connective tissue that lies in a series of transverse folds

Figure 28.20 The Vagina and Components of the Vulva.

The vulva refers to the external genitals of the female. called vaginal rugae. Dendritic cells in the mucosa are antigen-presenting cells (described in Section 22.4). Unfortunately, they also participate in the transmission of viruses—for example, H.I.V (the virus that causes A.I.D.S)—to a female during

Clinical Connection

Episiotomy

During childbirth, the emerging fetus normally stretches the perineal region. However, if it appears that the stretching could be excessive, a physician may elect to perform an episiotomy epizotome; epis-= vulva or pubic region; -otomy = incision), a perineal cut between the vagina and anus made with surgical scissors to widen the birth canal. The cut is made along the midline or at about a 45 degree angle to the midline.

Reasons for an episiotomy include a very large fetus, breech presentation (buttocks or lower limbs coming first), fetal distress (such as an abnormal heart rate), forceps delivery, or a short perineum. Following delivery, the incision is closed in layers with sutures that are absorbed within a few weeks.

Figure 28.20 Continued intercourse with an infected male. The mucosa of the vagina contains large stores of glycogen, the decomposition of which produces organic acids. The resulting acidic environment retards microbial growth, but it also is harmful to sperm. Alkaline components of semen, mainly from the seminal glands, raise the pH of fluid in the vagina and increase viability of the sperm.

Figure 28.20 summary: This figure consists of anatomical diagrams and light micrographs. The content includes a schematic showing a transverse plane of the vagina, a low-magnification histological section of the vaginal wall, a high-magnification view of the vaginal mucosa, and an anatomical overview of the female external genitalia. The histological images identify several layers of the vaginal wall, including the lumen, the mucosa composed of nonkeratinized stratified squamous epithelium and the lamina propria, a muscular layer divided into outer longitudinal and inner circular layers, and the outermost adventitia. The anatomical diagram labels external structures such as the mons pubis, clitoris, labia majora, labia minora, vaginal orifice, and anus. From these images, it can be inferred that the vaginal wall is structured to provide both protection and flexibility, with a thick epithelial lining to resist friction and a multi-layered muscular wall to support structural integrity and function.

The muscular layer is composed of an inner circular layer and an outer longitudinal layer of smooth muscle that can stretch considerably to accommodate the penis during sexual intercourse and a child during birth.

The adventitia, the superficial layer of the vagina, consists of areolar connective tissue. It anchors the vagina to adjacent organs such as the urethra and urinary bladder anteriorly and the rectum and anal canal posteriorly.

A thin fold of vascularized mucous membrane, called the hymen (= membrane), forms a border around and partially closes the inferior end of the vaginal opening to the exterior, the vaginal orifice (see Figure 28.20c). It is of variable size and shape and sometimes not even present. Sometimes the hymen completely covers the orifice, a condition called imperforate hymen imperforate. Surgery may be needed to open the orifice and permit the discharge of menstrual flow.

Vulva

The term vulva vulva = to wrap around) or pudendum refers to the external genitals of the female (Figure 28.20a). The following components make up the vulva:

• Anterior to the vaginal and urethral openings is the mons pubis monz PÜ-bis; mons = mountain), an elevation of adipose tissue covered by skin and coarse pubic hair that cushions the pubic symphysis.

• From the mons pubis, two longitudinal folds of skin, the labia majora (LÃ-bê-a ma-Jõ-ra; labia = lips; majora = larger), extend inferiorly and posteriorly. The singular term is labium majus. The labia majora are covered by pubic hair and contain an abundance of adipose tissue, sebaceous glands, and apocrine sudoriferous glands. They are homologous to the scrotum.

• Medial to the labia majora are two smaller folds of skin called the labia minora minora = smaller). The singular term is labium minus. Unlike the labia majora, the labia minora are devoid of pubic hair and fat and have few sudoriferous glands, but they do contain many sebaceous glands which produce antimicrobial substances and

provide some lubrication during sexual intercourse. The labia minora are homologous to the spongy urethra.

• The clitoris clitoris is a small cylindrical mass composed of two small erectile bodies, the corpora cavernosa, and numerous nerves and blood vessels. The clitoris is located at the anterior junction of the labia minora. A layer of skin called the prepuce of the clitoris prepuce is formed at the point where the labia minora unite and covers the body of the clitoris. The exposed portion of the clitoris is the glans clitoris. The clitoris is homologous to the glans penis in males. Like the male structure, the clitoris is capable of enlargement on tactile stimulation and has a role in sexual excitement in the female.

• The region between the labia minora is the vestibule. Within the vestibule are the hymen (if still present), the vaginal orifice, the external urethral orifice, and the openings of the ducts of several glands. The vaginal orifice, the opening of the vagina to the exterior, occupies the greater portion of the vestibule and is bordered by the hymen. Anterior to the vaginal orifice and posterior to the clitoris is the external urethral orifice, the opening of the urethra to the exterior. On either side of the external urethral orifice are the openings of the ducts of the paraurethral glands (par'-a-ü-RÉ-thral) or Skene's glands skenz. These mucus-secreting glands are embedded in the wall of the urethra. The paraurethral glands are homologous to the prostate. On either side of the vaginal orifice itself are the greater vestibular glands or Bartholin's glands bartolins (see Figure 28.21), which open by ducts into a groove between the hymen and labia minora. They produce a small quantity of mucus during sexual arousal and intercourse that adds to cervical mucus and provides lubrication. The greater vestibular glands are homologous to the bulbourethral glands in males. Several lesser vestibular glands secrete mucus during sexual arousal and intercourse and also open into the vestibule.

Figure 28.21 summary: This figure is an anatomical diagram. It illustrates the anterior view of the female perineum, showing a partially sectioned view of the urogenital and anal triangles. Key structures labeled include the pubic symphysis, clitoris, external urethral orifice, vaginal orifice, bulb of the vestibule, ischiocavernosus muscle, bulbospongiosus muscle, greater vestibular gland, superficial transverse perineal muscle, external anal sphincter, anus, gluteus maximus, ischial tuberosity, and coccyx. The diagram demonstrates the spatial organization of the pelvic floor, highlighting the division between the urogenital triangle, which contains the reproductive and urinary openings, and the anal triangle, which contains the digestive exit.

• The bulb of the vestibule (see Figure 28.21) consists of two elongated masses of erectile tissue just deep to the labia on either side of the vaginal orifice. The bulb of the vestibule becomes engorged with blood during sexual arousal, narrowing the vaginal orifice and placing pressure on the penis during intercourse. The bulb of the vestibule is homologous to the corpus spongiosum and bulb of the penis in males.

Table 28.2 summarizes the homologous structures of the female and male genital systems.

Table 28.2 summary: This table lists the corresponding homologous anatomical structures between the female and male reproductive systems, pairing organs and tissues that develop from the same embryonic origins.

Perineum

The perineum (per'-i-Ne-um) is the diamond-shaped area medial to the thighs and buttocks of both males and females (Figure 28.21). It contains the external genitals and anus. The perineum is bounded anteriorly by the pubic symphysis, laterally by the ischial tuberosities, and posteriorly by the coccyx. A transverse line drawn between the ischial tuberosities divides the perineum into an anterior urogenital triangle urogenital that contains the external genitals and a posterior anal triangle that contains the anus.

Mammary Glands

Each breast is a hemispheric projection of variable size anterior to the pectoralis major and serratus anterior muscles and attached to them by a layer of fascia composed of dense irregular connective tissue.

Each breast has one pigmented projection, the nipple, that has a series of closely spaced openings of ducts called lactiferous ducts (lak-tiff-e-rus), where milk emerges. The circular pigmented area of skin surrounding the nipple is called the areola (a-RÊ-ô-la = small space); it appears rough because it contains modified sebaceous glands. Strands of connective tissue called the suspensory ligaments of the breast (Cooper's ligaments) run between the skin and fascia and support the breast.

These ligaments become looser with age or with the excessive strain that can occur in long-term jogging or high-impact aerobics. Wearing a supportive bra can slow this process and help maintain the strength of the suspensory ligaments.

Within each breast is a mammary gland, a modified sudoriferous gland that produces milk (Figure 28.22). A mammary gland consists of 15 to 20 lobes, or compartments, separated by a variable amount of adipose tissue. In each lobe are several smaller compartments called lobules, composed of grapelike clusters of milk-secreting glands termed glandular alveoli (al-VË-o-lï = small cavities) embedded in connective tissue. Contraction of myoepithelial cells myoepithelial surrounding the glandular alveoli helps propel milk toward the nipples.

Figure 28.22 summary: This figure is an anatomical illustration showing a partial section of the human breast from an anterior perspective. The image depicts the internal and external structures of the breast, including the nipple, areola, and the underlying mammary duct system. It highlights the lobules containing glandular alveoli, secondary tubules, and lactiferous sinuses and ducts. The surrounding support structures are shown, such as the suspensory ligaments, adipose tissue in the subcutaneous layer, and the pectoralis major muscle, as well as the deeper rib and intercostal muscles. The illustration demonstrates the hierarchical organization of the mammary glands, where milk produced in the alveoli travels through a network of tubules and ducts to reach the nipple. It also shows the anatomical relationship between the glandular tissue and the muscular and skeletal structures of the chest wall.

When milk is being produced, it passes from the alveoli into a series of secondary tubules and then into the mammary ducts. Near the nipple, the mammary ducts expand slightly to form sinuses called lactiferous sinuses (lact-= milk), where some milk may be stored before draining into a lactiferous duct. Each lactiferous duct typically carries milk from one of the lobes to the exterior.

Figure 28.21 Perineum of a Female. (Figure 11.13 Shows the Perineum of a Male.)

The perineum is a diamond-shaped area that includes the urogenital triangle and the anal triangle.

Greater vestibular gland Superficial transverse perineal muscle Q Why is the anterior portion of the perineum called the urogenital triangle?

Figure 28.22 Mammary glands within the breasts.

The mammary glands function in the synthesis, secretion, and ejection of milk (lactation).

Clinical Connection

Breast Augmentation and Reduction

Breast augmentation (awg-men-TÃ-shun = enlargement), technically called augmentation mammaplasty mammaplaste, is a surgical procedure to increase breast size and shape. It may be done to enhance breast size for females who feel that their breasts are too small, to restore breast volume due to weight loss or following pregnancy, to improve the shape of breasts that are sagging, and to improve breast appearance following surgery, trauma, or congenital abnormalities. The most commonly used implants are filled with either a saline solution or silicone gel.

The incision for the implant is made under the breast, around the areola, in the armpit, or in the navel. Then a pocket is made to place the implant either directly behind the breast tissue or beneath the pectoralis major muscle.

The functions of the mammary glands are the synthesis, secretion, and ejection of milk; these functions, called lactation (lak-TÃ-shun), are associated with pregnancy and childbirth. Milk production is stimulated largely by the hormone prolactin from the anterior pituitary, with contributions from progesterone and estrogens. The ejection of milk is stimulated by oxytocin, which is released from the posterior pituitary in response to the sucking of an infant on the mother's nipple (suckling).

Clinical Connection

Fibrocystic Disease of the Breasts

The breasts of females are highly susceptible to cysts and tumors. In fibrocystic disease fibrosystic, the most common cause of breast lumps in females, one or more cysts (fluid-filled sacs) and thickenings of glandular alveoli develop. The condition, which occurs mainly in females between the ages of 30 and 50, is probably due to a relative excess of estrogens or a deficiency of progesterone in the postovulatory (luteal) phase of the reproductive cycle (discussed shortly). Fibrocystic disease usually causes one or both breasts to become lumpy, swollen, and tender a week or so before menstruation begins.

Breast reduction or reduction mammaplasty is a surgical procedure that involves decreasing breast size by removing fat, skin, and glandular tissue. This procedure is done because of chronic back, neck, and shoulder pain; poor posture; circulation or breathing problems; a skin rash under the breasts; restricted levels of activity; self-esteem problems; deep grooves in the shoulders from bra strap pressure; and difficulty wearing or fitting into certain bras and clothing. The most common procedure involves an incision around the areola, down the breast toward the crease between the breast and abdomen, and then along the crease.

The surgeon removes excess tissue through the incision. In most cases, the nipple and areola remain attached to the breast. However, if the breasts are extremely large, the nipple and areola may have to be reattached at a higher position.

28.3 The Female Reproductive Cycle

Objective

- Compare the major events of the ovarian and uterine cycles.

During their reproductive years, nonpregnant females normally exhibit cyclical changes in the ovaries and uterus. Each cycle takes about a month and involves both oogenesis and preparation of the uterus to receive a fertilized ovum. Hormones secreted by the hypothalamus, anterior pituitary, and ovaries control the main events.

The ovarian cycle is a series of events in the ovaries that occur during and after the maturation of an oocyte. The uterine (menstrual) cycle is a concurrent series of changes in the endometrium of the uterus to prepare it for the arrival of a fertilized ovum that will develop there until birth. If fertilization does not occur, ovarian hormones wane, which causes the functional layer of the endometrium to slough off. The general term female reproductive cycle encompasses the ovarian and uterine cycles, the hormonal changes that regulate them, and the related cyclical changes in the breasts and cervix.

Hormonal Regulation of the Female Reproductive Cycle

Gonadotropin-releasing hormone (GnRH) secreted by the hypothalamus controls the ovarian and uterine cycles (Figure 28.23). GnRH stimulates the release of follicle-stimulating hormone (F.S.H) and luteinizing hormone (L.H) from the anterior pituitary. F.S.H initiates follicular growth, while L.H stimulates further development of the ovarian follicles. In addition, both F.S.H and L.H Figure 28.23 Secretion and physiological effects of estrogens, progesterone, relaxin, and inhibin in the female reproductive cycle. Dashed red lines indicate negative feedback inhibition.

Figure 28.23 summary: This figure is a flow chart depicting the hormonal regulation of the female reproductive system. It illustrates the feedback loops between the hypothalamus, anterior pituitary gland, and the ovaries, showing how GnRH triggers the release of FSH and LH, which in turn stimulate follicle growth, ovulation, and the formation of the corpus luteum. These processes lead to the secretion of estrogens, inhibin, relaxin, and progesterone, each performing specific functions such as promoting reproductive structure maintenance, inhibiting FSH release, relaxing uterine muscles, and preparing the endometrial lining. The diagram concludes that these hormones exert negative feedback on the hypothalamus and pituitary gland to regulate the secretion of GnRH, FSH, and LH.

The uterine and ovarian cycles are controlled by gonadotropin-releasing hormone (GnRH) and ovarian hormones (estrogens and progesterone). stimulate the ovarian follicles to secrete estrogens. L.H stimulates the theca cells of a developing follicle to produce androgens. Under the influence of F.S.H, the androgens are taken up by the granulosa cells of the follicle and then converted into estrogens.

At midcycle, L.H triggers ovulation and then promotes formation of the corpus luteum, the reason for the name luteinizing hormone. Stimulated by L.H, the corpus luteum produces and secretes estrogens, progesterone, relaxin, and inhibin.

At least six different estrogens have been isolated from the plasma of human females, but only three are present in significant quantities: beta (β)-estradiol (es-tra-Di-ol), estrone, and estriol estriol. In a nonpregnant woman, the most abundant estrogen is β-estradiol, which is synthesized from cholesterol in the ovaries.

Estrogens secreted by ovarian follicles have several important functions (Figure 28.23): They:

• Promote the development and maintenance of female reproductive structures, secondary sex characteristics, and the breasts. The secondary sex characteristics include distribution of adipose tissue in the breasts, abdomen,

mons pubis, and hips; voice pitch; a broad pelvis; and pattern of hair growth on the head and body.

• Increase protein anabolism, including the building of strong bones. In this regard, estrogens are synergistic with growth hormone G.H.

- Lower blood cholesterol level, which is probably the reason that women under age 50 have a much lower risk of coronary artery disease than do men of comparable age.

• Every month, after menstruation occurs, estrogens stimulate proliferation of the basal layer to form a new functional layer that replaces the one that has sloughed off.

- Moderate levels in the blood inhibit both the release of GnRH by the hypothalamus and secretion of L.H and F.S.H by the anterior pituitary.

Progesterone, secreted mainly by cells of the corpus luteum, cooperates with estrogens to prepare and maintain the endometrium for implantation of a fertilized ovum and to prepare the mammary glands for milk secretion. High levels of progesterone also inhibit secretion of GnRH and L.H.

The small quantity of relaxin produced by the corpus luteum during each monthly cycle relaxes the uterus by inhibiting contractions of the myometrium. Presumably, implantation of a fertilized ovum occurs more readily in a “quiet” uterus. During pregnancy, the placenta produces much more relaxin, and it continues to relax uterine smooth muscle. At the end of pregnancy, relaxin also increases the flexibility of the pubic symphysis and may help dilate the uterine cervix, both of which ease delivery of the baby.

Inhibin is secreted by granulosa cells of growing follicles and by the corpus luteum after ovulation. It inhibits secretion of F.S.H and, to a lesser extent, L.H.

Phases of the Female Reproductive Cycle

The duration of the female reproductive cycle typically ranges from 24 to 36 days. For this discussion, we assume a duration of 28 days and divide it into four phases: the menstrual phase, the preovulatory phase, ovulation, and the postovulatory phase (Figure 28.24).

Figure 28.24 summary: This figure consists of a conceptual diagram and a corresponding line chart. The diagram illustrates the hormonal control and synchronization between the ovarian cycle and the uterine menstrual cycle, showing the progression from primordial follicles to the corpus albicans and the subsequent changes in the endometrial lining. The line chart tracks the concentration of various hormones, including FSH, LH, estrogens, and progesterone, over a typical cycle. The data indicates that the follicular phase is characterized by rising estrogen levels, which trigger a sharp peak in LH and FSH leading to ovulation. Following ovulation, the luteal phase is dominated by high levels of progesterone and estrogens produced by the corpus luteum, which support the secretory phase of the endometrium. A decline in these hormone levels eventually leads to the breakdown of the endometrial lining, resulting in menstruation.

Menstrual Phase The menstrual phase menstrual, also called menstruation (men'-stroo-Ã-shun) or menses menses = months), lasts for roughly the first 5 days of the cycle. (By convention, the first day of menstruation is day 1 of a new cycle.)

Events in the Ovaries Under the influence of F.S.H, several primordial ovarian follicles develop into primary ovarian follicles and then into secondary ovarian follicles. This developmental process may take several months to occur. Therefore, an ovarian follicle that begins to develop at the beginning of a particular menstrual cycle may not reach maturity and ovulate until several menstrual cycles later.

Events in the Uterus Menstrual flow from the uterus consists of 50 to 150 mL of blood, tissue fluid, mucus, and epithelial cells shed from the endometrium. This discharge occurs Figure 28.24 The female reproductive cycle. The length of the female reproductive cycle typically is 24 to 36 days; the preovulatory phase is more variable in length than the other phases. (a) Events in the ovarian and uterine cycles and the release of anterior pituitary hormones are correlated with the sequence of the cycle's four phases. In the cycle shown, fertilization and implantation have not occurred. (b) Relative concentrations of anterior pituitary hormones (F.S.H and L.H) and ovarian hormones (estrogens and progesterone) during the phases of a normal female reproductive cycle.

Estrogens are the primary ovarian hormones before ovulation; after ovulation, both progesterone and estrogens are secreted by the corpus luteum.

Figure 28.24 Continued

because the declining levels of progesterone and estrogens stimulate release of prostaglandins that cause the uterine spiral arterioles to constrict. As a result, the cells they supply become oxygen-deprived and start to die. Eventually, the entire functional and compact layers sloughs off. At this time the endometrium is very thin, about 2 to 5 millimeters, because only the basal layer remains. The menstrual flow passes from the uterine cavity through the cervix and vagina to the exterior.

Preovulatory Phase The preovulatory phase preovulatory is the time between the end of menstruation and ovulation. The preovulatory phase of the cycle is more variable in length than the other phases and accounts for most of the differences in length of the cycle. It lasts from days 6 to 13 in a 28-day cycle.

Events in the Ovaries Some of the secondary ovarian follicles in the ovaries begin to secrete estrogens and inhibin. By about day 6, a single secondary ovarian follicle in one of the two ovaries has outgrown all of the others to become the dominant ovarian follicle. Estrogens and inhibin secreted by the dominant ovarian follicle decrease the secretion of F.S.H, which causes other, less well-developed ovarian follicles to stop growing and degenerate. Fraternal (nonidentical) twins or triplets result when two or three secondary ovarian follicles become codominant and later are ovulated and fertilized at about the same time.

Normally, the one dominant secondary ovarian follicle becomes the tertiary ovarian follicle, which continues to enlarge until it is more than 20 millimeters in diameter and ready for ovulation (see Figure 28.13). This ovarian follicle forms a blister-like bulge due to the swelling antrum on the surface of the ovary. During the final maturation process, the tertiary ovarian follicle continues to increase its production of estrogens (Figure 28.24).

With reference to the ovarian cycle, the menstrual and preovulatory phases together are termed the follicular phase follicular because ovarian follicles are growing and developing.

Events in the Uterus Estrogens liberated into the blood by growing ovarian follicles stimulate the repair of the endometrium; cells of the basal layer undergo mitosis and produce new functional and compact layers. As the endometrium thickens, the short, straight endometrial glands develop, and the arterioles coil and lengthen as they penetrate the functional layer. The thickness of the endometrium approximately doubles, to about 4 to 10 millimeters. With reference to the uterine cycle, the preovulatory phase is also termed the proliferative phase proliferative because the endometrium is proliferating.

Ovulation Ovulation, the rupture of the tertiary ovarian follicle and the release of the secondary oocyte into the pelvic cavity, usually occurs on day 14 in a 28-day cycle. During ovulation, the secondary oocyte remains surrounded by its zona pellucida and corona radiata.

The high levels of estrogens during the last part of the pre-ovulatory phase exert a positive feedback effect on the cells that secrete L.H and gonadotropin-releasing hormone (GnRH) and cause ovulation, as follows (Figure 28.25): ① A high concentration of estrogens stimulates more frequent release of GnRH from the hypothalamus. It also directly stimulates gonadotrophs in the anterior pituitary to secrete L.H. ② GnRH promotes the release of F.S.H and additional L.H by the anterior pituitary. ③ L.H causes rupture of the tertiary ovarian follicle and expulsion of a secondary oocyte about 9 hours after the peak of the L.H surge. The ovulated oocyte and its corona radiata cells are usually swept into the uterine tube.

Figure 28.25 summary: This figure is a biological diagram illustrating a physiological feedback loop. It depicts the hormonal interaction between the hypothalamus, the anterior pituitary gland, and the ovary to trigger ovulation. The process begins when high levels of estrogens from a nearly mature ovarian follicle stimulate the hypothalamus to release GnRH and the anterior pituitary to release LH. This GnRH further promotes the release of FSH and an increased amount of LH. The resulting surge of LH acts on the ovary, causing the rupture of the tertiary ovarian follicle and the release of a secondary oocyte, which leaves behind a corpus hemorrhagicum. The diagram demonstrates that a positive feedback mechanism involving estrogens and gonadotropin-releasing hormone culminates in a luteinizing hormone surge, which is the direct trigger for ovulation.

From time to time, an oocyte is lost into the pelvic cavity, where it later disintegrates. The small amount of blood that sometimes leaks into the pelvic cavity from the ruptured follicle can cause pain, known as mittelschmerz mitelshmarts = pain in the middle), at the time of ovulation.

An over-the-counter home test that detects a rising level of L.H can be used to predict ovulation a day in advance.

Postovulatory Phase The postovulatory phase of the female reproductive cycle is the time between ovulation and onset of the next menses. In duration, it is the most constant part of the female reproductive cycle. It lasts for 14 days in a 28-day cycle, from day 15 to day 28 (see Figure 28.24).

Figure 28.25 High levels of estrogens exert a positive feedback effect (red arrows) on the hypothalamus and anterior pituitary, thereby increasing secretion of GnRH and L.H.

Clinical Connection

Female Athlete Triad: Disordered Eating, Amenorrhea, and Premature Osteoporosis

The female reproductive cycle can be disrupted by many factors, including weight loss, low body weight, disordered eating, and vigorous physical activity. The observation that three conditions—disordered eating, amenorrhea, and osteoporosis—often occur together in female athletes led researchers to coin the term female athlete triad.

Many athletes experience intense pressure from coaches, parents, peers, and themselves to lose weight to improve performance. Hence, they may develop disordered eating behaviors and engage in other harmful weight-loss practices in a struggle to maintain a very low body weight. Amenorrhea (a-men-o-Re-a; a-without; -men-= month; -rrhea = a flow) is the absence of menstruation. The most common causes of amenorrhea are pregnancy and menopause. In female athletes, amenorrhea results from reduced secretion of gonadotropin-releasing hormone, which decreases the Events in One Ovary After ovulation, the tertiary ovarian follicle collapses, and the basement membrane between the granulosa cells and the theca interna breaks down. Once a blood clot forms from minor bleeding of the ruptured ovarian follicle, the follicle becomes the corpus hemorrhagicum hemorajikum; hemo-= blood; rrhagic-= bursting forth) (see Figure 28.13). Theca interna cells mix with the granulosa cells as they all become transformed into corpus luteum cells under the influence of L.H. Stimulated by L.H, the corpus luteum secretes progesterone, estrogens, relaxin, and inhibin. The luteal cells also absorb the blood clot. With reference to the ovarian cycle, this phase is also called the luteal phase luteal.

Later events in an ovary that has ovulated an oocyte depend on whether the oocyte is fertilized. If the oocyte is not fertilized, the corpus luteum has a life span of only 2 weeks. Then, its secretory activity declines, and it degenerates into a corpus albicans (see Figure 28.13). As the levels of progesterone, estrogens, and inhibin decrease, release of GnRH, F.S.H, and L.H rises due to loss of negative feedback suppression by the ovarian hormones. Follicular growth resumes and a new ovarian cycle begins.

If the secondary oocyte is fertilized and begins to divide, the corpus luteum persists past its normal 2-week life span. It is “rescued” from degeneration by human chorionic gonadotropin (hCG) coreonic. This hormone is produced by the chorion of the embryo beginning about 8 days after fertilization. Like L.H, hCG stimulates the secretory activity of the corpus luteum. The presence of hCG in maternal blood or urine is an indicator of pregnancy and is the hormone detected by home pregnancy tests.

Events in the Uterus Progesterone and estrogens produced by the corpus luteum promote growth and coiling of the endometrial glands, vascularization of the superficial endometrium, release of L.H and F.S.H. As a result, ovarian follicles fail to develop, ovulation does not occur, synthesis of estrogens and progesterone wanes, and monthly menstrual bleeding ceases. Most cases of the female athlete triad occur in young women with very low amounts of body fat. Low levels of the hormone leptin, secreted by adipose cells, may be a contributing factor.

Because estrogens help bones retain calcium and other minerals, chronically low levels of estrogens are associated with loss of bone mineral density. The female athlete triad causes “old bones in young women.” In one study, amenorrheic runners in their twenties had low bone mineral densities, similar to those of postmenopausal women 50 to 70 years old! Short periods of amenorrhea in young athletes may cause no lasting harm. However, long-term cessation of the reproductive cycle may be accompanied by a loss of bone mass, and adolescent athletes may fail to achieve an adequate bone mass; both of these situations can lead to premature osteoporosis and irreversible bone damage. and thickening of the endometrium to 12 to 18 millimeters (0.48 to 0.72 in.). Because of the secretory activity of the endometrial glands, which begin to secrete glycogen, this period is called the secretory phase of the uterine cycle. These preparatory changes peak about 1 week after ovulation, at the time a fertilized ovum might arrive in the uterus. If fertilization does not occur, the levels of progesterone and estrogens decline due to degeneration of the corpus luteum. Withdrawal of progesterone and estrogens causes menstruation.

Figure 28.26 summarizes the hormonal interactions and cyclical changes in the ovaries and uterus during the ovarian and uterine cycles.

Figure 28.26 summary: This figure is a detailed flow chart illustrating a biological feedback loop. It depicts the hormonal interactions between the hypothalamus, anterior pituitary, ovaries, and uterus during the menstrual cycle. The diagram tracks the secretion of various hormones and their subsequent effects on follicle development, ovulation, and the state of the uterine lining. The process demonstrates that low levels of progesterone and estrogens trigger the release of stimulating hormones, while moderate levels of estrogens exert an inhibitory effect. High levels of estrogens eventually stimulate a surge in hormone release to trigger ovulation. The cycle concludes with the degeneration of the corpus luteum, leading to a drop in hormone levels and the onset of menstruation, which restarts the cycle through positive feedback to the hypothalamus.

26. Describe the function of each of the following hormones in the uterine and ovarian cycles: GnRH, F.S.H, L.H, estrogens, progesterone, and inhibin.

27. Briefly outline the major events of each phase of the uterine cycle, and correlate them with the events of the ovarian cycle.

28. Prepare a labeled diagram of the major hormonal changes that occur during the uterine and ovarian cycles.

Figure 28.26 Summary of Hormonal Interactions in the Ovarian and Uterine Cycles.

Hormones from the anterior pituitary regulate ovarian function, and hormones from the ovaries regulate the changes in the endometrial lining of the uterus.

28.4 The Human Sexual Response

Objective • Compare the sexual responses of males and females.

During heterosexual sexual intercourse, also called copulation or coitus (KÖ-i-tus), the erect penis is inserted into the vagina. The similar sequence of physiological and emotional changes experienced by both males and females before, during, and after intercourse is termed the human sexual response. William Masters and Virginia Johnson, who began their pioneering research on human sexuality in the late 1950s, divided the human sexual response into four phases: excitement, plateau, orgasm, and resolution.

During the excitement phase, there is vasocongestion—engorgement with blood—of genital tissues, resulting in erection of the penis in men and erection of the clitoris and swelling of the labia and vagina in women. In addition, vasocongestion causes the breasts to swell and the nipples to become erect. The excitement phase is also associated with an increase in the secretion of fluid that lubricates the walls of the vagina. When the connective tissue of the vagina becomes engorged with blood, lubricating fluid oozes from the capillaries and seeps through the epithelial lining via a process called transudation.

Glands within the cervical mucosa and the greater vestibular glands contribute a small quantity of lubricating mucus. Without satisfactory lubrication, sexual intercourse is difficult and painful for both partners and inhibits orgasm. Other changes that occur during the excitement phase include increased heart rate and blood pressure, increased skeletal muscle tone throughout the body, and hyperventilation.

Direct physical contact (as in kissing or touching), especially of the penis, clitoris, nipples of the breasts, and earlobes is a potent initiator of excitement. However, anticipation or fear; memories; visual, olfactory, and auditory sensations; and fantasies can enhance or diminish the likelihood that excitement will occur.

The changes that begin during excitement are sustained at an intense level in the plateau phase, which may last for only a few seconds or for many minutes. During this phase, many females and some males display a sex flush, a rashlike redness of the face and chest due to vasodilation of blood vessels in those parts of the body. The head of the penis increases in diameter and the testes swell.

Late in the plateau phase, pronounced vasocongestion of the lower third of the vagina swells the tissue and narrows the opening. Because of this response, the vagina grips the penis more firmly.

Generally, the briefest phase is {orgasm (climax)} , during which both sexes experience several rhythmic muscular contractions about 0.8 sec apart, accompanied by intense, pleasurable sensations and a further increase in blood pressure, heart rate, and respiratory rate. The sex flush is also most prominent at this time. In males, contraction of smooth muscle in the walls of the epididymis, vas deferens, and ejaculatory ducts as well as secretion of fluid by the accessory male genital glands cause semen to move into the urethra (emission). Then, rhythmic contractions of skeletal muscles at the base of the penis propel semen out of the penis (ejaculation). In males, orgasm usually accompanies ejaculation.

In women, if effective sexual stimulation continues, orgasm may occur, associated with 3 to 12 rhythmic contractions of the skeletal muscles that underlie the vulva. Reception of the ejaculate provides little stimulus for a female, especially if she is not already at the plateau phase; this is why a female partner does not automatically experience orgasm simultaneously with her partner. In both males and females, orgasm is a total body response that may produce milder sensations on some occasions and more intense, explosive sensations at other times.

Whereas females may experience two or more orgasms in rapid succession, males enter a refractory period, a recovery time during which a second ejaculation and orgasm is physiologically impossible. In some males, the refractory period lasts only a few minutes; in others it lasts for several hours. A female does not have to experience an orgasm for fertilization to occur.

In the final phase—resolution, which begins with a sense of profound relaxation—genital tissues heart rate, blood pressure, breathing, and muscle tone return to the unaroused state. If sexual excitement has been intense but orgasm has not occurred, resolution takes place more slowly.

The four phases of the human sexual response are not always clearly separated from one another and may vary considerably among different people, and even in the same person at different times.

Checkpoint

28.5 Birth Control Methods and Abortion

Objectives • Compare the effectiveness of the various types of birth control methods.

• Explain the difference between induced and spontaneous abortions.

Birth control or contraception refers to restricting the number of children by various methods designed to control fertility and prevent conception. No single, ideal method of birth control exists. The only method of preventing pregnancy that is 100% reliable is complete abstinence, the avoidance of sexual intercourse. Several other methods are available; each has its advantages and disadvantages. These include surgical sterilization, hormonal methods, intrauterine devices, spermicides, barrier methods, and periodic abstinence.

Table 28.3 provides the failure rates for various methods of birth control. Although it is not a form of birth control, in this section we will also discuss abortion, the premature expulsion of the products of conception from the uterus.

Table 28.3 summary: The table compares failure rates of various birth control methods under perfect and typical use conditions. Surgical sterilization and hormonal methods generally exhibit the lowest failure rates, with minimal differences between perfect and typical use. In contrast, barrier methods and periodic abstinence show significantly higher failure rates, which increase substantially when moving from perfect to typical use. Spermicides alone and emergency contraception also show high failure rates, while using no method results in the highest probability of failure.

Birth Control Methods

Surgical Sterilization Sterilization is a procedure that renders an individual incapable of further reproduction.

The principal method for sterilization of males is a vasectomy vasektome; -ectomy = cut out), in which a portion of each ductus (vas) deferens is removed (Figure 28.27a). In order to gain access to the ductus deferens, an incision is made with a scalpel (conventional procedure) or a puncture is made with special forceps (non-scalpel vasectomy). Next the ducts are located and cut, each is tied (ligated) in two places with stitches, and the portion between the ties is removed. Although sperm production continues in the testes, sperm can no longer reach the exterior. The sperm degenerate and are destroyed by phagocytosis. Because the blood vessels are not cut, testosterone levels in the blood remain normal, so vasectomy has no effect on sexual desire or performance. If done correctly, it is close to 100% effective. The procedure can be reversed, but the chance of regaining fertility is only 30 to 40%. Sterilization in females most often is achieved by performing a tubal ligation (li-GÃ-shun), in which both uterine tubes are tied closed and then cut (Figure 28.27b). This can be achieved in a few different ways. "Clips" or "clamps" can be placed on the uterine tubes, the tubes can be tied and/or cut, and sometimes they are cauterized, that is, destroyed by heat to stop bleeding. In any case, the result is that the secondary oocyte cannot pass through the uterine tubes, and sperm cannot reach the oocyte.

Non-Incisional Sterilization Essure® is one means of non-incisional sterilization that is an alternative to tubal ligation. In the Essure® procedure, a soft micro-insert coil made of polyester fibers and metals (nickel-titanium and stainless steel) is inserted with a catheter into the vagina, through the uterus, and into each uterine tube. Over a three-month period, the insert stimulates tissue growth (scar tissue) in and around itself, blocking the uterine tubes.

As with tubal ligation, the secondary oocyte cannot pass through the uterine tubes, and sperm cannot reach the oocyte. Unlike tubal ligation, non-incisional sterilization does not require general anesthesia.

Hormonal Methods Aside from complete abstinence or surgical sterilization, hormonal methods are the most effective means of birth control. Oral contraceptives (the pill) contain hormones designed to prevent pregnancy. Some, called combined oral contraceptives C.O.C's, contain both progestin (hormone with actions similar to progesterone) and estrogens.

The primary action of C.O.C's is to inhibit ovulation by suppressing the gonadotropins F.S.H and L.H. The low levels of F.S.H and L.H usually prevent the development of a dominant follicle in the ovary. As a result, levels of estrogens do not rise, the midcycle L.H surge does not occur, and ovulation does not take place. Even if ovulation does occur, as it does in some cases, C.O.C's may also block implantation in the uterus and inhibit the transport of ova and sperm in the uterine tubes.

Progestins thicken cervical mucus and make it more difficult for sperm to enter the uterus. Progestin-only pills thicken cervical mucus and may block implantation in the uterus, but they do not consistently inhibit ovulation.

Among the noncontraceptive benefits of oral contraceptives are regulation of the length of menstrual cycle and decreased menstrual flow (and therefore decreased risk of anemia). The pill also provides protection against endometrial and ovarian cancers and reduces the risk of endometriosis. However, oral contraceptives may not be advised for women with a history of blood clotting disorders, cerebral blood vessel damage, migraine headaches, hypertension, liver malfunction, or heart disease. Women who take the pill and smoke face far higher odds of having a heart attack or stroke than do nonsmoking pill users. Smokers should quit smoking or use an alternative method of birth control.

Following are several variations of oral hormonal methods of contraception:

• Combined pill. The combined pill contains both progestin and estrogens and is typically taken once a day for 3 weeks to prevent pregnancy and regulate the menstrual cycle. The pills taken during the fourth week are inactive (do not contain hormones) and permit menstruation to occur. An example is Yasmin ^{} .

• Extended cycle birth control pill. Containing both progestin and estrogens, the extended cycle birth control pill is taken once a day in 3-month cycles of 12 weeks of hormone-containing pills followed by 1 week of inactive pills. Menstruation occurs during the thirteenth week. An example is Seasonale®.

• Minipill. The minipill contains low dose progestin only and is taken every day of the month. An example is Micronar®.

Non-oral hormonal methods of contraception are also available. Among these are the following:

• Contraceptive skin patch. The contraceptive skin patch (Ortho Evra®) contains both progestin and estrogens delivered in a skin patch placed on the upper outer arm, back, lower abdomen, or buttocks once a week for 3 weeks. At the end of each week, the patch is removed from one location and then a new one is placed elsewhere. During the fourth week no patch is used.

• Vaginal contraceptive ring. A flexible doughnut-shaped ring about 5 centimeters (2 in.) in diameter, the vaginal contraceptive ring (NuvaRing®) contains estrogens and progesterone and is inserted by the female herself into the vagina. It is left in the vagina for 3 weeks to prevent conception and then removed for one week to permit menstruation.

• Emergency contraception (E.C). Emergency contraception (E.C), also known as the morning-after pill, consists of progestin and estrogens or progestin alone to prevent pregnancy following unprotected sexual intercourse. The relatively high levels of progestin and estrogens in E.C pills provide inhibition of F.S.H and L.H secretion. Loss of the stimulating effects of these gonadotropic hormones causes the ovaries to cease secretion of their own estrogens and progesterone. In turn, declining levels of estrogens and progesterone induce shedding of the uterine lining, thereby blocking implantation. One pill is taken as soon as possible but within 72 hours of unprotected sexual intercourse. The second pill must be taken 12 hours after the first. The pills work in the same way as regular birth control pills.

• Hormone injections. Hormone injections are injectable progestins such as Depo-provera® given intramuscularly by a health-care practitioner once every 3 months.

Intrauterine Devices An intrauterine device (I.U.D) is a small object made of plastic, copper, or stainless steel that is inserted by a health-care professional into the cavity of the uterus. I.U.D's prevent fertilization from taking place by blocking sperm from entering the uterine tubes. The I.U.D most commonly used in the United States today is the Copper T 380.A ^{} , which is approved for up to 10 years of use and has long-term effectiveness comparable to that of tubal ligation. Some women cannot use I.U.D's because of expulsion, bleeding, or discomfort.

Spermicides Various foams, creams, jellies, suppositories, and douches that contain sperm-killing agents, or spermicides spermicides, make the vagina and cervix unfavorable for sperm survival and are available without prescription. They are placed in the vagina before sexual intercourse. The most widely used spermicide is nonoxynol-9, which kills sperm by disrupting their plasma membranes. A spermicide is more effective when used with a barrier method such as a male condom, vaginal pouch, diaphragm, or cervical cap.

Barrier Methods Barrier methods use a physical barrier and are designed to prevent sperm from gaining access to the uterine cavity and uterine tubes. In addition to preventing pregnancy, certain barrier methods (male condom and vaginal pouch) may also provide some protection against sexually transmitted diseases S.T.D's such as AIDS. In contrast, oral contraceptives and I.U.D's confer no such protection. Among the barrier methods are the male condom, vaginal pouch, diaphragm, and cervical cap.

A male condom is a nonporous latex covering placed over the penis that prevents deposition of sperm in the female reproductive tract. A vaginal pouch, sometimes called a female condom, is designed to prevent sperm from entering the uterus. It is made of two flexible rings connected by a polyurethane sheath.

One ring lies inside the sheath and is inserted to fit over the cervix; the other ring remains outside the vagina and covers the female external genitals. A diaphragm is a rubber, dome-shaped structure that fits over the cervix and is used in conjunction with a spermicide. It can be inserted by the female up to 6 hours before intercourse. The diaphragm stops most sperm from passing into the cervix and the spermicide kills most sperm that do get by. Although diaphragm use does decrease the risk of some S.T.D's, it does not fully protect against H.I.V infection because the vagina is still exposed.

A cervical cap resembles a diaphragm but is smaller and more rigid. It fits snugly over the cervix and must be fitted by a health-care professional. Spermicides should be used with the cervical cap.

Periodic Abstinence A couple can use their knowledge of the physiological changes that occur during the female reproductive cycle to decide either to abstain from intercourse on those days when pregnancy is a likely result, or to plan intercourse on those days if they wish to conceive a child. In females with normal and regular menstrual cycles, these physiological events help to predict the day on which ovulation is likely to occur.

The first physiologically based method, developed in the 1930s, is known as the rhythm method. It involves abstaining from sexual activity on the days that ovulation is likely to occur in each reproductive cycle. During this time (3 days before ovulation, the day of ovulation, and 3 days after ovulation) the couple abstains from intercourse. The effectiveness of the rhythm method for birth control is poor. in many women due to the irregularity of the female reproductive cycle.

Another system is the sympto-thermal method (S.T.M), a natural, fertility-awareness-based method of family planning that is used to either avoid or achieve pregnancy. S.T.M utilizes normally fluctuating physiological markers to determine ovulation such as increased basal body temperature and the production of abundant, clear, stretchy cervical mucus that resembles uncooked egg white. These indicators, reflecting the hormonal changes that govern female fertility, provide a double-check system by which a female knows when she is or is not fertile.

Sexual intercourse is avoided during the fertile time to avoid pregnancy. S.T.M users observe and chart these changes and interpret them according to precise rules.

Figure 28.27 summary: This figure consists of two anatomical diagrams illustrating surgical sterilization procedures. The first diagram depicts the male reproductive system, highlighting the testis, scrotum, and penis, with a detailed inset showing the cutting of the ductus deferens during a vasectomy. The second diagram shows the female reproductive system, including the vagina, uterus, and uterine tubes, with insets demonstrating different methods of tubal ligation such as clamping, tying and cutting, or cauterizing the uterine tubes. These procedures result in permanent sterilization by physically interrupting the pathway required for gametes to meet, thereby rendering the individual incapable of biological reproduction.

Abortion

Abortion refers to the premature expulsion of the products of conception from the uterus, usually before the 20th week of pregnancy. An abortion may be spontaneous (naturally occurring; also called a miscarriage) or induced (intentionally performed).

There are several types of induced abortions. One involves mifepristone mifpriston, also known as R.U 486. It is a hormone approved only for pregnancies 9 weeks or less when taken with misoprostol (a prostaglandin). Mifepristone is an antiprogestin; it blocks the action of progesterone by binding to and blocking progesterone receptors. Progesterone prepares the uterine endometrium for implantation and then maintains the uterine lining after implantation.

If the level of progesterone falls during pregnancy or if the action of the hormone is blocked, menstruation occurs, and the embryo sloughs off along with the uterine lining. Within 12 hours after taking mifepristone, the endometrium starts to degenerate, and within 72 hours it begins to slough off. Misoprostol stimulates uterine contractions and is given after mifepristone to aid in expulsion of the endometrium.

Another type of induced abortion is called vacuum aspiration (suction) and can be performed up to the 16th week of pregnancy. A small, flexible tube attached to a vacuum source is inserted into the uterus through the vagina. The embryo or fetus, placenta, and lining of the uterus are then removed by suction. For pregnancies between 13 and 16 weeks, a technique called dilation and evacuation is commonly used. After the cervix is dilated, suction and forceps are used to remove the fetus, placenta, and uterine lining.

From the 16th to 24th week, a late-stage abortion may be employed using surgical methods similar to dilation and evacuation or through nonsurgical methods using a saline solution or medications to induce abortion. Labor may be induced by using vaginal supositories, intravenous infusion, or injections into the amniotic fluid through the uterus.

30. How do oral contraceptives reduce the likelihood of pregnancy?

31. How do some methods of birth control protect against sexually transmitted diseases?

32. What is the problem with developing an oral contraceptive pill for males?

28.6 Development of the Genital Systems

Objectives

• Explain how genetic sex is determined.

- Describe the development of the male and female reproductive systems.

Recall from Chapter 3 that somatic cells are diploid (2n): They contain 23 pairs of homologous chromosomes, for a total of 46 chromosomes. Of these chromosomes, there are 22 pairs of autosomes and one pair of sex chromosomes. Autosomes code for the overall form of the human body and for specific traits such as eye color and height. The two sex chromosomes—a large X chromosome and a smaller Y chromosome—determine the genetic sex of an individual. In a genetic female, somatic cells contain two X chromosomes. In a genetic male, somatic cells contain one X and one Y chromosome. Determination of genetic sex by the sex chromosomes is known as sex determination.

In gametes (sperm or eggs), which are haploid (n), there are only 23 total chromosomes. Of these chromosomes, there are 22 autosomes and 1 sex chromosome. In sperm, the sex chromosome is either X or Y—approximately half of the sperm produced by meiosis contain an X and the other half of a Y. In an egg, the sex chromosome is always an X. Genetic sex is established at the moment of conception by the type of sperm (X-bearing or Y-bearing) that fertilizes the egg. If an X-bearing sperm fertilizes the egg, the embryo formed will be a genetic female (20). If a Y-bearing sperm fertilizes the egg, the embryo formed will be a genetic male X.Y.

The early embryo is bipotential, which means that it has the ability to form either male or female genital organs. The first step in the development of the genital organs occurs in response to the genetic sex of the embryo. If the embryo is genetically male, testes develop; if the embryo is genetically female, ovaries develop. Once testes form in a male embryo, they begin to secrete androgens (masculinizing hormones), which cause a male genital tract and male external genitals to develop. Female embryos, which contain ovaries instead of testes, do not produce testicular androgens. The lack of testicular androgens in a female embryo causes a female genital tract and female external genitals to develop by default. Such a default pathway is ideal because both male and female embryos are exposed to high levels of estrogens and progesterone from the mother's placenta and ovaries during pregnancy. If female sex hormones played a role in sex differentiation, then all embryos (whether genetically male or female) would develop female genital organs.

Sex differentiation is the process by which genital organs develop along male or female lines. To understand the steps involved in sex differentiation, you will first examine how the internal genital organs are formed and then you will discover how the external genitalia are developed.

The gonads develop from gonadal ridges that arise from growth of intermediate mesoderm. During the fifth week of development, the gonadal ridges appear as bulges just medial to the mesonephros (intermediate kidney) (Figure 28.28). Adjacent to the gonadal ridges are the mesonephric ducts mesonefrik, which eventually develop into structures of the genital system in males. A second pair of ducts, the parame-sonephric ducts paramesonefrik, develop lateral to the mesonephric ducts and eventually form structures of the genital system in females. Both sets of ducts empty into the urogenital sinus. An early embryo has the potential to follow either the male or the female pattern of development because it contains both sets of ducts and genital ridges that can differentiate into either testes or ovaries.

Figure 28.28 summary: This figure is a series of anatomical diagrams. It illustrates the embryological development of the reproductive system from an undifferentiated stage into male and female structures. The diagrams track the transformation of the mesonephric and paramesonephric ducts, gonadal ridges, and the urogenital sinus through various weeks of gestation up until birth. The content demonstrates that male development involves the persistence of the mesonephric ducts to form the epididymis and vas deferens while the paramesonephric ducts degenerate. Conversely, female development is characterized by the degeneration of the mesonephric ducts and the fusion of the paramesonephric ducts to form the uterus and uterine tubes. It can be concluded that both sexes begin with a similar set of precursor structures, and sexual differentiation is driven by the selective retention and degeneration of these ductal systems.

Cells of a male embryo have one X chromosome and one Y chromosome. The male pattern of development is initiated by a “master switch” gene on the Y chromosome named S.R.Y, which stands for Sex-determining Region of the Y chromosome. When the S.R.Y gene is expressed during development, its protein product causes the primitive nurse cells to begin to differentiate in the testes during the seventh week. The developing nurse cells secrete a hormone called Müllerian-inhibiting substance (M.I.S), which causes apoptosis of cells within the paramesonephric ducts. As a result, those cells do not contribute any functional structures to the male reproductive system.

Stimulated by human chorionic gonadotropin (hCG), primitive interstitial endocrine cells in the testes begin to secrete the androgen testosterone during the eighth week. Testosterone then stimulates development of the mesonephric duct on each side into the epididymis, ductus deferens, ejaculatory duct, and seminal glands. The testes connect to the mesonephric duct through a series of tubules that eventually become the seminiferous tubules. The prostate and bulbourethral glands are endodermal outgrowths of the urethra.

Cells of a female embryo have two X chromosomes and no Y chromosome. Because S.R.Y is absent, the gonadal ridges develop into ovaries, and because M.I.S is not produced, the paramesonephric ducts flourish. The distal ends of the paramesonephric ducts fuse to form the uterus and vagina; the unfused

Figure 28.28 Development of the Internal Genital Systems.

proximal portions of the ducts become the uterine tubes. The mesonephric ducts degenerate without contributing any functional structures to the female genital system because of the absence of testosterone. The greater and lesser vestibular glands develop from endodermal outgrowths of the vestibule.

The external genitals of both male and female embryos (penis and scrotum in males and clitoris, labia, and vaginal orifice in females) also remain undifferentiated until about the eighth week. Before differentiation, all embryos have the following external structures (Figure 28.29):

Figure 28.29 summary: This figure is a series of anatomical diagrams. It illustrates the developmental progression of human external genitalia from an undifferentiated embryonic stage to the stage near birth, comparing male and female pathways. The diagrams show how common precursor structures, such as the genital tubercle, urethral folds, and labioscrotal swellings, differentiate into distinct organs. In male development, these structures evolve into the glans penis, penis, and scrotum. In female development, they transition into the clitoris, labia majora, labia minora, and the vestibule. The figure demonstrates that both male and female external genitalia originate from the same embryonic tissues, which then diverge based on biological development.

1. Urethral (urogenital) folds. The paired urethral (urogenital) folds develop from mesoderm in the cloacal region (see Figure 26.23).

2. Urethral groove. An indentation between the urethral folds, the urethral groove is the opening into the urogenital sinus.

3. Genital tubercle. The genital tubercle is a rounded elevation just anterior to the urethral folds.

Figure 28.29 Development of the External Genitals.

The external genitals of male and female embryos remain undifferentiated until about the eighth week.

4. Labioscrotal swelling. The labioscrotal swelling labeoscrotal consists of paired, elevated structures lateral to the urethral folds.

In male embryos, some testosterone is converted to a second androgen called dihydrotestosterone (D.H.T). D.H.T stimulates development of the urethra, prostate, and external genitals (scrotum and penis). Part of the genital tubercle elongates and develops into a penis. Fusion of the urethral folds forms the spongy urethra and leaves an opening to the exterior only at the distal end of the penis, the external urethral orifice. The labioscrotal swellings develop into the scrotum.

In the absence of D.H.T, the genital tubercle gives rise to the clitoris in female embryos. The urethral folds remain open as the labia minora, and the labioscrotal swellings become the labia majora. The urethral groove becomes the vestibule.

After birth, androgen levels decline because hCG is no longer present to stimulate secretion of testosterone.

Checkpoint

33. How does the type of sperm (X-bearing or Y-bearing) determine the genetic sex of the embryo?

34. Describe the role of hormones in the differentiation of the Wolffian ducts, the Müllerian ducts, and the external genitalia.

28.7 Aging and the Genital Systems

Objective

• Describe the effects of aging on the genital systems.

During the first decade of life, the genital system is in a juvenile state. At about age 10, hormone-directed changes start to occur in both sexes. Puberty (PÜ-ber-të = maturity) is the period when secondary sexual characteristics begin to develop and the potential for sexual reproduction is reached. The onset of puberty is marked by pulses or bursts of L.H and F.S.H secretion, each triggered by a pulse of GnRH. Most pulses occur during sleep.

As puberty advances, the hormone pulses occur during the day as well as at night. The pulses increase in frequency during a 3-to 4-year period until the adult pattern is established. The stimuli that cause the GnRH pulses are still unclear, but a role for the hormone leptin is starting to unfold. Just before puberty, leptin levels rise in proportion to adipose tissue mass. Interestingly, leptin receptors are present in both the hypothalamus and anterior pituitary. Mice that lack a functional leptin gene from birth are sterile and remain in a prepubertal state.

Giving leptin to such mice elicits secretion of gonadotropins, and they become fertile. Leptin may signal the hypothalamus that long-term energy stores (triglycerides in adipose tissue) are adequate for reproductive functions to begin.

In females, the genital cycle normally occurs once each month from menarche menarke, the first menses, to menopause, the permanent cessation of menses. Thus, the female genital system has a time-limited span of fertility between menarche and menopause. For the first 1 to 2 years after menarche, ovulation only occurs in about 10% of the cycles and the luteal phase is short. Gradually, the percentage of ovulatory cycles increases, and the luteal phase reaches its normal duration of 14 days. With age, fertility declines. Between the ages of 40 and 50 the pool of remaining ovarian follicles becomes exhausted.

As a result, the ovaries become less responsive to hormonal stimulation. The production of estrogens declines, despite copious secretion of F.S.H and L.H by the anterior pituitary. Many women experience hot flashes and heavy sweating, which coincide with bursts of GnRH release. Other symptoms of menopause are headache, hair loss, muscular pains, vaginal dryness, insomnia, depression, weight gain, and mood swings.

Some atrophy of the ovaries, uterine tubes, uterus, vagina, external genitals, and breasts occurs in postmenopausal women. Due to loss of estrogens, most women experience a decline in bone mineral density after menopause. Sexual desire (libido) does not show a parallel decline; it may be maintained by suprarenal sex steroids.

The risk of having uterine cancer peaks at about 65 years of age, but cervical cancer is more common in younger women.

In males, declining genital function is much more subtle than in females. Healthy men often retain genital capacity into their eighties or nineties. At about age 55 a decline in testosterone synthesis leads to reduced muscle strength, fewer viable sperm, and decreased sexual desire. Although sperm production decreases 50 to 70% between ages 60 and 80, abundant sperm may still be present even in old age.

Enlargement of the prostate to two to four times its normal size occurs in most males over age 60. This condition, called benign prostatic hyperplasia B.P.H hyperplazea, decreases the size of the prostatic urethra and is characterized by frequent urination, nocturia (having to urinate at night), hesitancy in urination, decreased force of urinary stream, post-voiding dribbling, and a sensation of incomplete emptying.

Checkpoint

35. What changes occur in males and females at puberty?

36. What do the terms menarche and menopause mean?

To appreciate the many ways that the genital systems contribute to homeostasis of other body systems, examine Focus on Homeostasis: Contributions of the Genital Systems. Next, in Chapter 29, you will explore the major events that occur during pregnancy and you will discover how genetics (inheritance) plays a role in the development of a child.

Disorders: Homeostatic Imbalances

Genital System Disorders in Males

Testicular Cancer Testicular cancer is the most common cancer in males between the ages of 20 and 35. More than 95% of testicular cancers arise from spermatogonia within the seminiferous tubules. An early sign of testicular cancer is a mass in the testis, often associated with a sensation of testicular heaviness or a dull ache in the lower abdomen; pain usually does not occur. To increase the chance for early detection of a testicular cancer, all males should perform regular self-examinations of the testes.

The examination should be done starting in the teen years and once each month thereafter. After a warm bath or shower (when the scrotal skin is loose and relaxed) each testis should be examined as follows. The testis is grasped and gently rolled between the index finger and thumb, feeling for lumps, swellings, hardness, or other changes. If a lump or other change is detected, a physician should be consulted as soon as possible.

Prostate Disorders Because the prostate surrounds part of the urethra, any infection, enlargement, or tumor can obstruct the flow of urine. Acute and chronic infections of the prostate are common in postpubescent males, often in association with inflammation of the urethra. Symptoms may include fever, chills, urinary frequency, frequent urination at night, difficulty in urinating, burning or painful urination, low back pain, joint and muscle pain, blood in the urine, or painful ejaculation. However, often there are no symptoms. Antibiotics are used to treat most cases that result from a bacterial infection.

In acute prostatitis, the prostate becomes swollen and tender. Chronic prostatitis is one of the most common chronic infections in men of the middle and later years. On examination, the prostate feels enlarged, soft, and very tender, and its surface outline is irregular.

Prostate cancer is the leading cause of death from cancer in men in the United States, having surpassed lung cancer in 1991. Each year it is diagnosed in almost 200,000 U.S. men and causes about 33,000 deaths. The amount of P.S.A (prostate-specific antigen), which is produced only by prostate epithelial cells, increases with enlargement of the prostate and may indicate infection, benign enlargement, or prostate cancer. A blood test can measure the level of P.S.A in the blood. Males over the age of 40 should have an annual examination of the prostate gland.

In a digital rectal exam, a physician palpates the gland through the rectum with the fingers (digits). Many physicians also recommend an annual P.S.A test for males over age 50. Treatment for prostate cancer may involve surgery, cryotherapy, radiation, hormonal therapy, and chemotherapy. Because many prostate cancers grow very slowly, some urologists recommend “watchful waiting” before treating small tumors in men over age 70.

Focus on Homeostasis

Contributions of the Genital (Reproductive) Systems for All Body Systems

Image summary: This figure is an anatomical illustration. It depicts a full-body human female figure overlaid with a series of horizontal parallel lines. The illustration shows that the linear pattern covers the entire body from the neck down to the feet, including the limbs and torso.

• The male and female genital systems produce gametes (sperm and oocytes) that unite to form embryos and fetuses, which contain cells that divide and differentiate to form all of the organ systems of the body

Image summary: This is an anatomical illustration. The figure displays the external human forms of a male and a female, with internal reproductive organs superimposed over the pelvic regions. The illustration highlights the structural differences between the male and female reproductive systems, showing the location and arrangement of the organs relative to the body. It can be inferred that the male and female bodies possess distinct biological reproductive architectures, with the female system featuring internal organs like the uterus and ovaries, while the male system consists of different specialized structures.

Integumentary Systems

• Androgens promote the growth of body hair

• Estrogens stimulate the deposition of fat in the breasts, abdomen, and hips • Mammary glands produce milk

• Mammary glands produce milk

• Skin stretches during pregnancy as the fetus enlarges

Skeletal System

• Androgens and estrogens stimulate the growth and maintenance of bones of the skeletal system

Muscular System

• Androgens stimulate the growth of skeletal muscles

Nervous System

• Androgens inuence libido (sex drive)

• Estrogens may play a role in the development of certain regions of the brain in males

Endocrine System

• Testosterone and estrogens exert feedback effects on the hypothalamus and anterior pituitary gland

Cardiovascular System

• Estrogens lower blood cholesterol level and may reduce the risk of coronary artery disease in women under age 50

Lymphoid (Lymphatic) Systems and Immunity

• The presence of an antibiotic-like chemical in semen and the acidic pH of vaginal fluid provide innate immunity against microbes in the genital tract

Respiratory System

• Sexual arousal increases the rate and depth of breathing

Digestive System

• The presence of the fetus during pregnancy crowds the digestive organs, which leads to heartburn and constipation

Urinary System

• In males, the portion of the urethra that extends through the prostate and penis is a passageway for urine as well as semen

Erectile Dysfunction Erectile dysfunction (E.D), previously termed impotence, is the consistent inability of an adult male to ejaculate or to attain or hold an erection long enough for sexual intercourse. Many cases of impotence are caused by insufficient release of nitric oxide, which relaxes the smooth muscle of the penile arterioles and erectile tissue. The drug Viagra® (sildenafil) enhances smooth muscle relaxation by nitric oxide in the penis.

Other causes of erectile dysfunction include diabetes mellitus, physical abnormalities of the penis, systemic disorders such as syphilis, vascular disturbances (arterial or venous obstructions), neurological disorders, surgery, testosterone deficiency, and drugs (alcohol, antidepressants, antihistamines, antihypertensives, narcotics, nicotine, and tranquilizers). Psychological factors such as anxiety or depression, fear of causing pregnancy, fear of sexually transmitted infections, religious inhibitions, and emotional immaturity may also cause E.D.

Genital System Disorders in Females

Premenstrual Syndrome and Premenstrual Dysphoric Disorder Premenstrual syndrome (P.M.S) is a cyclical disorder of severe physical and emotional distress. It appears during the postovulatory (luteal) phase of the female reproductive cycle and dramatically disappears when menstruation begins. The signs and symptoms are highly variable from one woman to another. They may include edema, weight gain, breast swelling and tenderness, abdominal distension, backache, joint pain, constipation, skin eruptions, fatigue and lethargy, greater need for sleep, depression or anxiety, irritability, mood swings, headache, poor coordination and clumsiness, and cravings for sweet or salty foods. The cause of P.M.S is unknown. For some women, getting regular exercise; avoiding caffeine, salt, and alcohol; and eating a diet that is high in complex carbohydrates and lean proteins can bring considerable relief.

Premenstrual dysphoric disorder (P.M.D.D) is a more severe syndrome in which P.M.S-like signs and symptoms do not resolve after the onset of menstruation. Clinical research studies have found that suppression of the reproductive cycle by a drug (leuprolide) that interferes with GnRH (gonadotropin-releasing hormone) decreases symptoms significantly. Because symptoms reappear when estradiol or progesterone is given together with leuprolide, researchers propose that P.M.D.D is caused by abnormal responses to normal levels of these ovarian hormones. S.S.R.I's (selective serotonin reuptake inhibitors) have shown promise in treating both P.M.S and P.M.D.D.

Endometriosis Endometriosis endometriosis; endo-= within; metri-= uterus; -osis = condition) is characterized by the growth of endometrial tissue outside the uterus. The tissue enters the pelvic cavity via the open uterine tubes and may be found in any of several sites—on the ovaries, the rectouterine pouch, the outer surface of the uterus, the sigmoid colon, pelvic and abdominal lymph nodes, the cervix, the abdominal wall, the kidneys, and the urinary bladder. Endometrial tissue responds to hormonal flow. - is inside or outside the uterus. - issue proliferates and - outside the -ility.

Symptoms include premenstrual pain or unusually severe menstrual pain.

Breast Cancer One in eight women in the United States faces the prospect of breast cancer. After lung cancer, it is the second-leading cause of death from cancer in U.S. women. Breast cancer can occur in males but is rare. In females, breast cancer is seldom seen before age 30; its incidence rises rapidly after menopause. An estimated 5% of the nearly 277,000 cases diagnosed each year in the United States, particularly those that arise in younger women, stem from inherited genetic mutations (changes in the D.N.A). Researchers have now identified two genes that increase susceptibility to breast cancer: B.R.C.A.1 (breast cancer 1) and B.R.C.A.2. Mutation of B.R.C.A.1 also confers a high risk for ovarian cancer.

In addition, mutations of the p53 gene increase the risk of breast cancer in both males and females, and mutations of the androgen receptor gene are associated with the occurrence of breast cancer in some males. Because breast cancer generally is not painful until it becomes quite advanced, any lump, no matter how small, should be reported to a physician at once. Early detection—by breast self-examination and mammograms—is the best way to increase the chance of survival.

The most effective technique for detecting tumors less than 1 centimeters (0.4 in.) in diameter is mammography mammografe; -graphy = to record), a type of radiography using very sensitive x-ray film. The image of the breast, called a mammogram (see Table 1.3), is best obtained by compressing the breasts, one at a time, using flat plates. A supplementary procedure for evaluating breast abnormalities is ultrasound. Although ultrasound cannot detect tumors smaller than 1 centimeters in diameter (which mammography can detect), it can be used to determine whether a lump is a benign, fluid-filled cyst or a solid (and therefore possibly malignant) tumor.

Among the factors that increase the risk of developing breast cancer are a family history of breast cancer, especially in a mother or sister; nulliparity (never having borne a child) or having a first child after age 35; (3) previous cancer in one breast; exposure to ionizing radiation, such as x-rays; excessive alcohol intake; and cigarette smoking.

The American Cancer Society provides current recommendations for breast cancer screening:

Treatment for breast cancer may involve hormone therapy, chemotherapy, radiation therapy, lumpectomy lumpectome (removal of the tumor and the immediate surrounding tissue), a modified or radical mastectomy, or a combination of these approaches. A radical mastectomy mastektome; mast-= breast) involves removal of the affected breast along with the underlying pectoral muscles and the axillary lymph nodes. (Lymph nodes are removed because metastasis of cancerous cells usually occurs through lymphatic or blood vessels.) Radiation treatment and chemotherapy may follow the surgery to ensure the destruction of any stray cancer cells.

Another modality that is used to help detect breast cancer is called digital tomosynthesis, also called 3.D mammography, digital breast tomosynthesis D.B.T, or simply "tomo". In conventional mammography, x-rays of each breast are taken from two different angles: top to bottom and side to side and the image produced is a single 2-dimensional image. In digital tomosynthesis, on the other hand, x-ray images of each breast are taken from many angles as the x-ray tube moves in an arc around each breast. The result is a series of 3-dimensional images (slices), which are viewed individually by a radiologist. You can compare the difference between conventional mammography and digital tomosynthesis in the two images shown below. Some of the reported benefits of digital tomosynthesis are that it provides a clearer image of breast masses, especially in dense breast tissue; greater accuracy in identifying the shape, and location of abnormalities; fewer false positives and thus fewer callbacks; and less compression of the breasts during the examination, resulting in less discomfort.

Several types of chemotherapeutic drugs are used to decrease the risk of relapse or disease progression. Tamoxifen (Nolvadex®) is an antagonist to estrogens that binds to and blocks receptors for estrogens, thus decreasing the stimulating effect of estrogens on breast cancer cells. Tamoxifen has been used for 20 years and greatly reduces the risk of cancer recurrence.

Herceptin®, a monoclonal antibody drug, targets an antigen on the surface of breast cancer cells. It is effective in causing regression of tumors and retarding progression of the disease. The early data from clinical trials of two new drugs, Femara® and Amimidex®, show relapse rates that are lower than those for tamoxifen.

These drugs are inhibitors of aromatase, the enzyme needed for the final step in synthesis of estrogens. Finally, two drugs—tamoxifen and Evista® (raloxifene)—are being marketed for breast cancer prevention. Interestingly, raloxifene blocks estrogen receptors in the breasts and uterus but activates estrogen receptors in bone. Thus, it can be used to treat osteoporosis without increasing a woman's risk of breast or endometrial (uterine) cancer.

Ovarian and Cervical Cancer Even though ovarian cancer is the sixth most common form of cancer in females, it is the leading cause of death from all gynecological malignancies (excluding breast cancer) because it is difficult to detect before it metastasizes (spreads) beyond the ovaries. Risk factors associated with ovarian cancer include age (usually over age 50); race (whites are at highest risk); family history of ovarian cancer; more than 40 years of active ovulation; nulliparity or first pregnancy after age 30; a high-fat, low-fiber, vitamin A-deficient diet; and prolonged exposure to asbestos or talc. Early ovarian cancer has no symptoms or only mild ones associated with other common problems, such as abdominal discomfort, heartburn, nausea, loss of appetite, bloating, and flatulence. Later-stage signs and symptoms include an enlarged abdomen, abdominal and/or pelvic pain, persistent digestive disturbances, urinary complications, menstrual irregularities, and heavy menstrual bleeding.

Cervical cancer is a carcinoma of the cervix of the uterus that affects about 12,000 females a year in the United States with a mortality rate of about 4,000 annually. It begins as a precancerous condition called cervical dysplasia displazea, a change in the number, shape, and growth of cervical cells, usually the squamous cells. Sometimes the abnormal cells revert to normal; other times they progress to cancer, which usually develops slowly. In most cases, cervical cancer can be detected in its earliest stages by a Pap test (see Clinical Connection: Papanicolaou Test in Section 4.4). Almost all cervical cancers are caused by several types of human papillomavirus (H.P.V); other types of H.P.V cause genital warts (described later).

It is estimated that about 20 million Americans are currently infected with H.P.V. In most cases, the body fights off H.P.V through its immune responses, but sometimes it causes cancer, which can take years to develop. H.P.V is transmitted via vaginal, anal, and oral sex; the infected partner may not have any signs or symptoms. The signs and symptoms of cervical cancer include abnormal vaginal bleeding (bleeding between periods, after intercourse, or after menopause, heavier and longer than normal periods, or a continuous vaginal discharge that may be pale or tinged with blood). There are several ways to decrease the risk of H.P.V infection. These include avoiding risky sexual practices (unprotected sex, sex at an early age, multiple sex partners, or partners who engage in high-risk sexual activities), a weakened immune system, and not getting the H.P.V vaccine. Two vaccines are available to protect males and females against the types of H.P.V that cause most types of cervical cancer (Gardasil® and Ceravix®). Treatment options for cervical cancer include loop electrosurgical excision procedure leep; cryotherapy, freezing abnormal cells; laser therapy, the use of light to burn abnormal tissue; hysterectomy, radical hysterectomy; pelvic exteneration, the removal of all pelvic organs; radiation; and chemotherapy.

Vulvovaginal Candidiasis Candida albicans is a yeastlike fungus that commonly grows on mucous membranes of the digestive canal and genitourinary tracts. The organism is responsible for vulvovaginal candidiasis vulvovaginal can-di-Dí-a-sis), the most common form of vaginitis (vaj-i-Ní-tis), inflammation of the vagina. Candidiasis is characterized by severe itching; a thick, yellow, cheesy discharge; a yeasty odor; and pain.

The disorder, experienced at least once by about 75% of females, is usually a result of proliferation of the fungus following antibiotic therapy for another condition. Predisposing conditions include the use of oral contraceptives or cortisone-like medications, pregnancy, and diabetes.

Figure 1 summary: This figure consists of two medical imaging scans. The images display mammography views of breast tissue, showing a dense, irregular mass within the breast parenchyma. The comparison between the images suggests that different imaging techniques or views provide varying levels of detail and contrast, with one image highlighting the mass more prominently than the other. This indicates that conventional mammography is used to detect and characterize abnormal growths in the breast.

Sexually Transmitted Infections

A sexually transmitted infection (S.T.I) is one that is spread by sexual contact. In most developed countries of the world, such as those of Western Europe, Japan, Australia, and New Zealand, the incidence of S.T.I's has declined markedly during the past 25 years. In the United States, by contrast, S.T.I's have been rising to near-epidemic proportions; they currently affect more than 65 million people. AIDS and hepatitis B, which are sexually transmitted infections that also may be contracted in other ways, are discussed in Chapters 22 and 24, respectively.

Chlamydia Chlamydia klamidea is a sexually transmitted infection caused by the bacterium Chlamydia trachomatis (chlamy-= cloak). (Figure A). This unusual bacterium cannot reproduce outside body cells; it “cloaks” itself inside cells, where it divides. At present, chlamydia is the most prevalent sexually transmitted infection in the United States. In most cases, the initial infection is asymptomatic and thus difficult to recognize clinically. In males, urethritis is the principal result, causing a clear discharge, burning on urination, frequent urination, and painful urination. Without treatment, the epididymides may also become inflamed, leading to sterility. In 70% of females with chlamydia, symptoms are absent, but chlamydia is the leading cause of pelvic inflammatory disease. The uterine tubes may also become inflamed, which increases the risk of ectopic pregnancy (implantation of a fertilized ovum outside the uterus) and infertility due to the formation of scar tissue in the tubes.

Trichomoniasis Trichomoniasis (trik'-o-mo-Ni-a-sis) is a very common S.T.I and is considered the most curable. It is caused by the protozoan Trichomonas vaginalis, which is a normal inhabitant of the vagina in females and urethra in males (Figure B). Most infected people do not have any signs or symptoms. When symptoms are present, they include itching, burning, genital soreness, discomfort with urination, and an unusual-smelling discharge in females. Males experience itching or irritations in the penis, burning after urination or ejaculation, or some discharge. Trichomoniasis can increase the risk of infection with other S.T.I's, such as H.I.V and gonorrhea.

Gonorrhea Gonorrhea (gon-o-Re-a) (Figure C) or “the clap” is caused by the bacterium Neisseria gonorrhoeae. In the United States, 1 million to 2 million new cases of gonorrhea appear each year, most among individuals aged 15 to 29 years. Discharges from infected mucous membranes are the source of transmission of the bacteria either during sexual contact or during the passage of a newborn through the birth canal. The infection site can be in the mouth and throat after oral-genital contact, in the vagina and penis after genital intercourse, or in the rectum after recto-genital contact.

Males usually experience urethritis with profuse pus drainage and painful urination. The prostate and epididymis may also become infected. In females, infection typically occurs in the vagina, often with a discharge of pus. Both infected males and females may harbor the disease without any symptoms, however, until it has progressed to a more advanced stage; about 5 to 10% of males and 50% of females are asymptomatic.

In females, the infection and consequent inflammation can proceed from the vagina into the uterus, uterine tubes, and pelvic cavity. An estimated 50,000 to 80,000 women in the United States are made infertile by gonorrhea every year as a result of scar tissue formation that closes the uterine tubes. If bacteria in the birth canal are transmitted to the eyes of a newborn, blindness can result.

Administration of a 1% silver nitrate solution in the infant's eyes prevents infection.

Syphilis Syphilis, caused by the bacterium Treponema pallidum treponema palidum (Figure D), is transmitted through sexual contact or exchange of blood, or through the placenta to a fetus. The disease progresses through several stages. During the primary stage, the chief sign is a painless open sore, called a {chancre} shanker, at the point of contact. The chancre heals within 1 to 5 weeks. From 6 to 24 weeks later, signs and symptoms such as a skin rash, fever, and aches in the joints and muscles usher in the secondary stage, which is systemic—the infection spreads to all major body systems. When signs of organ degeneration appear, the disease is said to be in the tertiary stage. If the nervous system is involved, the tertiary stage is called {neurosyphilis} . As motor areas become damaged extensively, victims may be unable to control urine and bowel movements.

Eventually they may become bedridden and unable even to feed themselves. In addition, damage to the cerebral cortex produces memory loss and personality changes that range from irritability to hallucinations.

Genital Herpes Genital herpes is an incurable S.T.I. Type 2 herpes simplex virus H.S.V-2 causes genital infections (Figure E), producing painful blisters on the prepuce, glans penis, and penile shaft in males and on the vulva or sometimes high up in the vagina in females. The blisters disappear and reappear in most patients, but the virus itself remains in the body. A related virus, type I herpes simplex virus H.S.V-1, causes cold sores on the mouth and lips and is not considered a sexually transmitted infection. Infected individuals typically experience recurrences of symptoms several times a year.

Human Papillomavirus (H.P.V) Infection Human papillomaviruses H.P.V's are a group of about 200 related viruses that infect human skin and mucous membranes (Figure F). Human papillomavirus (H.P.V) infection is the most commonly sexually transmitted infection in the United States (about 80 million persons are infected) and about 14 million cases are diagnosed annually. Most people infected with H.P.V don't know they are infected and may never develop signs or symptoms. H.P.V infection is highly contagious and the virus is spread by direct contact. Certain H.P.V types, called low-risk H.P.V's, do not cause cancer but can cause genital warts (described in the next paragraph) on or around the genitals and anus and skin warts in other parts of the body, such as the hands.

Other H.P.V types, referred to as high-risk H.P.V's, may cause different types of cancers. These include cervical, vulvar, and vaginal cancers in females, penile cancer in males, and oropharyngeal and anal cancers in both genders. H.P.V is transmitted by intimate contact with infected areas of the skin or mucous membranes. Sexual contact routes of transmission include vaginal, anal, and oral sex.

There is no specific treatment for persistent H.P.V infections, although treatments are available for skin warts, genital warts, precancerous cervical lesions, and cancers resulting from H.P.V infections. There are several vaccines (Gardasil®, Gardasil® 9, and Cervarix®) that are available to prevent H.P.V infection with the most common cancer-forming H.P.V types. Although these vaccines provide strong protection against new H.P.V infections, they are not effective for infections that are already established or any diseases caused by H.P.V.

Genital Warts Genital warts typically appear as single or multiple bumps in the genital area and are caused by several types of human papillomavirus (H.P.V). The lesions can be flat or raised, small or large, or shaped like a cauliflower with multiple fingerlike projections (Figure G). Nearly 1 million people in the United States develop genital warts annually. Genital warts can be transmitted sexually and may appear weeks or months after sexual contact, even if an infected partner has no signs or symptoms of the disease. In most cases, the immune system defends against H.P.V and the infected cells revert to normal within two years.

When immunity is ineffective, lesions appear. There is no cure for genital warts, although topical gels are often useful treatments. The vaccine Gardasil® is available to protect against most genital warts.

Figure A summary: This figure is a light microscopy image. It displays a cervical smear containing various cellular structures, specifically highlighting a comparison between a healthy cell and one infected with Chlamydia. The infected cell is characterized by the presence of intracellular inclusions, whereas the normal cell lacks these features. The image demonstrates that Chlamydia infection results in distinct morphological changes within the host cells of the cervical smear.

Figure B summary: This figure is a scanning electron micrograph. It displays a Trichomonas vaginalis parasite attached to the surface of a vaginal epithelial cell. The image illustrates the physical interaction and adherence of the pathogen to the host tissue, demonstrating how the parasite anchors itself to the epithelial layer of the vagina.

Figure C summary: This figure is a light microscopy image. It displays a vaginal smear containing numerous white blood cells and clusters of Neisseria gonorrhoeae bacteria, which appear as very small spherical structures. The presence of these tiny spheres associated with the inflammatory cells indicates a bacterial infection in the sampled area.

Figure D summary: This figure is a micrograph. It displays two individual Treponema pallidum bacteria. The image reveals that these bacteria possess a characteristic spiral or helical shape, indicating a morphology typical of spirochetes.

Figure E summary: This figure is a transmission electron micrograph. It depicts a high-magnification view of a cellular environment containing a spherical viral particle embedded within the cytoplasm. The image shows the internal structure of the virus and its spatial relationship to the surrounding cellular components and the outer boundary of the cell. The presence of the particle within the cell indicates an intracellular stage of the viral life cycle, demonstrating the successful entry or assembly of the virus within the host cell.

Figure F summary: This figure is a micrograph. It displays the structural morphology of the Human papillomavirus, showing a roughly spherical viral particle with a textured surface. The image demonstrates that the virus possesses a dense, symmetric capsid structure, which is characteristic of the papillomavirus family.

Figure G summary: This is a clinical photograph. The image displays a large, irregular, and cauliflower-like growth located in the genital region. The presence of these characteristic fleshy protrusions indicates a diagnosis of genital warts.

Medical Terminology

Castration kastrashun = to prune) Removal, inactivation, or destruction of the gonads; commonly used in reference to removal of the testes only.

Colposcopy kolposkope; colpo-= vagina; -scopy = to view) Visual inspection of the vagina and cervix of the uterus using a cul-poscope, an instrument that has a magnifying lens (between 5× and 50×) and a light. The procedure generally takes place after an unusual Pap smear.

Culdoscopy kuldoskope; -cul-= cul-de-sac; -scopy = to examine) A procedure in which a culdoscope (endoscope) is inserted through the posterior wall of the vagina to view the rectouterine pouch in the pelvic cavity.

Dysmenorrhea (dis-men-ör-E-a; dys-= difficult or painful) Pain associated with menstruation; the term is usually reserved to describe menstrual symptoms that are severe enough to prevent a woman from functioning normally for one or more days each month. Some cases are caused by uterine tumors, ovarian cysts, pelvic inflammatory disease, or intrauterine devices.

Dyspareunia disparoonya; dys-= difficult; -para-= beside; eune = lie within) Pain during sexual intercourse. It may occur in the genital area or in the pelvic cavity, and may be due to inadequate lubrication, inflammation, infection, an improperly fitting diaphragm or cervical cap, endometriosis, pelvic inflammatory disease, pelvic tumors, or weakened uterine ligaments.

Endocervical curettage kuretahzh; curette = scraper) A procedure in which the cervix is dilated and the endometrium of the uterus is scraped with a spoon-shaped instrument called a curette; commonly called a D and C (dilation and curettage).

Fibroids (Fi-broyds; fibro-= fiber; -eidos = resemblance) Noncancerous tumors in the myometrium of the uterus composed of muscular and fibrous tissue. Their growth appears to be related to high levels of estrogens. They do not occur before puberty and usually stop growing after menopause. Symptoms include abnormal menstrual bleeding and pain or pressure in the pelvic area.

Hermaphroditism hermaphroditism The presence of both ovarian and testicular tissue in one individual.

Chapter Review

Review

28.1 Male Genital System

1. The male genital organs include the testes, epididymidis, ductus deferens, ejaculatory ducts, seminal glands, urethra, prostate, bulbourethral glands, and penis. The scrotum is a sac that hangs from the root of the penis and consists of loose skin and underlying subcutaneous tissue; it supports the testes. The temperature of the testes is regulated by the cremaster muscles, which either contract to elevate the testes and move them closer to the pelvic cavity or relax and move them farther from the pelvic cavity. The dartos muscle causes the scrotum to become tight and wrinkled.

Hypospadias hypospadeas; hypo-= below) A common congenital abnormality in which the urethral opening is displaced. In males, the displaced opening may be on the underside of the penis, at the penoscrotal junction, between the scrotal folds, or in the perineum; in females, the urethra opens into the vagina. The problem can be corrected surgically.

Leukorrhea (loo'-ko-Re-a; leuko-= white) A whitish (nonbloody) vaginal discharge containing mucus and pus cells that may occur at any age and affects most women at some time.

Menorrhagia menorajea; meno-= menstruation; -rhage = to burst forth) Excessively prolonged or profuse menstrual period. May be due to a disturbance in hormonal regulation of the menstrual cycle, pelvic infection, medications (anticoagulants), fibroids (noncancerous uterine tumors composed of muscle and fibrous tissue), endometriosis, or intrauterine devices.

Oophorectomy oophorektome; oophor-= bearing eggs) Removal of the ovaries.

Orchitis (or-Ki-tis; orchi-= testes; -itis = inflammation) Inflammation of the testes, for example, as a result of the mumps virus or a bacterial infection.

Ovarian cyst The most common form of ovarian tumor, in which a fluid-filled ovarian follicle or corpus luteum persists and continues growing.

Pelvic inflammatory disease (P.I.D) A collective term for any extensive bacterial infection of the pelvic organs, especially the uterus, uterine tubes, or ovaries, which is characterized by pelvic soreness, lower back pain, abdominal pain, and urethritis. Often the early symptoms of P.I.D occur just after menstruation. As infection spreads, fever may develop, along with painful abscesses of the genital organs.

Salpingectomy salpinjektome; salpingo = tube) Removal of a uterine tube.

Smegma smegma the secretion, consisting principally of desquamated epithelial cells, found chiefly around the external genitals and especially under the foreskin of the male.

2. The testes are paired oval glands (gonads) in the scrotum containing seminiferous tubules, in which sperm are made; nurse cells, which nourish sperm and secrete inhibin; and interstitial endocrine cells, which produce the male sex hormone testosterone. The testes descend into the scrotum through the inguinal canals during the seventh month of fetal development. Failure of the testes to descend is called cryptorchidism.

3. Secondary oocytes and sperm, both of which are called gametes, are produced in the gonads. Spermatogenesis, which occurs in the testes, is the process whereby immature spermatogonia develop into sperm. The spermatogenesis sequence, which includes meiosis I, meiosis Two, and spermiogenesis, results in the formation of

four haploid sperm from each primary spermatocyte. Mature sperm consist of a head and a tail. Their function is to fertilize a secondary oocyte.

4. At puberty, gonadotropin-releasing hormone stimulates anterior pituitary secretion of F.S.H and L.H. L.H stimulates production of testosterone; F.S.H and testosterone stimulate spermatogenesis. Nurse cells secrete androgen-binding protein, which binds to testosterone and keeps its concentration high in the seminiferous tubule. Testosterone controls the growth, development, and maintenance of sex organs; stimulates bone growth, protein anabolism, and sperm maturation; and stimulates development of masculine secondary sex characteristics. Inhibin is produced by nurse cells; its inhibition of F.S.H helps regulate the rate of spermatogenesis.

5. The duct system of the testes includes the seminiferous tubules, straight tubules, and rete testis. Sperm flow out of the testes through the efferent ductules. The duct of epididymis is the site of sperm maturation and storage. The ductus deferens stores sperm and propels them toward the urethra during ejaculation.

6. Each ejaculatory duct, formed by the union of the duct from the seminal gland and ampulla of the ductus deferens, is the passageway for ejection of sperm and secretions of the seminal glands into the first portion of the urethra, the prostatic urethra.

7. The urethra in males is subdivided into three portions: the prostatic, membranous, and spongy urethra.

8. The seminal glands secrete an alkaline, viscous fluid that contains fructose (used by sperm for A.T.P production). Seminal fluid constitutes about 60% of the volume of semen and contributes to sperm viability. Prostatic fluid is a slightly acidic fluid that constitutes about 25% of the volume of semen and contributes to sperm motility. The bulbourethral glands secrete mucus for lubrication and an alkaline substance that neutralizes acid. Semen is a mixture of sperm and seminal fluid; it provides the fluid in which sperm are transported, supplies nutrients, and neutralizes the acidity of the male urethra and the vagina.

9. The penis consists of a root, a body, and a glans penis. Engorgement of the penile blood sinuses under the influence of sexual excitation is called erection.

28.2 Female Genital System

1. The female genital organs include the ovaries (gonads), uterine tubes or oviducts, uterus, vagina, and vulva. The mammary glands are part of the integumentary system and also are considered part of the female genital system.

2. The ovaries, the female gonads, are located in the superior portion of the pelvic cavity, lateral to the uterus. Ovaries produce secondary oocytes, discharge secondary oocytes (the process of ovulation), and secrete estrogens, progesterone, relaxin, and inhibin.

3. Oogenesis (the production of haploid secondary oocytes) begins in the ovaries. The oogenesis sequence includes meiosis I and meiosis Two, which goes to completion only after an ovulated secondary oocyte is fertilized by a sperm.

4. The uterine tubes transport secondary oocytes from the ovaries to the uterus and are the normal sites of fertilization. Ciliated cells and peristaltic contractions help move a secondary oocyte or fertilized ovum toward the uterus.

5. The uterus is an organ the size and shape of an inverted pear that functions in menstruation, implantation of a fertilized ovum, development of a fetus during pregnancy, and labor. It also is part of the pathway for sperm to reach the uterine tubes to fertilize a secondary oocyte. Normally, the uterus is held in position by a series of ligaments.

Histologically, the layers of the uterus are an outer perimetrium (serosa), a middle myometrium, and an inner endometrium.

6. The vagina is a passageway for sperm and the menstrual flow, the receptacle of the penis during sexual intercourse, and the inferior portion of the birth canal. It is capable of considerable stretching.

7. The vulva, a collective term for the external genitals of the female, consists of the mons pubis, labia majora, labia minora, clitoris, vestibule, vaginal and urethral orifices, hymen, and bulb of the vestibule, as well as three sets of glands: the paraurethral, greater vestibular glands, and lesser vestibular glands.

8. The perineum is a diamond-shaped area at the inferior end of the trunk medial to the thighs and buttocks.

9. The mammary glands are modified sweat glands lying superficial to the pectoralis major muscles. Their function is to synthesize, secrete, and eject milk (lactation).

10. Mammary gland development depends on estrogens and progesterone. Milk production is stimulated by prolactin, estrogens, and progesterone; milk ejection is stimulated by oxytocin.

28.3 The Female Reproductive Cycle

1. The function of the ovarian cycle is to develop a secondary oocyte; the function of the uterine (menstrual) cycle is to prepare the endometrium each month to receive a fertilized egg. The female reproductive cycle includes both the ovarian and uterine cycles.

2. The uterine and ovarian cycles are controlled by GnRH from the hypothalamus, which stimulates the release of F.S.H and L.H by the anterior pituitary. F.S.H and L.H stimulate development of ovarian follicles and secretion of estrogens by the follicles. L.H also stimulates ovulation, formation of the corpus luteum, and the secretion of progesterone and estrogens by the corpus luteum.

3. Estrogens stimulate the growth, development, and maintenance of female genital structures; stimulate the development of secondary sex characteristics; and stimulate protein synthesis. Progesterone works with estrogens to prepare the endometrium for implantation and the mammary glands for milk synthesis.

4. Relaxin relaxes the myometrium at the time of possible implantation. At the end of a pregnancy, relaxin increases the flexibility of the pubic symphysis and helps dilate the uterine cervix to facilitate delivery.

5. During the menstrual phase, the functional and compact layers of the endometrium is shed, discharging blood, tissue fluid, mucus, and epithelial cells.

6. During the preovulatory phase, a group of ovarian follicles begins to undergo final maturation. One ovarian follicle outgrows the others and becomes dominant while the others degenerate. At the same time, endometrial repair occurs in the uterus. Estrogens are the dominant ovarian hormones during the preovulatory phase.

7. Ovulation is the rupture of the tertiary ovarian follicle and the release of a secondary oocyte into the pelvic cavity. It is brought about by a surge of L.H. Signs and symptoms of ovulation include increased basal body temperature; clear, stretchy cervical mucus; changes in the uterine cervix; and abdominal pain.

8. During the postovulatory phase, both progesterone and estrogens are secreted in large quantity by the corpus luteum of the ovary, and the uterine endometrium thickens in readiness for implantation.

9. If fertilization and implantation do not occur, the corpus luteum degenerates, and the resulting low levels of progesterone and estrogens allow discharge of the endometrium followed by the initiation of another reproductive cycle.

10. If fertilization and implantation do occur, the corpus luteum is maintained by hCG. The corpus luteum and later the placenta secrete progesterone and estrogens to support pregnancy and breast development for lactation.

28.4 The Human Sexual Response

1. The similar sequence of changes experienced by both males and females before, during, and after intercourse is termed the human sexual response; it occurs in four phases: excitement, plateau, orgasm, and resolution.

2. During excitement, there is vasocongestion (engorgement with blood) of genital tissues. Other changes that occur during this phase include increased heart rate and blood pressure, increased skeletal muscle tone throughout the body, and hyperventilation.

3. During the plateau phase, the changes that began during the excitement phase are sustained at an intense level.

4. During orgasm, there are several rhythmic muscular contractions, accompanied by pleasurable sensations and a further increase in blood pressure, heart rate, and respiration rate.

5. During the resolution phase, genital tissues, heart rate, blood pressure, breathing, and muscle tone return to the unaroused state.

28.5 Birth Control Methods and Abortion

1. Birth control methods include complete abstinence, surgical sterilization (vasectomy, tubal ligation), non-incisional sterilization, hormonal methods (combined pill, extended cycle pill, minipill, contraceptive skin patch, vaginal contraceptive ring, emergency contraception, hormonal injections), intrauterine devices, spermicides, barrier methods (male condom, vaginal pouch, diaphragm, cervical cap), and periodic abstinence (rhythm and sympto-thermal methods).

2. Contraceptive pills of the combination type contain progestin and estrogens in concentrations that decrease the secretion of F.S.H and L.H and thereby inhibit development of ovarian follicles and ovulation, inhibit transport of ova and sperm in the uterine tubes, and block implantation in the uterus.

3. An abortion is the premature expulsion from the uterus of the products of conception; it may be spontaneous or induced.

Critical Thinking Questions

1. Twenty-three-year-old Monica and her husband Bill are ready to start a family. They are both avid bicyclists and weight-lifters who carefully watch what they eat and pride themselves on their "buff" bodies. However, Monica is having difficulty becoming pregnant. Monica hasn't had a menstrual period for some time but informs the doctor that is normal for her. After consulting with her physician, the doctor tells Monica that she needs to cut back on her exercise routine and "put on some weight" in order to get pregnant. Monica is outraged because she figures she will gain enough weight when she is pregnant! Explain

28.6 Development of the Genital Systems

1. The gonads develop from gonadal ridges that arise from growth of intermediate mesoderm. In the presence of the S.R.Y gene, the gonads begin to differentiate into testes during the seventh week. The gonads differentiate into ovaries when the S.R.Y gene is absent.

2. In males, testosterone stimulates development of each mesonephric duct into an epididymis, ductus deferens, ejaculatory duct, and seminal glands, and Müllerian-inhibiting substance causes the paramesonephric duct cells to die. In females, testosterone and M.I.S are absent; the paramesonephric ducts develop into the uterine tubes, uterus, and vagina and the mesonephric ducts degenerate.

3. The external genitals develop from the genital tubercle and are stimulated to develop into typical male structures by the hormone dihydrotestosterone (D.H.T). The external genitals develop into female structures when D.H.T is not produced, the normal situation in female embryos.

28.7 Aging and the Genital Systems

1. Puberty is the period when secondary sex characteristics begin to develop and the potential for sexual reproduction is reached.

2. The onset of puberty is marked by pulses or bursts of L.H and F.S.H secretion, each triggered by a pulse of GnRH. The hormone leptin, released by adipose tissue, may signal the hypothalamus that long-term energy stores (triglycerides in adipose tissue) are adequate for reproductive functions to begin.

3. In females, the reproductive cycle normally occurs once each month from menarche, the first menses, to menopause, the permanent cessation of menses.

4. Between the ages of 40 and 50, the pool of remaining ovarian follicles becomes exhausted and levels of progesterone and estrogens decline. Most women experience a decline in bone mineral density after menopause, together with some atrophy of the ovaries, uterine tubes, uterus, vagina, external genitals, and breasts. Uterine and breast cancer increase in incidence with age.

5. In older males, decreased levels of testosterone are associated with decreased muscle strength, waning sexual desire, and fewer viable sperm; prostate disorders are common.

to Monica what has happened to her and why weight gain could help her achieve her goal of pregnancy.

2. The term “progesterone” means “for gestation (or pregnancy).” Describe how progesterone helps prepare the female body for pregnancy and helps maintain pregnancy.

3. After having borne five children, Mark's wife, Isabella, insists that he have a vasectomy. Mark is afraid that he will "dry up" and won't be able to perform sexually. How can you reassure him that his reproductive organs will function fine?

Answers to Figure Questions

28.1 The gonads (testes) produce gametes (sperm) and hormones; the ducts transport, store, and receive gametes; the accessory male genital glands secrete materials that support gametes; and the penis assists in the delivery and joining of gametes.

28.2 The cremaster and dartos muscles help regulate the temperature of the testes.

28.3 The tunica vaginalis and tunica albuginea are tissue layers that cover and protect the testes.

28.4 The interstitial endocrine cells of the testes secrete testosterone.

28.5 As a result of meiosis I, the number of chromosomes in each cell is reduced by half.

28.6 The sperm head contains the nucleus with 23 highly condensed chromosomes and an acrosome that contains enzymes for penetration of a secondary oocyte; the neck contains centrioles that produce microtubules for the rest of the tail; the midpiece contains mitochondria for A.T.P production for locomotion and metabolism; the principal and end pieces of the tail provide motility.

28.7 Nurse cells secrete inhibin.

28.8 Testosterone inhibits secretion of L.H, and inhibin inhibits secretion of F.S.H.

28.9 The seminal glands are the accessory male genital glands that contribute the largest volume to seminal fluid.

28.10 Two tissue masses called the corpora cavernosa penis and one corpus spongiosum penis contain blood sinuses that fill with blood that cannot flow out of the penis as quickly as it flows in. The trapped blood engorges and stiffens the tissue, producing an erection. The corpus spongiosum penis keeps the spongy urethra open so that ejaculation can occur.

28.11 The testes are homologous to the ovaries; the glans penis is homologous to the clitoris; the prostate is homologous to the paraurethral glands; and the bulbourethral glands are homologous to the greater vestibular glands (see Table 28.2).

28.12 The mesovarium anchors the ovary to the broad ligament of the uterus and the uterine tube; the ovarian ligament anchors it to the uterus; the suspensory ligament anchors it to the pelvic wall.

28.13 Ovarian follicles secrete estrogens; the corpus luteum secretes progesterone, estrogens, relaxin, and inhibin.

28.14 Most ovarian follicles undergo atresia (degeneration).

28.15 Primary oocytes are present in the ovary at birth, so they are as old as the woman. In males, primary spermatocytes are continually being formed from stem cells (spermatogonia) and thus are only a few days old.

28.16 Fertilization most often occurs in the ampulla of the uterine tube. 28.17 Ciliated columnar epithelial cells and peg cells (nonciliated cells with microvilli) line the uterine tubes.

28.18 The endometrium is a highly vascularized, secretory epithelium that provides the oxygen and nutrients needed to sustain a fertilized egg; the myometrium is a thick smooth muscle layer that supports the uterine wall during pregnancy and contracts to expel the fetus at birth.

28.19 The basal layer of the endometrium provides cells to replace those that are shed (the functional and compact layers) during each menstruation.

28.20 Anterior to the vaginal opening are the mons pubis, clitoris, prepuce, and external urethral orifice. Lateral to the vaginal opening are the labia minora and labia majora.

28.21 The anterior portion of the perineum is called the urogenital triangle because its borders form a triangle that encloses the urethral (uro-) and vaginal (-genital) orifices.

28.22 Prolactin, estrogens, and progesterone regulate the synthesis of milk. Oxytocin regulates the ejection of milk.

28.23 The principal estrogen is beta estradiol.

28.24 The hormones responsible for the proliferative phase of endometrial growth are estrogens; for ovulation, L.H; for growth of the corpus luteum, L.H; and for the midcycle surge of L.H, estrogens.

28.25 The effect of rising but moderate levels of estrogens is negative feedback inhibition of the secretion of GnRH, L.H, and F.S.H.

28.26 This is negative feedback, because the response is opposite to the stimulus. A reduced amount of negative feedback due to declining levels of estrogens and progesterone stimulates release of Gerh, which in turn increases the production and release of F.S.H and L.H, ultimately stimulating the secretion of estrogens.

28.27 Yes, sperm production continues following a vasectomy, but they no longer reach the exterior; they degenerate and are destroyed by phagocytosis.

28.28 The S.R.Y gene on the Y chromosome is responsible for the development of the gonads into testes.

28.29 The presence of dihydrotestosterone stimulates differentiation of the external genitals in males; its absence allows differentiation of the external genitals in females.

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