Blood and Its Components

1. Functions of Blood

Blood is a specialized connective tissue that circulates throughout the body carrying out three broad categories of function:

A. Transport

- Blood transports oxygen (O 2) from the lungs to the tissues and carbon dioxide (C-O 2) from the tissues back to the lungs; it also carries nutrients absorbed from digestion and hormones released by endocrine glands to their target organs.

B. Regulation

- Blood helps regulate pH (keeping the body's internal environment from becoming too acidic or too basic), body temperature (by absorbing and redistributing heat as it circulates), and fluid balance (by exchanging water with body tissues).

C. Protection

- Blood protects the body through immunity (white blood cells and antibodies defend against pathogens) and clotting (platelets and clotting proteins prevent excessive blood loss after injury).

Remember!

• 3 Functions of Blood — Transport, Regulation, Protection (T-R-P).

Image summary: An anatomical illustration showing blood flowing from a blood vessel into a surrounding area, depicting the various components of blood within the yellow plasma. The image labels red blood cells, white blood cells, and platelets to illustrate the cellular composition and liquid medium of blood.

• Transport = O 2, C-O 2, nutrients, hormones. Regulation = pH, temperature, fluid balance. Protection = immunity, clotting.

2. Physical Characteristics of Blood

Blood has distinct, measurable physical properties that are frequently tested:

- Volume: approximately 5 to 6 liters in males and 4 to 5 liters in females. Blood makes up roughly 8% of total body weight.

- Color: bright red when it is oxygen-rich (oxygenated, as in arterial blood) versus dark red when it is oxygen-poor (deoxygenated, as in venous blood). The color difference comes from how oxygen binds to the iron in hemoglobin.

- pH: blood is slightly basic (alkaline), with a normal range of 7.35 to 7.45. A pH below 7.35 is called acidosis, and above 7.45 is called alkalosis.

- Viscosity: blood is about 3 to 5 times thicker (more viscous) than water, mainly due to the presence of red blood cells and plasma proteins.

- Temperature: blood normally sits at about 38 degrees Celsius, which is slightly higher than average body surface temperature.

Image summary: A photo showing five syringes filled with blood, arranged vertically. The top syringe is labeled "VENOUS BLOOD" and contains dark red blood; the bottom syringe is labeled "ARTERIAL BLOOD" and contains bright red blood, with those in between showing a gradient of color. The image illustrates the visual difference in oxygenation levels between venous and arterial blood.

• Volume: Males approximately 5 to 6 L, Females approximately 4 to 5 L.

• Normal blood pH = 7.35 to 7.45 (slightly alkaline) — this is a classic exam number to memorize.

• Bright red = oxygenated (arterial); Dark red = deoxygenated (venous).

Blood is 3 to 5 times more viscous than water; average temperature is approximately 38 degrees Celsius.

Common Misconception: "Is Blood Blue?"

A common myth is that deoxygenated (venous) blood is blue. This is false. The lecture clarifies:

- Blood in arteries, and blood freshly exposed to air, is bright red.

- Blood in veins, and dried blood, is dark rusty red — not blue.

- Human blood is never actually blue. The bluish appearance of some veins seen through the skin is an optical illusion caused by the way light scatters as it passes through skin and tissue — it does not reflect the true color of the blood itself.

Remember!

• Human blood is never blue — it is always some shade of red (bright red when oxygenated, dark rusty red when deoxygenated).

- Veins look blue through skin only because of how light scatters through tissue — this is a common trick question in exams.

3. Blood Components

When a blood sample is centrifuged (spun in a machine to separate it by density), it separates into two main layers:

Plasma (~55% of blood volume): the straw-colored, liquid portion of blood. It is mostly water and also contains:

- Proteins — albumin (maintains blood osmotic pressure/volume), globulins (transport substances and include antibodies), and fibrinogen (essential for blood clotting)

- Electrolytes (ions such as sodium, potassium, calcium)

- Also carries nutrients, wastes, and dissolved gases throughout the body

Formed Elements (~45% of blood volume): the cellular portion of blood, consisting of:

- Red Blood Cells (R.B.C's) — the most abundant formed element, found in the bottom (heaviest) layer after centrifugation

- White Blood Cells (W.B.C's) and Platelets — found in a thin, whitish layer called the "buffy coat," sitting between the plasma and the R.B.C's

Image summary: A diagram of a blood sample in a test tube, separated into layers. The top yellow layer is labeled as plasma and is shown to contain ions, water, proteins, nutrients, wastes, and gases; the middle thin layer consists of white blood cells and platelets, and the bottom red layer consists of red blood cells. The diagram illustrates the composition and separation of blood into its liquid and cellular components.

Blood = Plasma (~55%) + Formed Elements (~45%).

• Plasma proteins to memorize: Albumin (maintains blood volume/pressure), Globulins (transport + antibodies), Fibrinogen (clotting).

• In a centrifuged blood sample: Plasma floats on top to Buffy coat (W.B.C's plus Platelets) in the middle, thin layer to R.B.C's settle at the bottom (heaviest).

4. Formation of Blood Cells (Hematopoiesis)

Hematopoiesis: the process by which all blood cells — including red blood cells, white blood cells, and platelets — are produced.

Key facts about hematopoiesis:

- It occurs in the bone marrow (specifically the red bone marrow) after birth.

- It begins with hematopoietic stem cells (H.S.C's), unspecialized cells capable of dividing and developing into any type of blood cell.

- H.S.C's differentiate into two major lineages:

- Myeloid lineage — gives rise to red blood cells, platelets, and most types of white blood cells (monocytes, basophils, eosinophils, neutrophils)

Image summary: A diagram illustrating the sources of macrophages, showing an embryonic macrophage providing a valid pathway (indicated by a checkmark) and an adult macrophage showing an invalid pathway (indicated by a red X) for blood cell formation within the bone marrow. The figure demonstrates that embryonic macrophages, rather than adult ones, contribute to specific blood cell formation processes in the bone marrow.

- Lymphoid lineage — gives rise to lymphocytes (B-cells, T-cells, and N.K cells)

- Several key regulatory factors control and stimulate this process:

- Erythropoietin (E.P.O) — stimulates red blood cell production

- Thrombopoietin (T.P.O) — stimulates platelet production

- Granulocyte colony-stimulating factor (G-C.S.F) — stimulates production of granulocytes (a group of white blood cells including neutrophils)

- Granulocyte-macrophage colony-stimulating factor (G.M-C.S.F) — stimulates production of both granulocytes and macrophages

Reading the Hematopoiesis Lineage Diagram

The lecture's diagram traces the full "family tree" of blood cell development, starting from a single hematopoietic stem cell at the top and branching downward into all mature blood cell types:

- Hematopoietic Stem Cell splits into two progenitor (parent) cell lines:

- Common Myeloid Progenitor to develops into: Red Blood Cells, Platelets, and a Myeloblast, which further develops into Monocytes, Basophils, Eosinophils, and Neutrophils

Image summary: A biological diagram showing red bone marrow in a femur producing hematopoietic stem cells (HSCs), which then differentiate into red blood cells, white blood cells, and platelets. The illustration depicts the process of hematopoiesis, where a single stem cell source gives rise to all types of blood cells.

Image summary: A flow diagram of hematopoiesis showing a hematopoietic stem cell differentiating into two main lineages: a common myeloid progenitor and a common lymphoid progenitor. The myeloid lineage further branches into red blood cells, platelets, and myeloblasts, with the latter giving rise to monocytes, basophils, eosinophils, and neutrophils. The lymphoid lineage progresses through a lymphoblast to produce B-cells, T-cells, and NK-cells. The diagram illustrates how a single stem cell progenitor diversifies into all the specialized cells of the immune and blood systems.

- Common Lymphoid Progenitor to develops into a Lymphoblast, which further develops into B-cells, T-cells, and N.K-cells (Natural Killer cells)

Why this diagram matters: it shows that all blood cells share a single common ancestor cell (the H.S.C), but branch into two very different "families" (myeloid versus lymphoid) depending on their ultimate function — the myeloid line focuses mostly on oxygen transport, clotting, and innate defenses, while the lymphoid line focuses on adaptive/specific immunity.

• Hematopoiesis = formation of all blood cells; happens in the (red) bone marrow after birth.

• One Stem Cell to 2 lineages: Myeloid (R.B.C's, Platelets, Monocytes, Basophils, Eosinophils, Neutrophils) versus Lymphoid (B-cells, T-cells, N.K-cells).

• 4 Regulatory factors: E.P.O = red cells; T.P.O = platelets; G-C.S.F = granulocytes; G.M-C.S.F = granulocytes + macrophages.

5. Red Blood Cells (R.B.C's)

Red blood cells, or erythrocytes, are the most numerous blood cells and are specialized for oxygen transport. Key characteristics:

- Biconcave in shape (like a disc pinched in the middle on both sides) — this shape increases surface area for gas exchange and allows R.B.C's to flex through narrow capillaries.

- Anucleate — mature R.B.C's have no nucleus, which leaves more internal space to pack in hemoglobin.

- Contain hemoglobin, the iron-containing protein responsible for binding and transporting oxygen (and giving blood its red color).

- Have a lifespan of about 120 days.

- Old or damaged R.B.C's are removed (destroyed) by the spleen.

Remember!

Image summary: A 3D medical illustration showing numerous red blood cells flowing together in a dark red space. It is an anatomical depiction used to visualize blood cells, with no data or analytical result to report.

• R.B.C shape = biconcave + anucleate to maximizes surface area for O₂ exchange and flexibility, but also means R.B.C's cannot divide/repair themselves.

• R.B.C lifespan approximately 120 days; old R.B.C's are recycled/destroyed mainly in the spleen (sometimes called the "R.B.C graveyard").

6. White Blood Cells (W.B.C's)

White blood cells, also called leukocytes, are responsible for protecting the body from infection — they are the cellular basis of the immune system.

The Five Types of White Blood Cells

Table: Columns: WBC Type, Main Role. Row 1. WBC Type: Neutrophils. Main Role: First responders to acute bacterial infection; the most abundant WBC type. Row 2. WBC Type: Eosinophils. Main Role: Defend against parasites and are involved in allergic reactions. Row 3. WBC Type: Basophils. Main Role: Release histamine, contributing to inflammation and allergic responses. Row 4. WBC Type: Monocytes / Macrophages. Main Role: Carry out phagocytosis — engulfing and digesting pathogens, debris, and dead cells. Row 5. WBC Type: Lymphocytes. Main Role: Include B-cells, T-cells, and NK (Natural Killer) cells — responsible for specific/adaptive immunity.

Remember!

Image summary: A diagram illustrating the five types of white blood cells: neutrophil, eosinophil, basophil, monocyte, and lymphocyte. Each cell is depicted with its characteristic shape and nucleus structure to highlight their distinct morphologies. The purpose is to provide a visual guide to identifying different types of leukocytes.

• 5 Types of W.B.C's: Neutrophils, Eosinophils, Basophils, Monocytes, Lymphocytes.

• Quick associations: Neutrophils = bacteria; Eosinophils = parasites/allergies; Basophils = histamine/inflammation; Monocytes/Macrophages = phagocytosis ("eat" pathogens); Lymphocytes = B, T, N.K cells (adaptive immunity).

• Classic memory aid for relative abundance (most to least): Never Let Monkeys Eat Bananas = Neutrophils, Lymphocytes, Monocytes, Eosinophils, Basophils.

7. Platelets

Platelets, also called thrombocytes, are:

- Colorless cell fragments — not complete cells — derived from larger bone-marrow cells called megakaryocytes.

• Packed with alpha (alpha) granules and dense granules, which store clotting factors and chemical signals released when platelets are activated.

- Key players in hemostasis — the process that stops bleeding.

The illustration in the lecture visually compares the three formed elements of blood side-by-side: Red Blood Cells (large, biconcave, red), White Blood Cells (larger, spiky/irregular, pale), and Platelets (small, irregular fragments) — helping you recognize each cell type by size and shape under a microscope or diagram.

Remember!

Image summary: A medical illustration of various blood components, featuring labels pointing to red blood cells, white blood cells, and platelets. The image serves to visually distinguish the different cell types by their characteristic sizes and shapes within a bloodstream.

• Platelets (thrombocytes) = cell fragments, not whole cells — they come from megakaryocytes in the bone marrow.

• Contain alpha granules and dense granules that release clotting substances when activated.

• Size comparison for identification: R.B.C's are the most numerous and biconcave; W.B.C's are the largest and have a nucleus; Platelets are the smallest, irregular fragments.

8. Hemostasis

Hemostasis: the physiological process that stops bleeding and keeps blood contained within a damaged blood vessel. It occurs in three main steps, plus a follow-up process:

1. Vascular Spasm — Immediately after injury, the smooth muscle in the wall of the damaged blood vessel contracts, narrowing (constricting) the vessel. This reduces blood flow and blood loss right away.

2. Platelet Plug Formation — Platelets recognize the damaged vessel wall and stick to it (and to each other), clumping together to form a temporary "platelet plug" that seals small breaks in the vessel.

3. Coagulation (Clotting Cascade) — A series of chemical reactions among clotting factors in the plasma produces fibrin, a mesh-like protein that reinforces the platelet plug and traps blood cells, forming a stable clot.

4. Fibrinolysis — Once the vessel has healed, the clot is no longer needed and is gradually broken down and removed, restoring normal blood flow through the vessel.

Remember!

: Image summary: A diagram illustrating the first step of hemostasis, labeled as vascular spasm. It shows a blood vessel with a breach in the wall, where the surrounding vessel narrows in response to the injury while red blood cells and platelets flow through the lumen. This process narrows the vessel to reduce blood loss from the site of injury.

Image summary: A diagram illustrating the second step of blood clotting, showing platelets aggregating at a break in a blood vessel wall to create a platelet plug. This process physically blocks the site of injury to stop blood loss.

Image summary: A diagram of a blood vessel during the coagulation process, showing red blood cells and platelets surrounding a white mass labeled as fibrin. This illustrates step 3 of coagulation, where fibrin forms a mesh to create a clot and seal a breach in the vessel wall.

• 3 Main Steps of Hemostasis (in order): Vascular Spasm leads to Platelet Plug Formation leads to Coagulation (Clotting Cascade), followed by Fibrinolysis (clot breakdown once healing is complete).

• Mnemonic: "Very Platelets Clot Fast" = Vascular spasm, Platelet plug, Coagulation, Fibrinolysis.

• Fibrin is the key structural protein of a stable clot — it is produced only after the coagulation cascade is triggered.

9. Blood Groups and Types

A person's blood type is determined by two separate classification systems used together:

- A.B.O system — classifies blood into four groups: A, B, A.B, and O, based on the presence or absence of specific antigens (marker molecules) on the surface of red blood cells.

- Rhesus (Rh) factor — an additional antigen that is either present (Rh-positive, +) or absent (Rh-negative, -) on the R.B.C surface. Combined with the A.B.O group, this creates the familiar 8 blood types (e.g., A+, A−, O+, O−, etcetera).

The A.B.O Blood Group System

Each A.B.O blood type is defined by the combination of antigens on the red blood cell surface and the antibodies present in the plasma. Antibodies in the plasma will attack any "foreign" antigen not native to that person's own blood type — this is the basis of transfusion compatibility.

Table: Columns: ABO Blood Group, Antigens on RBC Surface, Antibodies in Plasma. Row 1. ABO Blood Group: Group A. Antigens on RBC Surface: A antigen. Antibodies in Plasma: Anti-B. Row 2. ABO Blood Group: Group B. Antigens on RBC Surface: B antigen. Antibodies in Plasma: Anti-A. Row 3. ABO Blood Group: Group AB. Antigens on RBC Surface: A and B antigens. Antibodies in Plasma: None. Row 4. ABO Blood Group: Group O. Antigens on RBC Surface: None. Antibodies in Plasma: Anti-A and Anti-B.

How to read this table: a person with Group A blood has A antigens on their R.B.C's, so their plasma naturally contains Anti-B antibodies (because their immune system does not attack its own "A" antigen, but will attack "B" antigen as foreign). The same logic applies to each group — notice that Group O has no antigens at all, while Group A.B has no antibodies at all.

Blood Type Compatibility for Transfusions

Table: Columns: A, B, AB, O. Row 1. Red Blood Cell Type. A: Image. B: Image. AB: Image. O: Image. Row 2. Antibodies in Plasma. A: Image Anti-B. B: Image Anti-A. AB: None. O: Image Anti-A and Anti-B. Row 3. Antigens in Red blood Cell. A: A antigen. B: B antigen. AB: A and B antigens. O: None. Row 4. Blood Types Compatible in an Emergency. A: A, o. B: B, o. AB: A, B, AB, O (AB ^+ is the universal recipient). O: O (O is the universal donor).

Because antibodies in the recipient's plasma will attack incompatible donor antigens (causing a dangerous transfusion reaction), blood types must be matched carefully. Two blood types have special significance:

O-negative (O-) is the universal donor — because Group O R.B.C's have no A or B antigens (and no Rh antigen), they generally will not trigger an antibody attack in a recipient of any blood type. This is why O-blood is used in emergencies when a patient's blood type is unknown.

A.B-positive (A.B+) is the universal recipient — because Group A.B plasma has no Anti-A or Anti-B antibodies, and the person already has both antigens (plus Rh) on their own cells, they can safely receive blood from any A.B.O/Rh type.

Table: Columns: Blood Type, Can Give To, Can Receive From. Row 1. Blood Type: A+. Can Give To: A+, ab+. Can Receive From: A+, a-, o+, o-. Row 2. Blood Type: A-. Can Give To: A+, a-, ab+, ab-. Can Receive From: A-, o-. Row 3. Blood Type: B+. Can Give To: B+, ab+. Can Receive From: B+, B-, o+, o-. Row 4. Blood Type: B-. Can Give To: B+, B-, ab+, ab-. Can Receive From: B-, o-. Row 5. Blood Type: AB+. Can Give To: AB+ only. Can Receive From: Everyone (universal recipient). Row 6. Blood Type: AB-. Can Give To: Ab+, ab-. Can Receive From: Ab-, a-, B-, o-. Row 7. Blood Type: O+. Can Give To: O+, a+, B+, ab+. Can Receive From: O+, o-. Row 8. Blood Type: O-. Can Give To: Everyone (universal donor). Can Receive From: O- only.

• 2 systems combine to make a full blood type: A.B.O system (A, B, A.B, O based on antigens) + Rh factor (+ or −).

• O = universal Donor (no A/B antigens to attack); A.B = universal Recipient (no Anti-A/Anti-B antibodies to attack incoming blood).

• Antigen/Antibody rule: your plasma makes antibodies against whichever A.B.O antigen(s) you do not have on your own R.B.C's. Group A leads to Anti-B; Group B leads to Anti-A; Group A.B leads to no antibodies; Group O leads to both Anti-A and Anti-B.

• Rh-negative individuals can safely receive only Rh-negative blood (an Rh− person exposed to Rh+ blood will develop anti-Rh antibodies).

Quick Summary Table: Blood at a Glance

Table: Columns: Topic, Key Points to Remember. Row 1. Topic: Functions. Key Points to Remember: Transport, Regulation, Protection. Row 2. Topic: Physical Traits. Key Points to Remember: Volume 5–6L (M) / 4–5L (F); pH 7.35 to 7.45; 3 to 5 times water viscosity; approximately 38 degrees Celsius; always red, never blue. Row 3. Topic: Components. Key Points to Remember: Plasma (~55%: water, albumin, globulins, fibrinogen, electrolytes) + Formed Elements (~45%: RBC, WBC, Platelets). Row 4. Topic: Hematopoiesis. Key Points to Remember: Blood cell formation in bone marrow; HSC to Myeloid & Lymphoid lineages; regulated by EPO, TPO, G-CSF, GM-CSF. Row 5. Topic: Red Blood Cells. Key Points to Remember: Erythrocytes; biconcave, anucleate; carry hemoglobin; approximately 120-day lifespan; destroyed in spleen. Row 6. Topic: White Blood Cells. Key Points to Remember: Leukocytes; Neutrophils, Eosinophils, Basophils, Monocytes/Macrophages, Lymphocytes (B, T, NK). Row 7. Topic: Platelets. Key Points to Remember: Thrombocytes; cell fragments from megakaryocytes; role in hemostasis. Row 8. Topic: Hemostasis. Key Points to Remember: Vascular spasm to Platelet plug formation to Coagulation cascade to Fibrinolysis. Row 9. Topic: Blood Groups. Key Points to Remember: ABO system (A, B, AB, O) + Rh factor (+/−); O− equals universal donor; AB+ equals universal recipient.