Blood Vessels and Circulation

Structure & Functions of Blood Vessels · Cardiovascular System in Psychology

Comprehensive Exam Reviewer — Based on the Lecture Slide Deck

Riddle from the slides: "I'm a highway with no traffic lights, where red travelers rush in one direction and blue travelers in another. At the center is a tireless pump that never sleeps. What am I?"

Answer: The cardiovascular system — arteries carry oxygen-rich ("red") blood away from the heart, veins carry deoxygenated ("blue") blood back, and the heart is the pump that never stops beating.

Introduction to Blood Vessels

Blood vessels — tubular structures that carry blood throughout the body.

Image summary: This diagram illustrates the human circulatory system and the different types of blood vessels. It shows the larger systemic layout within a human body, highlighting the heart, lungs, aorta, and vena cava, alongside a detailed inset showing the progression of blood flow from an artery to an arteriole, through a network of capillaries, and then through a venule into a vein. The purpose of the diagram is to show how blood is transported from the heart to the body's tissues via arteries and returned to the heart via veins.

Main Types (in order of blood flow)

How to read the diagram: The slide shows the pathway of blood flow through the five main vessel types, arranged from the heart outward and back. This sequence is the backbone of the whole chapter — memorize the order!

Arteries leads to Arterioles leads to Capillaries leads to Venules leads to Veins

The body-wide diagram also shows major named vessels: the ay-or-tuh (the large elastic artery leaving the heart) and the vena cava (the large vein returning blood to the heart), along with the heart and lungs as central hubs of circulation.

Functions of Blood Vessels

Transport — carrying blood (and everything in it) throughout the body.

Nutrient & gas exchange — delivering oxygen and nutrients to tissues, removing carbon dioxide.

Waste removal — carrying metabolic waste products away from tissues.

• Regulation of blood pressure — vessels can constrict or dilate to control pressure.

• Thermoregulation — adjusting blood flow near the skin to conserve or release body heat.

Remember!

The vessel order Arteries goes to Arterioles goes to Capillaries goes to Venules goes to Veins describes one full loop of systemic circulation — blood leaves the heart through arteries and returns through veins.

General Structure of Blood Vessel Walls

How to read the diagram: The 3-D cutaway of an artery wall peels back each layer so you can see how they stack — from the outside in: tunica externa (outermost), tunica media (middle), and tunica intima (innermost, touching the blood itself).

The innermost surface facing the lumen (the hollow center where blood flows) also has a basement membrane anchoring the endothelium.

Most blood vessels (except capillaries) are built from three concentric layers, called tunics (from Latin "tunica" = coat/covering).

Table: Columns: Tunic, Location, Composition & Function. Row 1. Tunic: Tunica Intima. Location: Innermost layer (touches blood). Composition & Function: Endothelium + subendothelial layer; provides a smooth surface that reduces friction and prevents clotting.. Row 2. Tunic: Tunica Media. Location: Middle layer. Composition & Function: Smooth muscle & elastic fibers; regulates vessel diameter through contraction/relaxation.. Row 3. Tunic: Tunica Externa. Location: Outermost layer. Composition & Function: Connective tissue; anchors the vessel to surrounding structures.. Row 4. Remember! — Mnemonic for the 3 Tunics (inside to outside) Intima (Inner) to Media (Middle) to Externa (Exterior) Think "I'M Exiting" as you move from the lumen outward!.

Key Structural Difference: Arteries versus Veins

How to read the diagram: The side-by-side cutaway of a vein and an artery shows the vein (left, blue) has a valve inside its lumen, while the artery (right, red) does not. Both share the same three tunics, but the proportions differ.

Remember!

Arteries have a thicker tunica media (to withstand high pressure from the heart's pumping); veins have valves (to prevent backflow of blood moving against gravity, especially in the limbs).

Arteries

Arteries — carry blood away from the heart, under high pressure.

Types of Arteries

Image summary: A diagram of an artery wall showing a cross-section of its structural layers. The wall is composed of three concentric layers: the outer tunica externa, the middle tunica media, and the inner tunica intima, with the innermost layer resting on a basement membrane. This illustrates the multilayered composition of the arterial wall.

Image summary: A diagram comparing the anatomical structure of a vein and an artery. Both share three wall layers: the innermost epithelium of tunica intima, the middle tunica media, and the outer tunica externa. The vein is distinguished by the presence of a valve to prevent backflow and a thinner tunica media compared to the artery. These structures illustrate how arteries are built for high-pressure transport while veins are adapted for lower pressure and one-way flow.

How to read the diagram: Two artery cross-sections are compared side by side. Both show the same three tunics (externa, media, intima), but the elastic artery's tunica media is packed with more elastic fibers (shown as wavy lines), while the muscular artery's tunica media has more smooth muscle relative to elastic tissue — and shows small colored dots representing scattered elastic fibers among the muscle.

Table: Columns: Type, Example, Key Feature. Row 1. Type: Elastic Arteries. Example: Aorta. Key Feature: High elasticity; acts as a pressure reservoir — stretches when the heart pumps and recoils to keep blood moving between heartbeats.. Row 2. Type: Muscular Arteries. Example: Distributing arteries to organs. Key Feature: Distribute blood to specific organs; walls are more muscular to allow more precise control of blood flow..

Features of Arteries (in general)

- Thick walls — built to withstand high pressure

- Small lumen (hollow center) relative to wall thickness

- Strong elastic recoil — the wall springs back after stretching, helping propel blood forward

Remember!

Image summary: A diagram of an elastic artery wall showing three concentric layers: the outermost Tunica externa, a thick middle Tunica media, and the innermost Tunica intima. This structural arrangement allows the artery to withstand and distribute the pressure of blood flow.

Image summary: A diagram of a muscular artery cross-section showing its three concentric layers: the outermost tunica externa, a thick middle tunica media consisting of smooth muscle, and the innermost tunica intima. This structure illustrates the layered histological composition of a muscular artery.

Elastic arteries (like the ay-or-tuh) act like a pressure reservoir that smooths out the pulsing rhythm of the heartbeat into steadier, continuous blood flow.

Arterioles

Arterioles — the smallest branches of arteries; they control blood flow into the capillaries.

How to read the diagram: The arteriole cross-section looks similar to the artery diagrams but is drawn much thinner overall — notice the tunica media has only a few visible smooth muscle fibers rather than a thick muscular band, reflecting its smaller size and thinner wall.

Image summary: A diagram of an arteriole wall showing its three concentric layers: the outermost tunica externa, a thick middle layer of smooth muscle called the tunica media, and the innermost tunica intima. This structure illustrates the histological organization of a small artery, where the prominent tunica media allows for the regulation of blood flow.

Table: Columns: Aspect, Description. Row 1. Aspect: Structure. Description: Thin tunica media with only a few layers of smooth muscle.. Row 2. Aspect: Role in BP regulation. Description: Vasoconstriction (narrowing) increases resistance to blood flow; vasodilation (widening) decreases resistance.. Row 3. Aspect: Clinical note. Description: Arterioles are the major site of peripheral resistance in the circulatory system — this makes them central to the development of hypertension (high blood pressure).. Row 4. Aspect: Remember! — Vasoconstriction versus Vasodilation.

Table: Columns: Aspect, Description. Row 1. Aspect: Vasoconstriction (narrowing) to resistance to blood pressure Vasodilation (widening) to resistance to blood pressure. Description: to.

Capillaries

Capillaries are the site of exchange between blood and tissues — the whole purpose of the circulatory system (delivering nutrients/oxygen, picking up waste) actually happens here.

How to read the diagram: The capillary bed diagram shows a red artery entering on the left, branching into a dense mesh of capillaries (shown transitioning from red to purple to blue, reflecting oxygen being given up to tissue cells), then converging into a blue vein on the right. This color gradient visually represents how blood loses oxygen as it passes through the capillary bed and picks up carbon dioxide/waste.

Structure

Capillaries

Image summary: A diagram of a capillary bed showing the flow of blood from an artery through an arteriole into a network of capillaries, and then through a venule into a vein. The network surrounds tissue cells, illustrating how blood vessels branching into smaller capillaries facilitate the exchange of materials with surrounding tissues.

Capillaries are made of only a single endothelial cell layer plus a basement membrane — no tunica media or externa. This extremely thin wall is what allows efficient exchange.

Exchange Mechanisms

- Diffusion — movement of substances from high to low concentration.

- Filtration — fluid pushed out of the capillary by blood pressure.

- Osmosis — movement of water across the membrane based on concentration gradients.

• Transcytosis — vesicle-mediated transport of substances across the endothelial cell.

Types of Capillaries

How to read the diagram: Three capillary cross-sections are compared side by side, showing increasing "leakiness" from left to right. Continuous capillaries have an unbroken endothelial layer with only tiny intercellular clefts (gaps between cells). Fenestrated capillaries have visible pores (fenestrations) punched through the cells. Sinusoids have large intercellular gaps and an incomplete basement membrane, making them the leakiest of all.

Table: Columns: Continuous, Fenestrated, Sinusoid. Row 1. Continuous: Image. Fenestrated: Image. Sinusoid: Image.

Table: Columns: Type, Structure, Example Locations. Row 1. Type: Continuous. Structure: Tight junctions between cells; least permeable type.. Example Locations: Brain (forms the blood-brain barrier). Row 2. Type: Fenestrated. Structure: Has pores (fenestrations) for filtration.. Example Locations: Kidneys, intestines.

Table: Columns: Type, Structure, Example Locations. Row 1. Type: Sinusoids. Structure: Large gaps allow passage of cells & large proteins.. Example Locations: Liver, bone marrow. Row 2. Type: Remember! The 'leakiness' of capillaries matches the organ's job: the brain needs a tight barrier (continuous) to protect neural tissue, the kidneys need to filter blood (fenestrated), and the liver/bone marrow need to let whole cells pass through (sinusoids)..

Veins

Veins — return blood to the heart, under low pressure.

How to read the diagram: The artery-vs-vein cross-section comparison shows the vein (b) with a noticeably larger, more irregularly-shaped lumen and a visible valve flap inside it, compared to the artery (a) which has a smaller, rounder lumen and no valve. Both share the same three tunics, labeled identically, but the vein's tunica media is visibly thinner relative to its total wall.

Structure

- Thinner walls than arteries (since venous pressure is much lower)

- Larger lumen (helps compensate for low pressure by allowing more volume to flow)

Image summary: Two anatomical diagrams comparing the structure of an artery and a vein. Both contain a lumen and are composed of three layers: the tunica intima, tunica media, and tunica externa. The artery features a thicker tunica media and a narrower lumen, while the vein has a thinner wall, a wider lumen, and includes a valve to prevent backflow. The point is to illustrate the structural differences that reflect their different functions in the circulatory system.

- Valves — one-way flaps that prevent backflow of blood, especially important in the limbs where blood must travel against gravity back to the heart.

Types of Veins

How to read the diagram: The leg diagram (shaped like an "H") shows how superficial veins (near the skin surface) connect to deep veins (running alongside arteries, deeper in the tissue) via perforating veins that pierce through the connective tissue layer. Arrows show blood flowing upward (toward the heart) in both systems. An inset box zooms into a spider/varicose vein pattern.

Table: Columns: Type, Description. Row 1. Type: Superficial Veins. Description: Located under the skin; visible (e.g., the veins you can sometimes see on your arms).. Row 2. Type: Deep Veins. Description: Located deeper in the body; accompany (run alongside) arteries..

Image summary: A diagram of the venous system in a limb, showing the anatomical relationship between the skin, superficial veins, deep veins, and the perforating veins that connect them. The diagram illustrates how dysfunction in these vessels leads to the formation of spider and varicose veins. The point is to show how blood flow abnormalities in the venous network result in visible superficial vein disease.

Table: Columns: Type, Description. Row 1. Type: Perforating Veins. Description: Connect the superficial and deep venous systems, allowing blood to move between them..

Clinical Notes: Varicose Veins & Deep Vein Thrombosis (D.V.T)

Varicose veins — swollen, twisted veins (often visible in the legs) that occur when valves fail and blood pools instead of flowing efficiently back to the heart.

Deep vein thrombosis (D.V.T) — a blood clot that forms in a deep vein, most often in the leg.

How to read the D.V.T diagram: A side-by-side comparison of "Normal anatomy" and "Deep vein thrombosis" of the lower leg shows the D.V.T leg with visible redness (erythema) and swelling. A callout box notes that calf swelling, erythema, and leg warmth are clinical indications that a patient may have D.V.T — these are the signs to watch for.

: Image summary: A photo showing the lower leg and ankle of a person, featuring prominent, bulging, and twisted veins beneath the skin. This is a clinical image depicting varicose veins in the lower extremity.

Image summary: A photograph of a person's torso showing prominent, winding, and dilated blue veins visible beneath the skin. The image is captioned "Spider Veins," and it serves to illustrate the visual appearance of this vascular condition.

Remember! — Watch for D.V.T The photo comparison of varicose veins (bulging, rope-like veins visible under the skin of the leg/ankle) versus spider veins (finer, web-like clusters of small blue/purple veins) illustrates that these conditions exist on a spectrum of venous insufficiency.

Image summary: Two side-by-side anatomical views of a lower right leg. The left image labels the venous system, including the femoral, popliteal, posterior tibial, anterior tibial, and great saphenous veins. The right image depicts the leg with redness and swelling in the calf area. The figure illustrates that calf swelling, erythema, and warmth are clinical indications of deep vein thrombosis.

Calf swelling + erythema (redness) + leg warmth = classic warning signs of deep vein thrombosis. D.V.T is a medical concern because a clot can potentially travel to the lungs (pulmonary embolism).

Varicose Veins

Spider Veins

Normal anatomy

Deep vein thrombosis

Venules

How to read the diagram: This diagram shows the full color-graded pathway again — artery (red) arrow arteriole arrow capillaries (color transition) arrow venule arrow vein (blue) — with venules highlighted as the vessels immediately downstream of the capillary bed, before blood consolidates into full-sized veins.

Venules — small vessels that collect blood exiting the capillaries and funnel it into veins.

Image summary: A diagram of the blood vessel network showing the transition from a red artery on the right to a blue vein on the left. The flow moves from the artery through smaller arterioles, into a web of capillaries where gas exchange occurs, and then back through venules into the vein. The diagram illustrates the continuous pathway of blood circulation from the heart to the tissues and back.

Table: Columns: Aspect, Description. Row 1. Aspect: Function. Description: Collect blood from capillaries and channel it into veins.. Row 2. Aspect: Structure. Description: Very thin walls; porous, allowing continued exchange similar to capillaries.. Row 3. Aspect: Role in inflammation. Description: White blood cells (WBCs) exit the circulation here through a process called diapedesis..

Table: Columns: Aspect, Description. Row 1. Aspect: Diapedesis — the process by which white blood cells squeeze through the walls of venules (and capillaries) to leave the bloodstream and enter tissue, typically in response to infection or injury (part of the inflammatory response)..

Anastomoses

Anastomoses — direct connections between blood vessels without an intervening capillary bed.

How to read the diagram: The "simple arteriovenous anastomosis" diagram shows an arteriole connecting directly to a venule via a short shunt vessel, bypassing the capillary bed entirely (the capillary bed is shown separately, below, as an alternate/parallel route). This illustrates how blood can take a shortcut around the capillaries when the shunt is open.

Image summary: A diagram of a vascular anastomosis showing an arteriole that splits into two paths: one leading into a capillary bed and the other bypassing it to lead directly into a venule. This structure allows blood to detour around a capillary network, effectively regulating blood flow to specific tissues.

Table: Columns: Type, Description. Row 1. Type: Arterial Anastomoses. Description: Connections between arteries that help maintain blood supply to tissue even if one artery becomes blocked.. Row 2. Type: Venous Anastomoses. Description: Common in the skin; provide alternative drainage routes for venous blood.. Row 3. Type: Arteriovenous Anastomoses. Description: Direct artery-to-vein connections (shunts) that bypass the capillary bed entirely..

Image summary: An anatomical diagram of the arterial blood supply to the upper abdomen, showing the celiac axis and superior mesenteric artery with their key branches, including the common hepatic artery, gastroduodenal artery, and inferior pancreaticoduodenal artery. The diagram illustrates the vascular network and the connecting points, or anastomoses, between these arterial systems to ensure collateral blood flow.

Image summary: An anatomical diagram of venous anastomoses showing connections between the portal venous system and the systemic venous system. It highlights specific junctions, such as the esophageal branch connecting the left gastric vein to the azygos vein and the veins of the anterior abdominal wall connecting to the paraumbilical vein. The diagram illustrates how blood can be shunted between these two systems, particularly in the context of portal hypertension.

Image summary: A diagram of a vascular shunt, also known as an arteriovenous anastomosis, showing a direct connection between an arteriole and a venule. In this configuration, the precapillary sphincter is closed, diverting blood flow away from the capillary bed and directly into the venule. The purpose of this structure is to bypass the capillary network to regulate blood flow.

How to read the vascular shunt diagram: The "Vascular Shunt/Arteriovenous anastomosis" illustration shows a precapillary sphincter (a ring of smooth muscle that controls entry into a capillary bed) in the closed position — when closed, blood is diverted directly from the arteriole (red) to the venule (blue) through the shunt vessel, bypassing the surrounding capillary network entirely.

Simple arteriovenous anastomosis (Anastomosis arteriovenosa simplex)

Clinical Relevance

• Coronary circulation — arterial anastomoses around the heart provide backup blood supply if one coronary vessel becomes narrowed or blocked, which is clinically important in heart disease.

: Image summary: An anatomical diagram of a human heart labeling major structures including the aorta, superior and inferior vena cava, pulmonary artery, pulmonary veins, coronary blood vessels, and the heart muscle. The diagram serves to identify the primary vessels and tissues responsible for blood transport and cardiac function.

• Surgical grafts — surgeons create artificial anastomoses (connecting one vessel to another) during procedures like bypass surgery.

How to read the surgical anastomosis diagram: Three techniques are illustrated — end-to-end anastomosis (two vessel ends stitched directly together in a line), end-to-side anastomosis (one vessel's end is stitched into the side of another, forming a T-shape/branch), and side-to-side anastomosis (two vessels are stitched together along their sides, creating a shared opening). Surgeons choose the technique based on the size and orientation of the vessels being joined — for example, in coronary artery bypass grafting.

Remember!

Image summary: Three diagrams illustrating different types of surgical anastomosis. End-to-end anastomosis shows two vessel ends joined linearly; end-to-side anastomosis shows the end of one vessel joined to the side of another; and side-to-side anastomosis shows the sides of two vessels joined along their lengths. The diagrams compare the three primary configurations for reconnecting tubular structures.

Anastomoses act as "detour routes" for blood — they provide backup pathways so that tissue doesn't lose its blood supply entirely if one vessel becomes blocked.

End-to-end anastomosis

Side-to-side anastomosis

Blood Distribution in the Body

This section describes where the body's total blood volume is located at any given moment, at rest.

Table: Columns: Location, Approx. % of Total Blood Volume (at rest). Row 1. Location: Systemic veins & venules. Approx. % of Total Blood Volume (at rest): approximately 64% (this is the body's main blood reservoir). Row 2. Location: Systemic arteries & arterioles. Approx. % of Total Blood Volume (at rest): approximately 13%. Row 3. Location: Pulmonary circulation (vessels to/from lungs). Approx. % of Total Blood Volume (at rest): approximately 9%. Row 4. Location: Heart. Approx. % of Total Blood Volume (at rest): approximately 7%. Row 5. Location: Capillaries. Approx. % of Total Blood Volume (at rest): approximately 7%. Row 6. Location: Remember! — Veins Are the Blood Reservoir Systemic veins and venules hold about 64% (nearly two-thirds) of all blood in the body at rest — this is why veins are called the "blood reservoir" of the circulatory system. Redistribution of this blood occurs during exercise and hemorrhage (blood loss) — the body shifts blood from the venous reservoir toward muscles or vital organs as needed..

Cardiovascular System in Psychology

The cardiovascular system's core job is to transport oxygen, nutrients, hormones, and remove waste — but in psychology, it's also central to emotion, stress, and mental health.

Components and Psychology Connection

- Heart rate changes with emotion (fear, excitement) and stress response (sympathetic activation).

- Hormones like cortisol and adrenaline travel in the blood — this is the physical link connecting physiology and mood.

- Blood flow changes influence brain oxygenation, which affects cognition and alertness.

A. Autonomic Nervous System (A.N.S) Control

How to read this: The A.N.S has two branches that push cardiovascular activity in opposite directions — think of them as an accelerator and a brake.

Table: Columns: Branch, Nickname, Effect on Heart. Row 1. Branch: Sympathetic Nervous System (SNS). Nickname: "Fight or flight". Effect on Heart: Heart rate, blood pressure. Row 2. Branch: Parasympathetic Nervous System (PNS). Nickname: "Rest and digest". Effect on Heart: Slows heart rate.

Important in:

Anxiety disorders

• Panic attacks

• Stress regulation

B. Psychophysiological Measures

These are physiological signals researchers and clinicians use to study the mind-body connection:

Table: Columns: Measure, Definition. Row 1. Measure: Heart Rate (HR). Definition: Beats per minute — changes with emotion and cognitive load.. Row 2. Measure: Blood Pressure (BP). Definition: The force of blood on vessel walls — rises during acute stress.. Row 3. Measure: Heart Rate Variability (HRV). Definition: The variability (variation) between successive heartbeats; higher HRV equals better stress resilience.. Row 4. Measure: Remember! — HRV Higher Heart Rate Variability (HRV) is generally considered a GOOD sign — it reflects a more flexible, adaptable nervous system and better resilience to stress. Lower HRV is often linked to chronic stress or poor cardiovascular regulation..

C. Stress & Cardiovascular Health

Chronic stress leads to prolonged high cortisol and sympathetic activity, which leads to increased risk of hypertension (high blood pressure) and atherosclerosis (hardening/narrowing of arteries from plaque buildup).

Psychological interventions such as mindfulness and Cognitive Behavioral Therapy (C.B.T) can lower heart rate and blood pressure — demonstrating a direct, measurable link between psychological treatment and cardiovascular function.

Remember!

This is a key exam concept: the mind-body connection isn't just metaphorical — chronic psychological stress produces measurable physiological changes (via cortisol and sympathetic activation) that raise real cardiovascular disease risk over time.

Emotions and the Heart

How to read the diagram: The slide shows six simple emoji-style faces representing different emotions (fear, happiness, sadness, anger, surprise, contentment) — illustrating that a wide range of emotional states each produce a distinct, recognizable cardiovascular response.

Table: Columns: Emotion, Cardiovascular Response. Row 1. Emotion: Fear. Cardiovascular Response: Rapid heart rate, shallow breathing.. Row 2. Emotion: Love / Excitement. Cardiovascular Response: Increased cardiac output; sometimes "butterflies" (a gut-heart interaction via the vagus nerve).. Row 3. Emotion: Anger. Cardiovascular Response: Increased blood pressure and vascular resistance.. Row 4. Emotion: Sadness. Cardiovascular Response: Slower, heavier heartbeat; in extreme cases, stress cardiomyopathy ("broken heart syndrome").. Row 5. Emotion: Stress cardiomyopathy ("Broken Heart Syndrome") — a real, temporary heart condition triggered by intense emotional stress (such as grief or shock), where the heart muscle weakens suddenly, mimicking a heart attack even without blocked arteries.. Row 6. Emotion: Remember! — Vagus Nerve The vagus nerve is a major nerve connecting the brain to the heart and gut..

The vagus nerve is a major nerve connecting the brain to the heart and gut, forming a key pathway for the "gut-heart" and "brain-heart" interactions mentioned with love/excitement — it's part of why strong emotions can be felt physically in the chest and stomach.