Blood Vessels

A complete set of vocabulary flashcards covering blood vessel anatomy and lumen dimensions, endothelial chemical control via Nitric Oxide and Endothelin, the 9 steps of Atherosclerosis, and the mechanism of thrombus formation.

Arteries

Blood vessels that carry blood away from the heart under high pressure, requiring thick, elastic walls to maintain continuous blood flow.

Tunica Intima

The innermost layer of a blood vessel wall, composed of an endothelium, a connective tissue basement membrane, and an internal elastic membrane.

Endothelium

A single layer of flat, tightly packed cells lining the inner blood vessel wall that provides a smooth, , prevents unwanted clotting, controls permeability, and releases nitric oxide.

Internal Elastic Membrane

A thin sheet of elastic fibres with small gaps (internal elastic lamina) that separates the tunica intima from the tunica media and allows arteries to stretch and recoil.

Tunica Media

The middle layer of an artery or vein wall consisting of smooth muscle cells and elastic fibres; thick in arteries to control vasoconstriction and vasodilation, but much thinner in veins.

Vasoconstriction

The narrowing of blood vessels caused by the contraction of smooth muscle in the tunica media.

Vasodilation

The widening of blood vessels caused by the relaxation of smooth muscle in the tunica media.

Tunica Externa

The outer layer of a blood vessel wall (tunica adventitia) composed mainly of collagen fibres and some elastic fibres, providing strength and anchoring the vessel to surrounding tissue.

External Elastic Membrane

A layer of elastic tissue found in larger arteries that separates the tunica media from the tunica externa, providing additional elasticity and support.

Veins

Blood vessels that carry blood back to the heart under low pressure,

Has: thin walls, wide lumens, and internal valves to prevent backflow.

Valves (Vein)

Structures formed by folds of the tunica intima endothelium in veins that prevent the backflow of blood under low pressure.

Capillaries

The narrowest blood vessels with walls one cell thick, consisting of an endothelium and basement membrane, allowing efficient material exchange between blood and tissue.

Lumen Width Differences

Arteries have narrow lumens to help maintain high blood pressure

capillaries have lumens just wide enough for one red blood cell

veins have wide lumens to carry large volumes of blood at low pressure.

L-arginine

An amino acid converted by enzymes in endothelial cells into nitric oxide (NO).

Nitric Oxide (NO)

A chemical released by endothelial cells inducing vasodilation, lowering blood pressure, and increasing oxygen delivery.

Anti-inflammatory Function of NO

inhibits white blood cell (WBC) adhesion and migration along vessel walls.

Anti-thrombotic Function of NO

inhibits platelet adhesion and aggregation.

Anti-hypertrophic Function of NO

inhibits smooth muscle cell proliferation and migration.

Endothelin

produced by endothelial cells, promotes vasoconstriction of blood vessels, resulting in elevated blood pressure.

Atherosclerosis Step 1: Irritant Damage

Endothelial cell damage caused by irritants such as

high blood pressure, smoking toxins, radiation, or high LDL cholesterol.

Atherosclerosis Step 2: Endothelial Dysfunction

Dying endothelial cells secrete cytokines promoting for scar formation and inflammation

shifting the endothelium to a pro-inflammatory, prothrombotic, and leaky state.

Atherosclerosis Step 3: Loss of Nitric Oxide

Loss of NO prevents vessel dilation, causing

chronic vasoconstriction and promoting platelet aggregation and clotting.

Atherosclerosis Step 4: WBC Attraction

Neutrophils target damaged endothelial cells and (ROS);

surviving endothelial cells express adhesion molecules that allow monocytes to stick and migrate into the tunica intima.

Atherosclerosis Step 5: LDL Entry and Oxidation

LDL cholesterol enters the permeable vessel wall and is converted to oxidised LDL by ROS from neutrophils, further attracting immune cells.

Atherosclerosis Step 6: Foam Cell Formation

Monocytes transform into macrophages, engulf oxidised LDL, and die, forming lipid-filled foam cells.

Atherosclerosis Step 7: Fatty Streak and Fibrous Cap

Foam cells and LDL deposits create a fatty streak in the vessel wall;

smooth muscle cells migrate in, lay down collagen and elastin, and deposit calcium to form a fibrous cap.

Atherosclerosis Steps 8 & 9: Plaque Rupture and Thrombosis

Advanced plaque narrows and weakens the vessel

if the fibrous cap ruptures, it creates a wound that triggers thrombus formation, which can block blood flow and cause

a stroke or heart attack.

von Willebrand factor (VWF)

A protein that acts as glue during platelet adhesion, enabling platelets to stick to exposed collagen at a vessel injury site.

Platelet Activation and Aggregation

Activated platelets change shape and release chemicals to attract more platelets, which then stick together linked by fibrinogen to form a temporary plug.

Fibrin Mesh

The final clot structure formed when the clotting cascade converts fibrinogen into fibrin, creating a strong mesh that traps platelets, red blood cells (RBCs), and white blood cells (WBCs).