Week 3: Types of Blood Vessels

Vocabulary flashcards covering major terms related to blood-vessel structure, function, and clinical conditions discussed in the lecture notes.

Artery

Blood vessel that carries blood away from the heart toward tissues; high-pressure, pulsatile, and known as a resistance vessel.

Vein

Blood vessel that returns blood from capillaries back to the heart; low-pressure, easily distensible, and called a capacitance vessel.

Capillary

Microscopic, thin-walled vessel that connects the smallest arteries to the smallest veins and permits exchange of gases, nutrients, and wastes.

Tunica interna (tunica intima)

Innermost vessel layer; simple squamous endothelium with thin areolar CT acting as a permeable membrane and signaling layer.

Endothelium

Simple squamous epithelial lining of the tunica interna that regulates permeability, secretes vasoactive chemicals, and initiates clotting when damaged.

Tunica media

Middle vessel layer containing smooth muscle, elastic tissue, and collagen; contraction or relaxation regulates lumen diameter.

Tunica externa (tunica adventitia)

Outermost vessel layer of connective tissue that anchors the vessel and provides passage for nerves, lymphatics, and vasa vasorum.

Vasa vasorum

Network of small vessels that supply oxygen and nutrients to the outer half of large vessel walls.

Elastic (conducting) arteries

Largest arteries (2.5–1.0 cm) with 40–70 elastic layers that stretch during systole and recoil during diastole; e.g., aorta, pulmonary trunk.

Distributing (muscular) arteries

Medium arteries (1.0–0.3 mm) with up to 40 smooth-muscle layers; deliver blood to specific organs and actively vasoconstrict/vasodilate.

Resistance arteries

Small arteries (300–10 μm) that regulate local blood flow and include arterioles; major contributors to peripheral resistance.

Arteriole

Smallest resistance artery feeding capillary beds and controlling how much blood an organ or tissue receives.

Metarteriole

Short vessel that directly links an arteriole to a venule, bypassing the capillary bed in some regions.

Capillary bed

Interconnected web of 10–100 capillaries supplied by one arteriole and drained by a venule; flow regulated by upstream arterioles.

Continuous capillary

Most common capillary; tight endothelial junctions with small intercellular clefts; found in skin, muscle, CNS.

Fenestrated capillary

Capillary with pores (fenestrations) that enhance filtration/absorption; located in kidneys, small intestine, endocrine glands.

Sinusoidal (discontinuous) capillary

Capillary with large gaps and irregular shape, allowing passage of proteins and formed elements; found in liver, spleen, bone marrow.

Postcapillary venule

Smallest vein (10–20 μm) collecting blood from capillaries; highly porous and involved in fluid exchange.

Muscular venule

Vein that receives blood from postcapillary venules and has one or two layers of smooth muscle.

Medium vein

Vein up to 10 mm in diameter (e.g., radial, great saphenous) that often possesses venous valves to prevent backflow.

Venous sinus

Vein with very thin walls, large lumen, and no smooth muscle; incapable of vasoconstriction (e.g., dural sinuses, coronary sinus).

Large vein

Largest veins (>10 mm) with smooth muscle in all tunics; includes venae cavae, pulmonary, renal, and internal jugular veins.

Resistance vessels

Functional name for arteries reflecting their ability to withstand and regulate high, fluctuating blood pressure.

Capacitance vessels

Functional name for veins, highlighting their capacity to hold ~64 % of the body’s blood volume.

Aneurysm

Weak, bulging point in an arterial wall that pulsates and risks rupture; commonly in abdominal aorta or Circle of Willis.

Arteriosclerosis

Chronic thickening and hardening of arterial walls, often from lipid deposits, aging, or hypertension.

Hypertension

Persistently elevated blood pressure that strains arterial walls and promotes aneurysm formation.

Varicose veins

Dilated, twisted superficial veins caused by valve failure and venous wall weakening; commonly occur in the legs.

Carotid sinuses

Baroreceptors in internal carotid artery walls that sense blood-pressure changes and signal the brainstem.

Carotid bodies

Chemoreceptors at common carotid bifurcations monitoring blood O2, CO2, and pH to adjust respiration.

Aortic bodies

Chemoreceptors in the aortic arch transmitting blood-gas information to the brainstem via vagus nerves.

Anastomosis

Point where two blood vessels merge without intervening capillaries, providing alternate routes of flow.

Arterial anastomosis

Convergence of two or more arteries supplying the same region, e.g., cerebral arterial circle (Circle of Willis).

Venous anastomosis

One vein empties directly into another, providing numerous alternate venous return pathways.

Arteriovenous anastomosis

Direct passage of blood from an artery to a vein, bypassing capillary beds; aids thermoregulation in digits, ears.

Simple diffusion

Passive movement of gases (O2, CO2) across membranes down their concentration gradients; primary exchange mechanism in capillaries.

Smooth muscle (vascular)

Involuntary muscle in the tunica media that contracts to alter vessel diameter and regulate blood flow/pressure.

Venous valve

Infolding of a medium-vein endothelium that prevents backward flow of blood, especially in limbs.

Circle of Willis

Ring-like arterial anastomosis at the brain’s base that provides collateral cerebral circulation.