Cardiovascular System – Blood Vessels & Circulation (BIOL 2252 • Ch 20)

Vocabulary flashcards covering key terms, structures, pressures, regulatory mechanisms, and pathologies associated with blood vessels and circulation.

Artery

Blood vessel that carries blood away from the heart; generally oxygen-rich except in pulmonary and fetal circulation.

Vein

Blood vessel that carries blood toward the heart; generally oxygen-poor except in pulmonary and fetal circulation.

Capillary

Microscopic, porous blood vessel composed only of endothelium and basement membrane; site of exchange between blood and tissues.

Lumen

The central blood-containing space inside a vessel.

Tunica intima

Innermost vessel layer; simple squamous endothelium providing a slick, friction-reducing surface.

Tunica media

Middle layer of vessel wall; circular smooth muscle and elastin that regulate vasoconstriction and vasodilation.

Tunica externa

Outermost vessel layer of areolar connective tissue; anchors, protects, and may house vasa vasorum.

Vasa vasorum

Small blood vessels that supply the outer walls of large arteries and veins; “vessels to the vessels.”

Companion vessels

Arteries and veins that travel together and supply/drain the same body region.

Elastic artery

Largest, thick-walled conducting artery (e.g., aorta) rich in elastin; stretches with systole and recoils to propel blood.

Muscular artery

Medium, distributing artery with thick tunica media and prominent internal/external elastic laminae; active in vasoconstriction.

Arteriole

Smallest resistance artery (0.3 mm–10 µm) that controls flow into capillary beds and helps regulate systemic BP.

Vasoconstriction

Narrowing of vessel lumen due to smooth-muscle contraction, increasing resistance.

Vasodilation

Widening of vessel lumen due to smooth-muscle relaxation, decreasing resistance.

Vasomotor tone

Slight, continual arteriolar constriction maintained by sympathetic stimulation.

Resistance arteries

Arterioles whose changing diameter produces major variations in systemic resistance and blood pressure.

Continuous capillary

Most common capillary; continuous endothelial lining with intercellular clefts permitting passage of small molecules.

Fenestrated capillary

Capillary with endothelial pores (fenestrations) that allow greater fluid or small-protein movement; present in kidneys, intestines, endocrine glands.

Sinusoid

Capillary with discontinuous endothelium and basement membrane; large gaps allow passage of formed elements and proteins (e.g., liver, bone marrow).

Metarteriole

Vessel branch of an arteriole that feeds a capillary bed and leads to a thoroughfare channel.

Thoroughfare channel

Distal end of a metarteriole connecting directly to a post-capillary venule; bypasses true capillaries when sphincters are closed.

Precapillary sphincter

Band of smooth muscle regulating blood flow into true capillaries.

Perfusion

The volume of blood entering capillaries of a tissue per unit time (mL/min/g).

Arterial anastomosis

Connection of two or more arteries supplying the same region, providing collateral circulation.

Venous anastomosis

Interconnection of two or more veins draining the same area; more common than arterial anastomoses.

Arteriovenous anastomosis (shunt)

Direct vessel link that allows blood to bypass capillaries, common in fingers, toes, ears for thermoregulation.

Portal system

Vascular pathway with two consecutive capillary beds connected by a portal vein (e.g., hepatic portal system).

Blood hydrostatic pressure (HPb)

Capillary blood pressure pushing fluid out through vessel walls; ~35 mm Hg arteriole end, ~17 mm Hg venule end.

Colloid osmotic pressure (COPb)

Pull on water exerted by plasma proteins drawing fluid into capillaries (~26 mm Hg).

Net filtration pressure (NFP)

Difference between outward hydrostatic and inward osmotic forces; determines bulk flow direction across capillary walls.

Filtration

Bulk flow of fluid and solutes out of blood at the arterial end of capillaries.

Reabsorption

Bulk flow of fluid back into blood at the venous end of capillaries.

Bulk flow

Movement of large amounts of fluid and dissolved substances down a pressure gradient across capillary walls.

Capillary exchange

Process of diffusion, vesicular transport, and bulk flow that transfers gases, nutrients, and wastes between blood and tissues.

Myogenic response

Intrinsic vascular smooth-muscle reaction to stretch that keeps local blood flow constant despite systemic BP changes.

Autoregulation

Local adjustment of blood flow to match a tissue’s metabolic needs without external (neural) influence.

Reactive hyperemia

Transient, marked increase in blood flow to a tissue after its blood supply has been temporarily blocked.

Vasodilator

Chemical (e.g., histamine, nitric oxide) that relaxes vascular smooth muscle, increasing local blood flow.

Vasoconstrictor

Chemical (e.g., endothelin, thromboxane, angiotensin II) that contracts vascular smooth muscle, decreasing blood flow.

Blood pressure (BP)

Force per unit area exerted on vessel walls by blood; expressed in mm Hg.

Systolic pressure

Peak arterial pressure during ventricular contraction (e.g., 120 mm Hg).

Diastolic pressure

Lowest arterial pressure during ventricular relaxation (e.g., 80 mm Hg).

Pulse pressure

Difference between systolic and diastolic pressures; reflects arterial elasticity (e.g., 40 mm Hg).

Mean arterial pressure (MAP)

Average pressure propelling blood to tissues throughout the cardiac cycle; approx. DP + 1/3 PP (~93 mm Hg at 120/80).

Cardiovascular center

Medullary area consisting of cardiac and vasomotor centers that regulate CO and vessel diameter.

Vasomotor center

Part of cardiovascular center that controls sympathetic outflow to vascular smooth muscle, adjusting vessel tone.

Baroreceptor

Stretch receptor in carotid sinuses, aortic arch, and large arteries that senses BP changes and triggers reflexes.

Chemoreceptor

Sensor in aortic and carotid bodies detecting CO₂, pH, and O₂ changes, influencing respiration and BP.

Peripheral resistance

Opposition to blood flow due to friction within vessels; affected by viscosity, vessel length, and vessel radius.

Blood viscosity

Thickness of blood; increased viscosity raises resistance and BP.

Renin-Angiotensin System (RAS)

Hormonal cascade where renin converts angiotensinogen → Ang I → Ang II (via ACE); Ang II raises BP via vasoconstriction, thirst, and aldosterone/ADH release.

Angiotensin II

Powerful vasoconstrictor produced by RAS; increases resistance, blood volume, and BP.

Aldosterone

Adrenal cortex hormone that increases Na⁺ and water reabsorption in kidneys, raising blood volume and BP.

Antidiuretic hormone (ADH)

Posterior pituitary hormone enhancing water reabsorption; at high levels causes vasoconstriction (vasopressin).

Atrial natriuretic peptide (ANP)

Heart atrial hormone that promotes vasodilation and Na⁺/water loss, lowering blood volume and BP.

Epinephrine / Norepinephrine

Adrenal medulla catecholamines that increase cardiac output and, via α₁ receptors, cause vasoconstriction (β₂ causes vasodilation in heart/skeletal muscle).

Skeletal muscle pump

Mechanism where contracting muscles compress deep veins, propelling blood toward the heart; valves prevent backflow.

Respiratory pump

Pressure changes during breathing that aid venous return by moving blood toward the thorax.

Venous return

Volume of blood flowing back to the heart per minute; aided by pumps and venoconstriction.

Capacitance vessels

Veins that serve as blood reservoirs, containing ~65 % of blood at rest.

Blood reservoir

Storage function of systemic veins that can shift blood into circulation via venoconstriction during activity.

Deep Vein Thrombosis (DVT)

Formation of a clot in a deep vein, usually in the calf; risk of pulmonary embolism if clot dislodges.

Circulatory shock

Condition of inadequate tissue perfusion due to failed cardiac output or low venous return (e.g., hypovolemic, vascular, cardiogenic shock).

Hypertension

Chronic high BP ≥140/90 mm Hg; increases risk of atherosclerosis, heart failure, stroke, renal disease.

Hypotension

Chronically low BP ≤90/60 mm Hg; may cause fatigue, dizziness, and fainting.

Atherosclerosis

Progressive disease with atheroma (plaque) formation in arterial walls, narrowing lumen and reducing flow.

Aneurysm

Bulging, weakened area of arterial wall prone to rupture; common in aorta and cerebral arteries.

Total cross-sectional area

Combined lumen diameters of all vessels of a given type; largest in capillaries, causing slow flow.

Velocity of blood flow

Speed of blood movement; inversely related to total cross-sectional area—slowest in capillaries.

Blood flow (F)

Volume of blood moving through the circulation per time; proportional to pressure gradient (ΔP) and inversely to resistance (R).

Portal vein

Vein that carries blood between two capillary beds in a portal system (e.g., hepatic portal vein).