Cardiovascular System – Blood Vessels & Circulation

Question-and-Answer flashcards covering vessel structure, hemodynamics, pressure regulation, capillary exchange, and related clinical correlations.

What are the three tunics (layers) that make up the wall of most blood vessels?

Tunica interna (intima), tunica media, and tunica externa (adventitia).

Which vessel layer contains smooth muscle and is primarily responsible for vasoconstriction and vasodilation?

Tunica media.

Which vessel layer consists of endothelium lining the lumen and a basement membrane?

Tunica interna (intima).

Which vessel layer anchors the vessel to surrounding tissues and may contain vasa vasorum?

Tunica externa (adventitia).

How do arteries differ structurally from veins?

Arteries have thicker tunica media, smaller lumens, and no valves; veins have thinner walls, larger lumens, and often possess valves.

What structure prevents back-flow of blood in many veins, especially of the limbs?

Venous valves formed by folds of the tunica interna.

What is meant by the "cardiovascular (vascular) tree"?

The hierarchical arrangement of vessels from large arteries (aorta) → medium arteries → arterioles → capillaries → venules → veins → venae cavae.

Which type of vessel is the main site of nutrient, gas, and waste exchange?

Capillaries.

Approximately how long would all of the body’s blood vessels be if placed end-to-end?

Roughly 60,000 miles (about 100,000 km).

At any given moment, where is most of the body’s blood volume located?

In the systemic veins and venules (about 60–65%).

Why are capillaries uniquely suited for exchange?

They have very thin walls (one endothelial cell thick), extremely large total cross-sectional area, and very slow blood velocity.

Which vessels have the greatest total cross-sectional area?

Capillaries.

Where is blood flow velocity the slowest, and why is this advantageous?

In capillaries; slow flow maximizes time for exchange of gases, nutrients, and wastes.

Define blood flow.

The volume of blood moving through a vessel, organ, or the entire circulation per unit time (mL/min).

Define blood pressure (BP).

The force per unit area exerted on a vessel wall by the contained blood, usually measured in mm Hg.

Define peripheral resistance (R).

Opposition to blood flow, largely determined by vessel radius, length, blood viscosity, and turbulence.

What is the fundamental hemodynamic relationship among flow, pressure, and resistance?

Flow (F) = ΔP / R (Ohm’s law of the circulation).

Which single variable has the greatest moment-to-moment influence on peripheral resistance?

Vessel radius; small changes cause large resistance changes (R ∝ 1/r⁴).

How does systolic pressure differ from diastolic pressure?

Systolic pressure is the peak arterial pressure during ventricular contraction; diastolic is the lowest just before the next ventricular ejection.

What is pulse pressure, and how is it calculated?

The difference between systolic and diastolic pressures (PP = SP – DP).

Why does arterial stiffening (e.g., atherosclerosis) raise systolic pressure?

Reduced arterial compliance means the same stroke volume is forced into a less distensible vessel, increasing peak (systolic) pressure.

List the three major factors that determine mean arterial pressure (MAP).

Cardiac output, total peripheral resistance, and blood volume.

Name the three main components the body adjusts to regulate blood pressure moment by moment.

Cardiac output, peripheral resistance, and blood volume.

What reflex monitors arterial pressure and provides rapid neural feedback?

The baroreceptor (baroreflex) mechanism located in carotid sinuses and aortic arch.

Which division of the autonomic nervous system causes most arteriolar vasoconstriction?

Sympathetic nervous system via vasomotor fibers releasing norepinephrine.

What are the four broad categories of blood-pressure regulation mechanisms presented?

Local control, chemical/hormonal control, neural control, and renal (long-term) control.

Give two examples of hormones that increase blood pressure by raising blood volume or resistance.

Angiotensin II (vasoconstrictor) and aldosterone (increases Na⁺ and water reabsorption).

What is capillary hydrostatic pressure (HP_b)?

The blood pressure within capillaries that tends to push fluid out into the interstitial space.

What is colloid osmotic pressure (COP_b) in capillaries, and what mainly creates it?

The osmotic pull exerted by plasma proteins (especially albumin) that draws fluid into the capillary.

At the arterial end of a typical capillary, does filtration or reabsorption predominate, and why?

Filtration, because capillary hydrostatic pressure exceeds colloid osmotic pressure, causing net fluid exit.

At the venous end of a capillary, what pressure relationship causes reabsorption?

Colloid osmotic pressure exceeds hydrostatic pressure, drawing fluid back into the capillary.

What is edema, and how can capillary dynamics produce it?

Excess interstitial fluid accumulation; occurs when filtration exceeds reabsorption plus lymphatic return (e.g., ↑HP or ↓COP).

How would an acute rise in systemic blood pressure affect capillary exchange?

It increases capillary hydrostatic pressure, shifting the balance toward filtration and promoting edema.

How does severe blood loss alter capillary exchange?

Lower capillary hydrostatic pressure favors reabsorption, pulling fluid from tissues into the bloodstream to help restore volume.

Why does liver disease often lead to peripheral edema?

Reduced plasma protein synthesis lowers COP, decreasing reabsorption and increasing fluid loss to tissues.

How does high plasma electrolyte concentration influence blood volume?

It raises plasma osmotic pressure, promoting fluid influx into blood, increasing blood volume and BP (corrected by kidneys).

What clinical problem occurs when a deep-vein thrombosis breaks loose and travels to the lungs?

Pulmonary embolism (pulmonary thromboembolism).

State Poiseuille’s law’s implication for vessel radius and flow.

Flow ∝ r⁴; doubling radius increases flow 16-fold, highlighting radius as the dominant resistance factor.

Why do veins contain valves but arteries generally do not?

Veins operate under low pressure and must prevent backflow as blood returns to the heart; arterial pressure is sufficiently high to maintain forward flow.

What is vasa vasorum?

Small blood vessels within the walls of larger arteries and veins that supply nutrients to those vessel walls.

Which vessels act as pressure reservoirs, and which act as volume reservoirs?

Elastic arteries act as pressure reservoirs; systemic veins act as volume reservoirs.

What is meant by "turbulence" in blood flow, and how does it affect resistance?

Chaotic fluid flow due to irregular surfaces or abrupt changes in diameter; increases resistance and may cause murmurs/bruits.

Explain why arteriole radius changes allow redistribution of blood flow during exercise.

Arterioles supplying active tissues dilate (decreased resistance) while others constrict, directing limited cardiac output to where it’s needed most.

Which part of the vascular tree shows the steepest drop in blood pressure, and why?

Arterioles, because their small diameter and adjustable resistance dissipate much of the pressure energy.