Chapter 20 – Vessels and Circulation

70 Question-and-Answer flashcards covering key concepts from Chapter 20: Vessels and Circulation, including vessel structure, capillary exchange, blood pressure regulation, clinical conditions, and hormonal control.

What are the three major types of blood vessels?

Arteries, capillaries, and veins.

Which vessels convey blood from the heart to capillaries?

Arteries.

Which vessels exchange substances between blood and tissues?

Capillaries.

Which vessels transport blood from capillaries back to the heart?

Veins.

As arteries branch away from the heart, how do lumen diameter, elastic fibers, and smooth muscle change?

Lumen diameter and elastic fibers decrease, while relative smooth-muscle content increases.

Name the three basic types of arteries.

Elastic arteries, muscular arteries, and arterioles.

What size range defines elastic (conducting) arteries?

Diameters from 2.5 cm to 1 cm.

What key feature allows elastic arteries to propel blood during diastole?

A large proportion of elastic fibers that stretch and recoil.

Muscular (distributing) arteries have what diameter range?

1 cm to 0.3 mm.

What is the primary function of muscular arteries?

They distribute blood to specific body regions and can vasoconstrict or vasodilate.

What diameter range defines arterioles?

0.3 mm to 10 µm.

What is "vasomotor tone"?

Slight, continual constriction of arteriolar smooth muscle.

Which brain region regulates vasomotor tone?

The vasomotor center in the brainstem.

How do arterioles influence systemic blood pressure?

By regulating peripheral resistance and blood flow distribution.

Define atherosclerosis.

A progressive disease involving formation of atheromatous plaques in arterial walls.

What is an atheroma?

A plaque consisting of lipid and fibrous tissue that thickens the tunica intima and narrows the lumen.

Which blood lipid disorder is a major risk factor for atherosclerosis?

Hypercholesterolemia (high blood cholesterol).

Name two common treatments for significant atherosclerotic narrowing.

Percutaneous angioplasty and coronary bypass surgery.

What is an aneurysm?

A localized bulge in an arterial wall due to thinning and weakening.

Which arteries are most often affected by aneurysms?

The aorta and arteries at the base of the brain.

What is the average diameter of a typical capillary?

8–10 µm.

Which capillary type has tight junctions with intercellular clefts but no fenestrations?

Continuous capillaries.

Which capillary type contains pores that increase permeability to fluids and small molecules?

Fenestrated capillaries.

Which capillary type has large gaps and an incomplete basement membrane for passage of large substances?

Sinusoids.

What vessels branch from a metarteriole to form most of a capillary bed?

True capillaries.

What is the role of a precapillary sphincter?

It regulates blood flow into a true capillary.

Define vasomotion.

The cyclic contraction and relaxation of precapillary sphincters.

Approximately what fraction of the body’s capillary beds are open at any moment?

About one-quarter.

What is perfusion?

The amount of blood entering capillaries per minute per gram of tissue (mL/min/g).

What are venules?

The smallest veins, 8–100 µm in diameter, draining capillaries.

Why do many medium and large veins contain valves?

To prevent blood from pooling and to ensure one-way flow toward the heart.

How can systemic veins act as blood reservoirs?

They store large blood volumes that can be shifted into circulation by venous constriction.

What is a simple vascular pathway?

A single major artery, capillary network, and vein supplying/draining an organ.

Define an arterial anastomosis.

Two or more arteries converging to supply the same region.

What is a venous anastomosis?

Two or more veins draining the same region—very common.

What is an arteriovenous anastomosis (shunt)?

A direct connection that transports blood from an artery into a vein, bypassing capillaries.

Describe a portal system.

Two capillary beds in sequence connected by a portal vein.

How does total cross-sectional area relate to blood flow velocity?

Velocity is inversely related; the large area in capillaries leads to slow flow.

List the three main processes of capillary exchange.

Diffusion, vesicular transport, and bulk flow.

The diffusion route across capillary walls depends primarily on what factor?

The size of the diffusing particle.

How does vesicular transport move substances across capillary endothelium?

By pinocytosis and exocytosis of fluid-filled vesicles.

Define bulk flow.

The mass movement of fluid and solutes driven by pressure gradients across a capillary wall.

What is the difference between filtration and reabsorption in capillaries?

Filtration moves fluid out of blood; reabsorption moves fluid back into blood.

What is blood hydrostatic pressure (HPb)?

The force exerted per unit area by blood on the vessel wall, promoting filtration.

What creates blood colloid osmotic pressure?

Plasma proteins (mainly albumin) pulling water into the blood, promoting reabsorption.

At which end of a capillary is net filtration pressure highest?

The arterial end.

Roughly what percent of filtered fluid is not reabsorbed and must be picked up by the lymphatic system?

About 15%.

What does "degree of vascularization" refer to?

The extent of blood vessel networks within a tissue.

Define angiogenesis.

The formation of new blood vessels.

What is the purpose of the myogenic response in arterioles?

To keep local blood flow constant despite systemic pressure changes.

At rest, total blood flow equals which cardiac parameter?

Cardiac output (≈ 5.25 L/min).

What is the blood pressure gradient?

The change in pressure from one end of a vessel to the other, driving blood flow.

How is pulse pressure calculated?

Systolic pressure minus diastolic pressure.

Provide the formula for mean arterial pressure (MAP).

MAP = diastolic pressure + 1/3 (pulse pressure).

What is the role of the skeletal muscle pump?

Contraction of limb muscles squeezes veins to enhance venous return.

How does the respiratory pump aid venous return?

Pressure changes during breathing move blood toward the heart.

What life-threatening complication can arise from deep vein thrombosis?

Pulmonary embolus.

What causes varicose veins?

Nonfunctional venous valves leading to blood pooling and vein dilation.

Name the three primary factors that influence peripheral resistance.

Blood viscosity, vessel length, and vessel radius.

How does increased blood viscosity affect resistance?

It increases resistance to flow.

How is blood flow related mathematically to vessel radius?

Flow is proportional to the radius raised to the fourth power (F ∝ r⁴).

Via which cranial nerve do carotid sinus baroreceptors send signals?

Glossopharyngeal nerve (CN IX).

Which chemical changes stimulate peripheral chemoreceptors to raise blood pressure?

High CO₂, low pH, or very low O₂ levels.

Which hormones released from the adrenal medulla raise blood pressure?

Epinephrine and norepinephrine.

What is the effect of atrial natriuretic peptide (ANP) on blood pressure?

It decreases blood pressure through vasodilation and increased urine output.

How does aldosterone help maintain blood pressure?

By increasing renal reabsorption of sodium and water, thus raising blood volume.

List two major actions of antidiuretic hormone (ADH).

Increases water reabsorption in the kidneys and, in high amounts, causes vasoconstriction.

What blood pressure values define hypertension?

Systolic > 140 mm Hg and/or diastolic > 90 mm Hg.

What values define hypotension?

Systolic < 90 mm Hg and/or diastolic < 60 mm Hg.