Chapter 19 – Blood Vessels and Circulation

Vocabulary flashcards covering vessel anatomy, types, hemodynamics, regulatory mechanisms, clinical terms, special circulatory routes, and fetal circulation.

Blood Vessel

Dynamic tube that carries blood; includes arteries, capillaries, and veins.

Lumen

Central blood-containing space of a vessel.

Tunica Intima

Innermost vessel layer; endothelium plus basement membrane that minimizes friction.

Tunica Media

Middle layer of smooth muscle and elastin; mediates vasoconstriction and vasodilation.

Tunica Externa (Adventitia)

Outermost layer of collagen fibers; anchors vessel and houses vasa vasorum.

Artery

Vessel carrying blood away from the heart; walls thick and elastic to withstand high pressure.

Elastic Artery

Largest artery type; pressure reservoir that expands during systole and recoils during diastole.

Muscular Artery

Medium-sized distributing artery with thick smooth-muscle wall; active in vasoconstriction.

Arteriole

Smallest artery; major resistance vessel that regulates blood flow into capillary beds.

Capillary

Microscopic exchange vessel composed of endothelium and basement membrane only.

Continuous Capillary

Least permeable capillary with tight junctions and small intercellular clefts; common in skin, muscle, lung, CNS.

Fenestrated Capillary

Capillary containing pores (fenestrations) for rapid filtration/absorption; found in kidneys, intestines, endocrine glands.

Sinusoid Capillary

Leakiest capillary with large clefts and incomplete basement membrane; in liver, spleen, bone marrow, adrenal medulla.

Capillary Bed

Interwoven network of capillaries between arteriole and venule where exchange occurs.

Metarteriole

Short vessel linking arteriole to capillary; possesses precapillary sphincters.

Precapillary Sphincter

Cuff of smooth muscle regulating blood entry into true capillaries.

Vascular Shunt

Metarteriole–thoroughfare channel that bypasses true capillaries.

Venule

Small vein receiving blood from capillaries; very porous to WBCs and fluid.

Vein

Vessel returning blood to heart; thin wall, large lumen, contains valves; acts as blood reservoir.

Capacitance Vessel

Alternate term for veins due to their large blood-holding capacity.

Varicose Vein

Dilated painful vein formed when incompetent valves allow blood pooling.

Blood Flow

Volume of blood moving through a vessel, organ, or entire circulation per minute.

Blood Pressure (BP)

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

Peripheral Resistance

Opposition to flow from blood viscosity, vessel length, and especially vessel diameter.

Systolic Pressure

Arterial pressure during ventricular contraction; higher of the two BP values.

Diastolic Pressure

Arterial pressure during ventricular relaxation; lower BP value.

Pulse Pressure

Difference between systolic and diastolic pressure; felt as the pulse.

Mean Arterial Pressure (MAP)

Average arterial pressure that drives blood into tissues; ≈ Diastolic + ⅓ Pulse Pressure.

Vasoconstriction

Narrowing of vessel lumen by smooth-muscle contraction, raising resistance and BP.

Vasodilation

Widening of vessel lumen by smooth-muscle relaxation, lowering resistance and BP.

Baroreceptor

Stretch receptor in carotid sinuses & aortic arch that triggers reflex changes in HR and vessel diameter to stabilize BP.

Chemoreceptor

Sensor responding to blood CO₂, pH, or O₂ changes; stimulates increased cardiac output and vasoconstriction.

Skeletal Muscle Pump

Venous return mechanism where contracting muscles squeeze veins, propelling blood toward heart.

Respiratory Pump

Venous return aid produced by thoracic pressure changes during breathing.

Sympathetic Venoconstriction

Reflex constriction of venous smooth muscle under sympathetic tone to improve venous return.

Hypertension

Chronic resting BP ≥ 140/90 mm Hg; major risk for heart, vascular, and renal disease.

Hypotension

Resting BP below 90/60 mm Hg; problematic when circulation to tissues is inadequate.

Circulatory Shock

Condition where blood vessels cannot deliver adequate blood; includes hypovolemic, vascular, and cardiogenic types.

Intrinsic Control (Autoregulation)

Local regulation of blood flow within a tissue by altering its own arteriolar resistance.

Extrinsic Control

Systemic regulation of blood flow via nerves (sympathetic) and hormones.

Diffusion

Passive movement of substances down concentration gradients across capillary walls.

Transcytosis

Active transport of large molecules across endothelial cells via vesicles.

Hydrostatic Pressure

Physical force exerted by fluid against a surface; drives filtration out of capillaries.

Colloid Osmotic Pressure

Osmotic pull created by plasma proteins drawing water into capillaries.

Edema

Excess interstitial fluid due to imbalance between filtration, reabsorption, and lymphatic drainage.

Portal System

Vascular route where blood passes through two capillary beds before returning to heart (e.g., hepatic portal).

Arterial Anastomosis

Connection between two arteries providing collateral blood supply.

Venous Anastomosis

Interconnection of veins; provides alternate venous drainage.

Foramen Ovale

Fetal interatrial opening that shunts blood from right to left atrium; becomes fossa ovalis after birth.

Ductus Arteriosus

Fetal vessel connecting pulmonary artery to aorta, bypassing lungs; turns into ligamentum arteriosum.

Ductus Venosus

Fetal shunt bypassing liver by linking umbilical vein to inferior vena cava; becomes ligamentum venosum.

Umbilical Vein

Fetal vessel carrying oxygenated blood from placenta to fetus.

Umbilical Arteries

Paired fetal vessels returning deoxygenated blood to placenta.

Fetal Hemoglobin

O₂-binding protein with higher affinity than adult hemoglobin to ensure fetal oxygen uptake.