Chapter 20: The Circulatory System - Blood Vessels and Circulation

Vocabulary flashcards covering blood pressure, vascular resistance, autonomic and hormonal regulation, capillary dynamics, venous return mechanisms, circulatory shock, and systemic circulation from Chapter 20.

Blood Flow

The amount of blood flowing through an organ, tissue, or blood vessel in a given time, expressed in units of $\text{mL/min}$.

Perfusion

The rate of blood flow per given volume or mass of tissue in a given time, expressed in units of $\text{mL/min/g}$.

Systolic Pressure

The peak arterial blood pressure measured during ventricular contraction (ventricular systole).

Diastolic Pressure

The minimum arterial blood pressure measured during ventricular relaxation (ventricular diastole) between heartbeats, with a normal young adult resting blood pressure value of $120/75\,\text{mm}\,\text{Hg}$.

Peripheral Resistance

The opposition to flow that blood encounters in vessels away from the heart, which hinges on three variables: blood viscosity, vessel length, and vessel radius.

Laminar Flow

The normal pattern of blood flow in which fluid moves in concentric parallel layers, flowing fastest in the center of the vessel lumen and slower near the vessel walls due to friction.

Vasomotion

A quick change in vessel radius, consisting either of vasoconstriction caused by smooth muscle contraction or vasodilation caused by smooth muscle relaxation.

Autoregulation

The ability of tissues to regulate their own blood supply; described by the metabolic theory of autoregulation wherein inadequate perfusion leads to waste accumulation that stimulates vasodilation.

Reactive Hyperemia

An increase in blood flow above normal levels that occurs after the blood supply to a tissue has been temporarily cut off and then restored.

Angiogenesis

The growth of new blood vessels stimulated by growth factors, occurring in the regrowth of the uterine lining, around coronary artery obstructions, in exercised muscle, and in malignant tumors.

Baroreflex

An automatic, negative feedback neural response to blood pressure changes; detected by carotid sinuses and communicated via the glossopharyngeal nerve to inhibit sympathetic cardiac and vasomotor neurons while stimulating vagal fibers.

Chemoreflex

An autonomic neural response to changes in blood chemistry—specifically $\text{pH}$, and concentrations of $\text{O}_2$ and $\text{CO}_2$—detected by carotid and aortic bodies.

Medullary Ischemic Reflex

An automatic neural response to a drop in perfusion to the brain, wherein the medulla oblongata triggers sympathetic signals that increase heart rate, contractile force, and cause widespread vasoconstriction to raise systemic blood pressure.

Venoconstriction

The contraction of smooth muscle fibers in medium-sized veins stimulated by sympathetic nerves from the vasomotor center, reducing venous diameter to maintain arterial blood volume during blood loss.

Angiotensin II

A potent vasoconstrictor hormone that raises blood pressure and increases blood volume by promoting $\text{Na}^+$ and water retention by the kidneys.

Atrial Natriuretic Peptide (ANP)

A hormone secreted by the heart that increases urinary sodium excretion, reduces total blood volume, and promotes vasodilation, thereby lowering blood pressure.

Tunica Interna (Tunica Intima)

The innermost layer of a blood vessel wall that lines the lumen, consisting of simple squamous endothelium overlying a basement membrane and an internal elastic membrane in arteries.

Conducting (Elastic) Arteries

The largest caliber arteries—such as the aorta, pulmonary trunk, common carotid, subclavian, and common iliac arteries—that expand during ventricular systole and recoil during diastole to dampen blood pressure fluctuations.

Distributing (Muscular) Arteries

Medium-sized arteries that distribute blood to specific organs, characterized by a thick layer of smooth muscle; examples include the brachial, femoral, renal, and splenic arteries.

Metarterioles

Short microvessels that link arterioles to capillaries, featuring smooth muscle cells forming precapillary sphincters around the entrances to capillary beds.

Aneurysm

A weak point in an artery or the heart wall forming a thin-walled, pulsating sac prone to rupture; commonly occurring in the abdominal aorta, renal arteries, and the arterial circle at the base of the brain.

Continuous Capillaries

The most common capillary type, characterized by endothelial cells joined by tight junctions to form an uninterrupted tube with narrow intercellular clefts, surrounded by contractile pericytes.

Fenestrated Capillaries

Capillaries found in organs requiring rapid absorption or filtration (such as the kidneys and small intestine), possessing endothelial cells riddled with filtration pores (fenestrations).

Sinusoids (Discontinuous Capillaries)

Irregular, blood-filled spaces with wide gaps and large fenestrations found in the liver, bone marrow, and spleen that allow large proteins, clotting factors, and new blood cells to pass into circulation.

Thoroughfare Channel

A continuous channel extending from a metarteriole through a capillary bed directly into a venule, bypassing capillary exchange when precapillary sphincters are closed.

Venous Sinuses

Veins with exceptionally thin walls, large lumens, and no smooth muscle tunic, rendering them incapable of vasomotion.

Varicose Veins

Superficial veins that have become permanently distended and tortuous due to blood pooling in the lower limbs, causing the cusps of venous valves to pull apart and fail.

Portal System

A circulatory route where blood flows through two consecutive capillary networks before returning to the heart, found in the hepatic portal system, between the hypothalamus and anterior pituitary, and in the kidneys.

Arteriovenous Anastomosis (Shunt)

A vascular connection in which an artery flows directly into a vein, bypassing capillary beds entirely.

Arterial Anastomosis

A junction where two arteries merge, providing collateral (alternative) routes of blood supply to a tissue, commonly found in coronary circulation and around joints.

Venous Return

The flow of blood back to the heart, driven by a pressure gradient, gravity, the skeletal muscle pump, the thoracic (respiratory) pump, and cardiac suction.

Thoracic (Respiratory) Pump

A venous return mechanism in which inhalation expands the thoracic cavity, decreasing thoracic cavity pressure while increasing abdominal pressure to push venous blood upward toward the heart.

Skeletal Muscle Pump

A mechanism of venous return in the limbs where contraction of surrounding skeletal muscle compresses veins, forcing blood through one-way valves toward the heart while preventing backflow.

Edema

The abnormal accumulation of excess fluid in a tissue, caused by increased capillary filtration, reduced capillary absorption, or obstructed lymphatic drainage.

Circulatory Shock

Any clinical state in which cardiac output is insufficient to meet the body’s metabolic demands, broadly categorized into cardiogenic shock and low venous return (LVR) shock.

Hypovolemic Shock

The most common form of low venous return (LVR) shock, caused by a substantial loss of blood volume due to trauma, hemorrhage, severe burns, or dehydration.

Septic Shock

A form of vascular shock triggered by bacterial toxins that cause widespread vasodilation and abnormally increased capillary permeability.

Anaphylactic Shock

A severe systemic immune reaction to an antigen characterized by extensive histamine release, generalized vasodilation, and increased capillary permeability.

Compensated Shock

The initial stage of circulatory shock in which homeostatic mechanisms successfully maintain blood pressure and bring about spontaneous recovery.

Decompensated Shock

An advanced, life-threatening stage of circulatory shock that ensues when homeostatic mechanisms fail, initiating detrimental positive feedback loops that damage cardiac and cerebral tissue.

Transient Ischemic Attacks (TIAs)

Brief, temporary episodes of cerebral ischemia caused by arterial spasms, lasting from seconds to hours and producing dizziness, weakness, vision loss, or aphasia.

Cerebral Vascular Accident (CVA)

A stroke; the sudden death of brain tissue caused by ischemia, typically resulting from atherosclerosis, thrombosis, or a ruptured aneurysm.

Brachiocephalic Trunk

The first branch originating from the aortic arch that branches into the right common carotid artery and the right subclavian artery.

Circle of Willis (Cerebral Arterial Circle)

An arterial anastomosis situated on the base of the brain encircling the pituitary gland, formed by branches of the basilar and internal carotid arteries.

Great Saphenous Vein

The longest superficial vein of the lower limb, ascending medially along the leg and thigh, frequently harvested for coronary artery bypass graft procedures.