Circulatory System: Blood Vessels and Circulation

Comprehensive vocabulary flashcards covering the anatomy of blood vessels, hemodynamics, capillary exchange, regulatory mechanisms, and clinical conditions associated with the circulatory system.

Arteries

Blood vessels that carry blood away from the heart.

Veins

Blood vessels that carry blood back to the heart.

Capillaries

Microscopic vessels that connect the smallest arteries to the smallest veins to create a circuit; they are the primary site for the exchange of gases, nutrients, and wastes.

Tunica interna (tunica intima)

The innermost layer of a blood vessel wall that is exposed to blood and consists of an endothelium overlying a basement membrane.

Endothelium

A simple squamous epithelium that acts as a selectively permeable barrier, secretes chemicals for vasomotion, and normally repels blood cells to prevent clotting.

Tunica media

The middle layer of the vessel wall consisting of smooth muscle, collagen, and elastic tissue; it strengthens vessels and controls diameter through contraction.

Tunica externa (tunica adventitia)

The outermost layer of a vessel wall composed of loose connective tissue that anchors the vessel and provides passage for nerves and lymphatic vessels.

Vasa vasorum

Small vessels that supply blood to the outer part of larger blood vessels.

Conducting (elastic or large) arteries

The biggest arteries, such as the aorta, which expand during systole and recoil during diastole to maintain blood pressure and flow.

Distributing (muscular or medium) arteries

Arteries like the brachial or femoral that distribute blood to specific organs; smooth muscle constitutes three-fourths of their wall thickness.

Resistance (small) arteries

Arteries with a thicker tunica media in proportion to their lumen than large arteries; arterioles are the smallest of this category.

Metarterioles

Short vessels that link arterioles directly to venules, providing shortcuts that allow blood to bypass capillary beds.

Aneurysm

A weak point in an artery or heart wall that forms a thin-walled, bulging sac that pulsates and may rupture.

Carotid sinuses

Baroreceptors located in the walls of the internal carotid artery that monitor blood pressure and signal the brainstem via the glossopharyngeal nerve.

Carotid bodies

Chemoreceptors located near the branch of the common carotids that monitor blood chemistry ($pH$, $CO_2$, and $O_2$) to adjust respiratory rate.

Continuous capillaries

Capillaries found in most tissues where endothelial cells form a continuous tube with intercellular clefts that allow for the passage of solutes like glucose.

Pericytes

Cells that wrap around continuous capillaries and contain contractile proteins to regulate blood flow.

Fenestrated capillaries

Capillaries with endothelial cells riddled with filtration pores (fenestrations) to allow rapid absorption or filtration of small molecules.

Sinusoids

Irregular blood-filled spaces in the liver, bone marrow, and spleen with large fenestrations that allow proteins and new blood cells to enter circulation.

Precapillary sphincters

Smooth muscle cells in metarterioles that control flow into capillary beds; when contracted, blood bypasses the capillaries.

Postcapillary venules

The smallest veins, which are even more porous than capillaries and serve as the site where leukocytes leave the bloodstream.

Venous sinuses

Veins with especially thin walls, large lumens, and no smooth muscle, such as the dural sinuses, which are not capable of vasoconstriction.

Varicose veins

Abnormally distended veins caused by the failure of venous valves, leading to blood backflow and pooling, often seen in the lower legs.

Portal system

A circulatory route where blood flows through two consecutive capillary networks before returning to the heart, such as between the intestines and the liver.

Anastomosis

A point where two blood vessels other than capillaries merge, providing alternative routes for blood flow.

Perfusion

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

Systolic pressure

The peak arterial blood pressure recorded during ventricular contraction.

Diastolic pressure

The minimum arterial blood pressure recorded during ventricular relaxation between heartbeats.

Pulse pressure

The difference between systolic and diastolic pressure, representing the stress exerted on small arteries by pressure surges.

Mean arterial pressure (MAP)

The average blood pressure calculated as diastolic pressure + (one-third of pulse pressure); it most influences the risk of edema or kidney failure.

Arteriosclerosis

The stiffening of arteries due to the deterioration of elastic tissues in the artery walls.

Peripheral resistance

The opposition to flow that blood encounters in vessels away from the heart, determined by blood viscosity, vessel length, and vessel radius.

Blood viscosity

The thickness of blood, primarily determined by RBC count and albumin concentration.

Laminar flow

The movement of blood in layers, where flow is faster in the center of the vessel and slower near the walls due to friction.

Autoregulation

The ability of tissues to regulate their own blood supply based on the metabolic theory that waste accumulation stimulates vasodilation.

Vasoactive chemicals

Substances such as histamine, bradykinin, and prostaglandins secreted by platelets or endothelial cells to stimulate vasomotor responses.

Reactive hyperemia

A dramatic increase in blood flow above normal levels that occurs after a tissue's blood supply is cut off and then restored.

Vasomotor center

An integrating center in the medulla oblongata that exerts sympathetic control over blood vessels throughout the body.

Baroreflex

An automatic, negative feedback response to changes in blood pressure, used for short-term regulation such as postural changes.

Medullary ischemic reflex

An automatic response to a drop in brain perfusion where the medulla oblongata triggers widespread vasoconstriction and increased heart rate to restore flow.

Angiotensin II

A potent hormone and vasoconstrictor that raises blood pressure; its production is blocked by ACE inhibitors used to treat hypertension.

Aldosterone

A 'salt-retaining hormone' that promotes sodium retention by the kidneys, which leads to water retention and supported blood pressure.

Natriuretic peptides

Hormones secreted by the heart that lower blood pressure by increasing sodium excretion by the kidneys and promoting vasodilation.

Transcytosis

A process where endothelial cells move materials across their cytoplasm using pinocytosis or receptor-mediated endocytosis followed by exocytosis.

Colloid osmotic pressure (COP)

The osmotic pressure resulting from plasma proteins like albumin that draws fluid into capillaries; it opposes hydrostatic pressure.

Edema

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

Skeletal muscle pump

A mechanism of venous return where contracting limb muscles squeeze blood through veins, and valves prevent backflow.

Thoracic (respiratory) pump

A mechanism of venous return where inhalation creates a pressure gradient that forces blood in the inferior vena cava upward toward the heart.

Circulatory shock

Any state in which cardiac output is insufficient to meet the body's metabolic needs.

Cardiogenic shock

Circulatory shock caused by inadequate pumping of the heart, often resulting from myocardial infarction.

Hypovolemic shock

The most common form of low venous return shock, caused by a loss of blood volume through trauma, burns, or dehydration.

Septic shock

A state of circulatory shock where bacterial toxins trigger widespread vasodilation and increased capillary permeability.

Transient ischemic attacks (TIAs)

Brief episodes of cerebral ischemia characterized by dizziness, vision loss, or paralysis, which often serve as early warnings of a stroke.

Cerebral vascular accident (CVA)

Commonly known as a stroke, it is the sudden death of brain tissue caused by ischemia resulting from atherosclerosis, thrombosis, or a ruptured aneurysm.

Ascites

Abnormal abdominal distention due to serous fluid accumulation in the peritoneal cavity, frequently caused by portal hypertension and liver obstruction.