Structure and Function of Blood Vessels

This set of flashcards covers key terms and definitions related to the structure and function of blood vessels, essential for understanding cardiovascular physiology.

Arteries

Thick-walled muscular blood vessels that efficiently transport oxygen-rich blood away from the heart to the rest of the body, with the exception of the pulmonary arteries which carry deoxygenated blood to the lungs.

Capillaries

Microscopic and extremely thin-walled (typically one cell thick) blood vessels that form networks connecting arterioles and venules, serving as the primary sites for the exchange of oxygen, nutrients, and waste products between the blood and surrounding tissues.

Veins

Blood vessels with thinner walls and larger lumens than arteries, equipped with valves to prevent backflow, that primarily transport deoxygenated blood from the body tissues back towards the heart, with the exception of the pulmonary veins which carry oxygenated blood from the lungs to the heart.

Tunics

The three distinct layers that compose the walls of most blood vessels: the tunica interna (innermost), tunica media (middle), and tunica externa (outermost), each contributing to the vessel's structure and function.

Tunica interna

The innermost layer of a blood vessel, composed of a smooth simple squamous epithelium (endothelium) and a thin subendothelial layer, which provides a friction-reducing surface for blood flow and plays a role in vessel function and disease.

Tunica media

The middle layer of a blood vessel, primarily composed of circularly arranged smooth muscle cells and elastic fibers. This layer is responsible for regulating the diameter of the vessel lumen through vasoconstriction and vasodilation, thereby controlling blood flow and blood pressure.

Vasoconstriction

The physiological process of narrowing of the blood vessel lumen, specifically due to the contraction of the smooth muscle within the tunica media. This action decreases blood flow to a region and can increase systemic blood pressure.

Vasodilation

The physiological process of widening or increasing the diameter of the blood vessel lumen, resulting from the relaxation of the smooth muscle cells in the tunica media. This action increases blood flow to a region and can decrease systemic blood pressure.

Vasa vasorum

Literally 'vessels of vessels,' these are small blood vessels that supply oxygen and nutrients to the walls of larger blood vessels, especially arteries and veins, whose thick walls cannot be nourished solely by diffusion from the blood passing through their lumen.

Companion vessels

A term referring to an artery and a vein that are typically found next to each other, supplying or draining blood from the same body region, often running within the same connective tissue sheath.

Capillary beds

Interconnected networks of capillaries that are the functional units for substance exchange between blood and tissues. They are supplied by an arteriole and drained by a venule, with blood flow regulated by precapillary sphincters.

Precapillary sphincter

A ring of smooth muscle located at the origin of a true capillary from a metarteriole. These sphincters control the blood flow into individual capillaries, allowing blood to be directed to specific tissues based on metabolic demand.

Hydrostatic pressure

The physical force exerted by a fluid against a structure, such as the walls of capillaries. In the blood, capillary hydrostatic pressure (CHP) forces fluid and dissolved substances out of the blood vessel into the interstitial fluid.

Colloid osmotic pressure

A form of osmotic pressure exerted by large proteins (colloids), primarily albumin, within the blood plasma. This pressure, often referred to as blood colloid osmotic pressure (BCOP), tends to pull fluid from the interstitial space back into the blood vessel.

Renin-angiotensin system

A crucial hormonal system (also known as the Renin-Angiotensin-Aldosterone System, RAAS) that plays a central role in regulating long-term blood pressure, fluid balance, and electrolyte balance in the body through a cascade involving renin, angiotensin II, and aldosterone.

Hypertension

A chronic medical condition characterized by abnormally high systemic blood pressure, typically defined as a sustained systolic pressure of 130 mmHg or higher or a diastolic pressure of 80 mmHg or higher, increasing the risk for heart disease, stroke, and kidney failure.

Hypotension

A condition characterized by abnormally low systemic blood pressure, generally defined as a systolic pressure below 90 mmHg or a diastolic pressure below 60 mmHg. It can lead to symptoms like dizziness and fainting due to inadequate blood flow to organs.

Pulmonary circulation

The specific division of the cardiovascular system that transports deoxygenated blood from the right ventricle of the heart to the lungs for oxygenation and carbon dioxide removal, and then returns the newly oxygenated blood to the left atrium of the heart.

Hepatic portal system

A specialized part of the circulatory system where veins carrying nutrient-rich and potentially toxin-laden blood from the digestive organs (stomach, intestines, pancreas, spleen) do not return directly to the heart, but instead converge and transport this blood to the liver for processing before it enters the general circulation.

Atrial natriuretic peptide

A hormone primarily released by the atria of the heart in response to elevated blood volume and atrial stretching. Its main function is to decrease blood pressure by promoting vasodilation, increasing sodium and water excretion by the kidneys, and inhibiting renin and aldosterone release.

Systolic pressure

The maximum blood pressure exerted in the arteries during ventricular systole, which is the contraction phase of the ventricles when blood is ejected into the aorta and pulmonary artery. This is the higher number recorded in a blood pressure reading.

Diastolic pressure

The minimum blood pressure remaining in the arteries during ventricular diastole, which is the relaxation phase of the ventricles when they are refilling with blood. This is the lower number recorded in a blood pressure reading.