The Cardiovascular System: Blood Vessels and Circulation

These flashcards cover the vocabulary and key physiological concepts of the cardiovascular system, including vessel structure, hemodynamics, capillary exchange, and fetal circulation.

Lumen

The hollow central passageway of a blood vessel.

Vasa vasorum

Known as "vessels of vessels," these nourish the walls of large vessels and remove waste.

Nervi vasorum

Known as "nerves of vessels," these control the constriction and dilation of blood vessel walls.

Tunica intima

The innermost tissue layer of a blood vessel, also called the tunica interna, composed of endothelium (simple squamous epithelium) and a basement membrane.

Endothelins

Local chemicals released by the endothelium that cause vasoconstriction to increase blood pressure.

Tunica media

The middle layer of blood vessels made of smooth muscle and elastin fibers; it is typically the thickest layer in arteries.

Tunica externa

Also known as tunica adventitia, this outer layer of collagen and elastin fibers anchors and protects vessels while preventing overstretching.

Elastic arteries

Also called conducting vessels, these are larger than $10\,mm$ in diameter and contain more elastin than smooth muscle; found nearest the heart.

Muscular arteries

Also called distribution vessels, these range from $0.1\,mm$ to $10\,mm$ in diameter and contain more smooth muscle than elastin.

Arterioles

Also called resistance vessels, these lead to capillaries and consist primarily of smooth muscle with little elastin, having a lumen less than $0.03\,mm$.

Perfusion

The process of supplying blood directly to the tissues via capillaries.

Continuous capillaries

The most abundant capillary type, characterized by an uninterrupted endothelium and incomplete tight junctions known as intercellular clefts.

Fenestrated capillaries

Capillaries with numerous pores (fenestrations) in the endothelium that allow rapid fluid and larger molecule exchange; found in the kidneys and small intestine.

Sinusoid capillaries

Capillaries with large fenestrations and an incomplete basement membrane found where cells must enter or leave circulation, such as in the liver, bone marrow, and spleen.

Precapillary sphincters

Circular smooth muscle cells that open and close to regulate blood flow into capillary beds.

Capacitance vessels

A term for veins, which act as blood reservoirs holding $60\text{--}64\%$ of total blood volume at any given time.

Venous valves

Folds of the tunica intima in large veins of the extremities that function to prevent the backflow of blood.

Blood flow ($F$)

Also called tissue perfusion, it is the volume of blood flowing through a vessel, organ, or the entire circulation per unit time, measured in $\text{mL/min}$.

Systolic pressure

The peak pressure exerted on vessel walls as blood is ejected from the heart during ventricular contraction.

Diastolic pressure

The minimum blood pressure at the end of ventricular relaxation.

Pulse pressure

The numerical difference between systolic and diastolic pressure; normally about $25\%$ of systolic pressure.

Mean Arterial Pressure (MAP)

The average force driving blood into vessels, calculated as $\text{Diastolic BP} + \frac{1}{3} \text{Pulse Pressure}$; normal range is $70\text{--}110\,mmHg$.

Compliance

The ability of a blood vessel to expand; increased compliance results in decreased blood pressure.

Blood viscosity

The thickness of blood that contributes to resistance; it is directly proportional to blood pressure.

Skeletal muscle pump

The mechanism where contraction of skeletal muscles surrounding veins increases pressure to help push blood against gravity toward the heart.

Respiratory pump

Pressure changes in the thoracic and abdominal cavities during breathing that create a gradient to assist venous return.

Filtration

The movement of materials out of the bloodstream toward the tissues.

Reabsorption

The movement of materials from the tissues into the bloodstream.

Capillary Hydrostatic Pressure (CHP)

The force generated by fluids in a vessel (blood pressure) that pushes material out of the bloodstream.

Blood Colloid Osmotic Pressure (BCOP)

The suction into the bloodstream generated by immovable plasma proteins.

Net Filtration Pressure (NFP)

The balance of forces calculated as $NFP = CHP - BCOP$.

Baroreceptors

Stretch-sensitive receptors that detect changes in blood pressure and send signals to the medulla oblongata.

Chemoreceptors

Sensors that detect changes in blood chemistry, including $pH$ and concentrations of $\text{O}_2$ or $\text{CO}_2$.

Hepatic portal system

The circulatory pathway that delivers blood from digestive organs to the liver for processing via the hepatic portal vein.

Foramen ovale

A fetal shunt in the interatrial septum that allows blood to flow from the right atrium to the left atrium.

Ductus arteriosus

A temporary fetal vessel that connects the pulmonary trunk to the aorta.

Ductus venosus

A fetal vessel that links the umbilical vein to the inferior vena cava, largely bypassing the liver.