The Cardiovascular System: Blood Vessels and Circulation

A Comprehensive vocabulary set covering blood vessel structure, physiology of blood flow, capillary exchange, and fetal development.

Artery

A blood vessel that carries blood away from the heart, where it branches into ever-smaller vessels.

Arteriole

A very small artery that leads to a capillary; also known as a resistance vessel due to its role in slowing blood flow and causing a drop in blood pressure.

Capillary

A microscopic channel that supplies blood to the tissues in a process called perfusion and serves as the site for nutrient and waste exchange.

Venule

An extremely small blood vessel, generally $8-100\text{ micrometers}$ in diameter, that carries blood from capillaries to a vein.

Vein

A blood vessel that conducts blood toward the heart and is equipped with valves to promote unidirectional flow.

Lumen

The hollow passageway through which blood flows within a blood vessel.

Vasa Vasorum

Small blood vessels located within the walls of larger arteries and veins that provide nourishment and remove waste from the vessel's cells.

Nervi Vasorum

Minute nerves within the walls of blood vessels that control the contraction and dilation of smooth muscle.

Tunica Intima

The innermost tissue layer of a blood vessel composed of an endothelial lining and a thin layer of connective tissue.

Endothelium

The specialized simple squamous epithelium that lines the tunica intima and is continuous throughout the entire vascular system.

Tunica Media

The substantial middle layer of a vessel wall containing smooth muscle and elastic fibers; it is generally the thickest layer in arteries.

Tunica Externa

The outermost sheath of a blood vessel composed primarily of collagenous fibers and connective tissue; it is normally the thickest tunic in veins.

Vasoconstriction

The decrease in blood flow as smooth muscle in the tunica media contracts, making the lumen narrower and increasing blood pressure.

Vasodilation

The increase in blood flow as smooth muscle in the tunica media relaxes, widening the lumen and decreasing blood pressure.

Elastic Artery

A large-diameter vessel (typically $> 10\text{ mm}$) located close to the heart with abundant elastic fibers that allow it to expand and recoil.

Muscular Artery

A vessel with a thick tunica media and a higher percentage of smooth muscle that plays a leading role in vasoconstriction; also known as a distributing artery.

Continuous Capillary

The most common type of capillary, found in almost all vascularized tissues, featuring a complete endothelial lining and tight junctions.

Fenestrated Capillary

A capillary with pores (fenestrations) in addition to tight junctions, making it permeable to larger molecules; common in the small intestine and kidneys.

Sinusoid Capillary

The least common capillary type, featuring flattened shapes and extensive intercellular gaps for the passage of large molecules and cells; found in the liver and bone marrow.

Metarteriole

A vessel with structural characteristics of both an arteriole and a capillary that supplies blood to a capillary bed.

Precapillary Sphincters

Circular smooth muscle cells that surround a capillary at its origin and regulate the flow of blood into the capillary bed.

Vasomotion

The irregular, pulsating flow of blood through a capillary bed, regulated by chemical signals like oxygen and carbon dioxide levels.

Skeletal Muscle Pump

A mechanism that increases pressure in veins via the contraction of surrounding skeletal muscle to counteract gravity and move blood toward the heart.

Capacitance Vessels

A term for veins due to their high capacitance, meaning their ability to distend and store a high volume of blood efficiently even at low pressure.

Blood Pressure

The force exerted by blood upon the walls of blood vessels or chambers of the heart, measured in $mmHg$.

Systolic Pressure

The higher value in a blood pressure ratio reflecting the arterial pressure resulting from ventricular contraction (systole).

Diastolic Pressure

The lower value in a blood pressure ratio representing the arterial pressure during ventricular relaxation (diastole).

Pulse Pressure

The difference between the systolic pressure and the diastolic pressure.

Mean Arterial Pressure (MAP)

The average force driving blood into vessels that serve the tissues, approximated as: $MAP \text{ = diastolic BP} + \frac{1}{3}(\text{systolic BP} - \text{diastolic BP})$.

Compliance

The ability of a compartment, such as a blood vessel, to expand to accommodate increased content.

Viscosity

The thickness of blood, which is directly proportional to resistance and inversely proportional to flow.

Filtration

The pressure-driven movement of fluid and solutes from a capillary into the interstitial fluid.

Reabsorption

The movement of fluid from the interstitial fluid back into the capillaries, driven primarily by osmotic pressure.

Capillary Hydrostatic Pressure (CHP)

The force exerted by blood against the wall of a capillary; the primary force driving filtration.

Blood Colloidal Osmotic Pressure (BCOP)

The pressure created by the concentration of colloidal proteins in the blood that draws water back into the vessel from tissue fluid.

Net Filtration Pressure (NFP)

The interaction of hydrostatic and osmotic pressures; calculated as $NFP = CHP - BCOP$.

Baroreceptor

A specialized stretch receptor located in the aorta and carotid sinuses that monitors blood pressure and signals the cardiovascular center.

Chemoreceptor

A specialized sensory receptor that monitors levels of oxygen, carbon dioxide, and hydrogen ions ($pH$) to maintain vascular homeostasis.

Angiotensin II

A powerful vasoconstrictor that increases blood pressure and stimulates the release of ADH and aldosterone.

Arteriosclerosis

A condition characterized by the loss of compliance or 'hardening' of the arteries, often leading to hypertension.

Atherosclerosis

A specific type of arteriosclerosis involving the build-up of plaques (fatty, calcified deposits) within the walls of the vessel.

Circulatory Shock

A life-threatening condition where the circulatory system is unable to maintain blood flow to adequately supply tissues with oxygen and nutrients.

Hypovolemic Shock

A form of shock caused by the excessive loss of blood volume, often due to hemorrhage, dehydration, or severe burns.

Angiogenesis

The process of developing new blood vessels from existing ones.

Foramen Ovale

A shunt in the fetal heart consisting of an opening in the interatrial septum that allows blood to flow from the right atrium to the left atrium.

Ductus Arteriosus

A short, muscular fetal vessel that connects the pulmonary trunk to the aorta to bypass the nonfunctional lungs.

Ductus Venosus

A temporary fetal blood vessel that allows oxygenated blood from the placenta to bypass the liver and go directly to the fetal heart.