3: Hemodynamics: Blood Pressure Control and Capillary Exchange

Vocabulary practice flashcards defining key physiological concepts, anatomical structures, regulatory hormones, and transport mechanisms in cardiovascular hemodynamics and capillary exchange.

Cardiovascular (CV) Center

A medullary brain region that integrates afferent sensory input from higher brain centers, proprioceptors, baroreceptors, and chemoreceptors, regulating heart rate, myocardial contractility, and blood vessel diameter via autonomic efferent pathways.

Proprioceptors

Sensory receptors that monitor joint movements and send sensory input to the cardiovascular center to stimulate rapid increases in heart rate at the onset of physical activity.

Baroreceptors

Pressure-sensitive sensory receptors located in blood vessels that monitor arterial blood pressure and transmit nerve impulses to the cardiovascular center to regulate hemodynamic stability.

Chemoreceptors

Sensory receptors that monitor blood chemical composition—specifically acidity ($\text{H}^+$), $\text{CO}_2$, and $\text{O}_2$ levels—and provide afferent input to the cardiovascular center.

Vagus Nerves

Parasympathetic cranial nerves transmitting efferent impulses from the cardiovascular center to the heart to decrease heart rate.

Cardiac Accelerator Nerves

Sympathetic nerves conveying output from the cardiovascular center to the heart to increase both heart rate and myocardial contractility.

Vasomotor Nerves

Sympathetic nerves that innervate the vascular smooth muscle within the tunica media of blood vessels to regulate blood vessel diameter.

Vasoconstriction

The reduction of a blood vessel's lumen diameter caused by a high rate of sympathetic vasomotor nerve firing; narrowing lumen diameter by $16\%$ reduces blood flow by half.

Vasodilation

The widening of a blood vessel's lumen diameter resulting from a low rate of sympathetic vasomotor nerve firing; increasing lumen diameter by $19\%$ doubles blood flow.

Angiotensin II

A peptide hormone that raises blood pressure by inducing systemic vasoconstriction (reducing vascular space) and by stimulating the secretion of aldosterone from the adrenal glands.

Aldosterone

An adrenal hormone that increases blood volume and blood pressure by promoting sodium and water reabsorption from the kidney filtrate back into the circulating blood.

Antidiuretic Hormone (ADH)

Also known as vasopressin; a hormone that raises blood pressure by inducing vasoconstriction and expanding blood volume through the reduction of urination and sweating.

Atrial Natriuretic Peptide (ANP)

A hormone released by cardiac atrial muscle cells in response to high blood volume that lowers blood pressure by stimulating arteriole and venule vasodilation, increasing urination, and decreasing aldosterone secretion.

Capillary Exchange

The movement of substances between blood plasma and interstitial fluid through three primary mechanisms: diffusion, transcytosis, and bulk flow.

Continuous Capillary

A capillary type with intact endothelial walls and narrow intercellular clefts that permits diffusion of water-soluble solutes (glucose, amino acids, electrolytes) and lipid-soluble materials ($\text{O}_2$, $\text{CO}_2$, steroids), but blocks blood cells and most plasma proteins.

Fenestrated Capillary

A capillary type characterized by numerous small pores (fenestrations) in the endothelial cell walls that allow greater permeability to small water-soluble solutes while still excluding large plasma proteins and formed elements.

Sinusoid

A highly permeable capillary with large intercellular gaps and an incomplete basement membrane, allowing whole cells (such as red blood cells in red bone marrow) and large proteins (such as albumin and fibrinogen from the liver) to pass freely.

Transcytosis

A mechanism of capillary exchange transporting small amounts of large molecules across endothelial linings via caveolae-mediated endocytosis, cytoskeletal vesicular transit, and exocytosis (e.g., antibodies, transferrin, insulin).

Caveolae

Small flask-like invaginations in the plasma membrane of capillary endothelial cells where plasma proteins concentrate before being internalized into transport vesicles during transcytosis.

Bulk Flow

The passive, pressure-driven movement of large numbers of ions, molecules, or particles together in the same direction in a fluid, functioning to balance relative volumes of blood and interstitial fluid.

Blood Hydrostatic Pressure (BHP)

The pressure exerted by water in blood plasma against capillary walls, generated by the pumping action of the heart, which drives fluid from capillaries into interstitial spaces to promote filtration.

Blood Colloid Osmotic Pressure (BCOP)

The osmotic pressure produced by colloidal suspensions of nondiffusible plasma proteins (such as albumin) that pulls water from interstitial spaces into capillaries, promoting reabsorption.

Interstitial Fluid Hydrostatic Pressure (IFHP)

The physical pressure exerted by interstitial fluid against the exterior of capillary walls (typically measured at $0\,\text{mmHg}$), which opposes filtration and promotes reabsorption.

Interstitial Fluid Osmotic Pressure (IFOP)

The osmotic pressure exerted by proteins dispersed within the interstitial spaces (typically around $1\,\text{mmHg}$), pulling fluid out of capillaries into interstitial spaces to promote filtration.

Filtration

The pressure-driven movement of fluid and solutes from blood into the interstitial fluid, occurring primarily at the arterial end of capillaries at an average volume of $20\,\text{L/day}$.

Reabsorption

The pressure-driven movement of fluid and solutes from interstitial fluid back into the blood, occurring primarily at the venous end of capillaries at an average volume of $17\,\text{L/day}$.

Edema

An abnormal accumulation of fluid in the tissues occurring when interstitial fluid volume increases by $30\%$ or more above normal, caused by excess filtration (elevated BHP or capillary permeability) or inadequate reabsorption (decreased BCOP).