Physiology Flashcards

During which phase of the cardiac cycle does left ventricular volume remain at its maximum?

Answer: Isovolumetric contraction

After the mitral valve closes and before the aortic valve opens, the ventricle contracts with volume fixed at end-diastolic volume.

A patient stands up quickly from a supine position. Which immediate change occurs in the carotid sinus baroreflex?

Answer: Decreased baroreceptor firing and increased sympathetic outflow

Venous pooling lowers arterial pressure, reducing carotid sinus stretch and firing, which disinhibits sympathetic output.

Oxygen consumption is 250 mL/min, arterial O2 content is 200 mL/L, and mixed venous O2 content is 150 mL/L. What is the cardiac output?

Answer: 5 L/min

By the Fick principle, CO = 250 / (200 − 150) = 5 L/min.

Which substance's clearance provides the most accurate measurement of glomerular filtration rate?

Answer: Inulin

Inulin is freely filtered and neither reabsorbed nor secreted, so its clearance equals GFR.

Selective constriction of the efferent arteriole produces which combination of changes?

Answer: ↑GFR, ↓RPF, ↑filtration fraction

Efferent constriction raises glomerular capillary pressure (↑GFR) while reducing plasma flow, so FF = GFR/RPF rises.

Antidiuretic hormone increases water reabsorption primarily by which mechanism?

Answer: Inserting aquaporin-2 channels into principal cells of the collecting duct via V2 receptors

V2 receptor activation raises cAMP, driving aquaporin-2 insertion into the apical membrane of collecting duct principal cells.

Which nephron segment reabsorbs the largest fraction of filtered sodium?

Answer: Proximal convoluted tubule

The proximal convoluted tubule reabsorbs about two-thirds of filtered sodium isosmotically.