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MCAT Question A Day - 6/7/13 - Answer!

Portions of the afferent arteriole, efferent arteriole, distal convoluted tubule, and renal corpuscle make up the juxtaglomerular apparatus, which produces renin. The juxtaglomerular apparatus is involved with regulation of

A.  glucose.
B.  pH.
C.  wastes.
D.  blood pressure.

The correct answer is (D). Renin, secreted by cells of the juxtaglomerular apparatus, activates a sequence that eventually converts the blood protein angiotensinogen to angiotensin I and II. This stimulates the release of aldosterone by the adrenal cortex, so that extra Na1 ions are reabsorbed at the distal convoluted tubules. Water follows by osmosis, increasing blood volume and subsequently increasing stroke volume (Starling’s law). The increased stroke volume increases cardiac output and blood pressure (renin-angiotensin system).