Cells of the macula densa in the kidney function to:
a. Constrict the diameter of the afferent arteriole supplying the glomerulus
b. Reabsorb amino acids from the urine
c. React to urinary sodium and chloride and stimulate juxtaglomerular cells to se-crete renin
d. Secrete angiotensin to elevate blood pressure during conditions of dehydration
e. Secrete sodium into the urine
ANS: C
Specialized cells of the distal tubule, constituting the macula densa, monitor urinary levels of so-dium and chloride. In response to changes in these ions, macula densa cells secrete adenosine triphosphate into their environment, which binds to so-called purinergic receptors on juxtaglo-merular cells and regulates their function.
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