An athlete has become dehydrated during a long race in hot weather. Which of the following physiologic processes will occur in an attempt to protect the athlete's extracellular fluid volume?

Question

A) Dilation of the afferent and efferent arterioles
B) Release of ADH from the posterior pituitary
C) Increased water reabsorption in the ascending limb of the loop of Henle
D) Increased water reabsorption in the distal convoluted tubule

Answer 1

Ans: B
Feedback:
ADH assists in the maintenance of the extracellular fluid volume by controlling the permeability of the medullary collecting tubules. Osmoreceptors in the hypothalamus sense an increase in osmolality of extracellular fluids and stimulate the release of ADH from the posterior pituitary gland. In exerting its effect, ADH, also known as vasopressin, binds to receptors on the basolateral side of the tubular cells. Binding of ADH to the vasopressin receptors causes water channels, known as aquaporin-2 channels, to move into the luminal side of the tubular cell membrane, producing a marked increase in water permeability. The ascending limb of the loop of Henle and the distal convoluted tubule are largely impermeable to water, and arteriole dilation does not directly increase the amount of water reabsorbed from glomerular filtrate.