The function of the countercurrent multiplier is to

Correct Answer: A

Rationale: Countercurrent multiplier increases NaCl in the medullary interstitium, not decreases, or affects potassium. This defines concentration gradient, key for water reabsorption, contrasting with potassium roles.

Correct Answer: D

Rationale: Kidneys synthesize calcitriol, secrete erythropoietin, and perform gluconeogenesis all apply. This encompasses metabolic roles, vital for homeostasis, contrasting with single contributions.

Correct Answer: C

Rationale: Renal corpuscle comprises Bowman's capsule and glomerular capillaries, not collecting duct, arteries, or loop. This defines corpuscle, key for filtration, contrasting with tubular parts.

Correct Answer: B

Rationale: Efferent vessel is an arteriole, not venule, capillaries, or artery. This specifies glomerular vasculature, key for pressure, contrasting with venous or capillary terms.

Correct Answer: A

Rationale: Hydrostatic pressure drives glomerular filtration, not colloidal (opposes), osmotic (retains), or none. This identifies filtration force, key for GFR, contrasting with opposing pressures.