What molecule adds to the increased solute concentration in the lowest part of the renal medulla?

Correct Answer: B

Rationale: Urea adds to medullary solute concentration recycles in collecting duct (e.g., ~1200 mOsm with NaCl). Sugar is reabsorbed not medullary. Proteins are filtered out not concentrated. Bicarbonate is pH-related not osmotic. Urea's contribution distinguishes it, key to concentration gradient, unlike filtered or pH solutes.

Correct Answer: D

Rationale: All dialysis (blood filtering), CAPD (peritoneal), transplant treat renal failure (e.g., replace kidney function). Dialysis alone omits options partial. CAPD alone excludes others limited. Transplant alone ignores temporaries insufficient. Comprehensive treatments distinguish it, key to renal management, unlike singular approaches.

Correct Answer: D

Rationale: Vasa recta acts as a countercurrent exchanger maintains medullary gradient (e.g., loops with Loop of Henle). Afferent arterioles supply not exchange. Urethra drains no countercurrent. Trigone is bladder not exchanger. Vasa recta's exchange distinguishes it, critical for concentration, unlike supply or drainage structures.

Correct Answer: B

Rationale: Each H secreted pairs with Na reabsorption e.g., Na /H exchanger in PCT maintains electroneutrality. pH doubling is logarithmic false. Aldosterone isn't directly tied separate control. pH decrease is blood not tubule effect. Na reabsorption distinguishes it, key to ion balance, unlike pH or hormonal errors.

Correct Answer: A

Rationale: Increased cardiac output boosts GFR e.g., more blood pressure (~55 mmHg) at glomerulus. Lower BP decreases GFR opposite. Less fluid reduces volume not GFR directly. Temperature affects skin not kidneys. Cardiac output's effect distinguishes it, key to filtration rate, unlike pressure drop or external factors.