Aldosterone stimulates the kidneys to:

Correct Answer: C

Rationale: Aldosterone stimulates Na and water reabsorption e.g., collecting duct ENaC channels, raising BP. H excretion is intercalated cells not aldosterone's focus. Water excretion opposes diuresis not retention. Na /Ca² misaligns Ca² separate. Na /water retention distinguishes it, critical for volume control, unlike excretion or ion errors.

Correct Answer: B

Rationale: Water returns from PCT by osmosis follows Na gradient (e.g., isosmotic reabsorption). Active transport moves Na not water directly. Facilitated diffusion is glucose not water. Carrier molecules aid solutes not primary water. Osmosis's passive flow distinguishes it, critical for PCT water recovery, unlike active or facilitated mechanisms.

Correct Answer: A

Rationale: Water reabsorption from Loop of Henle (descending) depends on NaCl movement out e.g., thick ascending pumps create gradient (~1200 mOsm). Acid is distal not Loop. Glucose is PCT not here. Uric acid is minor not gradient driver. NaCl's role distinguishes it, critical for countercurrent, unlike other solutes.

Correct Answer: A

Rationale: The JGA monitors blood volume senses pressure via JG cells (e.g., renin adjusts). Medulla oblongata controls breathing not volume. Midbrain is motor unrelated. Hypothalamus senses osmolarity not volume directly. JGA's volume role distinguishes it, key to RAAS, unlike neural or osmotic structures.

Correct Answer: A

Rationale: Pyelonephritis is kidney infection e.g., bacterial ascent (pelvis/nephrons). Cystitis is bladder not kidney. Urethritis is urethra lower. Hypertension is BP not infection. Pyelonephritis's site distinguishes it, key to renal pathology, unlike lower tract or unrelated conditions.