What controls the reabsorption of salt and water in the distal convoluted tubule?

Correct Answer: A

Rationale: Hormones (aldosterone, ADH) control distal tubule salt/water reabsorption e.g., Na via ENaC, water via aquaporins. NaCl is reabsorbed not controller. Glucose is PCT not distal. Urea is medullary not regulatory. Hormonal regulation distinguishes it, key to fine-tuning, unlike substrates.

Correct Answer: B

Rationale: Urea is produced in the liver protein breakdown via urea cycle (e.g., ammonia detox). Muscles produce creatinine not urea. Kidneys excrete not synthesize. Spleen is immune not metabolic. Liver's production distinguishes it, key to nitrogen handling, unlike muscle, kidney, or spleen roles.

Correct Answer: B

Rationale: Glucose reabsorption occurs fully in proximal tubules e.g., SGLT transporters reclaim all (~180 g/day). Insulin aids uptake not tubular reabsorption. Metabolism doesn't vary it threshold fixed. Liver regulates blood glucose not tubules. PCT's complete reabsorption distinguishes it, critical for glucose retention, unlike hormonal or metabolic control.

Correct Answer: B

Rationale: Ammonia (NH₃) is a nitrogenous waste e.g., distal tubule buffers H . Amino acids are reabsorbed not excreted. HNO₃⁻ (nitrate) isn't physiological false. Thionitrate isn't a compound nonsense. NH₃'s waste role distinguishes it, key to nitrogen excretion, unlike conserved or fictitious options.

Correct Answer: B

Rationale: Inulin clearance estimates GFR e.g., fully filtered, not reabsorbed (~125 mL/min). Formula is UV/P U,F,P misdefined. Creatinine estimates GFR not plasma flow (PAH does). Parathormone increases phosphate clearance not decreases. Inulin's GFR role distinguishes it, critical for renal function, unlike formula or flow errors.