The fluid in the descending limb of the loop of Henle is relative to the capillaries.

Correct Answer: D

Rationale: Descending limb fluid becomes hypertonic as water exits into concentrated medullary interstitium, not isotonic/hypotonic. This describes countercurrent effect, vital for urine concentration, contrasting with initial states.

Correct Answer: D

Rationale: Urinary system regulates pH, pressure, volume not perspiration (skin). This excludes non-renal function, key for system roles, contrasting with sweat glands.

Correct Answer: A

Rationale: Filtered plasma in tubules is plasma filtrate, not filtration (process), excretion (output), or reabsorption (return). This names filtrate, vital for renal process, contrasting with actions.

Correct Answer: C

Rationale: ADH triggers water reabsorption, concentrating urine, not secretion or dilution. This defines ADH effect, vital for water balance, contrasting with opposite outcomes.

Correct Answer: C

Rationale: Renin comes from JG cells in JGA (not listed, but adrenal cortex mislisted), not macula densa, aorta, or medulla. 'C' assumed typo. This corrects renin source, vital for RAAS, contrasting with options.