Which area actually secretes renin into the blood?

Correct Answer: C

Rationale: Juxtaglomerular (JG) cells secrete renin to regulate blood pressure, not the macula densa (senses NaCl), JG apparatus (collective structure), or cortical nephron (unit). This pinpoints renin's source, key for RAAS, contrasting with broader terms.

Correct Answer: A

Rationale: Creatinine is filtered and excreted without a threshold, unlike ascorbic acid, sodium, and citric acid (reabsorbed to limits). This identifies non-threshold excretion, key for GFR assessment, contrasting with regulated solutes.

Correct Answer: C

Rationale: Renal pyramids reside in the medulla, not columns, cortex, or pelvis (collecting). This locates pyramids, key for concentrating urine, contrasting with cortical structures.

Correct Answer: D

Rationale: Ketones appear in urine during fat breakdown (ketosis), not urea (protein), uric acid (purine), or glycine (amino acid). This highlights ketonuria, key for metabolic states, contrasting with nitrogenous waste.

Correct Answer: B

Rationale: Kidneys receive ~25% of cardiac output (1.2 L/min), not 10%, 50%, or 65%. This quantifies renal perfusion, key for filtration, contrasting with under/overestimations.