The countercurrent multiplier mechanism occurs at the

Correct Answer: B

Rationale: Countercurrent multiplier in the loop of Henle concentrates urine, not PCT, DCT, or collecting ducts (ADH effect). This locates concentration mechanism, key for osmolarity, contrasting with other segments.

Correct Answer: D

Rationale: Kidney is vital (filters blood), unlike hand, ear, nose (non-essential). This distinguishes organ necessity, critical for survival, contrasting with appendages.

Correct Answer: A

Rationale: Filtration occurs in the renal corpuscle (glomerulus), not tubule, duct, or cortex (region). This pinpoints filtration site, key for GFR, contrasting with reabsorption areas.

Correct Answer: A

Rationale: Juxtamedullary nephron corpuscles lie near cortex-medulla junction, not macula densa or pyramid junctions. This positions deep nephrons, key for urine concentration, contrasting with mislocations.

Correct Answer: C

Rationale: Juxtaglomerular apparatus (JGA) regulates BP via renin, not tubule, nephron alone, or all. This pinpoints RAAS control, key for hypertension, contrasting with broader structures.