Which structure monitors the osmolarity of the blood?

Correct Answer: D

Rationale: The hypothalamus monitors blood osmolarity osmoreceptors trigger ADH (e.g., water balance). JGA senses pressure not osmolarity directly. Medulla oblongata is respiratory not osmotic. Midbrain is motor unrelated. Hypothalamus's osmotic role distinguishes it, critical for hydration, unlike pressure or neural sites.

Correct Answer: C

Rationale: Juxtaglomerular (JG) cells secrete renin e.g., JGA responds to low BP. Macula densa senses NaCl signals JG, doesn't secrete. Glomerular epithelial (podocytes) filter not secrete. Basement membrane is structural not cellular. JG's renin role distinguishes it, key to RAAS, unlike sensing or structural parts.

Correct Answer: A

Rationale: Renal diabetes (glycosuria) spills glucose into urine at low blood levels e.g., defective PCT transporters (threshold <180 mg/dL). Hemorrhage unrelated blood loss issue. ADH affects water not glucose. Youth prevalence is diabetes mellitus not renal. Low-threshold spill distinguishes it, critical for renal glycosuria, unlike unrelated causes.

Correct Answer: B

Rationale: Cl⁻ reabsorption follows Na electrostatic attraction (e.g., PCT Na /Cl⁻ cotransport). Aldosterone boosts Na indirectly Cl⁻, not permeability. Ca² retention is separate unrelated. Osmotic gradient drives water not Cl⁻ directly. Na attraction distinguishes it, critical for electroneutrality, unlike hormonal or osmotic drivers.

Correct Answer: C

Rationale: Macula densa is in the distal tubule senses NaCl, signals JGA (e.g., renin regulation). Proximal tubule reabsorbs not senses. Afferent arteriole supplies not tubular. Efferent is post-glomerular unrelated. Distal location distinguishes it, key to feedback, unlike proximal or vascular parts.