A 22-year-old previously healthy male complains of dysuria. Genital examination is normal. Urinalysis shows 5 to 10 white blood cells per high power field. Which of the following antibiotic regimens is MOST appropriate?

Correct Answer: C

Rationale: Azithromycin 1 g + ofloxacin 400 mg once treats urethritis (e.g., Chlamydia/gonorrhea) in young males with dysuria 5-10 WBC fits STD, most appropriate. Ciprofloxacin 2 weeks is pyelonephritis overkill. TMP-SMX 3 days is female UTI short. Cephalexin 7 days lacks STD coverage mismatch. STD regimen distinguishes it, key to age/context, unlike UTI-focused options.

Correct Answer: D

Rationale: Medullipin I (hypotensive) isn't linked to peritubular capillary endothelium, unlike PCT (brush border), bladder (transitional), DCT (macula densa), and afferent arterioles (renin). This corrects renal associations, key for physiology, contrasting with true pairings.

Correct Answer: A

Rationale: DCT reabsorbs Na+, Cl-, and water (ADH-dependent), but secretes K+ not reabsorbed. This distinguishes DCT ion handling, key for electrolyte balance, contrasting with reabsorption norms.

Correct Answer: C

Rationale: Mesangial cells are between capillaries, within lamina, phagocytic, and maintain it not part of JGA (JG cells, macula densa). This corrects mesangial role, key for glomerular function, contrasting with JGA involvement.

Correct Answer: C

Rationale: Ascending limb of Henle dilutes filtrate (NaCl reabsorption, water impermeable) not PCT, descending (concentrates), or collecting duct (ADH-dependent). This specifies diluting site, key for urine formation, contrasting with concentrating segments.