The caudal end of the pronephric duct opens in:

Correct Answer: C

Rationale: The pronephric duct's caudal end opens into the cloaca not primitive/definitive urogenital sinus (later), vesicourethral canal (bladder), or coelom. The cloaca is the early common chamber, critical for pronephric regression and mesonephric transition, contrasting with later subdivisions.

Correct Answer: B

Rationale: Urine from umbilicus is urachal fistula (patent allantois) not vitelline (gut), ectopia vesicae (exstrophy), or ectopic ureter/urethra. This identifies congenital leak, key for diagnosis, contrasting with other fistulae.

Correct Answer: D

Rationale: Low blood supply triggers renin release JGA senses pressure drop (e.g., activates RAAS). Aldosterone is adrenal not kidney-produced. ANH from heart opposes retention. Water isn't released reabsorbed. Renin's response distinguishes it, key to restoring perfusion, unlike hormones or fluid missteps.

Correct Answer: B

Rationale: The urethra carries urine from bladder to outside final exit (e.g., males ~20 cm, females ~4 cm). Ureters deliver to bladder not outside. Renal pelvis collects not exits. Glomerulus filters not transports. Urethra's external role distinguishes it, key to voiding, unlike internal structures.

Correct Answer: A

Rationale: Formed elements (RBCs, WBCs, platelets) and plasma proteins (e.g., albumin) can't filter too large for glomerular barrier. Glucose filters reabsorbed later. Salts filter freely small ions. Formed elements/glucose mispairs glucose filters. Proteins/salts mix filterable/non-filterable wrong. Size exclusion distinguishes it, key to filtration selectivity, unlike mixed options.