NEET 2025 Zoology Question 169 Solution

A portal venous system is a vascular arrangement in which blood collected from one capillary bed is conveyed via a portal vein into a second capillary network in an intermediate organ before returning to the heart.

• • In amphibians such as frogs, two well-developed portal venous circuits exist: the hepatic portal system and the renal portal system.
• • Humans and mammals retain the hepatic portal system and hypophysial portal system, but the renal portal system is absent (reduced/vestigial).

Tracing the blood vessels in the posterior body:

• • Deoxygenated venous blood from the hindlimbs and pelvic region is collected by the femoral and sciatic veins.
• • These bifurcate to form the renal portal veins, which enter the kidneys and break up into a secondary capillary plexus.
• • This allows the renal tubular epithelium to clear nitrogenous waste and filter blood directly from the lower extremities.
• • The blood is subsequently collected by renal veins into the postcaval vein (posterior vena cava).
• • Thus, the renal portal system specifically links the kidney and lower part of the body.

Evaluating Option (1):

• • The venous connection that links the intestine (alimentary canal) to the liver is the hepatic portal system.
• • Conflating the hepatic and renal portal systems is an examiner's deliberate trap.

The renal portal system acts to link the kidney and lower parts of the body, matching Option (4).