Question

The renal portal system of vertebrates is significant for
A. Elimination of excess fats by kidneys
B. Removing nitrogenous wastes in kidneys
C. Supplying food to the kidneys
D. Draining blood from the kidney

Answer 1

Hint: A renal portal system is a portal venous system. It supplies blood to renal tubules when glomerular filtration is down regulated or not present. Renal portal system is found in all vertebrates except mammals, hagfish and lampreys.

Complete answer:
In this question the significance of the renal portal system is asked. Portal system is a system of blood vessels that begins and ends in capillaries. The function of a portal system is transportation of product from one region to another region in relatively high concentrations and this system does not include heart. If the heart were involved in the blood circulation between those two regions, those products would be spread around the rest of the body and that product will not reach that particular place in such high concentration.
A renal portal system is a portal venous system. It supplies blood to renal tubules when glomerular filtration is down regulated or not present.
The main channel of renal portal is portal vein which brings venous blood circulation from tail and groin of kidney and drains nitrogenous waste from it and partially purifies it, then this blood goes to the heart .

> Option A is Elimination of excess fats by kidneys. As we know this portal system extracts nitrogenous waste not fat because fat does not pass through urine. So, this option is wrong.
> Option B is removing nitrogenous wastes in kidneys. As we already mentioned, the renal portal system extracts nitrogenous waste from the blood received from the groin and tail of the kidney and partially purifies it and sends it to the heart. So, this option is true.
> Option C is supplying food to the kidney. Food is absorbed in the stomach which mixes with blood and reaches the kidney. So, it doesn't supply food to the kidney and this option is wrong.
> Option D is draining blood from the kidney. This statement is wrong because the renal portal system drains nitrogenous waste from blood, not blood from the kidney.

The correct option is B. removing nitrogenous wastes in kidneys.

Note: There are 3 types of portal systems. Hepatic portal system, renal portal system and hypophyseal portal system. Only hepatic and hypophyseal portal systems found in humans.