Question

A portal system is that in which
A. A vein begins from an organ and ends in the heart.
B. An artery breaks up in an organ and restarts by the union of its capillaries.
C. The blood from the gut is brought into the kidneys before it is poured into the heart.
D. A vein breaks up in an organ into capillaries and restart by their union as a new vein in the same organ.

Answer 1

Hint:- The flow of blood through the portal vein to certain specific organs other than the heart is called portal circulation. A vein which collects blood from one organ by one set of capillaries and distributes blood to some other organ by another set of capillaries instead of sending it to the heart is called a portal vein.

Complete step-by-step solution:-A portal vein together with small veins by which it receives the blood and the capillaries by which it supplies blood to specific organs forms a portal system.
The vertebrates have two or three portal systems-hepatic, renal and hypophysial.
Hepatic portal system- It is present in all vertebrates including man. It carries the blood from the alimentary canal, pancreas and spleen to the liver. It brings digestion products such as glucose and amino acids from the alimentary canal to the liver.
Renal portal system- It is present in the fishes and amphibians and is reduced in reptiles and birds. It is absent in mammals. It supplies the blood from the posterior region of the body to the kidneys by the way of renal portal veins. It enables the kidney to remove waste products from the blood before sending it to the heart via renal veins and postcaval.
Hypophyseal portal system- It is a minor portal system in the pituitary body. It collects blood from the hypothalamus and distributes it to the anterior lobe of the pituitary.

Correct option: D. A vein breaks up in an organ into capillaries and restart by their union as new vein in the same organ.

Note:- The liver retains the excess sugar and converts it to glycogen, which is stored for the future use. The process is called glycogenesis. If the sugar level of the blood falls, glycogen is converted back to glucose which is carried to the bloodstream by hepatic veins.