Question

A portal system is a system in which
A. A vein starts from an organ and ends up 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 kidney before it is poured into posterior vena cava
D. A vein breaks up in an organ into capillaries and restarts by their union as a new vein in the same organ

Answer 1

Hint: It is a system that transports venous blood to the hepatic system for processing. It can be also defined as a part of the systemic circulation. The most important vessel in the portal system is the portal vein which is formed by the union of superior mesenteric vein and splenic vein.

Complete answer: A system in which the vessels are involved in the drainage system of the capillary beds of the gastrointestinal (GI) tract and the spleen in the capillary bed of the liver is known as the portal system. In the liver, the blood flow is unique and receives both the oxygenated and deoxygenated blood. The perfusion pressure and the partial pressure of oxygen (pO2) are lower in the portal blood than the other organs of the body. Blood flows through the branches of the portal vein through the cavities between the hepatocellular sinusoids. Blood passes through the hepatic artery branches and then mixes into the sinusoids to supply oxygen to the liver cells or hepatocytes. This mixture then percolates into the central vein through sinusoids and drains into the hepatic veins. Finally, the hepatic veins drain into the inferior vena cava. It involves breaking up of a vein in an organ into capillaries and restarting by their union as a new vein in the same organ.
Hence, the correct answer is option D.

Note: Examples of the portal system include the hepatic portal system, the hypophyseal portal system, and (in non-mammals) the renal portal system. In a portal venous system, the capillary bed and blood vessels are known as connecting vessels.