What is the hepatic portal system?
**Portal system is a system of blood vessels which arises from capillary bed of one organ and ends at the capillary bed of another organ. Hepatic portal flows from wall of GI tract to liver.
Large arteries emerge from heart, divide repeatedly in smaller branches to distribute the blood ultimately in capillary system. From the capillary bed, venules arise and continue to join together to form large veins draining blood back into heart.
Biology is science of exception: there are veins which arise from one organ (from capillaries) and enter in another organ (and once again end in capillary bed), without going back to heart. These unique blood vessels form portal system. Thus portal system always carries deoxygenated blood, and hence these are called portal veins.
At least three portal systems are reported from vertebrates: hepatic portal, renal portal and hypothalamo-hypophyseal portal systems. Hepatic portal vein carries absorbed nutrients from wall of intestine to deliver in liver. Liver also receives normal arterial supply through hepatic artery. All blood from liver drains via hepatic vein .