Portal system is a system of blood vessels that begins and ends in capillaries. Hepatic portal carries nutrients from digestion to the liver to store and metabolize, after a meal.
Portal system can be defined as a part of the systemic circulation, in which blood draining from the capillary bed of one structure flows through larger vessels to supply the capillary bed of another structure, before returning to the heart.
Simply, a system of blood vessels that begins and ends in capillaries is called portal system. Following is a diagram showing the blood circulation of the body. We can see hepatic portal vein here (a part of portal system), this vein begins in a capillary (of intestines) and ends in another capillary (of liver).
The hepatic portal circulation travels from the intestine of the digestive tract to the liver.
The function of this portal system is to carry nutrients from the digestive tract to the liver after a meal to store and metabolize.
Diagram of hepatic portal system :