what is the functional nature of the portal system and how does it differ from normal venous return flow?
The hepatic portal system carries out hepatic portal circulation. This refers to the blood flow through the liver. Veins from the spleen, stomach, pancreas, gallbladder, and intestines do not dump their blood directly into the inferior vena cava as do the veins from other abdominal organs. Instead, blood from these organs is funnelled to the liver before it re-enters the regular venous pathway to the heart.
The hepatic portal system is used by the body as a defense mechanism to de-toxify blood before it returns to the general circulation. The liver tries to cleanse the blood and remove potential harmful substances before the blood is returned to the heart muscle. It is a protective device the body uses to help maintain homeostasis.
Luckily, the hepatic portal system is active when a large amount of alcohol is ingested. The blood alcohol content is lowered as the blood from the stomach passes through the liver.