Hepatoportal Ystem
The hepatoportal system is a unique arrangement of blood vessels leading to and from the liver. The vast majority of the circulatory system is arranged in such a way that blood containing oxygen is delivered by arteries and then capillaries to various organ systems. Oxygen then leaves the blood, feeding the organs. Oxygen-depleted blood is then picked up from these same capillaries, and carried through veins back to the heart, where it is recirculated to the lungs to pick up oxygen again.
In the case of the hepatoportal system, the blood leaving capillaries throughout the intestinal system is carried by the hepatic vein NOT to the heart for re-oxygenation, but to a second set of capillaries within the liver. This blood is rich in all types of nutrients which it has picked up from the intestines. The hepatic vein sends this nutrient-rich blood through a capillary system in the liver, as well as into tiny little spaces within the liver, called liver sinuses. Here, various nutrients which the liver is responsible for processing and storing are removed from the blood. Toxins and waste products are also removed by the liver, and are processed to make them less dangerous.
After passing through the hepatoportal system, the blood is sent into the inferior vena cava, which delivers it to the heart for re-oxygenation. Because blood arriving at the liver via the hepatic vein has already passed through the capillary beds of the intestines, it is mostly depleted of oxygen by the time it gets to the liver. Therefore, oxygenated blood is sent to the liver through the hepatic artery, a branch off of the aorta.
The major difference, then, between the hepatoportal system, and blood circulation through other organs, is the fact that the blood passes through two sets of capillaries prior to its return to the heart: that of the intestines, followed by that of the liver.
Major disease processes involving the hepatoportal system most commonly stem from liver damage and scarring, called cirrhosis. Cirrhosis can be due to a number of underlying diseases, although by far the most common etiology is damage from alcohol abuse. The scarring of cirrhosis blocks the outflow of blood through the hepatoportal system, resulting in high blood pressure within the hepatoportal system. This high blood pressure (called portal hypertension) is conveyed to nearby capillary systems, particularly that of the esophagus. As a result, severe, difficult-to-control, life-threatening bleeding (hemorrhaging) can take place. Other types of processes which can interfere with appropriate flow through the hepatoportal system include damage due to hepatitis (an infection and inflammation of the liver), tumors, congenital defects (defects which are present at birth), or worm infestation.
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