Blood Circulation in the Liver

The liver's place in the circulation

Blood flow

The liver receives blood from two sources. Oxygenated blood is supplied in the hepatic artery, a branch of the celiac trunk from the abdominal aorta. Venous blood from the entire gastrointestinal tract (containing nutrients from the intestines) is brought to the liver by the hepatic portal vein. On reaching the liver the portal vein divides into thousands of which pass in between the lobules and terminate in the sinusoids. The blood leaves the liver via a central vein in each lobule, which drains in the hepatic vein.

Functions
The circulation of blood in the liver is so arranged that very large volumes of blood come into close contact with the cells of the lobules.The cells are thus in a favorable position both to absorb materials from the blood and also secret materials into it. This they do all the time, for the real task of the liver is to maintain in the blood the correct concentrations of many of its constituents. Hepatocytes carry out most of the tasks attributed to the liver, but the phagocytic Kupffer cells that line the sinusoids are responsible for cleansing the blood.

Formation of bile
When the red cells of the blood become worn out they are destroyed by the cells of the reticuloendothelial system. In this process bilirubin is formed, and this is carried by the blood to the liver. Together with several other substances it is secreted by the liver as bile.

The plasma proteins
In the blood plasma there are three soluble proteins which are essential for our well-being. These proteins are albumin, globulin, and fibrinogen, and all of them are largely formed in the liver. Albumin and globulin are important, for they control the amount of water that the blood draws out of the tissues as it flows through the capillaries. Fibrinogen is the precursor of the substance fibrin which is responsible for the formation of the blood clots which form on the top of wounds.