Each tissue of the human body has a specialized function, reflected in its anatomy and metabolic activity. Skeletal muscle allows directed motion; adipose tissue stores and releases energy in the form of fats, which serve as fuel throughout the body; the brain pumps ions across plasma membranes to produce electrical signals.
The liver plays a central processing and distributing role in metabolism and furnishes all other organs and tissues with an appropriate mix of nutrients via the bloodstream. The functional centrality of the liver is indicated by the common reference to all other tissues and organs as “extrahepatic” or “peripheral.”
The liver is a vital organ of vertebrates and some other animals. It is a reddish brown wedge shaped organ with four lobes of unequal size and shape. It is the heaviest internal organ and the largest gland in the human body. It is located in the upper right quadrant of the abdomen, and rests just below the diaphragm to the right of the stomach. The liver is connected to two large blood vessels; the hepatic artery and portal vein. The hepatic artery carries oxygen-rich blood from the aorta, whereas the portal vein carries blood rich in digested nutrients from the entire gastrointestinal tract and also from the spleen and pancreas. These blood vessels subdivide into small capillaries known as liver sinusoids, which then lead to a lobule. Lobules are the functional units of the liver. Each lobule is made up of millions of hepatic cells (hepatocytes) which are the basic metabolic cells. The liver has two main cell types. Kupffer cells are phagocytes, important in immune function and hepatocytes, of primary interest here, which transform dietary nutrients into the fuels and precursors required by other tissues and export them via the blood. The liver’s highly specialized tissue consisting of mostly hepatocytes regulates a wide variety of biochemical reactions.
The liver is the body’s central metabolic clearing house. It functions to maintain the proper levels of nutrients in the blood for use by the brain, muscles, and other tissues. The liver
is uniquely situated to carry out this task because all the nutrients absorbed by the intestines except fatty acids are released into the portal vein, which drains directly into the liver.
