Structure of the Liver
The liver is the largest organ inside the body, located in the upper right quadrant of the abdomen. A healthy adult liver weighs about 3 pounds and spans the width of the torso. The liver has two lobes, divided by a ligament. The right lobe is larger, and each lobe contains thousands of structures called lobules. The lobules are all connected to tiny ducts, which connect to larger ducts, which then connect to the hepatic duct. The hepatic duct has two branches. On branch carries bile from the liver to the gall bladder and the other carries bile to the duodenum of the small intestine. The gall bladder is not part of the liver but it sits in a space on the underside of the liver, next to the stomach. The liver has more than 500 functions and is considered a multisystem organ.
The Liver's Blood Supply
The liver has two major blood vessels: the hepatic artery and the hepatic portal vein. Imagine that the liver is a water treatment plant. All the water has to be cleaned and treated before use, including the plant's own water supply. The treatment water comes into the processing plant through one pipe while the plant gets clean drinking water through another pipe. The two streams never mix. The hepatic artery carries the "drinking water" that feeds the liver and the hepatic portal vein carries the "treatment water" that the liver has to clean. The liver cleans and processes blood constantly and holds about 13 percent of the body's total blood supply at any given time.
How the Liver Functions
The liver processes blood by intercepting the blood leaving the digestive tract. When we eat, the digestive tract breaks the food down into its component parts and absorbs them into the capillary beds surrounding the small intestines. The blood from the capillaries drains into the hepatic portal vein and travels to the liver. The liver then performs its many functions, including filtering toxins and drugs out of the blood. The liver also removes bacteria from the blood stream. It regulates blood clotting and produces proteins for blood plasma production. As a storage vessel, it stores excess glucose as glycogen and also stores vitamin A. As part of the excretory system, it deposits the waste products back into the intestines or sends them to the kidneys for elimination. All of the blood that leaves the intestinal tract has to go through the liver before going out to the rest of the body.
Bypassing the Intestinal Tract
Some elements bypass the intestinal tract and go directly into the blood stream without passing through the liver. Some of these elements, like therapeutic drugs, are beneficial and need to hit the blood stream before the liver can eliminate them. Others, like cigarette smoke, are harmful and can do damage. These elements do eventually make it to the liver--the circulatory system is a closed loop and all blood eventually runs through the intestines and to the hepatic portal vein.
