The Liver
The liver is the largest organ in the body. In the healthy adult, it weighs about 3 pounds. The liver is wedge-shaped, with the top part wider than the bottom. It is located immediately below the diaphragm and occupies the entire upper right quadrant of the abdomen.
Vital Functions
The liver performs over 500 vital functions. Damage to the liver can impair these and many other processes. Among them are the following:
Processing Healthful Nutrients. It processes all of the nutrients the body requires, including proteins, glucose, vitamins, and fats.
Bile Production. The liver produces bile, a green-colored fluid that is formed in the liver and helps the body absorb fats and fat-soluble vitamin. Bile is formed from bilirubin, a yellow-green pigment produced from the breakdown of hemoglobin, the oxygen-carrying component in red blood cells. Bile contains bile salts, fatty acids, cholesterol, and other substances. Bile travels from the liver to the gallbladder, where it is stored until after a meal. It is then secreted into the intestines where it helps digest fat.
Eliminating Toxins. One of the liver's major functions is to render harmless potentially toxic substances, including alcohol, ammonia, nicotine, drugs, and harmful by-products of digestion.
Recycling Blood. The liver and spleen removes old red blood cells from the blood. The iron contained in them is recycled in the bone marrow to make new red blood cells.
The Liver's Architecture
The vital processes the liver performs rely on well-organized liver architecture.
The Building Blocks. The basic building blocks of the liver are the following structures:
- Bile ducts
- Blood vessels
- Working liver tissue (called the parenchyma)
- Supportive (connective) tissue
The Architecture. The liver is a built on a framework of lobes:
- The lobes. The liver is divided into two major lobes, a right and a smaller left, that are separated by tough, fibrous connective tissue.
- The lobules. The liver's two major lobes contain about 100,000 smaller lobes, called lobules. Each lobule contains microscopic columns of liver cells and blood vessels. Bracing the corners of each lobule column are an artery and a vein that carry blood and a bile duct that drains bile.
- The arteries and veins. The arteries bring oxygen-rich blood to nourish the liver cells. The veins supply the liver cells with blood containing the nutrients and toxins that the liver cells process. A central vein runs through each column and collects the processed blood from both sources. These veins join to form the hepatic vein.
- The bile ducts. The bile ducts in the column corners collect bile draining from tiny canals around the liver cells. These ducts eventually join to form the large common bile duct that leads from the liver to the gallbladder.
The Liver's Blood Supply
The liver is rich in blood. It holds about a pint, or 13% of the body's supply. It is furnished with blood from two large vessels, the hepatic artery and the portal vein, and is drained of blood by the hepatic vein. (The word "hepatic" derives from the Latin word for liver.)
The hepatic artery. This artery supplies blood from the heart directly to the liver. This blood nourishes the liver.
The portal vein. The portal vein carries to the liver blood that has been circulating through the stomach, spleen, and intestine. The liver processes this blood, extracting nutrients and toxins.
The hepatic vein. This vein carries blood from the liver and connects to the inferior vena cava, a large vein that conducts blood back to the heart.
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