The liver is a large, glandular organ present in all vertebrate animals. In all vertebrates, including man, the liver has similar structure and functions. The liver is reddish brown in color, has the consistency of foam rubber, and is shaped like a 3 sided pyramid. The liver is located on the right side of the abdominal cavity, covered by the ribs. The gallbladder, a small pouch that stores bile, is partially embedded at the bottom at the back of the liver. Also in contact with the liver are the large and small intestines, and the stomach.
The human liver is divided into the larger right lobe and the smaller left lobe. The right lobe is about six times larger than the left one. The liver has a double blood supply. The portal vein which brings venous blood from the stomach, the intestines, and the spleen and the hepatic artery rings oxygenated arterial blood. These two supplies bring about 40 fluid ounces (1,200 milliliters) of blood to the liver every minute.
Weight of the Human liver: Liver is the largest internal organ, amounting to 2% to 3% of an adult's body weight. The liver of the average man weighs from 3 to 3.5 pounds and in an average woman it weighs from 2.6 to 3 pounds.
Major Function of Liver:
- Storage of food substances and changing fat and protein into glucose.
- It regulates the amount of certain necessary substances in the bloodstream.
- It also helps excrete certain harmful substances from the bloodstream.
- Manufacture of bile, a substance necessary for the digestion of fats.
- The liver is also responsible for replacing its own cells. About half the liver cells die and are replaced every six months.
Storage of Fats, Carbohydrates, Protein, Vitamin and Minerals:
- Fats, carbohydrates, proteins, vitamin and minerals are essential for energy, growth and tissue repair, these substations, with the exception of fats and the fat-soluble vitamin A, D, E, and K, are absorbed from the small intestine into the portal vein, reaching the liver before going to other parts of the body. When they are abundant, as after a meal, the liver cells store them, releasing them back into the blood when the supply is diminished. Sufficient quantities of vitamin A can be stored in the liver for a year or two. Vitamin D and B12 can be stored in sufficient quantities for a few months, while other vitamins can be stored for shorter periods. The minerals such as iron, zinc, copper, magnesium, and manganese are also stored in the liver. It is possible that other minerals are also stored in the liver.
- Glucose or blood sugar, the result of carbohydrate digestion, is stored in the liver cells as glycogen. When the level of glucose in the blood is low, glycogen is converted back into glucose and released into the blood. The liver can convert both amino acids and fat into glucose or other substances used for energy.
Regulates Necessary Substances in the Blood:
- The liver plays an important role in regulating the glucose concentration in the blood, the liver stores glucose when it is plentiful and releases it as it is needed. The stores of glycogen in the liver are not very intensive; as they are depleted, new glucose is manufactured from amino acids and fatrought to the liver from faty deposits in the body.
- The thyroid, adrenal, and sex glands release powerful hormones into the blood. The action of these hormones would persist a long time if the liver will not remove them from the blood and inactivate them.
- Normal blood clotting depends on the presence of proper amounts of different coagulating proteins in the blood. Most of these proteins, which include fibrinogen and prothrombin, are manufactured by the liver cells and released in proper amounts into the blood.
Removes Harmful Substances: Every day the body produces waste products from the natural wearing out of tissues. If these substances are allowed to accumulate, it will be harmful to the healthy tissues in the body. The liver has highly efficient ways of removing each of these substances.
- Nucleic acids are converted into uric acid, and nitrogen is used to make urea. Both of these products are harmless to the body and are released into the bloodstream to be excreted in the urine.
- Hemoglobin, which is red in color, is converted into bilirubin, a bright yellow material used in making bile. Bilirubin also is responsible for the brown color of the feces. When some disease or disorder prevails bilirubin from being excreted into the intestine, it accumulates in the blood, causing the skin and eyes to become yellow-a condition known as jaundice.
- The liver also removes about 80% of the medicine the person takes; it is either removed directly by the liver or is changed into a form that can be excreted by the kidneys. Alcohol is also modified by the liver before it is removed from the body.
Helps in the Formation of Bile: Bile functions as an important digestive juice. It is the liver's vehicle for removing unwanted materials from the body. Produced continuously, the liver manufactures from 13 to 32 ounces of bile daily.
Bile contains 97% water, 2.5% bile salts, and 0.5% other solids, including bilirubin, cholesterol, and fatty acids. From the liver, bile travels to the gallbladder, where it is stored and concentrated. After it is concentrated, the bile may contain up to 50% bile salts. Some of the bile salts are excreted in the feces, but about 90% are absorbed from the small intestine, travel back to the liver, and are used to produce more bile.