Posted on 01 Oct 2012 20:08
Among all the organs, only the brain is capable of more functions than the liver. In fact, the sheer multitude of its jobs is staggering. It is the largest glandular organ of the body and is located just below the diaphragm in the upper right part of the abdominal cavity. The human liver is reddish-brown in color weighs an average of about 3 pounds and resembles calf liver in color and texture. When our liver is diseased or so severely damaged that it cannot function properly, we cannot live long.
The liver is enclosed in a fibrous capsule and divided by connective tissue into two halves called lobes. The right lobe is large than the left one. The right lobe is itself subdivided in into three lobes: the right lobe proper, the quadrate lobe, and the caudate lobe. The connective tissue that separates the right and left lobes is called the falciform ligament and this tissue also attaches the liver to the abdominal wall, in the front.
In addition to its attachment to the abdominal wall, the liver is also attached to the diaphragm by the coronary ligament, which is a tissue similar to that of the falciform ligament.
All the lobes are separated into numerous small hepatic lobules and these lobules are the functional units of the organ. Each lobule has many hepatic cells that radiate outward from a central vein. Groups of these cells are separated by hepatic sinusoids. The sinusoids allow nutrient-rich blood to be brought in from the digestive tract, via the portal vein, to nourish the hepatic cells. The sinusoids have Kupffer cells attached to their inner lining and these cells remove most of the bacteria from the blood by phagocytosis. From the sinusoids, the blood passes into the central veins of the lobules and then out of the liver.
The lobules have many thin bile canals that receive secretions from the hepatic cells and these canals unite with the canals of neighboring lobules to form large ducts, which converge to form hepatic ducts. These, in turn, merge to form the common hepatic duct.
Many of the liver's jobs have to do with the metabolism and regulation of nutrients. The liver has important functions for carbohydrate, lipid, and protein metabolism. Some of the highlights are given below.
Liver and Nearby Organs
Liver Function for Carbohydrates
The carbohydrate actions of the liver basically mean that the liver helps to maintain normal blood sugar levels. It can respond to various hormones and decrease or increase blood glucose, because it:
- Converts fructose and galactose to glucose
- Forms and stores glycogen
- Breaks down glycogen to glucose to release it as needed
- Breaks down glucose for energy if it is needed
- Forms glucose from amino acids and glycerol if needed
Liver Function for Proteins
- Makes many different nonessential amino acids when they are in short supply in the body
- Removes excess amino acids from the blood and deanimates them or converts them to other aminos that may be needed.
- Inactivates hormone molecules to be excreted by the liver
- Takes ammonia from the blood and converts it to urea, a less toxic compound, so it can be sent to the kidneys for excretion
- Makes other proteins for the body such as DNA and RNA bases
- Makes plasma proteins like clotting factors (fibrinogen, prothrombin, and clotting factors V, VII, IX, X) plus albumin, globulin, etc.
Liver Functions for Lipids
- Makes or breaks down lipoproteins, triglycerides, phospholipids, and cholesterol
- Breaks down fatty acids for energy at a very high rate
- Gets lipids ready for transport to other organs by forming phospholipids around them
- Makes bile for the gallbladder to use to digest fat. The liver makes and excretes bile continuously, which is sent to the gallbladder which stores and concentrates it between meals for use when needed.
- Makes ketone bodies when needed
Other Important Functions of the Liver
- Removes from the blood and detoxifies alcohol, drugs, wastes from nutrient metabolism, and poisons
- Absorbs bilirubin caused by the destruction of old red blood cells
- Stores fat-soluble vitamins like vitamins A, D, E, B12, and K
- Also stores iron when the concentration in the blood is excessive, to be released when the iron level is low enough
- Forms vitamin A
- Secretes heparin, an anticoagulant
- Stores minerals