Human liver chemical factory of the body

Human liver is indeed a big chemical factory. It performs hundreds of biochemical functions necessary for maintaining life and health.

The liver is situated in the upper abdominal cavity on the right side immediately under the diaphragm. It weighs about 1.5 kilograms.

It is made up of two lobes-right and left. It receives abundant blood and has dual blood supply one from the aorta and another from the intestine. It receives about 25 percent of the cardiac output.

Oxygenated blood from the aorta is delivered through the hepatic artery which is a branch of the celiac artery. The celiac artery arises directly from the front of the abdominal aorta just below the opening in the diaphragm for the aorta.

The portal vein drains blood from the digestive system into the liver supplying absorbed nutrients. This is deoxygenated blood. The liver is unique in that it receives both oxygenated and deoxygenated blood.

The branches of the portal vein pass in between sheets of liver cells forming sinusoids. A sinusoid is a small blood vessel with more permeable walls. Oxygenated blood from the hepatic artery mixes with the portal blood in the sinusoids.

The sinusoids contain special celles called Kupffer cells. They swallow old and damaged red blood cells break them down and release the products for further metabolism. They also kill bacteria and protect the body against infections.

Liver’s capacity for regeneration is remarkable. Even if more than half of liver is removed the remaining part will grow rapidly and reproduce the lost part.

Functions of liver

The carbohydrates in the food we eat are broken down into simple sugars called monosaccharides (glucose, fructose and galactose are monosaccharides). Glucose is transported into liver. Liver is capable of converting this to glycogen and storing it.

Glucose is the main fuel for all the tissues and is the only fuel for brain. That is why a person loses consciousness if the blood glucose level drops to very low level. When the level of glucose in the blood goes down liver breaks down glycogen into glucose and releases it to blood.

The proteins in the food are broken down into amino acids which are carried to liver. When needed liver can convert these amino acids into glucose or use them to build proteins.

Liver converts ammonia which is produced as a result of metabolism of amino acids into urea. If ammonia accumulates in the blood it adversely affects the brain. This happens in some inborn errors of metabolism where the enzymes needed for converting ammonia into urea are lacing. Some conditions are fatal.

Liver also metabolizes most of the drugs we take. Hence special precaution is required while prescribing drugs to a person with liver disease. Paracetamol one of the most widely used drugs for fever and pain may turn into poison in a person with liver disease.

Liver plays an important role in digestion of fats. Liver secretes a juice called bile which is greenish in color. Bile is stored in a small bag like structure called gall bladder. From there it is carried through a tube called bile duct into the upper portion of small intestine called duodenum. Bile contains bile acids which help in absorption of fats by emulsification. The absorption of fat soluble vitamins also depends on blie.

Liver is responsible for excretion of bilirubin which is produced from heme. Heme is produced as a result of breakdown of red blood cells. Bilirubin is not water soluble. Liver combines this with glucuronic acid (a precess known as conjugation) and excretes it in bile. It is ultimately passed out along with feces.

Liver synthesizes all the plasma proteins except gamma globulin. Human plasma contains 3 main types of proteins-albumin, globulin and fibrinogen. Globulins consist of alpha, beta and gamma globulins. These proteins are responsible for the colloid osmotic pressure of blood which is necessary for holding water inside the blood vessels.

If the level of these proteins comes down water seeps outside the blood vessels and collects in the space outside cells (extracellular space) causing swelling of the body (edema). Some of these proteins also act as carriers for other substances. Gamma globulin plays an important role in immunity. Fibrinogen is necessary for the normal clotting of the blood.

The liver synthesizes most of the cholesterol in the body. Some people have wrong concepts about cholesterol and think it is bad. But cholesterol is essential for life. It is an important constituent of cell membrane. It is also necessary for the synthesis of many hormones like testosterone and estrogen.

The clotting factors are also systhesized by liver. These substances along with fibrinogen are necessary for the normal clotting of the blood whenever there is injury to blood vessles.

Apart from storing glucose in the form of glycogen liver also stores iron, copper and vitamin B 12.

Care for your liver: Your liver has so many tasks to perform. Please do not add to its burden. Be careful in taking medicines. Consult a doctor before taking them. Eat a balanced diet. Consuming excess of proteins and fat will increase the work load of the liver.

Alcohol is a major cause of liver damage. It leads to a condition called fatty liver which later leads to scarring of the liver (cirrhosis). Cirrhosis predisposes to cancer.

Alcoholic hepatitis is an acute inflammation of the liver, accompanied by the destruction of liver cells. Symptoms may include fever, jaundice and right upper abdominal pain.

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