Main Functions of Liver

The liver is a vital organ, without which it is not possible to survive. In addition to being the largest solid organ and largest gland in the body, the liver is also responsible for hundreds of functions in our body.

Liver structure
Liver structure

What is the liver?

The liver is a large massive organ, approximately 20 cm in diameter, 17 cm in height and a mean weight of 1.4 kg, located in the upper right quadrant of the abdominal cavity just below the diaphragm.

The blood supply of the liver is made by two routes, the hepatic artery (20-40%) and the portal vein (60-80%). The liver is an organ so vascularized that it gets to receive 1.5 liter of blood per minute.

One of the most interesting features of the liver is its incredible ability to regenerate, being able to return to normal size even after having more than 50% of its volume surgically removed.

The liver is a complex organic factory, with hundreds of functions, among the most important, removing toxins from the blood and processing food from the intestines.

Functions of the liver

Liver cells, called hepatocytes, contain thousands of enzymes that are responsible for the metabolism of substances in the blood, whether they are beneficial or harmful to our body. The liver is also capable of storing nutrients and other useful substances, as well as producing proteins and vitamins essential for our health.

Science already knows more than 500 functions of the liver, let us briefly speak of the principles:

1. Metabolization of digested nutrients

The process of digestion consists in the breakdown of nutrients into smaller and smaller molecules, until they can be absorbed by the mucosa of the intestines and then released into the bloodstream.

All bloodstream from the digestive tract drains into the portal vein, so that no nutrient or ingested substance can reach the rest of the body without first passing through the liver.

This process is of paramount importance, for it is the liver who controls how much, how, in what form each substance from food will pass into the rest of the body. Examples:

A. Fats

The digestion process breaks down the fats into small molecules, called fatty acids and glycerol. These are the molecules absorbed by the intestines and thrown towards the portal vein. In the liver this fat is transformed into various substances, such as phospholipids or cholesterol, which are essential in the production of our cells.

The liver also uses fats to synthesize lipoproteins, such as HDL, VLDL, and LDL, which are the molecules responsible for the transport of cholesterol through the blood.

The liver also determines whether the fat ingested will be used to generate energy or will be stored. If the individual consumes excess fats, the liver transforms glycerol and fatty acid into triglycerides, storing them in the subcutaneous tissue, creating layers of adipose tissue (the famous little hands). Conversely, if the body needs extra energy sources, the adipose tissue breaks the triglycerides back into glycerol and the fatty acid, sending them back to the liver so they can be available as a source of energy for the cells.

B. Proteins

The digestion process breaks down the ingested proteins into molecules called amino acids. The liver is the organ that decides the fate of these amino acids, being able to use them as:
  • source for the production of proteins essential for the body, such as albumin, globulins, lipoproteins, coagulation factors, etc.;
  • source for muscle mass formation;
  • source for fat production, because if necessary, the liver can transform amino acids into triglycerides, in a process called lipogenesis;
  • source for glucose production, in a process called gluconeogenesis.

Patients with severe liver disease have low levels of protein in the blood, mainly albumin. Loss of muscle mass is also common due to the loss of ability to deal with the amino acids received from the diet. The deficiency of coagulation factors causes these patients to present a higher risk of bleeding.

The digestion of proteins produces amino acids, but also generates ammonia, a substance toxic to the body. The liver is responsible for metabolizing ammonia, transforming it into urea, an infinitely less toxic substance. Patients with cirrhosis and liver failure lose the ability to metabolize ammonia, causing it to accumulate in the body, leading to so-called hepatic encephalopathy, a process of intoxication of the neurons.

C. Glucose

Ingested carbohydrates are transformed into glucose molecules, which is the main energy source of cells. When a large amount of glucose reaches the liver, it releases one part into the bloodstream and stores another in the form of glycogen so that it can be used as a source of energy during periods of fasting or physical activity. If the liver is already full of glycogen, but the individual continues to ingest excess carbohydrates, it is then transformed into triglycerides (lipogenesis) and sent to the subcutaneous tissues. That's why eating a lot of carbohydrate makes you fat.

Patients with severe liver disease may present with hypoglycemia, since the liver can no longer store glucose in the form of glycogen, making the patient not have glucose reserves readily available during the fasting periods.

2. Metabolization of toxic substances

Like any nutrients, any other substance ingested will also pass through the liver before it reaches the rest of the body, including medicines, drugs, environmental toxins, and alcohol.

Hepatocytes are rich in cytochrome P450, the name given to a family of enzymes that have the ability to metabolize, inactivate and facilitate elimination by the kidneys of various substances.

The most famous example of the process of detoxification performed by the liver is the metabolization of alcoholic beverages. Alcohol is an extremely toxic substance, but to some extent can be consumed, because the liver has the ability to turn it into acetic acid, a much less toxic metabolite and easily eliminated by the kidneys through the urine.

The liver is also able to deactivate substances produced by the body itself, such as hormones, preventing excess of them circulating through the blood.

Patients with liver disease should avoid alcohol and certain medications because the liver will no longer be able to metabolize them properly.

3. Production of bile

Our red blood cells are cells that have an average life span of 120 days. When they get old, they are taken to the spleen where they are destroyed. One of the products released in this process is bilirubin, a yellow-green pigment. The bilirubin produced in the spleen is not soluble in water and therefore can not be eliminated by the kidneys, and the liver has this role.

Bilirubin is metabolized in the liver and added to bile, a substance that helps in the digestion of fats. The bile produced by the liver is part stored in the gallbladder and part released in the intestine, to facilitate the digestion process. The presence of bilirubin in bile is responsible for the brown color of the feces. Patients with liver or bile duct diseases that prevent the drainage of bile into the intestines present problems of fat digestion and whitish feces.

If the liver loses the ability to metabolize and excrete bilirubin, it accumulates in the blood and eventually deposits on the skin, making it yellowish, a sign we call jaundice.

4. Production of essential substances to the organism

In addition to the production of important proteins such as albumin and clotting factors, as explained above, the liver is also capable of producing, metabolizing and storing a wide range of other substances, such as vitamins and iron.

5. Destruction of bacteria and other germs

The liver has defensive cells, called Kupffer cells, capable of killing germs and fragments of dead cells that pass through the liver.

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