The functions of liver in human body are given below:
 
1. Carbohydrate Metabolism

• Storage of glycogen: The excess of glucose in body is converted by liver into glycogen and liver stores that glycogen. Normally liver contains about 6% glycogen. By converting glucose to glycogen, the liver prevents the occurrence of hyperglycemia after a carbohydrate meal which could result in glucosuria.
• Conversion of glycogen to glucose: When the glucose level in blood falls down during long fasting, the liver converts the stored glycogen back into glucose to maintain the normal blood glucose level.
• Gluconeogenesis or the formation of glucose from non-carbohydrate compounds, e.g. Lactic acid and amino acid: When there is no glycogen available to be converted into glucose for need of body, the liver perform the Gluconeogenesis during which lever forms glucose from other non-carbohydrate compounds, e.g. lactic acid and amino acid.
• Conversion of monosaccharides, e.g. fructose and galactose to glucose

The removal of liver results in an abrupt and severe hyperglycemia and death occurs in a few hours.

2. Protein Metabolism

• Formation of plasma protein such as albumin (liver is the only source of albumin), alpha and beta globulins and many plasma factors which take part in blood clotting such as fibrinogen, prothrombin, factors V, VII and most probably also factors IX and X.
• Breakdown of amino acids by deamination.
• Formation of Urea: Ammonia which takes part in the formation of urea comes from the breakdown of amino acids in the body as well as from the intestine where ammonia is produced by bacterial putrefaction. Ammonia from the intestines is absorbed into the portal blood that carries it to the liver where it is converted to urea. This is a detoxicating function of the liver.
• Transamination, Transpeptidation, etc

3. Fat Metabolism

• Formation of ketone bodies: However, ketone bodies are not utilized by the liver.
• Formation of lipoproteins.
• Synthesis of cholesterol and its esters; cholesterol is also secreted in bile.
• Formation of Phospholipids such lecithins and cephalins.
• Saturation, desaturation, shortening and lengthening of fatty acids.

4. Secretion of bile

Bile is formed continuously at the rate of about 23 ml/hour during waking hours and 15 ml/hour during sleep. It is excreted from small canaliculi into larger bile capillaries and thence into the bile duct.

5. Metabolism of Bile Pigments

Bilirubin is brought to the liver as hemobilirubin which is a complex of bilirubin with plasma proteins. The liver cells split this complex and the released bilirubin is conjugated with glucuronic acid and H2SO4 forming water soluble derivatives of bilirubin (cholebilirubin) which are excreted in bile. Within the intestinal lumen urobilinogen is formed as a result of reduction bilirubin by the intestinal bacteria, about one-half of which is reabsorbed and reaches the liver through portal blood. Most of it is again excreted in bile as bilirubin. But a smaller part enters the blood circulation and is excreted in urine as urobilinogen.

6. Metabolism of Bile Salts

Bile salts are sterols which are derived from cholesterol. Cholic acid and chenodexycholic acid are the most important bile acids quantitatively and are conjugated with glycine and taurine in the liver cells. Conjugate bile acids thus formed appear in the hepatic bile as sodium salts (bile salts) in a concentration of 1%. Most of the bile salts which enter the intestinal tract are reabsorbed into the portal blood and on reaching the liver are again secreted into the bile. Liver makes 0.8 gram bile salts every day. The bile salts help in the digestion and absorption of fats and fat soluble vitamins.

7. Formation of Blood Cells

In the intra-uterine life, liver is concerned with the formation of red blood cells. However, this function is lost at birth but the liver retains the potentiality of formation of red blood cells and it may restart forming these cells under certain circumstances.

8. Destruction of Blood Cells

The Kupffer cells of the liver are concerned with destruction of erythrocytes and formation of bilirubin. The iron liberated from the destroyed red blood cells is stored in the liver.

9. Formation of Heparin

Liver is not the main source of heparin in the body but this fact is of historical importance because heparin was first obtained from liver. Actually this is the function of mast cells of the connective tissue and not of liver parenchymal cells.

10. Storage Function
The liver stores many important compounds like iron and vitamins such as A, D, K, B12, Folic acid etc. It also stores blood and helps in the regulation of blood volume by preventing an abrupt increase in blood volume after one drinks excess of water.

11. Detoxification Function

Detoxication reactions are those biochemical changes in body which converts molecules which get access to the body compounds which are more readily excretable. It should be noted, however, that in many reactions the toxicity is not completely eliminated but is only lessened. This function of the liver is described below in detail.

• Foreign compounds may get entry into the body in the following ways.
• Putrefaction in the intestine through bacterial enzymatic action on normal digestion products.

Substances taken as drugs, preservatives of foods, etc.

The biochemical reactions involved in the detoxication can be classed under four main types, i.e. conjugation, hydrolysis, oxidation and reduction. In many cases, however, more than one of these processes are involved.

Conjugation:

• The most common type of conjugation is that which involves the production of an ester or other type of linkage with glucuronic acid which is produced from glucose. For these reactions, glucuronic acid is first activated to UDP-glucuronic acid. Chloramphenicol, trichlorethanol (derived from chloral hydrate), steroids and bilirubin are examples of compounds which are conjugated with glucuronic acid.
• Glycine can also take part in conjugation. The compounds which get conjugated with this amino acid are benzoic acid, nicotinic acid, p-aminobenzoic acid, etc.
• Sulfation is also involved in many detoxication reactions. Indole and skatole which are derived from tryptophan are converted to indoxyle and skatoxyl which then form corresponding sulfates to be excreted in urine. Phenol (derived from tyrosine) and paracresol are also (partly) excreted in the urine as their sulfates.
• Methylation reactions: Examples are methylation of Pyridine and nicotinic acid.
• Acetylation reactions: For examples, sulfonamide drugs are partly detoxicated by this process.

Hydrolysis:

• Acetyl salicyclic acid (aspirin) is hydrolyzed to acetic acid and salicyclic acid.
• Di-isopropylfluorophosphate (DFP) and astropine also undergo hydrolysis.

Reduction:

• Picric acid is converted to picramic acid; in this process, the nitro group is reduced to amino group.
• Trinitrotoluence (TNT): Its nitro group reduced to amino group.
• Chloral hydrate is reduced to trichloroethanol

Oxidation:

• Oxidation of amines, e.g. tyramine, histamine, cadaverine, putrescine which are derived from tyrosine, histidine, lysine and ornithine respectively.
• Methanol is oxidized to formic acid which is very toxic and is very slowly eliminated.
• The tranquilizer drug meprobamate (Miltown, Equanil) is oxidized to hydroxymeprobamate.
• The sulfur derived from S-containing amino acids is oxidized to sulfates which are then excreted in urine.