The liver is thought to be responsible for up to 500 functions. Some are mentioned below:- Blood supply: The liver receives blood supply from the hepatic portal vein and hepatic arteries. The hepatic portal vein delivers approximately 75% of the liver's blood supply, and carries venous blood drained from the spleen, gastrointestinal tract, and its associated organs. The hepatic arteries supply arterial blood to the liver, accounting for the remaining quarter of its blood flow.
- Storage of large quantity of blood: During emergency situation such as blood loss, the hepatic sinusoids contract sending stored blood into circulation.
- Destruction of haemoglobin: Destruction of haemoglobin forms pigments such as bilirubin.
- Production of Bile: Bile is a digestive juice produced by liver. It is carried through hepatic ducts and is temporarily stored in gall bladder. The cystic duct from the gallbladder joins with the common hepatic duct to form the common bile duct. Bile either drains directly into the duodenum via the common bile duct, or is temporarily stored in the gallbladder via the cystic duct.
- Chief site of metabolism of protein, carbohydrates and fats: It involves the breakdown and synthesis of glucose, amino acids, fatty acids, glycerol and inter-conversion of carbohydrates, protein and fats.
- Synthesis and storage of Glycogen: The liver synthesizes and stores approximately 100 g of glycogen via glycogenesis, the formation of glycogen from glucose. When needed, the liver releases glucose into the blood by performing glycogenolysis, the breakdown of glycogen into glucose.
- Gluconeogenesis: It is the synthesis of glucose from certain amino acids, lactate or glycerol. Adipose and liver cells produce glycerol by breakdown of fat, which the liver uses for gluconeogenesis.
- Production of clotting factors: Some of the proteins synthesized by the liver include coagulation factors I (fibrinogen), II (prothrombin), V, VII, VIII, IX, X, XI, XIII, as well as protein C, protein S and antithrombin.
- Synthesis of substances heparin: It prevents blood clotting
- Production of Red Blood Cells: In the first trimester fetus, the liver is the main site of red blood cell production. By the 32nd week of gestation, the bone marrow has almost completely taken over that task.
- Production for thrombopoietin: It is a glycoprotein hormone that regulates the production of platelets by the bone marrow.
- Lipid metabolism: It performs cholesterol synthesis, lipogenesis, the production of triglycerides, and a bulk of the body's lipoproteins are synthesized in the liver.
- Role in digestion: It produces and excretes bile (a yellowish liquid) required for emulsifying fats and help the absorption of vitamin K from the diet. Some of the bile drains directly into the duodenum, and some is stored in the gallbladder.
- Production of insulin-like growth factor 1 (IGF-1): It is a polypeptide protein hormone that plays an important role in childhood growth and continues to have anabolic effects in adults.
- Breakdown of insulin and other hormones.
- Breakdown of bilirubin via glucuronidation, facilitating its excretion into bile.
- Breakdown and excretion of many waste products.
- Breakdown or modification of toxic substances (e.g., methylation) and most medicinal products in a process called drug metabolism. This sometimes results in toxication, when the metabolite is more toxic than its precursor. Preferably, the toxins are conjugated to avail excretion in bile or urine.
- Breakdown of ammonia into urea as part of the urea cycle, and the urea is excreted in the urine.
- Storage of many substances: Examples: glucose (in the form of glycogen), vitamin A (1–2 years' supply), vitamin D (1–4 months' supply), vitamin B12 (1–3 years' supply), vitamin K, iron, and copper.
- Immunological effects: The mononuclear phagocyte system of the liver contains many immunologically active cells, acting as a 'sieve' for antigens carried to it via the portal system.
- Production of albumin: It is the most abundant protein in blood serum. It is essential in the maintenance of osmotic pressure, and acts as a transport for fatty acids and steroid hormones.
- Synthesis of angiotensinogen: It is a hormone responsible for raising the blood pressure when activated by renin. Renin is an enzyme released when the kidney senses low blood pressure.
- Generation of heat to maintain body temperature.