Liver Function Tests

Liver Function Tests

The Liver

The liver is the largest organ in the human body. It weighs 1.2 to 1.5 kg in adult. It is located in the right upper quadrant of the abdomen and is attached beneath the diaphragm by its ligaments. It is divided into four lobes, left, right, quadrate and caudate. These are supplied by the left and right branches of the portal vein and the hepatic artery. The biliary drainage is into the left and right hepatic ducts. A thin connective-tissue capsule covers the entire liver surface.

The majority of cells in the liver (nearly 2/3rd of liver mass) are hepatocytes. The remaining cell types are Kupffer cells, stellate (fat storing) cells, endothelial cells of blood vessels, cells of bile ducts and supporting structures. Hepatocytes demonstrate pinocytotic and endocytotic activity with active and passive uptake os nutrients. Kupffer cells represent the largest group of fixed macrophages in the body. Hepatocytes perform various functions in maintaining homeostasis and health.

These functions include, the synthesis of albumin. coaqulation factors, carrier proteins, hormonal and growth factors, production of bile and its constituents
(bile salts, cholesterol, lecithin, phospholipids etc.), metabolism of glucose, glycogen, cholesterol, fatty
acids, amino acids, lipoproteins, drugs, bilirubin etc. The circulating system of the liver is characterized by a dual blood supply. Portal vein carries blood from the capillary bed of the alimentary tract, which is rich in nutrients absorbed from the gastrointestinal tract.

Hepatic artery (a t branch of the celiac trunk) carries
well-oxygenated blood to the liver. About 20 percent of the blood flow is Oxygen-rich blood from the hepatic artery, and 80 percent blood is nutrition-rich from the portal vein. The venous drainage from the liver is vía the right and left hepatic veins, which enter into inferior The portal triad consists of bile ducts that accompany the hepatic artery and portal vein. Bile flows from the hepatocytes into the bile canaliculi and ductules, to the larger intra-hepatic bile ducts, and finally to the left and right hepatic bile ducts. These emerge from the liver and form a common bile duct.

The gall bladder is divided into three segments, the Tündus, the body and the neck. It is 9 to 10 cm in length (in adults) and stores about 50 ml of bile. Innervation of the liver is provided by hepatic nerve piexus, which enters the liver at the porta hepatis. aldsympathetic innervation is derived from the preganglionic fibers of the vagus and sympathetic Innervation is derived from preganglionic fibers.

Liver Function Tests

• Excretory functions
  • Bile formation and excretion of bile into the intestine.
  • Secretion of products in the bile emanating from the liver parenchymal cells (which Comprises 60% of its mass) e.g. bile salts, bilirubin conjugates and cholesterol.
  • Excretion of substances withdrawn from the blood by hepatic activity, e.g. heavy metals, dyes such as bromsulfthalein and alkaline phosphatase.
• Metabolic functions: The liver is the center of metabolic activity for carbohydrate, protein and lipids.
  • Carbohydrates: Sugars and carbon residues from protein and fat are converted to glycogen. Glycogen is stored as a carbohydrate reserve.
  • Proteins: Amino acids are deaminated and ammonia is converted to urea. Immunoglobulins are synthesized in the cells of the reticuloendothel ial system. Albumin is synthesized by the parenchymal cells.
  • Lipids: The liver contains a store of neutral fat. Synthesis of cholesterol, bile acids, fats and lipoproteins take place in liver. Liver also plays important role in the esterification of cholesterol and other lipids.
• Protective functions and Detoxication
  • Kupffer cell activity in removing foreign bodies from blood (phagocytosis).
  • Detoxication by conjugation, methylation, Oxidation and reduction.
  • Removal of ammonia from blood, particularly that absorbed from the intestine by way of the portal vein. Ammonia formed in deamination of amino acids is converted to urea, which is excreted through urine.
• Hematologic functions: (Hematopoiesis and coagulation)
  • Blood formation in the embryo (and in some abnormal states in the adults.)
  • Production of blood coagulation factors (I to XIII, PK, HMWK, etc.) fibrinogen, prothrombin and heparin, which play important role in blood coagulation.
  • Destruction of erythrocytes (at the end of their respective lifespan.
• Circulatory functions
  • Transfer of blood from portal to systemic circulation.
  • Activity of its reticuloendothelial system (Kupffer cells) in immune mechanisms.
  • Blood Storage ( regulation of blood volume).