LIVER FUNCTION

• The liver is the largest internal organ, weighing about 1500 g.
• Liver performs complex functions including metabolism, detoxification, storage and excretion
• Liver is a relatively resilient organ that can

  regenerate cells that have been destroyed by

  some short-term injury or disease or have been

  removed.
• If the liver becomes completely nonfunctional for

  any reason, death will occur within

  approximately 24 hours due to hypoglycemia
• Liver weighs approximately 1.2-1.5 kg in a healthy adult
• the liver is divided unequally into two lobes by the falciform ligament
• the right lobe is 6 times larger than the left lobe
• The two major sources of blood supply of the liver is the hepatic artery and portal vein
• Hepatocytes are responsible for most of the metabolic functions of the liver
• Kupffer cells are macrophages that reside in the sinusoids of the liver
• hepatic artery is a branch or aorta that supplies oxygen-rich blood from the heart to the liver
• Hepatic artery provides approximately 25% of the total blood supply of the liver
• Portal vein – supplies nutrient-rich blood

  (collected as food is digested) from the

  digestive tract
• Portal vein provides approximately 75% of the total blood supply of the liver
• the hepatic artery and portal vein merge into the hepatic sinusoid
• The excretory system of the liver begins at the

  bile canaliculi.
• The bile canaliculi are small

  spaces between the hepatocytes that form

  intrahepatic ducts, where excretory products of

  the cells can drain.
• The right and left hepatic ducts merge to form the

  common hepatic duct, which is eventually

  joined with the cystic duct of the gallbladder to

  form the common bile duct.
• The lobules are the functional units of

  the liver, responsible for all metabolic and

  excretory functions performed by the liver.
• the liver contains two major cell types: Hepatocytes and Kupffer Cells
• Hepatocytes make up about 80% of the total mass of the liver and perform most of its functions.
• Kupffer cells are macrophages found on the surface of the endothelium lining the sinusoids.
• One of the most important functions of the liver is the processing and excretion of endogenous and exogenous substances into the bile or urine such as the major heme waste product, bilirubin. 
• The liver is the only organ that has the capacity to rid the body of heme waste products. 
• Bile is made up of bile acids or salts, bile pigments, cholesterol, and other substances extracted from the blood. 
• The body produces approximately 3 L of bile per day and excretes 1 L of what is produced. 
• Bilirubin is the principal pigment in bile, and it is derived from the breakdown of red blood cells.
• Unconjugated bilirubin - Bilirubin that is bound by albumin and transported to the liver. 
• unconjugated bilirubin is insoluble in water and cannot be removed from the body until it has been conjugated by the liver
• Once at the liver cell, unconjugated bilirubin flows into the sinusoidal spaces and is released from albumin so it can be picked up by a carrier protein called ligandin
• The conjugation (esterification) of bilirubin occurs in the presence of the enzyme uridine diphosphate glucuronosyltransferase (UDPGT)
• UDPGT transfers a glucuronic acid molecule to each of the two propionic acid side chains of bilirubin to form bilirubin diglucuronide, also known as conjugated bilirubin
• conjugated bilirubin is a type of bilirubin that is water soluble and to be secreted from the hepatocyte into the bile canaliculi
• Intestinal bacteria (especially the bacteria in the lower portion of the intestinal tract) work on conjugated bilirubin to produce mesobilirubin, which is reduced to form mesobilirubinogen and then urobilinogen (a colorless product). 
• The urobilin or stercobilin is what gives stool its brown color. 
• The metabolism of carbohydrates is one of the most important functions of the liver. 
• Almost all proteins are synthesized by the liver except for the immunoglobulins and adult hemoglobin.
• Glycogenolysis is the breakdown of stored glycogen to release glucose molecules into the bloodstream.
• Gluconeogenesis is the process whereby noncarbohydrate substances such as amino acids and fatty acids can be converted to glucose.
• One of the most important proteins synthesized by the liver is albumin