Liver

Liver

1. Structure

   • general
     • single largest organ; weighs ~1-1.5kg (~2% of body mass)
     • lies in upper right quadrant of the abdomen
     • consists of two lobes: left (smaller) and right (bigger)
     • made up of; hepatocytes, reticuloendothelial cells, Kupferr cells, biliary tract and blood vessels
   • blood supply
     • receives blood from two different sources
       • hepatic portal vein
         • contains nutrient rich, low, pressure, low oxygenated blood from the GIT
       • hepatic artery
         • contains high pressure, high oxygenated blood
     • blood leaves liver via the hepatic vein, which empties into the superior vena cava
   • made up of a pattern of lobules, which are hexagonal
     • each corner of the lobules contain portal triads
       • portal triad consists of bile duct, portal vein and hepatic artery
     • each lobule contains a central vein
       • hepatocytes radiate outward from the central vein
     • blood flows from the portal triads into the central vein via sinusoids
       • sinusoids contain Kupferr cells, which are phagocytic and play a protective role
     • bile flows in the opposite direction to the blood via the biliary canaliculi
       • it drains into the bile duct, then the hepatic duct and is stored in the gallbladder

2. Function

   • metabolism
     • glucose homeostasis
       • maintenance of blood glucose levels
       • glycogen storage and degradation
       • gluconeogenesis
     • amino acids
       • conversion to pyruvate for gluconeogensis
       • conversion to acetyl coA for fatty acid biosynthesis
       • deamination leading to formation of urea and ammonia
     • fatty acids
       • used for hepatic lipid synthesis
       • exported to adipose stores
       • beta-oxidation to provide energy
   • synthesis
     • the majority of serum proteins (apart from immunoglobins)
       • albumin
         • transports soluble blood components such as bilirubin, bile acids, fatty acids, steroids and maintains osmotic pressure
       • coagulation factors
         • synthesis of clotting factors V, VII, VIII, IX, X, prothrombin, fibrinogen
       • other proteins
         • complement proteins, acute phase proteins, specific binding proteins for vit. A, iron, copper
   • excretion
     • bile
       • a mixture of phospholipids, cholesterol, electrolytes and conjugated bilirubin
     • bilirubin
       • unconjugated bilirubin is transported in the blood attached to albumin. it travels to the liver where in is formed into conjugated bilirubin then actively secreted into bile
   • storage
     • storage site for iron (bound to ferritin, copper, fat soluble vitamins, glycogen and triacylglycerols
   • catabolism
     • catabolises endogenous and exogenous substances using P450. thisleads to individual variation depending on genetic make-up and exposure to foreign substances

3. Causes

   • toxic agents
     • lthough the liver usually detoxifies, it may be damaged by agents or their metabolites, if they are present in excess amounts
     • e.g. alcohol, paracetemol, aspirin, CCl4
   • IBEM
     • lack of certain enzymes can lead to defects in storage of glycogen and lipids
   • obstruction of biliary tract
     • the obstruction of bile flow within the biliary system may be due to gallstones or parasites
   • infections
     • non-viral
       • Weil's disease (leptospirosis)
         • contracted from animals and can cause jaundice, bleeding and renal failure
       • amoebic hepatitis
         • the amoeba infects the large intestine and migrates up hepatic portal vein causing hepatitis
     • viral
       • hepatitis
         • A
           • infectious hepatitis
           • spread by faecal-oral route
           • jaundice develops after 5-10 days
           • liver becomes enlarged and tender
           • rarely leads to fulminant hepatic failure and is never chronic
         • B
           • serum hepatitis
           • caught through contact with blood, semen and saliva
           • it can be acute, self limiting, fulminant, chronic or asymptomatic
         • C
           • accounts for ~5-10%
           • symptoms are less severe and do not usually lead to fulminant
       • yellow fever
         • more dangerous than viral hepatitiss
         • fects hepatocytes and is carried by moquitoes
         • death occurs in ~20% of cases, due to bleeding
       • Epstein-Barr
         • resposible for glandular fever
         • it can cause acute hepatitis and jaundice