Liver

• Liver


  Largest homeostatic organ (besides skin), multi-functional
• Liver

  • 2 lobes
  • Hexagonal units = LOBULES
  • Cells = hepatocytes
• Blood flow in liver

  1. Hepatic artery: supplies oxygen-rich blood

  2. Hepatic portal vein: carries nutrients from intestine for assimilation

  3. Hepatic vein: carries O₂-deficient blood away from liver
• Sinusoids


  Blood-filled spaces in which blood from hepatic artery + portal vein flows towards intralobular venule past hepatocytes
• Sinusoids

  • Thin endothelial cell lining with large intercellular spaces and incomplete basement membrane for exchange of material (blood <> hepatocyte)
  • Kuppfer cells (special macrophages) attached to wall involved in breakdown of old erythrocytes and ingestion of bacteria
• Bile


  Green/yellow liquid formed by liver cells, stored in gall bladder, involved in emulsification of fats, made of bile salts + pigments
• Hepatocytes


  • Prominent nuclei + Golgi apparatus
  • Many mitochondria and lysosomes
  • Rich in glycogen granules + fat droplets
  • Have microvilli on surface to ↑ S.A.
  • Many peroxisomes containing detox enzymes e.g. catalase which breaks down H₂O₂
• Carbohydrate metabolism

  1. Glycogenesis: conversion of glucose to glycogen under influence of insulin

  2. Glycogenolysis: breakdown of stored glycogen to glucose in blood, stimulated by glucagon and adrenaline + noradrenaline in times of stress

  3. Gluconeogenesis: synthesis of glucose from non-carbohydrate sources when glycogen stores are depleted, stimulated by low blood-glucose levels
• Breakdown of lactic acid

  Produced by anaerobic respiration in skeletal muscle, can later be converted to glucose
• Conversion of carbs to fats

  Excess carbs which cannot be immediately used or stored as glycogen are converted to fats (lipogenesis) and stored as adipose tissue
• Protein metabolism

  1. Deamination: removal of amino group (-NH₂) from excess amino acids

  2. Transamination: synthesis of non-essential amino acids by transfer of amino group (-NH₂)

  3. Detoxification/Urea formation: ammonia produced by deamination is converted to urea in Ornithine cycle

  4. Plasma protein production: produced from amino acids in liver
• Breakdown of erythrocytes and Hb

  Phagocytes break down old RBCs, globin amino acids, haem iron + biliverdin → bilirubin → bile
• Fat metabolism

  1. Lipogenesis: excess carbohydrates converted to fat

  2. Breakdown and synthesis of cholesterol: hepatocytes remove, break down and synthesise cholesterol

  3. Lipoprotein synthesis: used to shuttle hydrophobic molecules in blood and for chylomicrons

  4. Gluconeogenesis: if glucose is in short supply, fat broken down to glycerol and fatty acids for respiration
• Bile production

  Viscous, green/yellow liquid produced by hepatocytes, stored in gall bladder and released to duodenum, made of H₂O, bile salts and bile pigments
• Bile salts act as natural detergent, reduce surface tension of fat globules, emulsifying them into droplets with ↑ S.A for enzyme action during digestion
• Accumulation of cholesterol in bile salts can lead to gall stones
• Release of bile is stimulated by CCK
• Other functions of the liver

  • Vitamin and mineral storage
  • Hormone modification and inactivation
  • Detoxification
  • Removal of old RBCs, pathogens and parasites from circulation
  • Production of RBCs in foetus