Excretion and Liver

• Excretion


  The removal of metabolic waste products from the body
• Waste products of metabolism

  • Carbon dioxide
  • Bile pigments
  • Urea
• Sinusoids


  Channels surrounded by hepatocytes which take blood from the hepatic artery and hepatic portal vein towards the hepatic vein in the centre of the liver lobule
• Detoxification


  When the liver converts or breaks down toxic substances or waste products, e.g. lactate, alcohol, into non-harmful substances
• How the liver processes excess glucose in blood

  1. Insulin binds to receptors and triggers uptake of glucose into hepatocytes

  2. Glucose monosaccharides are joined together (via condensation reactions) to form the storage polysaccharide glycogen
• Deamination occurs in the mitochondria so that toxic ammonia does not come into contact with the rest of the organelles/cytoplasm. Also the organic acid product can be converted to oxaloacetate and enter the krebs cycle.
• Cycles


  Means there only need to be relatively small quantities of the reactants, such as ornithine, as they are constantly being regenerated by the cycle
• Why binge drinkers can get 'fatty liver'

  Dehydrogenation of alcohol uses NAD, which is also needed to breakdown fatty acids for respiration. If too much alcohol consumes, not enough NAD is present to process fatty acids, so they are converted back to lipids and stored in hepatocytes.
• Low levels of argininosuccinate (as not enough argininosuccinate synthetase to convert citrulline to argininosuccinate)
• Low protein diet means there are fewer excess amino acids to undergo deamination. Therefore less ammonia needs to enter the ornithine cycle and prevents toxic levels of ammonia building up.