excretion

• define the term excretion 


  removal of metabolic waste from the body
• how is the proximal convolutes tubule adapted to its function (2)

  • mitochondria for ATP for active transport
  • microvilli for increased SA for selective reabsorption
• what adaptations do hepatocytes have

  • flat/cuboidal for shorter diffusion distance
  • lots of mitochondria
  • large nuclei because lots of genes expressed
  • prominent Golgi apparatus for secreting bile
  • many glucose transporters
  • fenestrated to increase permeability
• how is bile secreted in the liver (1)

  • through canaliculi which collect bile and drains it into the gall bladder
• what are the main roles of the liver

  • deaminification of amino acids
  • detoxification of ethanol -> ethanal using alcohol dehydrogenase
  • glycogenesis
  • breakdown of lactic acid -> pyruvate
  • metabolism og hormones
• how is urea formed

  • NH2 + H -> NH3
  • ammonia is very soluble and toxic
  • NH3 + CO2 -> CO(NH2)2 + H2O
• in the ornithine cycle where is urea formed

  • in-between arginine and before ornithine
• why is dextrose solution used rather than water during peritoneal dialysis (4)

  • to remove excess water
  • so water potential of solution is lower than that of the bloods
  • water will move out by osmosis
  • otherwise cells would burst
• why does fluid during peritoneal dialysis have to be changed more often than haemodialysis

  • haemodialysis uses counter current flow , maintains conc gradient
  • can remove more waste
• describe the features of the Bowmans capsule and the glomerulus that allow them to perform their function effectively (4)

  • wider afferent arteriole than efferent maintains high hydrostatic pressure so tissue fluid is formed during ultrafiltration
  • passes through 3 layers : fenestrated capillary endothelium , basement membrane and Podocyte epithelial
  • red blood cells and plasma proteins cannot pass through
• explain the need for a close matching kidney (4)

  • kidney may have different antigens and recognised as non self
  • rejection by immune system
  • need for immunosuppressant drugs for the rest of his life
• describe the process of selective reabsorption

  • proximal convoluted tubule reabsorbs glucose , hormones and vitamins by active transport
  • Na+ are pumped out and Cl- and H2O diffuse down conc gradients
  • constant blood flow through capillaries maintain a steep concentration gradient
  • filtrate at the end of the PCT is isotonic with the blood