AHL Content Statements

• D3.3.7

  Role of the kidney in osmoregulation and excretion
  

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  Students should understand the distinction between excretion and osmoregulation. Osmoregulation is regulation of osmotic concentration. The units for osmotic concentration are osmoles per litre.
  

• D3.3.8

  Role of the glomerulus, Bowman’s capsule and proximal convoluted tubule in excretion
  

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  Students should appreciate how ultrafiltration remove solutes from blood plasma and how useful substances are then reabsorbed, to leave toxins and other unwanted solutes in the filtrate, which are excreted in urine.
  

• D3.3.9

  Role of the loop of Henle

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  Limit to active transport of sodium ions in the ascending limb to maintain high osmotic concentrations in the medulla, facilitating water reabsorption in the collecting ducts.
  

• D3.3.10

  Osmoregulation by water reabsorption in the collecting ducts

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  Include the roles of osmoreceptors in the hypothalamus, changes to the rate of antidiuretic hormone secretion by the pituitary gland and the resultant switches in location of aquaporins between cell membranes and intracellular vesicles in cells of the collecting ducts.
  

• B2.3.7

  Adaptations to increase surface area-to-volume ratios of cells
  

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  Include flattening of cells, microvilli and invagination. Use erythrocytes and proximal convoluted tubule cells in the nephron as examples.