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A-Level Biology OCR A

Cell Adh Collecting Tubule Medulla Tissue Fluid Water

Front Describe how ADH affects the kidney and explain how this allows osmoregulation.
Back Mechanism of ADH action:
  • ADH released from pituitary gland, travels through stream to collecting duct & distal convoluted tubule
  • Binds to receptors on cell membrane, triggering formation of cAMP (second messenger), causing cascade of events:
  • Vesicles in cells lining collecting duct/DCT fuse with cell surface membrane on side of cell in contact with medulla tissue fluid
  • Vesicle membranes contain aquaporins - when they are inserted in CSM, they make the cell permeable to water
  • This allows water to move out of tubule cells into tissue fluid of medulla and blood capillaries by osmosis

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