ADH - Anti-Diuretic Hormone

Hydrated people have large amounts of diluted urea in their urine
Dehydrated people have small amounts of concentrated urea in their urine
ADH is a 9 amino peptide
Synthesised in neuroendocrine cells in the supraoptic and parvoventricular nuclei of the hypothalamus
1. It is transported along the axons of these cells and stored in the neurohypophysis (posterior pituitary)
Conserves water by producing concentrated urine
Increases the medullary collecting duct permeability to water
1. Inserts AQP2 channels into the apical membrane of principal cells
  1. ADH
    1. V2 receptor
      1. Gs protein
        Adenylyl cyclase
        Increased cAMP level
        Protein Kinase A
        Synthesis and insertion of AQP2 channels into apical membrane
Increases the permeability of the inner medullary collecting duct to urea
1. Activates a cAMP protein cascade that phosphorylates the urea transporters on the apical membrane UT-A1 and UT-A3
  1. Increased urea in interstitium increases osmalarity of interstitium and causes reabsorbtion of water by osmosis
Also increases Na absorption by increasing the number of NaK2Cl symporters in thick ascending limb
Trigerrs for ADH: osmoreceptors detect a 2% hyperosmalarity and baroreceptors detecta 15% pressure fall
ADH can also act on V1 receptors to cause vasoconstriction and slow blood flow of vasa recta for longer time of equilibration
1. MInimises washout of solutes in inner medulla that causes reabsorption of water

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