Water reabsorption in kidneys

  1. 65% water reabsorption takes place in PCT.
  2. Water reabsorption is coupled with sodium reabsorption.
  3. Bulk of water reabsorption is secondary to sodium reabsorption.

Obligatory water reabsorption

  1. Independant of plasma osmolality/water balance.
  2. Occurs in PCT.
  3. Water reabsorbed isoosmotically and independant of ADH.

Facultative reabsorption

  1. Reabsorption of water depending upon plasma osmolality/water balance.
  2. Dependant on ADH.
  3. Occurs in late DCT and collecting duct.
  4. No reabsorption in absence of ADH.

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