05 Control Of Water Balance Flashcards
(9 cards)
What is water balance used for and what determines ECF volume
Plasma osmolarity
Level of salt
What are the different ways of getting rid water from body
Sweat (450 ml/day)
Faeces (100 ml/day)
Respiration (350 ml/day)
Urine (1500 ml/day)
How much water is reabsorbed independently of regulation
PCT: 70%
Loop of Henle: 10%
Identify 4 components that allow the generation of hyperosmolar environment in the interstitial space in medulla
- Counter current mechanism
- Active pumps in ascending loop of Henle which is permeable to water but not salt
- Descending limb is impermeable to salt but permeable to water
- urea permeable at the top of loop of Henle and collecting duct
Name the transporters of urea and what are their significance
UT-A1 and UT-A3 are located in the collecting duct
UT-A2 at the tip of loop of Henle
UT-B1 at the descending vasa recta
KO of UT-A2 causes hypotension and KO of UT-B1 causes inability to concentrate urine
Why does vasa recta not disturb the counter current gradient
It is very permeable to both water and salts. At the descending loop of Henle water enters interstitial fluid and at the ascending salt diffuses out (same movement as the tubules)
What stimulates the release of ATP and what effect does it have
Stimuli: increase in plasma osmolarity and reduction in volume
Effect: binds to V2 receptor on basolateral membrane of principle cells in collecting duct. This causes the insertion of water channel (AQP2) onto apical membrane and insertion of UT-A1 and 3 for urea transport
What is diabetes insipidis
It is a disorder of water balance causing extraction of excess water in urine. 3 types:
- no ADH
- mutant receptor
- resistance to ADH
What is the difference between thick and thin ascending loop of Henle
Thin ascending loop of Henle is in medulla whereas the other is in cortex. Moreover, thin ascending loop of Henle does not have NaCl pump
