Lecture 34- Wednesday, March 31 , 2010st
Total Balance of Sodium and Water
-Sodium (Na) and water are important components of the body fluids.
-Total-body balance of Na and water has to be maintained to sustain normal blood
pressure and life.
We are in water and sodium balance!
water intake = water output
sodium intake = sodium output
-Depending on intake:
water output can vary from 0.4 L/day to 25 L/day;
sodium chloride output can vary from 0.05 g/day to 25 g/day.
Basic Renal Processes for Sodium and Water
-Both sodium and water are freely filtered but ~99% is reabsorbed (no secretion).
-The majority of sodium and water reabsorption (~2/3) occurs in the proximal
-But the major hormonal control of reabsorption occurs on the DCT and CD.
1) Sodium reabsorption is an active process occurring in all tubular segments (except
the descending thin limb of Henle’s loop)
2) Water reabsorption is by diffusion and is dependent upon sodium reabsorption.
Active Sodium Reabsorption
-On the basolateral membrane:
Active Na /K -ATPase pumps transport sodium out of the cells and keep the
intracellular concentration of sodium low.
-On the apical (luminal) membrane: Sodium moves downhill from the tubular lumen into the tubular epithelial cells. Each
tubular segment has different mec+an+sms.
e.g. In the proximal tubule: Na -H antiporter