Renal sodium reabsorption
Renal reabsorption of sodium (
It is very efficient, since more than 25,000 mmoles/day of sodium is filtered into the nephron, but only ~100 mmoles/day, or less than 0.4% remains in the final urine.
Proximal tubule
Most of the reabsorption (65%) occurs in the proximal tubule. In the latter part it is favored by an electrochemical driving force, but initially it needs the
Loop of Henle
Sodium is reabsorbed in the
Distal tubule
In the distal convoluted tubule sodium is transported against an electrochemical gradient by sodium-chloride symporters.
Collecting duct
The
Regulation
Although only a fragment of total reabsorption happens here, it is the main part of intervention. This is e.g. done by endogenous production of aldosterone, increasing reabsorption. Since the normal excretion rate of sodium is ~100mmoles/day, then a regulation of the absorption of still more than 1000 mmoles/day entering the collecting duct system has a substantial influence of the total sodium excreted.
Overview table
| Characteristic | Proximal tubule | Loop of Henle | Distal convoluted tubule | Collecting duct system | |||||||
|---|---|---|---|---|---|---|---|---|---|---|---|
| S1 | S2 | S3 | Descending limb | Thin ascending limb
|
Thick ascending limb
|
Connecting tubule
|
Initial collecting tubule | Cortical collecting ducts | Medullary collecting ducts | ||
| Reabsorption (%) | 67%[2] | 25%[2] | 5%[2] | 3%[2] | |||||||
| Reabsorption (mmol/day) | ~17,000[2] | ~6,400[2] | ~1,300[2] | ~700[2] | |||||||
| Concentration (mM) | 142[3] | 142[3] | 100[3] | 70[3] | 40[3] | ||||||
| Electrical driving force (mV) | -3[3] | +3[3] | +15[3] | -5 to +5[3] | -40[3] | ||||||
| Chemical driving force (mV) | 0[3] | 0[3] | -9[3] | -19[3] | -34[3] | ||||||
| Electrochemical driving force (mV) | -3[3] | +3[3] | +6[3] | -24 to -14[3] | -74[3] | ||||||
Apical transport proteins |
Na-H antiporter[4] |
(Passively) | Na-H antiporter[4] and passively) |
Sodium-chloride symporter[4] | ENaC[4] | ||||||
Basolateral transport proteins |
Na+/K+-ATPase[4]
| ||||||||||
| Other reabsorption features | Isosmotic |
Principal cells, stimulated by aldosterone
| |||||||||
References
- ^ VI. Mechanisms of Salt & Water Reabsorption Archived 2007-02-10 at the Wayback Machine
- ^ ISBN 1-4160-2328-3. Page 776
- ^ ISBN 1-4160-2328-3. Page 777
- ^ ISBN 1-4160-2328-3. Page 778