Renal reabsorption of sodium (
Na+) is a part of
renal physiology. It uses
Na-H antiport, Na-glucose symport,
sodium ion channels (minor).
VI. Mechanisms of Salt & Water Reabsorption
It is stimulated by angiotensin II
Angiotensin is a peptide hormone that causes vasoconstriction and an increase in blood pressure. It is part of the renin–angiotensin system, which regulates blood pressure. Angiotensin also stimulates the release of aldosterone from the adre ...
and aldosterone
Aldosterone is the main mineralocorticoid steroid hormone produced by the zona glomerulosa of the adrenal cortex in the adrenal gland. It is essential for sodium conservation in the kidney, salivary glands, sweat glands, and colon. It plays a c ...
, and inhibited by atrial natriuretic peptide.
It is very efficient, since more than 25,000 m moles/day of sodium is filtered into the nephron, but only ~100 m moles/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 cotransporter SGLT and the Na-H antiporter. Sodium passes along an electrochemical gradient (passive transport) from the lumen into the tubular cell, together with water and chloride which also diffuse passively. Water is reabsorbed to the same degree, resulting in the concentration in the end of the proximal tubule being the same as in the beginning. In other words, the reabsorption in the proximal tubule is isosmotic
Osmotic concentration, formerly known as osmolarity, is the measure of solute concentration, defined as the number of osmoles (Osm) of solute per litre (L) of solution (osmol/L or Osm/L). The osmolarity of a solution is usually expressed as Osm/L ...
.
Loop of Henle
Sodium is reabsorbed in the thick ascending limb of loop of Henle, by Na-K-2Cl symporter and
Na-H antiporter. It goes against its chemical driving force, but the high electrical driving force renders the overall electrochemical driving force positive anyway, availing some sodium to diffuse passively either the transcellular or paracellular way.
Distal tubule
In the distal convoluted tubule sodium is transported against an electrochemical gradient by sodium-chloride symporters.
Collecting duct
The principal cells are the sodium-transporting cells in the collecting duct system
The collecting duct system of the kidney consists of a series of tubules and ducts that physically connect nephrons to a minor calyx or directly to the renal pelvis. The collecting duct system is the last part of nephron and participates in elect ...
.
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
Aldosterone is the main mineralocorticoid steroid hormone produced by the zona glomerulosa of the adrenal cortex in the adrenal gland. It is essential for sodium conservation in the kidney, salivary glands, sweat glands, and colon. It plays a c ...
, 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
References
{{renal physiology
Renal physiology