Renal sodium reabsorption

Renal reabsorption of sodium (Na⁺) is a part of renal physiology. It uses Na-H antiport, Na-glucose symport, sodium ion channels (minor)^[1]. It is stimulated by angiotensin II and aldosterone, and inhibited by atrial natriuretic peptide.

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.

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Proximal tubule

Most of the reabsorption (65%) occurs in the proximal tubule. In the latter part it is favoured by an electrochemical driving force, but initially it needs the cotransporter SGLT and the Na-H antiporter. Water is absorbed 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 absorption in the proximal tubule is isosmotic.

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.

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

Characteristics of Na⁺ reabsorption
Characteristic	proximal tubule			loop of Henle			Distal convoluted tubule	Collecting duct system
Characteristic	S1	S2	S3	descending limb	thin ascending limb	thick ascending limb	Distal convoluted tubule	connecting tubule	initial collecting tubule	cortical collecting ducts	medullary collecting ducts
reabsorption (%)	67%^[2]					25%^[2]	5%^[2]				3%^[2]
reabsorption (mmoles/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	SGLT, Na-H antiporter^[4]				(passively)	Na-K-2Cl symporter (Na-H antiporter^[4] and passively)	sodium-chloride symporter^[4]			ENaC^[4]
basolateral transport proteins	Na⁺/K⁺-ATPase^[4]
Other reabsorption features	isosmotic							by principal cells, stimulated by aldosterone

References

^ http://www2.kumc.edu/ki/physiology/course/six/6_1.htm
^ ^a ^b ^c ^d ^e ^f ^g ^h Walter F., PhD. Boron. Medical Physiology: A Cellular And Molecular Approaoch. Elsevier/Saunders. ISBN 1-4160-2328-3. Page 776
^ ^a ^b ^c ^d ^e ^f ^g ^h ⁱ ^j ^k ^l ^m ⁿ ^o ^p ^q ^r ^s ^t Walter F., PhD. Boron. Medical Physiology: A Cellular And Molecular Approaoch. Elsevier/Saunders. ISBN 1-4160-2328-3. Page 777
^ ^a ^b ^c ^d ^e Walter F., PhD. Boron. Medical Physiology: A Cellular And Molecular Approaoch. Elsevier/Saunders. ISBN 1-4160-2328-3. Page 778

v • d • e Urinary system, physiology: renal physiology and acid base physiology
Filtration	Renal blood flow - Ultrafiltration - Countercurrent exchange
Hormones affecting filtration	Antidiuretic hormone (ADH) - Aldosterone - Atrial natriuretic peptide
Secretion/clearance	Pharmacokinetics - Clearance of medications
Reabsorption	Solvent drag -Na⁺ - Cl^- -urea -glucose -oligopeptides -protein
Endocrine	Renin - Erythropoietin (EPO) - Calcitriol (Active vitamin D) - Prostaglandins
Assessing Renal function / Measures of dialysis	Glomerular filtration rate - Creatinine clearance - Renal clearance ratio - Urea reduction ratio - Kt/V - Standardized Kt/V - Hemodialysis product - PAH clearance (Effective renal plasma flow - Extraction ratio)
Acid base physiology	Fluid balance - Darrow Yannet diagram - Body water - Interstitial fluid - Extracellular fluid - Intracellular fluid/Cytosol - Plasma - Transcellular fluid - Base excess - Davenport diagram - Anion gap - Arterial blood gas
Buffering/compensation	Bicarbonate buffering system - Respiratory compensation - Renal compensation

Category: Physiology

This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Renal_sodium_reabsorption". A list of authors is available in Wikipedia.