Renal reabsorption of sodium (Na⁺

Sodium

Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

) is a part of renal physiology

Renal physiology

Renal physiology is the study of the physiology of the kidney. This encompasses all functions of the kidney, including reabsorption of glucose, amino acids, and other small molecules; regulation of sodium, potassium, and other electrolytes; regulation of fluid balance and blood pressure;...

. It uses Na-H antiport

Sodium-hydrogen antiporter

The sodium–hydrogen antiporter or sodium–hydrogen exchanger is a membrane protein found in many cells, and especially in those of the nephron of the kidney...

, Na-glucose symport, sodium ion channel

Sodium ion channel

Sodium channels are integral membrane proteins that form ion channels, conducting sodium ions through a cell's plasma membrane. They are classified according to the trigger that opens the channel for such ions, i.e...

s (minor). It is stimulated by angiotensin II and aldosterone

Aldosterone

Aldosterone is a hormone that increases the reabsorption of sodium ions and water and the release of potassium in the collecting ducts and distal convoluted tubule of the kidneys' functional unit, the nephron. This increases blood volume and, therefore, increases blood pressure. Drugs that...

, and inhibited by atrial natriuretic peptide

Atrial natriuretic peptide

Atrial natriuretic peptide , atrial natriuretic factor , atrial natriuretic hormone , or atriopeptin, is a powerful vasodilator, and a protein hormone secreted by heart muscle cells. It is involved in the homeostatic control of body water, sodium, potassium and fat...

.

It is very efficient, since more than 25,000 mmoles

Mole (unit)

The mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as an amount of a substance that contains as many elementary entities as there are atoms in 12 grams of pure carbon-12 , the isotope of carbon with atomic weight 12. This corresponds to a value...

/day of sodium is filtered into the nephron

Nephron

The renal tubule is the portion of the nephron containing the tubular fluid filtered through the glomerulus. After passing through the renal tubule, the filtrate continues to the collecting duct system, which is not part of the nephron....

, but only ~100 mmoles

Mole (unit)

The mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as an amount of a substance that contains as many elementary entities as there are atoms in 12 grams of pure carbon-12 , the isotope of carbon with atomic weight 12. This corresponds to a value...

/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 favoured by an electrochemical driving force, but initially it needs the cotransporter SGLT and the Na-H antiporter. 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.

Loop of Henle

Sodium is reabsorbed in the thick ascending limb of loop of Henle

Thick ascending limb of loop of Henle

The thick ascending limb of loop of Henle also known as distal straight tubule, is a segment of the nephron in the kidney. It can be divided into two parts: that in the renal medulla, and that in the renal cortex.-Medullary thick ascending limb:...

, by Na-K-2Cl symporter

Na-K-2Cl symporter

The Na-K-Cl cotransporter is a protein that aids in the active transport of sodium, potassium, and chloride into and out of cells. There are two varieties, or isoforms, of this membrane transport protein, called NKCC1 and NKCC2. NKCC1 is widely distributed throughout the body; it has important...

 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

Distal convoluted tubule

The distal convoluted tubule is a portion of kidney nephron between the loop of Henle and the collecting duct system.- Physiology :It is partly responsible for the regulation of potassium, sodium, calcium, and pH...

 sodium is transported against an electrochemical gradient by sodium-chloride symporter

Sodium-chloride symporter

The sodium-chloride symporter is a cotransporter in the kidney which has the function of reabsorbing sodium and chloride ions from the tubular fluid into the cells of the distal convoluted tubule of the nephron.It is a member of the SLC12...

s.

Collecting duct

The principal cells are the sodium-transporting cells in the collecting duct system

Collecting duct system

The collecting duct system of the kidney consists of a series of tubules and ducts that connect the nephrons to the ureter. It participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and antidiuretic hormone.There are several...

.

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

Aldosterone is a hormone that increases the reabsorption of sodium ions and water and the release of potassium in the collecting ducts and distal convoluted tubule of the kidneys' functional unit, the nephron. This increases blood volume and, therefore, increases blood pressure. Drugs that...

, 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 Proximal tubule The proximal tubule is the portion of the duct system of the nephron of the kidney which leads from Bowman's capsule to the loop of Henle.-Structure and appearance:...			loop of Henle Loop of Henle In the kidney, the loop of Henle is the portion of a nephron that leads from the proximal convoluted tubule to the distal convoluted tubule. Named after its discoverer F. G. J...			Distal convoluted tubule Distal convoluted tubule The distal convoluted tubule is a portion of kidney nephron between the loop of Henle and the collecting duct system.- Physiology :It is partly responsible for the regulation of potassium, sodium, calcium, and pH...	Collecting duct system Collecting duct system The collecting duct system of the kidney consists of a series of tubules and ducts that connect the nephrons to the ureter. It participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and antidiuretic hormone.There are several...
	S1	S2	S3	descending limb Descending limb of loop of Henle The descending limb of loop of Henle is the portion of the renal tubule constituting the first part of the loop of Henle.-Physiology:The permeability is as follows:...	thin ascending limb Thin ascending limb of loop of Henle The thin ascending limb of loop of Henle is a sub-portion of the loop of Henle in the juxtamedullary nephron of the kidney. The thin ascending limb is impermeable to water, and is also permeable to ions in particular Na and Cl...	thick ascending limb Thick ascending limb of loop of Henle The thick ascending limb of loop of Henle also known as distal straight tubule, is a segment of the nephron in the kidney. It can be divided into two parts: that in the renal medulla, and that in the renal cortex.-Medullary thick ascending limb:...		connecting tubule Connecting tubule In the kidney, the collecting tubule is a tubular segment of the renal collecting duct system that connects the distal convoluted tubule to the cortical collecting duct.-Classification:...	initial collecting tubule	cortical collecting ducts	medullary collecting ducts
reabsorption (%)	67%					25%	5%				3%
reabsorption (mmoles Mole (unit) The mole is a unit of measurement used in chemistry to express amounts of a chemical substance, defined as an amount of a substance that contains as many elementary entities as there are atoms in 12 grams of pure carbon-12 , the isotope of carbon with atomic weight 12. This corresponds to a value... /day)	~17,000					~6,400	~1,300				~700
Concentration (mM)	142		142			100	70			40
electrical driving force Membrane potential Membrane potential is the difference in electrical potential between the interior and exterior of a biological cell. All animal cells are surrounded by a plasma membrane composed of a lipid bilayer with a variety of types of proteins embedded in it...  (mV Volt The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the... )	-3		+3			+15	-5 to +5			-40
chemical driving force Chemical potential Chemical potential, symbolized by μ, is a measure first described by the American engineer, chemist and mathematical physicist Josiah Willard Gibbs. It is the potential that a substance has to produce in order to alter a system...  (mV Volt The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the... )	0		0			-9	-19			-34
electrochemical driving force (mV Volt The volt is the SI derived unit for electric potential, electric potential difference, and electromotive force. The volt is named in honor of the Italian physicist Alessandro Volta , who invented the voltaic pile, possibly the first chemical battery.- Definition :A single volt is defined as the... )	-3		+3			+6	-24 to -14			-74
apical transport proteins	SGLT, Na-H antiporter Sodium-hydrogen antiporter The sodium–hydrogen antiporter or sodium–hydrogen exchanger is a membrane protein found in many cells, and especially in those of the nephron of the kidney...				(passively)	Na-K-2Cl symporter Na-K-2Cl symporter The Na-K-Cl cotransporter is a protein that aids in the active transport of sodium, potassium, and chloride into and out of cells. There are two varieties, or isoforms, of this membrane transport protein, called NKCC1 and NKCC2. NKCC1 is widely distributed throughout the body; it has important...   (Na-H antiporter Sodium-hydrogen antiporter The sodium–hydrogen antiporter or sodium–hydrogen exchanger is a membrane protein found in many cells, and especially in those of the nephron of the kidney...  and passively)	sodium-chloride symporter Sodium-chloride symporter The sodium-chloride symporter is a cotransporter in the kidney which has the function of reabsorbing sodium and chloride ions from the tubular fluid into the cells of the distal convoluted tubule of the nephron.It is a member of the SLC12...			ENaC Epithelial sodium channel The epithelial sodium channel is a membrane-bound ion-channel that is permeable for Li+-ions, protons and especially Na+-ions. It is a constitutively active ion-channel...
basolateral  transport proteins	Na+/K+-ATPase Na+/K+-ATPase Na+/K+-ATPase is an enzyme located in the plasma membrane in all animals.- Sodium-potassium pumps :Active transport is responsible for cells containing relatively high...
Other reabsorption features	isosmotic							by principal cells, stimulated by aldosterone Aldosterone Aldosterone is a hormone that increases the reabsorption of sodium ions and water and the release of potassium in the collecting ducts and distal convoluted tubule of the kidneys' functional unit, the nephron. This increases blood volume and, therefore, increases blood pressure. Drugs that...