Renal physiology
Substance Description Proximal tubule Loop of Henle Distal tubule Collecting duct
Glucose If glucose is not reabsorbed by the kidney , it appears in the urine , in a condition known as glycosuria . This is associated with diabetes mellitus reabsorption ( almost 100% ) via sodium-glucose transport proteins ( apical ) and GLUT ( basolateral ) - - -
Oligopeptides , proteins , and amino acids All are reabsorbed nearly completely reabsorption - - -
Urea Regulation of osmolality . Varies with ADH reabsorption ( 50% ) via passive transport secretion - reabsorption in medullary collecting ducts
Sodium Uses Na-H antiport , Na-glucose symport , sodium ion channels ( minor ) reabsorption ( 65% , isosmotic ) reabsorption ( 25% , thick ascending , Na-K-2Cl symporter ) reabsorption ( 5% , sodium-chloride symporter ) reabsorption ( 5% , principal cells ) , stimulated by aldosterone via ENaC
Chloride Usually follows sodium . Active ( transcellular ) and passive ( paracellular ) reabsorption reabsorption ( thin ascending , thick ascending , Na-K-2Cl symporter ) reabsorption ( sodium-chloride symporter ) -
Water Uses aquaporin water channels . See also diuretic absorbed osmotically along with solutes reabsorption ( descending ) - reabsorption ( regulated by ADH , via arginine vasopressin receptor 2 )
Bicarbonate Helps maintain acid-base balance reabsorption ( 80-90% ) reabsorption ( thick ascending ) - reabsorption ( intercalated cells , via band 3 and pendrin )
Protons Uses vacuolar H+ATPase - - - secretion ( intercalated cells )
Potassium Varies upon dietary needs reabsorption ( 65% ) reabsorption ( 20% , thick ascending , Na-K-2Cl symporter ) - secretion ( common , via Na+/K+-ATPase , increased by aldosterone ) , or reabsorption ( rare , hydrogen potassium ATPase )
Calcium Uses calcium ATPase , sodium-calcium exchanger reabsorption reabsorption ( thick ascending ) via passive transport reabsorption in response to PTH and ↑ reabsorption with Thiazide Diuretics -
Magnesium Calcium and magnesium compete , and an excess of one can lead to excretion of the other reabsorption reabsorption ( thick ascending ) reabsorption -
Phosphate Excreted as titratable acid reabsorption ( 85% ) via sodium/phosphate cotransporter . Inhibited by parathyroid hormone - - -
Carboxylate reabsorption ( 100% ) via carboxylate transporters - - -
Other functions -- Maintaining homeostasis
The kidney is responsible for maintaining a balance of the following substances :
Renal physiology (Latin rēnēs, kidneys) is the study of the physiology of the kidney. This encompasses all functions of the kidney, including maintenance of acid-base balance; regulation of fluid balance; regulation of sodium, potassium, and other electrolytes; clearance of toxins; absorption of glucose, amino acids, and other small molecules; regulation of blood pressure; production of various hormones, such as erythropoietin; and activation of vitamin D.
Much of renal physiology is studied at the level of the nephron, the smallest functional unit of the kidney. Each nephron begins with a filtration component that filters the blood entering the kidney. This filtrate then flows along the length of the nephron, which is a tubular structure lined by a single layer of specialized cells and surrounded by capillaries. The major functions of these lining cells are the reabsorption of water and small molecules from the filtrate into the blood, and the secretion of wastes from the blood into the urine. Proper function of the kidney requires that it receives and adequately filters blood. This is performed at the microscopic level by many hundreds of thousands of filtration units called renal corpuscles, each of which is composed of a glomerulus and a Bowman's capsule. A global assessment of renal function is often ascertained by estimating the rate of filtration, called the glomerular filtration rate (GFR).