<Table> <Tr> <Td> </Td> <Td> This article may be confusing or unclear to readers . Please help us clarify the article . There might be a discussion about this on the talk page . (February 2007) (Learn how and when to remove this template message) </Td> </Tr> </Table> <Tr> <Td> </Td> <Td> This article may be confusing or unclear to readers . Please help us clarify the article . There might be a discussion about this on the talk page . (February 2007) (Learn how and when to remove this template message) </Td> </Tr> <P> In renal physiology, reabsorption or tubular reabsorption is the process by which the nephron removes water and solutes from the tubular fluid (pre-urine) and returns them to the circulating blood . It is called reabsorption (and not absorption) both because these substances have already been absorbed once (particularly in the intestines) and because the body is reclaiming them from a post glomerular fluid stream that is well on its way to becoming urine (that is, they will soon be lost to the urine unless they are reclaimed). Substances are reabsorbed from the tubule into the peritubular capillaries . This happens as a result of sodium transport from the lumen into the blood by the Na / K ATPase in the basolateral membrane of the epithelial cells . Thus, the glomerular filtrate becomes more concentrated, which is one of the steps in forming urine . Reabsorption allows many useful solutes (primarily glucose and amino acids), salts and water that have passed through Bowman's capsule, to return to the circulation . These solutes are reabsorbed isotonically, in that the osmotic potential of the fluid leaving the proximal convoluted tubule is the same as that of the initial glomerular filtrate . However, glucose, amino acids, inorganic phosphate, and some other solutes are reabsorbed via secondary active transport through cotransport channels driven by the sodium gradient . </P> <P> Renin--angiotensin system: </P>

Where are amino acids reabsorbed in the nephron