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For example, with glucose, some sugar appears in the urine at levels much lower than 300 mg/dL. [2] The point at which the effects start to appear is called " threshold ", and the difference between threshold and transport maximum is called " splay ".
Renal glucose reabsorption is the part of kidney (renal) physiology that deals with the retrieval of filtered glucose, preventing it from disappearing from the body through the urine. If glucose is not reabsorbed by the kidney, it appears in the urine, in a condition known as glycosuria .
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 postglomerular 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).
Also, tubular transport is Tm-limited and the reabsorption mechanism being saturated at a plasma concentration more than 20 times than usual shows a low level of splay. [13] Renal abnormalities of glucose excretion, causing glycosuria , [ 15 ] may happen as either a result of reduced Tm for glucose or because of an abnormally wide range of ...
[2] [3] SGLT1, encoded by the SLC5A1 gene, is primarily expressed in the late proximal tubule (S3 segment) and accounts for the remaining 3% of glucose reabsorption. [2] [3] In addition to SGLT1 and SGLT2, there are 10 other members in the human protein family SLC5A. [4] SLC5A4, also known as SGLT3, is a member of the sodium-glucose ...
Glycosuria is nearly always caused by an elevated blood sugar level, most commonly due to untreated diabetes. Rarely, glycosuria is due to an intrinsic problem with glucose reabsorption within the kidneys (such as Fanconi syndrome ), producing a condition termed renal glycosuria . [ 1 ]
Paracellular transport also has the benefit that absorption rate is matched to load because it has no transporters that can be saturated. In most mammals, intestinal absorption of nutrients is thought to be dominated by transcellular transport, e.g., glucose is primarily absorbed via the SGLT1 transporter and other glucose transporters .
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.