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The proximal tubule is the segment of the nephron in kidneys which begins from the renal pole of the Bowman's capsule to the beginning of loop of Henle.At this location, the glomerular parietal epithelial cells (PECs) lining bowman’s capsule abruptly transition to proximal tubule epithelial cells (PTECs).
SGLT2 is located in the early proximal tubule, and is responsible for reabsorption of 80-90% of the glucose filtered by the kidney glomerulus. [7] Most of the remaining glucose absorption is by sodium/glucose cotransporter 1 (SGLT1) in more distal sections of the proximal tubule. [8]
Tubular secretion occurs at Proximal Convoluted Tubule (PCT) and Distal Convoluted Tubule (D.C.T); for example, at proximal convoluted tubule, potassium is secreted by means of sodium-potassium pump, hydrogen ion is secreted by means of active transport and co-transport, i.e. anti-porter, and ammonia diffuses into renal tubule.
The transport of glucose across the proximal tubule cell membrane involves a complex process of secondary active transport (also known as co-transport). [3] This process begins with the Na + /K + ATPase on the basolateral membrane. This enzyme uses ATP to pump 3 sodium ions out of the cell into the blood while bringing 2 potassium ions into the ...
Firstly, the glucose in the proximal tubule is co-transported with sodium ions into the proximal convoluted tubule walls via the SGLT2 cotransporter. Some (typically smaller) amino acids are also transported in this way. Once in the tubule wall, the glucose and amino acids diffuse directly into the blood capillaries along a concentration gradient.
The collecting duct system of the kidney consists of a series of tubules and ducts that physically connect nephrons to a minor calyx or directly to the renal pelvis.The collecting duct participates in electrolyte and fluid balance through reabsorption and excretion, processes regulated by the hormones aldosterone and vasopressin (antidiuretic hormone).
Most of the reabsorption (65%) occurs in the proximal tubule. In the latter part it is favored by an electrochemical driving force, but initially it needs the cotransporter SGLT and the Na-H antiporter. Sodium passes along an electrochemical gradient (passive transport) from the lumen into the tubular cell, together with water and chloride ...
Water is 55% reabsorbed in the proximal tubule. Glucose at normal plasma levels is completely reabsorbed in the proximal tubule. The mechanism for this is the Na + /glucose cotransporter. A plasma level of 350 mg/dL will fully saturate the transporters and glucose will be lost in the urine.