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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).
The small intestine tract: This is where absorption takes place. [2] [3] [4] The brush borders of the intestinal lining are the site of terminal carbohydrate digestions. The microvilli that constitute the brush border have enzymes for this final part of digestion anchored into their apical plasma membrane as integral membrane proteins.
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]
The distal convoluted tubule has a different structure and function to that of the proximal convoluted tubule. Cells lining the tubule have numerous mitochondria to produce enough energy for active transport to take place. Much of the ion transport taking place in the distal convoluted tubule is regulated by the endocrine system.
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).
The descending loop of Henle receives isotonic (300 mOsm/L) fluid from the proximal convoluted tubule (PCT). The fluid is isotonic because as ions are reabsorbed by the gradient time system, water is also reabsorbed maintaining the osmolarity of the fluid in the PCT. Substances reabsorbed in the PCT include urea, water, potassium, sodium ...
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 epithelium in the thick segment of the descending limb consists of low simple cuboidal cells, which resemble those found in the proximal tubule.In contrast, the epithelium transitions to a simple squamous type in the thin segment, which is less metabolically active and has minimal surface specializations.