Tubular reabsorption

Tubular reabsorption - Tight junctions between tubule cells...

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Tubular reabsorption In healthy kidneys, nearly all of the desirable organic substances (proteins, amino acids, glucose)  are reabsorbed by the cells that line the renal tube. These substances then move into the peritubular  capillaries that surround the tubule. Most of the water (usually more than 99 percent of it) and many  ions are reabsorbed as well, but the amounts are regulated so that blood volume, pressure, and ion  concentration are maintained within required levels for homeostasis. Reabsorbed substances move from the lumen of the renal tubule to the lumen of a peritubular  capillary. Three membranes are traversed:  The luminal membrane, or the side of the tubule cells facing the tubule lumen The basolateral membrane, or the side of the tubule cells facing the interstitial fluids The endothelium of the capillaries
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Unformatted text preview: Tight junctions between tubule cells prevent substances from leaking out between the cells. Movement of substances out of the tubule, then, must occur through the cells, either by active transport (requiring ATP) or by passive transport processes. Once outside of the tubule and in the interstitial fluids, substances move into the peritubular capillaries or vasa recta by passive processes. The reabsorption of most substances from the tubule to the interstitial fluids requires a membrane-bound transport protein that carries these substances across the tubule cell membrane by active transport. When all of the available transport proteins are being used, the rate of reabsorption reaches a transport maximum (Tm), and substances that cannot be transported are lost in the urine....
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