Biology 1201A Lecture Notes - Lecture 34: Cotransporter, Collecting Duct System, Peritubular Capillaries

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Secondary active transport in the nephron: the proximal tubule has a brush border, with the glomerular filtrate entering the lumen of the nephron. Na+ out (using atp) and takes in 2 k+: this active pumping out of na+ means we"ll have a lower na+ concentration inside the cells of the tubule wall than inside the lumen. Na+ wants to leave the lumen, then, to go into the cell: a co-transporter symporter on the apical membrane takes advantage of this concentration gradient. In this case, it drives reabsorption of ca2+ through an antiporter. (the apical membrane of the cells of the tubule wall is porous to ca2+: recall that the peritubular capillaries run parallel to these tubules Thanks to the na+/k+ pump, the concentration of na+ in the capillary blood is higher than in the cell, so na+ will want to go back in. When na+ moves in, the ca2+ is simultaneously moved up its gradient (in opposite direction).

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