205textnotes43

205textnotes43 - • follows Na by osmosis • movement of...

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Unformatted text preview: • follows Na + by osmosis • movement of Na + and other co-transported solutes out of lumen and into the epithelial cell redistributes the total solute concentration between the lumen and epithelial cell • creates an osmotic flow of H 2 0 out of lumen and into epithelial cell via open water channels or via a paracellular pathway by crossing the tight junction that bind adjoining epithelial cells • highest permeability in proximal tubule, less permeable in loop of Henle and distal tubule. Hormonal Regulation of Water Re-absorption : (Figure 20-3, 20-4, 20-5, 20-6, 20-7; Table 20-1) • ADH (anti-diuretic hormone: also called vasopressin ) from posterior pituitary (Figure 20-7) • ADH stimulates production of proteins that compose H 2 0 channels in the collecting duct via cAMP cascade (Figure 20-6) • increased ADH ==> increase H 2 0 re-absorption (Figure 20-5, 20-8) • alcohol decreases ADH secretion • osmoreceptors in the hypothalamus regulate ADH secretion (Figure 20-7)-------------------------------------------------------------------------------------...
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