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Ionic mechanisms of kidney tubules

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Western University
Physiology 3120
Tom Stavraky

Human Physiology Monday, November 2, 2009 “Renal IV” Ionic Mechanisms of the Tubules • Ion concentrations  Sodium in the filtrate is derived from plasma, so also high (~150mM); therefore, sodium wants to leave the filtrate & enter the tubule cells (if channels available) • Proximal tubules (***CHART/DIAGRAM***)  65% filtrate reabsorbed here  Sodium reabsorbed via. . .  Sodium/amino acid symporter (luminal membrane) • Luminal membrane = membrane facing the tubule  Sodium/proton exchanger (luminal membrane); regulated hormonally • 1 sodium in, 1 hydrogen out  Maintenance of sodium concentration gradient via. . .  Sodium/potassium ATPase (basolateral membrane); regulated hormonally  Water moves into tubule cells  Water channels (aquaporins I); luminal & basolateral membranes  Paracellular (in between cells) movement of water  Almost all glucose reabsorbed in the proximal tubule via. . .  Sodium/glucose sympoter (luminal membrane)  Glucose uniporter (basolateral membrane)  Miscellaneous items  Amino acid uniporter (basolateral membrane)  Paracellular movement of potassium & chloride out of the filtrate • Descending loop of Henle  Almost only water is reabsorbed here via. . .  Water channels (aquaporin I);  Very few sodium moves, almost negligible, via. . .  Few sodium channels (luminal membrane)  To maintain concentration of sodium, need sodium/potassium ATPase on the basolateral membrane  Filtrate more concentrated when it leaves than when it enters (water removed) • Ascending loop of Henle  Membranes impermeable to water (no water channels)  Lots of sodium reabsorbed (also some potassium & chloride) via. . .  Sodium channels (luminal membrane)  Paracellular movement of sodium  Na/K/2Cl symporter (luminal membrane)  K/Cl symporter (basolateral membrane)  Na/K ATPase maintains concentration gradients (basolateral membrane)  Some potassium secretion through potassium channels
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