Physiology 3120 Lecture Notes - Proximal Tubule, Sodium Channel, Uniporter
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Monday, November 2, 2009
Ionic Mechanisms of the Tubules
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)
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
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
Filtrate more dilute when it leaves than when it enters
•Distal convoluted tubule
Membrane permeable to ions (Na, Cl, Ca), not permeable to water
Ions reabsorbed by. . .
Na/Cl symporter on luminal membrane
Na channel (luminal membrane)
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