Editing Tubular reabsorption & secretion
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*Mostly passive movement of solutes and water down their concentration gradients moves them from the tubular cell into the interstitial fluid between the tubular cells and the endothelial cells of the peritubular capillaries. | *Mostly passive movement of solutes and water down their concentration gradients moves them from the tubular cell into the interstitial fluid between the tubular cells and the endothelial cells of the peritubular capillaries. | ||
**Recall that there are two sets of capillaries in the kidney: glomerular and peritubular. | **Recall that there are two sets of capillaries in the kidney: glomerular and peritubular. | ||
- | *'''Movement of these reabsorbed solutes and water molecules from the ICF ( | + | *'''Movement of these reabsorbed solutes and water molecules from the ICF (intercellular fluid) to the blood is (of course) determined by the four Starling forces''': |
**Hydrostatic pressure of the blood and colloid osmotic pressure of the ICF force solutes to stay in the ICF. | **Hydrostatic pressure of the blood and colloid osmotic pressure of the ICF force solutes to stay in the ICF. | ||
***The hydrostatic pressure of the blood in the peritubular capillaries is much lower than it was at the glomerular capillaries. | ***The hydrostatic pressure of the blood in the peritubular capillaries is much lower than it was at the glomerular capillaries. | ||
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**Principle cells reabsorb Na and water while excreting K. | **Principle cells reabsorb Na and water while excreting K. | ||
**K secretion make sense because the Na / K ATPase on the basal surface of the principal epithelial cell generates a flow of Na into the blood (reabsorption, which H20 follows) and a flow of K out into the filtrate. | **K secretion make sense because the Na / K ATPase on the basal surface of the principal epithelial cell generates a flow of Na into the blood (reabsorption, which H20 follows) and a flow of K out into the filtrate. | ||
- | + | "K+ secretion is increased when urine flow increased due to diuretic action (problem of K+ wasting)." | |
- | + | What is causing the diuretic action? | |
- | ** | + | Why is K+ secretion increased? |
- | * | + | **Note: the more concentrated the urine, the more K+ lost. |
+ | ***This makes sense because concentrated urine occurs when Na reabsorption is high and when Na reabsorption is high, we know that lots of K+ is being exchanged for Na+. | ||