Can anyone explain to me the following:
If in the case of hypertonicity of the cell, the water will flow out in extracellular compartment and then K+ will follow due to increased difference in the concentration gradient between ICF and ECF. the water will not flow back because K+ contributes little to total osmolality. Am i right?
If in the case sodium ion, water outflow into ECF can cause decrease osmolality of the compartment. But will sodium like potassium also flow out down its concentration gradient?
POtassium: cell membrane is impermeable to potassium, set up according to Na-K ATPase
Sodium: cell membrane is impermeable to sodium, set up accordingot the Na-K-ATPase. Equivical to water. Disorders of sodium are actually disorders of sodium.
You've got a cell, sitting in your body. Hooray. Everything is good. Osmlarity of the blood is normal. Cell is plump, things are moving, the concentration of sodium is about 140 outside the cell, the concentration of potassium is about 4 outside the cell.
Then...
You get
too much "stuff" in the blood (i.e. Hypernatremia, i.e. Hypertonic solution around a normal cell). You lose water. You get dehydrated. Now, there is less water, and more stuff in the blood relative to the cell. If this change is acute, the only thing that shift is water. If you have too much stuff in the blood, i.e., not enough water, water is going to come from inside the cell to the blood to correct. Cell gets dehydrated. What moved? Water. Did sodium? Nope. Did potassium? Nope. Water. Dehydrated cells lead to symptoms.
Or...
You get
too much water in the blood (i.e. hyponatremia, i.e. hypotonic solution around a normal cell). That is, there isn't enough "stuff." If this change is acute, the only thing that will move is water, to balance. IF there is too much water relative to the cell, water is going to move into the cell. The cell swells. Swelling is bad. Swelling leads to symptoms. What moved? Water. Did sodium? Nope. Did potassium? Nope. Water. Water only.
To specifically address your question:
In a hypertonic environment, water will flow out of the cell, as you said. Potassium and Sodium shouldn't move. Unless the hypertonicity is charged, you will not adjust the membrane potential in any way. Na-K-ATPase still works. Concentration gradients are maintained. Unless you are asking about some nuance electrophysiology question,
water flows. Not K. Not Na. Anybody doing Step 1 Board Prep care to chime in?
