This is a pretty basic question on osmolality but I just don't understand what the prof was trying to say. So there's this type I diabetic and they injected an insufficient amount of insulin and so now her body can't use the glucose in her blood. Her blood glucose is 30 mM whereas the normal should be around 3.3-5.8 mM. Her body's coping by urinating a lot which is causing her to be dehydrated. The question is should she be treated with water?

This is what my prof said: NO

- b/c water will dilute everything in body
- your gonna give insulin which will cause glucose to come out then all of the sudden not enough solutes in blood
- when glucose comes out of the blood = edema
- she would be given saline .9 soution of nacl = isotonic = same osmality of blood b/c once you give insulin and glucose is taken up by cell, you wanna make sure everything is in the right compartments and by giving in something that is the proper concentration that's what will happen

This makes no sense to me. I don't really understand what she's trying to get across. I really don't understand what she means by "water will dilute everything in body" and "glucose coming out". Could someone please try to clarify this for me? Thanks!

Adding water will make the extracellular concentrations lower because concentration is a variable depending on the amount of solute per litre. As a result, glucose will come out because of diffusion. A hypotonic extracellular concentration will force glucose out to balance relative concentrations, maintaining equilibrium.

So if you give plain water, you're saying that glucose will leave the cells and go into the blood? But wouldn't water simply leave the blood and go into the cell? OR do both processes occur at the same time?

I wasn't thinking straight. I should've said that adding water would cause osmosis to occur and this to happen....
(The one on the right)

...because water would enter the cells - not just the blood cells, but surrounding cells. The problem with diabetes is that insulin is not produced and thus does not get target cells to release the glucose. Without treatment, there is a higher concentration of glucose inside than outside the cell. Insulin is a hormone which allows glucose to exit the cell.

If you treat the patient with water rather than insulin, the molecules that are small enough to diffuse through the membrane will end up leaving the cell, because of lowered extracellular concentrations, which is the problem arising from the first point your professor made. Consequently, water will rush into the cell. Most glucose will not exit the membrane (without insulin).

Originally Posted by justinsftw

I wasn't thinking straight. I should've said that adding water would cause osmosis to occur and this to happen....
(The one on the right)

...because water would enter the cells - not just the blood cells, but surrounding cells. The problem with diabetes is that insulin is not produced and thus does not get target cells to release the glucose. Without treatment, there is a higher concentration of glucose inside than outside the cell. Insulin is a hormone which allows glucose to exit the cell.

If you treat the patient with water rather than insulin, the molecules that are small enough to diffuse through the membrane will end up leaving the cell, because of lowered extracellular concentrations, which is the problem arising from the first point your professor made. Consequently, water will rush into the cell. Most glucose will not exit the membrane (without insulin).

Careful there, insulin DOES NOT cause glucose to exit the cell. It causes glucose uptake by cells! The problem in diabetes is due to a lack of insulin, glucose is not taken up by the cell - resulting in high blood glucose concentrations....

I'm not clear on what your original question is because I don't quite understand your prof's reasoning but here's the thing...

The p/t has a very high [glucose] in the blood, by treating with H2O, essentially you dilute the blood meaning that [H2O] >> [glucose] (in the blood). Therefore, basic laws of science - since solutes flow from high to low concentration, glucose will move out from the cells into the blood to accommodate for the decreased [glucose] in the blood due to administration of water. So yes this would not be an ideal treatment.

NaCl administration would increase the [solutes] in the blood. This would cause the glucose to move into the cell to accommodate for this increased solute concentration.

Originally Posted by SciMania

Careful there, insulin DOES NOT cause glucose to exit the cell. It causes glucose uptake by cells! The problem in diabetes is due to a lack of insulin, glucose is not taken up by the cell - resulting in high blood glucose concentrations....

That's what I was typing on my second post at first, but then I re-read her prof's comments.

Thank you very much, everyone! I really appreciate it!