Gibbs-Donnan Effect with Example of RBCs in Hyper- or Hypotonic Solutions

00:01 This is actually important.

00:02 I'm gonna talk briefly about the Gibbs-Donnan Effect and what we have on the right side here is an intracellular environment that's got a lot of fixed charge.

00:12 That's because the proteins that are in there have a lot of fixed charge and along with them, are going to be associated ions.

00:19 So, the proteins are indicated as the green-ish diamonds and then, we have potassium and usually, potassium is higher inside a cell than outside.

00:31 We have specific transporters to keep it that way, so, we can transport potassium in and keep it at a higher concentration.

00:39 It's just the way that the cell prefers to work.

00:41 There will be lower levels of sodium on the inside versus the outside.

00:46 Normally with all that fixed charge which is fixed largely negative charge, if the membrane is allowed to do what it wants to do and pores are allowed to do what they want to do, we might have sodium constantly rushing through a pore and coming into the inside of the cell.

01:04 To maintain normal levels of sodium, we have to pump it out and we use a sodium potassium ATPase at the bottom.

01:14 You see it there. We pump out three sodiums for each two potassiums that come in and that's the way we maintain inside and outside with certain concentrations of the important ions.

01:26 If we poison sodium potassium ATPase or we don't make enough ATP, in fact, now, the cell will swell.

01:35 Sodium will go in trying to find all that fixed negative charge on the protein and with it, with those ions comes water.

01:43 And so, the cell will swell and swell, and swell, and we can actually get rupture.

01:46 And when we talk about cell injury in a subsequent topic discussion, we will come back to this point.

01:52 Anyway, this also has ramifications in terms of the red blood cell or the erythrocytes.

01:58 So, the red blood cell basically doesn't have a functional sodium potassium ATPase and it exists in the bloodstream because the bloodstream is isotonic at the same osmotic parameters as the inside of the red blood cell. But if we change that environment by giving water or by getting dehydrated, we will actually change the morphology of the red cells because water is going in or going out. So, here's that example of pathology.

02:27 An unbalanced ionic environment when we cannot pump protons or when we cannot pump sodium ions.

02:34 For example now in the middle, we have a normal isotonic environment.

02:38 That red blood cell, very happy in its normal environment in the blood stream.

02:43 And the environment, the ionic environment inside and outside the cell are matched, so, the amount of water going in and out is matched and we have beautiful little red cells.

02:54 On the other hand, if we get dehydrated, we lose water.

02:57 The extra cellular space within the vessel, within the lumen becomes more ionically charged more sodium, then, we will have a greater concentration and we will see a net efflux of water out and the red blood cells can become crenated.

03:17 They become shriveled up little versions of themselves because we're not able to balance appropriately.

03:22 Conversely, if we put red blood cells into water, we will actually have now a very low concentration of sodium ions outside, very high concentration inside, water will want to go with all of those sodium ions and we'll get swollen cells that can eventually rupture which is why we don't ever administer intravenously water.

03:43 We have it always with sodium and chloride and in many cases, glucose to provide an isotonic solution.