Monday, October 16, 2017

Donnan Effect

Hello Awesomites :D

I was reviewing my 1st year physiology notes then I found this topic.
Let us begin. :D

We know that ions move across the membrane depending on 2 gradients :-
1. Concentration gradient (No. Of ions)
2. Electrical gradient (Charge of ions)

 The net movement of ion  is decided by the Electrochemical gradient.

I will do some calculations below. Caution point is when I will talk about electrical neutrality, I consider charge of ions.

Donnan Effect  ON DISTRIBUTION OF IONS has three effects:-
1. Because of charged proteins in cells, there are more osmotically active particles in cells than outside.
So what does it means? Animal cells do not have cell wall. Osmosis would make them swell and eventually rupture.

How to prevent this?
This implies need for evolution of pump (Na-K ATPase) to maintain osmotic equilibrium between cells and interstitial fluid across cell membrane.

2. At equilibrium the distribution of the permanent ions across the membrane is assymetric, an ELECTRICAL difference exists across the membrane.

What does it means?
K+ moves along its concentration gradient (as it is free to move)  lead to electrical disequilibrium.

This disequilibrium influence K+ to move continuously. Chloride also move it's side to equilibrate with charge.

Eventually ion concentration would stabilise (in diagram 64=64)  and individual solute concentration would not change over time (means 6 Na+ 4 Cl- 10 K+ 3 prot4- inside)
Gibbs Donnan force are responsible for development of a membrane charge due to passive process.

3.Because there are more proteins in plasma than in interstitial fluid,there is Donnan effect on ion movement across the capillary wall.

What do you mean by Donnan equilibrium?

Have a great day.
-Upasana Y. :)

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