Donnan effect of Ion movement across the capillary wall is due to?
Ans. B. Proteins. (Ref Ganong 23rd pg. no 6 & 7).Because there are more proteins in plasma than in interstitial fluid, there is a Donnan effect on ion movement across the capillary wall.DONNAN EFFECTWhen an ion on one side of a membrane cannot diffuse through the membrane, the distribution of other ions to which the membrane is permeable is affected in a predictable way. For example, the negative charge of a nondiffusible anion hinders diffusion of the diffusible cations and favors diffusion of the diffusible anions. Consider the following situation, in which the membrane (m) between compartments X and Y is impermeable to charged proteins (Prot) but freely permeable to K+ and Cl-. Assume that the concentrations of the anions and of the cations on the two sides are initially equal. Cl- diffuses down its concentration gradient from Y to X, and some K+ moves with the negatively charged Cl- because of its opposite charge. Therefore > Furthermore, + + > + that is, more osmotically active particles are on side X than on side Y.Donnan and Gibbs showed that in the presence of a nondiffusible ion, the diffusible ions distribute themselves so that at equilibrium their concentration ratios are equal:---=---Cross-multiplying, + = + This is the Gibbs-Donnan equation. It holds for any pair of cations and anions of the same valence.The Donnan effect on the distribution of ions has three effects in the body.# First, because of charged proteins (Prot ) in cells, there are more osmotically active particles in cells than in interstitial fluid, and because animal cells have flexible walls, osmosis would make them swell and eventually rupture if it were not for Na, K ATPase pumping ions back out of cells. Thus, normal cell volume and pressure depend on Na, K ATPase.# Second, because at equilibrium the distribution of permeant ions across the membrane (m in the example used here) is asymmetric, an electrical difference exists across the membrane whose magnitude can be determined by the Nernst equation# Third, because there are more proteins in plasma than in interstitial fluid, there is a Donnan effect on ion movement across the capillary wall.
Cations
Proteins
Anions
Albumin
General