Diffusion across a cell membrane?

[raid517]

Hi, I'm looking for information on blood and neuron cells. Specifically I need to know how the membrane transport mechanism in blood and neuron cells work? I am aware of concepts such as active diffusion, facilitated diffusion, and simple diffusion.

The task is to look at the membrane transport mechanisms in blood cells and to see how these compare with the membrane transport mechanism in neurons. (Apparently some of these mechanisms differ in some significant ways, but I'm not sure how yet?)

Also what would be a good choice to show these different membrane transport mechanisms? For example would red blood cells be better than white if I wanted to show the full range of the mechanisms involved, or would the reverse be true?

Are there any resources anyone can point to that would give me a nice clear explanation of any of this? Thanks!

 

[somasimple]

From this excellent book :
https://www.amazon.com/dp/0878934391/?tag=pfamazon01-20

A MODEL CELL
It is useful to begin with the model cell shown in Figure 5.1. This cell contains potassium,
sodium, chloride, and a large anion species, and it is bathed in a solution of
sodium and potassium chloride. Other ions present in real cells, such as calcium or magnesium,
are ignored for the moment, as their direct contributions to the resting membrane
potential are negligible. The extracellular and intracellular ion concentrations in
the model cell are similar to those found in frogs. In birds and mammals, ion concentrations
are somewhat higher; in marine invertebrates such as the squid, very much higher
(see Table 5.1). The model cell membrane is permeable to potassium and chloride, but
not to sodium or to the internal anion. There are three major requirements for such a
cell to remain in a stable condition:
1. The intracellular and extracellular solutions must each be electrically neutral. For example,
a solution of chloride ions alone cannot exist; their charges must be balanced
by an equal number of positive charges on cations such as sodium or potassium (otherwise
electrical repulsion would literally blow the solution apart).
2. The cell must be in osmotic balance. If not, water will enter or leave the cell, causing it
to swell or shrink, until osmotic balance is achieved. Osmotic balance is achieved when
the total concentration of solute particles inside the cell is equal to that on the outside.
3. There must be no net movement of any particular ion into or out of the cell.
Question : If quite every cell exchange involves a ionic change (concentration change), how is it possible to maintain the osmolarity or prevent any water flux?

Since diffusion is a ionic move and thus any ion flux involves a concentration change, how is it possible to stop any water flux?