4- LETS PUT EVERYTHING TOGETHER:

We are going to make it simple. We are going to look at the effects solutions have on the shape of a dialysis bag.

If you know how to do that, you should not have too much trouble when dealing with live systems. In live systems, the dialysis bag would be like your cells, solution B, your intracellular fluid and solution A your extracellular fluid.

  1. Is solution A hypertonic, hypotonic or isotonic to solution B in the dialysis bag?
  2. What are the movements of water between the two compartments?
  3. What is the effect of solution A on the shape of the dialysis bag?
These three questions are identical!

To predict what is happening you have to:

  1. Identify all the different type of solute particles in all the compartments of the system
    (NA+; glucose; Cl-, etc...)
  2. Figure out what each type of solute particles "want to do". Can they do it or not?
    Each type of solute particles want to move along its gradient of Potential Energy until equilibrium is reached (equilibrium means that its Potential Energy is the same in all the compartment).
    Can they do it or not? They can go from one compartment to another only if they are penetrating solute particles.
  3. Make them do it.
  4. THEN, figure out the overall concentration of all the solute particles (or osmolarity) in each compartments
  5. water also moves along its gradient of potential energy.
    Now that you know the osmolarity of the solutions and provided that all the other variables affecting potential energy of water (pressure, temperature etc..) are identical in all the compartments you can predict the movement of water.
  6. Now that you know how water moves, figure out how the shape of the dialysis bag will be affected.

Let see how it all works..