Osmosis Flashcards
What is meant by osmosis?
The net movement of water from area of high water concentration to area of low water concentration.
There are no barriers to water so the body is in osmatic equilibrium. Water can move freely between ECF and ICF.
What is the difference between osmosis and diffusion?
Diffusion is the movement of solute from area of high solute concentration to area of low solute concentration.
Osmosis is the movement of water.
What happens when we have osmosis but no diffusion?
Cell volume changes.
When we have diffusion we also have osmosis (water and solute move in opposite direction). When we have osmosis we may or may not have diffusion.
What happens when a solution of different concentration is separated by a barrier that is permeable to water only?
After time we will end up with the same concentration on both sides but different volumes (assuming the compartments are expandable).
Osmotic pressure is the pressure that must be applied to oppose osmosis.
What is osmolarity?
The total number of particles in a solution. (Penetrating and non-penetrating particles)
What is tonicity?
The number of non-penetrating particles in a solution.
More important than osmolarity because it affects cell volume.
What is cell volume dependant on?
Concentration of non-penetrating solutes on either side of the membrane.
What does isosmotic mean?
The solution has equal number of total solute particles as normal ECF.
Can be isotonic or hypotonic.
What does hypo-osmotic and hyper-osmotic mean?
Hypo-osmotic - solution with fewer total solute particles than normal ECF. Can only be hypotonic.
Hyper-osmotic - solution with greater total solute particles than normal ECF. Can be hypertonic, hypotonic or isotonic.
What does isotonic mean?
Solution has the same number of non-penetrating particles as normal ECF.
What does hypotonic and hypertonic mean?
Hypotonic - solution has fewer non-penetrating particles than normal ECF.
Hypertonic - solution has greater number of non-penetrating particles that normal ECF.
What happens when you place a RBC in water?
The cell will swell up and burst because water will move into the cell by osmosis due to the presence of non-penetrating particles inside the RBC.
What happens when you place a RBC in a hyper-osmotic aqueous urea solution?
Urea is penetrating, water is penetrating, there is nothing else in the solution. So the solution has no non-penetrating particles and hypotonic.
Urea will equilibulise across the cell membrane.
The RBC has non-penetrating particles inside and so a lower water concentration. Therefore water moves into the cell by osmosis. The cell will swell and burst.
What will happen to the volume of RBC’s in a patient with uraemia (excess urea in their blood)?
There will be no change because urea is a penetrating molecule. It will move into the cell by diffusion and equilibrate. (There is no net movement of particles)
What particles are major in determining the ECF tonicity?
Na+ and Cl-
