Forces Acting Across Membranes 3 Flashcards
Osmosis
Net movement of H2O from regions of high H2O concentration to regions of low H2O concentration
Diffusion
Net movement of solute from regions of high solute concentration to regions of low solute concentration
How is osmotic equilibrium maintained?
By the free movement of water
What will happen if a solution of different concentration is separated by a membrane permeable to H2O and the solute?
After a time there will be and equal concentration and an equal volume either side of the membrane
What will happen if a solution of different concentration is separated by a membrane permeable to only H2O?
After a time there will be equal concentrations either side of the membrane by different volumes
Osmotic pressure
The pressure required to prevent water movement
Why are cell membranes regarded as semi-permeable?
They are permeable to H2O and gases but some molecules in the ECF and ICF are unable to cross the membrane
Where do ions exchange readily?
Between the plasma and ISF
Why is the distribution of ions not equal across the ECF and ICF?
They do not penetrate the membrane
What determines the osmotic effect on H2O?
The number of solute particles
Osmolarity
Total number of particles in solution
What is the osmolarity of normal human plasma?
285mOsmol/L (often taken as 300) the same as within cells
What happens if there is a change in concentration of a solute that cannot cross the membrane?
Produces osmotic flux, causing a net movement of water n one direction or the other which changes the cell volume.
What is the volume of a cell at any time dependent on?
The concentration of non-penetrating solutes on either side of the membrane
What are non-penetrating particles of the ECF?
Na and Cl
