Forces Acting Across Membrane 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
What are non-penetrating particles of the ICF?
K and organic anions
Tonicity
The number of non-penetrating particles in solution
Isosmotic
A solution which has the same total number of solute particles as ECF
Hypo-osmotic
Solutions with fewer total solute particles
Hyper-osmotic
Solutions with greater number of total solute particles
Isotonic
A solution which has the same number of non-penetrating solute particles as ECF
Hypotonic
Solutions with fewer non-penetrating solute particles
Hypertonic
Solutions with greater number of non-penetrating particles
What determines tonicity?
Non-penetrating particles
What determines osmolarity?
Penetrating and non-penetrating particles
What is most of the 285mOsmol/L in the ECF attributed to?
The presence of Na and Cl which are non-penetrating particles therefor the tonicity of ECF is close to 285 mOsmol/L
What do plasma samples in the hospital give information about?
Osmolarity but not tonicity
What is the best fluid to administer?
0.9% saline (150mM) as it is isotonic
