Osmosis & dilution principle Flashcards
How does water move across membranes in the bodY?
Via aquaporins, protein water channels.
Down a concentration gradient.
Why is it important to remember osmolarity is affected by particles not molecules?
Because some solutes dissociate in solution to form multiple particles so the number of molecules isnt always representative of the osmolarity.
What is osmolarity measured in?
Osmoles.
This describes the numver of particles/L, e.g. 1M solution of glucose has an osmolarity of 1 osmol/L
What is the osmolarity of normal human plasma?
285mOsmol/L (the same as in cells); Usually taken as 300mOsmol/L for ease.
What does a change in concentration of a non-penetrating solute cause?
An osmotic flux or immediate net movement of water in one direction r another (changing cell volume)
What are the main non-penetrating solutes in the ECF?
Sodium and Potassium
Osmolarity?
The number of particles in solution
Tonicity?
The number of non-penetrating particles in solution.
What determines cell volume?
Tonicity
Whats an isosmotic solution?
One with the same total no. solute particles as the ECF
Whats an isotonic solution?
One with the same no. non-penetrating solute particles as ECF
Why is the tonicity of normal human ECF close to 285 mOsmol/L?
Because most of the solute particles in the ECF are non-penetratin (Na+/Cl- etc)
Why will a RBC in pure water undergo haemolysis?
- High non-penetrating solute numbers in the RBC ICF
- Water enters cell to try and balance tonicity
- Water causes RBC to swell & burst.
How is plasma volume (PV) measured using the dilution principle?
Plasma proteins cant cross the capillary wall
Therefore dyes or radioactive labels can be attched to plasma proteins.
How is the ECF measured usin the dilution principle?
Needs to be able to cross capillary walls but not cell membranes.
e.g. insulin, sucrose
