Module 5 - Fluid Balance - Lecture 2 Flashcards
What group of membrane protein is found in most cell membranes?
Aquaporins
What is osmosis?
The diffusion of water molecules from a region of high concentration to a region of low water concentration
How do you work out the water concentration of a litre of pure water?
Litre of pure water weighs 1000g and the molecular weight of water is 18, so 1000/18 = 55.5M
How do you reduce the water concentration?
By the addition of a solute such as glucose dissolved in water.
How is the concentration of biological solutions measured in?
Osmoles (1osmol is equal to the number of solute particles and describes the osmolarity of a solution ie the number of particles in a solution
What is osmotic flux?
Is when a solute cannot pass through the cell membrane, so any changes in the concentration produces an osmotic flux which changes the volume of the cell
Non-penetrating solutes
In ECF, sodium ions (Na+) and chloride ions (Cl-)
In ICP, potassium ions (K+) an organic anions
Selective Barrier
A cell membrane is a selective barrier permeable to some substances but not all. There is no barrier to water
What is osmotic pressure?
When a solution containing non-penetrating solutes is separated from pure water by a membrane, pressure must be applied to the solution to prevent flow of water into the solution
Increase in osmotic pressure
- greater osmolarity the greater the osmotic pressure
- lower the water concentration the higher the osmotic pressure
What determines the tonicity of the solution?
The number of non-penetrating solute particles, those which cannot cross the cell membrane
What is isotonic?
Isotonic is when a cell is placed in a non-penetrating solution of 300mOsm will neither swell or shrink
What is hypotonic?
When a cell is placed in a non-penetrating solution of <300mOsm will cause cells to swell
What is hypertonic?
When a cell is placed in a non-penetrating solution of >300Osm will cause cells to shrink
