Osmolarity And Tonicity Flashcards
Diffusion
Solute in solvent
Particles move randomly (brownian motion) from high concentration of solute to low concentration = down conc grad
Until equilibrium
Osmosis
Diffusion of water across semi - permeable membrane
(Permeable to water but not solute)
From high concentration of water to low concentration
Hydrostatic pressure
Pressure exerted by a stationary object on a fluid
Osmotic pressure
Measure of the tendency for water to move into a solution because of concentration of non-penetrating solutes and water
Relationship between hydrostatic pressure and osmotic pressure
Hydrostatic pressure opposes osmotic pressure
Net movement of water continues until opposing hydrostatic exactly counterbalances osmotic
Molarity
Number of moles in a solution
Mol/L
Osmolarity
Number of particles in a solution
Osm/L
(Cells approx 300 osm/L)
Toncity
Effect the solution has on cell volume
Cell may change shape due to net movement of water (may swell, burst or shrink)
Iso-osmotic
Having the same osmolarity or osmotic pressure in both fluids
Hyperosmotic
Large difference in osmolarity or osmotic pressure between the two fluids
Osmolality
Osmoles per weight (osm/kg)
Used for medical studies
Why is knowing about osmolarity and tonicity etc important?
Water is major constituent of human body and moves between body compartments e.g intracellular to extracellular
Important for kidneys
Useful for clinical investigations e.g. dehydration and kidney function
What is Brownian motion?
Random movement of particles in a fluid due to bumping of other molecules in the fluid
What happens in a membrane is permeable to a solute
Solute will move across the membrane until an equilibrium is reached
E.g.s of osmotic and hydrostatic pressure in the human body
Capillaries
Blood and lymphatic
Arterioles higher blood pressure than osmotic pressure = filtration
Venules lower blood pressure than osmotic pressure = reabsorption
