Osmolarity and tonicity Flashcards
What opposes osmosis
when a difference in hydrostatic pressure between the 2 compartments is created
What is hydrostatic pressure
the pressure exerted by a stationary fluid on an object – a “pushing force”
What is the osmotic pressure of a solution
a measure of the tendency for water to move into that solution because of its relative concentration of non-penetrating solutes and water – a “pulling force”
When does the net movement of water end
until the opposing hydrostatic pressure exactly counterbalances the osmotic pressure.
What is molarity
number of molecules in a solution (Mol/L) (n = m/mr)
What is osmolarity
number of particles in a solution (Osm/L)
How does the difference between molarity and osmolarity depend on the substance - glucose and salt
Glucose – molecules DO NOT separate out in solution therefore molarity and osmolarity are the same. However, NaCl separates out into 2 different ions (Na+ and Cl-) therefore the osmolarity is double the molarity.
What is tonicity
the effect the osmotic pressure gradient has no cell volume I.e., what will happen to the cell
What is an isotonic solution
relative concentration of solutes is the same inside and out of the cell. When a cell is in isotonic solution there is no net movement of water.
What is a hypertonic solution
solute concentration is higher outside the cell, so water leaves the cell causing it to shrink.
What is a hypotonic solution
solute concentration is higher inside the cell so water enters the cell causing it to expand.
What is the difference between osmolarity and osmolality
Osmolarity = osmoles per volume. Osmolality = osmoles per weight (typically kg)
What are the normal plasma values
280-295 mOsm/kg
Why is osmolality important
Investigation of clinical problems e.g., dehydration, kidney function
Water balance disorders - brain
can lead to abnormal brain function, cause: dehydration, cerebral edema
