Osmolarity & Osmotic Pressure

Osmolarity

Concentration of all dilutes in a solution

Units of osmolarity & osmolality

Osmolarity: Osm/L (osmoles per litre)(molar concentration - M)
Osmolality: Osm/kg

What are cell membranes permeable to?

Hydrophobic (lipid soluble) substances
Some small hydrophilic (polar) substances
No large polar substances (glucose)

What makes cell membranes for permeable to water (polar)

Presence of aquaporins (water channel)

Osmotic pressure

Pressure required to prevent osmosis
The greater the solute concentration the greater the osmotic pressure

Explain isosmotic, hyposmotic & hyperosmotic solutions effect on a cell

Isosmotic: cell osmolarity = solution osmolarity (no effect)
Hyposmotic: cell osmolarity > solution osmolarity (cell swells - haemolysis)
Hyperosmotic: cell osmolarity < solution osmolarity (cell shrivels - crenation)

Tonicity

Describes behaviour of cells in solutions

Body fluid osmolarity (mOsm/L)

270-300 mOsm/L

Plasma protein function & example

Plasma proteins provide osmotic pressure to keep fluid in blood vessels
E.g. Transferrin

What is hypoproteinemia & causes & what it causes

Low protein levels in the blood
Caused by liver &/or kidney disease, malabsorption & nutritional lack
Causes oedema

What is cerebral oedema? Causes? What it causes? Treatments?

Fluid accumulates in the brain
Caused by stroke, tumours, trauma...
Intracranial pressure increases - hypoxia, can lead to death
Treatment: osmotherapy (hypertonic solution of mannitol i.v.)