Osmosis – the diffusion of solvent (water) across a selectively permeable membrane from an area of less concentration of solutes (such as salt) into an area with a higher concentration of solutes.
If a patient has a drowns in salt water, the salt water in the lungs (which is of a higher solute concentration than blood) will draw fluid from the blood within the alveoli/pulmonary arteries, into the lungs.
Osmotic pressure – the force required to prevent the movement of water by osmosis across a selectively permeable membrane.
Hydrostatic pressure – basically this refers to the pressure that the fluid itself exerts. This means the higher the fluid, the greater the hydrostatic pressure due to the weight of the fluid exerting itself.
Isotonic solution: a solution with the same amount of solutes as the solution outside the selectively permeable membrane. As a result, the fluid does not shift anywhere, but remains constant.
Hypotonic solution: a solution with less solutes than the outside. This causes the fluid to leave the area and shift into an area with a greater concentration of solutes.
As a paramedic, if you were to inject sterile water into a patients vein, the fluid would shift into all the cells within the vasculature because they have a higher level of solutes.
Hypertonic solution: a solution with a higher amount of solutes than the outside area. This results in a shift of fluid from the outside into the area with greater solutes.
In paramedics, this would be like administering 50% Glucose to a patient – because of the high concentration of solutes in the 50% Glucose, fluid from the vasculature will automatically be drawn to that area.
For more examples of osmosis, please visit my examples of osmosis page.