osmosis and osmolality

1. 3.FLUID AND ELECTROLYTE MOVEMENTS
OSMOSIS AND OSMOLALITY
 when two different solutions are separated by a membrane that is impermeable to
the dissolved substances, fluid shifts through the membrane from the region of low
solute concentration to the region of high solute concentration until the solution
are of equal concentrations.
 This diffusion of water causes by a fluid concentration gradient is known as
osmosis.
 The magnitude of this force depends on the number of particles dissolved in the
solutions, not on ia a unit of fluid determines the osmolality of a solution, w/c
influences the movement of fluid between the fluid compartments.
TONICITY - ability of all the solutes to cause an osmotic driving force that promotes
water movement from one compartment to another.
 the control of tonicity determines the normal state of cellular hydration and cell
size.
effective osmoles : (capable affecting water movement)
 sodium
 mannitol
 glucose
 orbitol
Three other terms are associated with osmosis :
 OSMOTIC PRESSURE : amount of hydrostatic pressure needed to stop the flow of
water by osmosis. It is primarily determined by the concentration of solutes
 ONCOTIC PRESSURE : is the osmotic pressure exerted by proteins (albumin)
 OSMOTIC DIURESIS : increase in the urine output caused by the excretion of
substances such as (glucose, mannitol or contrast agents in the urine)

2. DIFFUSION
 natural tendency of a substance to move from an area of higher concentrations to
one of lower concenration
 it occurs through the random movement of ions and molecules
FILTRATION :
 hydrostatic pressure in the capillaries tends to filter fluid out of the intravascular
compartment into the interstitial fluid
 movement of water and solutes occurs from an area of high hydrostatic pressure to
an area of low hydrostatic pressure.
 filtration allows the kidneys to filter 180L of plasma per day.
SODIUM - POTASSIUM PUMP
 sodium concentration is greater in the ECF than in the ICF, and because of this
sodium tends to clear the cell by diffusion.
 this tendency is effect by the sodium-potassium pump, w/c is located in the cell
membrane and actively moves sodium from the cell into the ECF.
conversely, the high intracellular potassium concentration is maintained by pumping
potassium into the cell. by definition, active transport implies that energy must be
expended for the movement occur against a concentration gradient.