One One osmoleosmole is 1 gram molecular weight of undissociated is 1 gram molecular weight of undissociated solute. solute.

Thus, 180 grams of glucose, which is 1 gram molecular Thus, 180 grams of glucose, which is 1 gram molecular weight of glucose, is equal to 1 osmole of glucose because weight of glucose, is equal to 1 osmole of glucose because

glucose does not dissociate.glucose does not dissociate.Therefore, 1 gram molecular weight of NaCl (58.5 gm) is Therefore, 1 gram molecular weight of NaCl (58.5 gm) is

equal to 2 osmole because NaCl dissociates into Naequal to 2 osmole because NaCl dissociates into Na++ and Cl and Cl-- (and both are osmotically active).(and both are osmotically active).

A solution that has 1 osmole of solute dissolved in 1 A solution that has 1 osmole of solute dissolved in 1

Kilogram of water is said to have an Kilogram of water is said to have an OsmolalityOsmolality of 1 of 1 osmole per kilogram. osmole per kilogram.

A solution that has 1 osmole of solute dissolved in 1 liter A solution that has 1 osmole of solute dissolved in 1 liter

(1000 ml) of water is said to have an (1000 ml) of water is said to have an OsmolarityOsmolarity of 1 of 1 osmole per liter. osmole per liter.

1. Is a measure of the total number of dissolved particles in a solution 2. Ionic composition of the ICF fluid is different from that of ECF

3. But Osmolarity of ICF is equal to that of ECF.

Osmotic equilibrium is maintained rapidly between ICF and ECF

Isotonic fluid gain: e.g Intravenous infusion of isotonic saline (0.9 % NaCl, 5% glcose solution)

Isotonic fluid loss: Hemorrhage No net fluid shift occur

What happens? Water moves out of the cells to ECF until osmotic equilibrium is achieved

Cells shrink as water leaves them Neurons dehydration causes disturbances in brain function manifested as

mental confusion to coma.

What Causes thisWhat Causes this??

Dehydration due toDehydration due to:: Insufficient Insufficient

water intakewater intake Excessive Excessive

water loss water loss (vomiting or (vomiting or

diarrhea)diarrhea) Diabetes Diabetes

Insipidus Insipidus (deficiency of (deficiency of

ADH)ADH)

Accumulation Accumulation of high levels of high levels of osmoticallyof osmotically active solutes active solutes (urea in kidney (urea in kidney

failure)failure)

What happens? Water moves into the cells from ECF until osmotic equilibrium is achieved.

Pronounced swelling of neurons leads to brain dysfunctionSwelling of muscle leads to muscle weakness.

Hypertension and edema caused by expansion of plasma volume.

What Causes thisWhat Causes this??Over hydration: Over hydration:

Renal failure Renal failure with inability with inability

to excrete to excrete diluted urinediluted urine

Excessive drinking Excessive drinking (transient)(transient)

Increase in ADH Increase in ADH secretionsecretion

Water Water intoxication: intoxication:

condition of over condition of over hydration, hydration,

hypotonicity andhypotonicity and cellular swelling cellular swelling

from excess from excess waterwater..

Dye-dilution metod (Indicator-dilution)