 One osmole is 1 gram molecular weight of undissociated solute.  Thus, 180 grams of glucose, which is 1 gram molecular weight of glucose, is equal to 1 osmole of glucose because glucose does not dissociate.  Therefore, 1 gram molecular weight of NaCl (58.5 gm) is equal to 2 osmole because NaCl dissociates into Na + and Cl - (and both are osmotically active).  A solution that has 1 osmole of solute dissolved in 1 Kilogram of water is said to have an Osmolality of 1 osmole per kilogram.  A solution that has 1 osmole of solute dissolved in 1 liter (1000 ml) of water is said to have an Osmolarity of 1 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 this? Dehydration due to:  Insufficient water intake  Excessive water loss (vomiting or diarrhea)  Diabetes Insipidus (deficiency of ADH) Accumulation of high levels of osmotically active solutes (urea in kidney failure)

What happens ? Water moves into the cells from ECF until osmotic equilibrium is achieved. Pronounced swelling of neurons leads to brain dysfunction Swelling of muscle leads to muscle weakness. Hypertension and edema caused by expansion of plasma volume. What Causes this? Over hydration: Renal failure with inability to excrete diluted urine Excessive drinking (transient) Increase in ADH secretion Water intoxication: condition of over hydration, hypotonicity and cellular swelling from excess water.

Dye-dilution metod (Indicator-dilution)