The McGill Physiology Virtual Lab

Blood Laboratory

Red cell fragility > Osmotic hemolysis
  Cell membranes are semipermeable barriers, and osmotic gradients are established between intracellular and extracellular fluids which can cause water to flow into and out of the cells. The amount of osmotic pressure depends upon the difference between the concentration of non-diffusible ions on each side of the membrane.
The theoretical background for this exercise is to be reviewed in your text book.
The intracellular fluid of erythrocytes is a solution of salts, glucose, protein and hemoglobin. A 0.9% NaCl solution is said to be isotonic: when blood cells reside in such a medium, the intracellular and extracellular fluids are in osmotic equilibrium across the cell membrane, and there is no net influx or efflux of water.

When subjected to hypertonic media (e.g. 1.8% NaCl), the cells lose their normal biconcave shape, undergoing collapse (leading to crenation) due to the rapid osmotic efflux of water.

On the other hand, in a hypotonic environment (e.g. 0.4% NaCl or distilled water), an influx of water occurs: the cells swell, the integrity of their membranes is disrupted, allowing the escape of their hemoglobin (hemolysis) which dissolves in the external medium.



In this experiment, we make use of the property that the osmotic fragility (or susceptibility to hemolysis) of erythrocytes is not uniform, and the number of cells undergoing hemolysis depends on the degree of hypotonicity of the extracellular medium. The concentration of liberated hemoglobin in each test medium is an index of the extent of osmotic hemolysis. Your task is to examine the relationship between extent of hemolysis and osmolarity of the medium in which the erythrocytes are suspended.

To continue with the procedure of erythrocyte fragility, click here