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OBJECTIVES: To determine the fragility of the erythrocyte membrane against the hemolytic effect of NaCl solutions of varying concentrations

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PRACTICAL 4: OSMOTIC FRAGILITY OBJECTIVES: To determine the fragility of the erythrocyte membrane against the hemolytic effect of NaCl solutions of varying concentrations. INTRODUCTION: Osmosis is the diffusion of a solvent through a semi-permeable from a region of low solute concentration to a region of high solute concentration. The semi-permeable membrane is permeable to the solvent, but not to the solute, resulting in a chemical potential difference across the membrane which drives the diffusion. That is the solvent flows from the side of the membrane where the solution is weakest to the side it is strongest, until the solution on both sides of the membrane is the same strength (that is, until the chemical potential is equal on both sides). Red blood cells are bound by a membrane, which allows water to pass through while generally restricting the solutes. This process called osmosis, causes cells to shrink due to loss of water when in a hypotonic medium. This results in swelling and ultimately haemolysis as the cell bursts. The osmotic fragility test uses this fact to determine the concentration of solute inside the cell by subjecting it to the hemolytic effects of solutions of different concentrations. MATERIALS: 1. Ten test tube of NaCl (0.85%, 0.75%, 0.65%, 0.55%, 0.50%, 0.40%, 0.35%, 0.20%, 0.10% and 0%) 2. Distilled water 3. Blood 4. ...read more.


Therefore molarity of NaCl is equal to percentage of NaCl solution times 10 divide by RMM of NaCl solution. Concentration of NaCl Percentage of Haemolysis 0.15 0 0.13 2 0.11 11 0.09 14 0.08 31 0.07 79 0.06 85 0.03 92 0.02 96 0.00 100 *Graph should be Concentration of NaCl Vs Percentage of haemolysis Figure: Osmotic fragility curve (concentration of NaCl VS percentage of haemolysis) DISCUSSION: The osmotic fragility test measures the ability of red blood cells to retain their integrity in hypotonic solutions. A solution is hypotonic if its salt concentration is lower than that found in the blood, about 0.9% by weight. The test uses around 10 different hypotonic solutions varying in salinity from 0.1% to 0.9%. Each solution has a small amount of blood added to it. In a hypotonic solution, a red blood cell takes in water, lowering the salinity in the cell until it matches the salinity of the solution. This happens through the process of osmosis. Osmosis is the movement of solvent across a membrane from a lower concentration to a higher concentration. Figure: osmosis occurs on red blood cell. In this case, the solvent is water, the membrane is the membrane of the red blood cell and the concentration of salt in the solution is lower than the concentration in the cell. ...read more.


Recommend testing during a state of prolonged homeostasis with stable hematocrit. Figure: osmotic fragility test. Osmotic fragility of red cells increased in: 1. Hereditary spherocytosis. 2. Acquired spherocytosis. Osmotic fragility decreased in: 1. Thalassemia. 2. Iron deficiency anemia. 3. Sickle cell anaemia. QUESTION: 1. A test tube with blood in it has a particular solution added to it. After several minutes, the solution is not clear anymore, but becomes red. Which solution was added to the blood to obtain this result? 1. 0.9% saline 2. 5% saline 3. Distilled water 1. A 0.8% saline solution would be __________ to the cytosol of a cell. 1. Hypotonic 2. Hypertonic 3. Isotonic 1. If you placed a peeled apple or potato in 5% salt solution, it would: 1. Gain weight 2. Lose weight 3. Stay the same weight CONCLUSION: Osmotic fragility test is a test that measures the resistance to haemolysis of red blood cells (RBC) exposed to hypotonic solutions. RBC is exposed to a series of saline (NaCl) solutions with increasing dilution. The sooner haemolysis occurs; the greater is osmotic fragility of RBC. RBC remains same because it same as RBC concentration, Isotonic solution ? 0.9 % NaCl. RBC burst in hypotonic (< 0.9 % NaCl), and shrink (crenate) in hypertonic solutions (> 0.9 % NaCl). In hypotonic medium a membrane rupture occurs, allowing haemoglobin to exit from the cells. By measuring haemoglobin concentration, the percentage of haemolysis at different NaCl concentrations can be calculated. ...read more.

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