Osmotic Fragility Test, Exercises of Physiology

Download Osmotic Fragility Test and more Exercises Physiology in PDF only on Docsity! Osmotic Fragility Test October 2018 Physiology Lab-5 Asst. Lec. Zakariya A. Mahdi MSc Pharmacology Osmosis  Osmosis is the spontaneous net movement of solvent molecules through a semi-permeable membrane into a region of higher solute concentration, in the direction that tends to equalize the solute concentrations on the two sides. Isotonic solution  Isotonic solution: A solution that has the same salt concentration as cells and blood.  When cells are in isotonic solution, movement of water out of the cell is exactly balanced by movement of water into the cell. A 0.9% solution of NaCl (saline) is isotonic to animal cells. Hypertonic solution  In a hypertonic solution the total molar concentration of all dissolved solute particles is greater than the concentration in a cell.  If concentrations of dissolved solutes are greater outside the cell, the concentration of water outside is correspondingly lower. As a result, water inside the cell will flow outwards to attain equilibrium, causing the cell to shrink. Hypotonic solution  In a hypotonic solution the total molar concentration of all dissolved solute particles is less than that of a cell.  If concentrations of dissolved solutes are less outside the cell than inside, the concentration of water outside is correspondingly greater. When a cell is exposed to such hypotonic conditions, there is net water movement into the cell. Why the Test is performed؟ • This test is performed to detect thalassemia and hereditary spherocytosis . • Hereditary spherocytosis is a common disorder in which red blood cells are defective because of their round, ball- like (spherical) shape. These cells are more fragile than normal because they are less likely to expand. Why the Test is performed؟  Cells that are flatter than normal are more likely to expand, and thus have decreased osmotic fragility .  Thalassemia is an inherited condition that affects the portion of blood (hemoglobin) that carries oxygen. Why the Test is performed?  The test only indicates that a proportion of the red cells have decreased surface-to-volume ratios and are more susceptible to lysis in hypo- osmotic solutions.  Cells with increased surface-to-volume ratios, such as occur in thalassemia and iron deficiency, may show decreased osmotic fragility. Observation and Results : • Red cells in hypertonic saline. In hypertonic solutions, the RBCs , like other body cells, shrink (crenate) due to movement of water out of the cells (exosmosis). • Red cells in hypotonic saline. In hypotonic saline, water moves into the red cells (endosmosis). They swell up and lose their biconcave shape, becoming smaller and thicker. When they swell and become completely spherical, further increase in volume is not possible without an increase in their surface area. Discussion . Normal Range of Fragility • Normally, hemolysis begins in about( 0.45%) saline. • Hemolysis will be complete at 0.3 % NaCl. • No cells hemolyze in solutions of 0.5% saline and above. Medical applications A ) Increased red cell fragility (increased tendency to hemolysis) :It is seen in the following conditions: 1. Hereditary spherocytosis. 2. Autoimmune hemolytic anemia. 3. Toxic chemicals, poisons, infections, and some drugs (aspirin). 4. Deficiency of glucose 6-phosphate dehydrogenase (G6D).