P1 Osmosis & Osmotic Pressure PDF

P1.Osmosis & Osmotic pressure The students should be able to: ▪ Calculate osmotic pressure of a given solution. ▪ Demonstrate effect of changes of tonicity of solutions on cell size. ▪ Mention the osmotic fragility test. 1 ...

P1.Osmosis & Osmotic pressure The students should be able to: ▪ Calculate osmotic pressure of a given solution. ▪ Demonstrate effect of changes of tonicity of solutions on cell size. ▪ Mention the osmotic fragility test. 1  Osmotic Pressure ❖ Definition: It is the pressure needed to stop osmosis. ❖Importance: It is used to measure osmosis force. ❖ It depends on the number of dissolved solutes. ❖ To calculate the osmotic pressure of a solution: 1. Calculate the number of milli-osmole of substance/ liter. 2. Multiply calculated number of milliosmoles by 19.3. 2 1.Calculation of the number of milli-osmole of substance/ liter : This will depend if this substance is dissociated or not as follow: A. One milli-mole of un- dissociated substance = One milli-osmole EX: One milli-mole of glucose  will give one milli-osmole. B. One milli-mole of dissociated substance  will give > one milli-osmole. EX: One mole of NaCl = will give two milli-osmoles. 2. Multiply the calculated number of milliosmoles by 19.3 , why? ▪ As each 1 milli-osmole / L causes 19.3 mmHg osmotic pressure.  Activity 1 Calculate the osmotic pressure of the following solutions: Solution Osmotic pressure - Number of milliosmole / L = 2 - One millimole (Na Cl) /L - So osmotic pressure = 2 x 19.3 = 38.6 mmHg - Number of milliosmole / L = 3 - One millimole ( Ca Cl 2) /L - So osmotic pressure = 3 x 19.3 = mmHg - Number of milliosmole / L = 3 - Three millimole glucose / L - So osmotic pressure = 3 x 19.3 = 57.9 mmHg.  Tonicity ▪ Tonicity: Is the osmolality of any solution relative to plasma. ▪ Solutions are 3 types according to its tonicity: Solution Isotonic Hypertonic Hypotonic solution solution solution 5 1.Isotonic solution: Has same osmolality as plasma = 290 milliosmole /L. Effect: It causes no change in cell volume as it has same osmolarity of cells. 2. Hypotonic solution : Has osmolality < plasma ( i.e it means more diluted). Effect: It causes movement of water into cells  in cell swelling. 3. Hypertonic solution: Has osmolality > plasma (i.e concentrated) Effect: It causes movement of water out of cells  cell shrinkage. 7  Hypertonic solution Isotonic solution Hypotonic solution Type of solution ▪More than 5 % glucose ▪ 5% glucose ▪Less than 5 %glucose Concentration ▪More than 0.9% Na Cl ▪ 0.9 % NaCl ▪Less than 0.9% NaCl of solution Effect on cell Causes cell shrinkage Does not change Causes cell swelling shape shape of cell  Activity 2 Red blood corpuscles of a normal person were placed in a solution. Arrows indicate the direction of movement of water molecules. A. What is the tonicity of the used solution? B. If the used solution was glucose, what is the concentration of this solution? Osmotic fragility of Reb blood cells(RBCs) AS Biology, Cell membranes and Transport 10  OSMOTIC FRAGILITY OF RED BLOOD cells(RBCs) ❖ Definition: Ability of the red blood cells to resist hemolysis when suspended in hypotonic saline. ❖ Significance : This test determines osmotic fragility of RBCs. ❖Procedure: 1.Prepare dilutions of buffered Na-Cl and place it in the labeled test tube. 2. One drop of blood is added to each tube. 3. Wait for one hour. ❖Results in normal conditions: 1. Hemolysis starts at 0.5% NaCl. 2. Hemolysis is complete at 0.3% NaCl. ❖Explanation: 1. When RBCs are suspended in hypotonic saline  water diffuses into cells  their swelling and may rupture (= hemolysis). 2. However, red cells are not ruptured at the same time, Why? Because ,older red cells are more fragile than young ones & rupture earlier. So hemolysis starts normally at 0.5 % & completed at 0.3 % NaCl solution. ❖ Clinical importance: - Osmotic fragility of RBCs is abnormally increased in congenital spherocytosis. - Hemolysis starts early at 0.7% and is completed at 0.5. NB: - Hereditary spherocytosis causes problems with the outer layer of RBCs  So red blood cells become more fragile  causing their early destruction  this causes anemia. AS Biology, Cell membranes and Transport 15 AS Biology, Cell membranes and Transport 16 OSMOTIC FRAGILITY OF RED BLOOD cells(RBCs) AS Biology, Cell membranes and Transport 17 18