Physiological Solutions and Osmosis PDF

Fick’s principle Volume of compartment = amount of injected indicator divided by concentration of indicator in plasma Properties of indicator: 1. Inert 2. Non toxic 3. Well mixed 4. Easily to be measure 5. Unchanged or not used by body tissue 6. Doesn’t affect distribut...

Fick’s principle Volume of compartment = amount of injected indicator divided by concentration of indicator in plasma Properties of indicator: 1. Inert 2. Non toxic 3. Well mixed 4. Easily to be measure 5. Unchanged or not used by body tissue 6. Doesn’t affect distribution of water or substances in body tissue TBW indicator: 1. Penetrate blood plasma 2. Pass to ISF 3. Pass to ICF Examples: 1. Deuterium oxide or heavy water 2. Trillium oxide 3. Antipyrine or aminopyrine ECF indicator: 1. Penetrate blood plasma 2. Pass to ISF 3. Doesn’t pass to ICF Examples: 1. Inulin 2. Sodium thiocyanate IVF indicator: 1. Doesn’t penetrate blood plasma 2. Doesn’t pass to ISF 3. Doesn’t pass to ICF Examples: 1. Evan’s blue dye 2. Fibrinogen and albumin with radioactive iodine ICF is calculated indirectly (ICF = TBW-ECF) ISF is calculated indirectly (ISF = ECF – IVF) Osmosis Osmosis is the movement of water from area of low conc to area of high conc of solutes or from area of high conc to area of low conc of water (it is a specialized type of simple diffusion) Osmotic pressure: 1. It equals osmotic force 2. It stops osmosis 3. It is measured in mmHg 4. It depends on number (not size or mass) of molecules Mole: molecular weight of substance in grams Osmole: number of particles in one mole Osmolarity: number of osmoles in L of water Osmolality: number of osmoles in Kg of water Tonicity: osmolality of solutions relative to osmolality of plasma Osmolarity of ICF = osmolarity of ECF = 300 mOsm/L Clinical importance of plasma osmolarity: 1. Urine excretion 2. Blood volume 3. Irrigation of wounds by isotonic solutions 4. Diagnosis of Edema and osmotic diuresis Equilibrium potential Factors determining diffusion potential: 1. Polarity of electrical charge of ion 2. Concentration of ion inside and outside of membrane 3. Permeability of membrane to this ion Gibbs donnan equilibrium Significance of Gibbs Donnan equilibrium: 1- Because of charge proteins in cell, there are more osmotically active particles in cells than in ISF. Because cells have flexible membrane, osmosis makes them swell then rupture if Na-Ka ATPase pump doesn’t pump ions back out of the cell. Volume and pressure of cells is handled by Na-Ka ATPase pump. 2- Because at equilibrium, the distribution of ions across cell membrane is asymmetric, electrical difference across cell membrane exists whose magnitude is calculated by Nernst equation. In the figure shown in the department bock, the protein compartment X is more negative than the non-protein compartment Y. consequently, ions movement lines up across cell membrane. The ions movement is balanced when the concentration and electrical gradients are equal such as movements of Cl- and K+. 3- Because there are more charged proteins in cells than in ISF, there is donnan effect on ions movement across blood capillary. Physiological solutions Normal saline 0.9% NaCl: 1- Vehicle for parental drugs 2- Sterile irrigation medium 3- Electrolyte replenished fluid 4- Replacement for ECF defects Ringer’s solution 0.6 saline (found in amphibian tissues such as frog): 1- Vitro experiments on organs and tissues 2- Vitro muscle testing 3- Replacing ECF Tyrode’s solution 0.8 saline: 1- Culture medium 2- Irrigation of peritoneum Isotonic solution: Its conc of solute and water equals conc of solute and water of plasma No movement of water between plasma and solution, size of cells is kept constant Examples: 1- Normal saline 0.9% NaCl 2- 5% dextrose in water (D5W) 3- Lactated ringer’s solution Importance: 1- Inc volume of ECF 2- Used in fluid loss 3- Used in surgery 4- Used In dehydration 5- The risk of fluid is overload when a patient with hypertension or heart failure receives isotonic solution IV Hypotonic solution: Compared to plasma, it has higher conc of water and lower conc of solutes Movement of water from the solution to the cells which are swelled and ruptured Examples: 1- 0.33% saline 2- 0.225% saline 3- 0.45% saline Importance: 1- Intracellular dehydration 2- Diabetic ketoacidosis (DKA) 3- Hyperosmolar hyperglycemia Hypertonic solution: Compared to plasma, it has higher conc of solutes and lower conc of water Movement of water from cells to the solution, results in shrinkage of cells Examples: 1- 3% saline 2- 5% saline 3- 10% dextrose in water Importance: 1- Isolating living tissues Osmotic fragility test Clinical significance of osmotic fragility test (diagnosing of particular diseases): Hereditary spherocytosis Cells are much more fragile and spherical in shape. They start hemolysis at 0.75% saline and complete hemolysis at 0.5% saline B-thalassemia and iron deficiency anemia Cells are more rigid. They start hemolysis at 0.4% or 0.3% saline Sickle cell anemia Cells are much more rigid. They start hemolysis at 0.1% saline Factors affecting the fragility of RBCs: The fragility of RBCs depends on S/V or surface area to volume ration. In other words, the higher S/V ration gives RBCs the ability to accommodate much more volume without rupture or lysis The benefits of RBCs being biconcave in shape: It produces larger surface area than spherical cells It enhances flexibility of cells allowing RBCs to be squeezed in small capillaries without rupture It results in minimal tension to increase their volume in venous blood due to carriage of CO2 from tissues it gives RBCs the ability to increase their volume up to 70% before the membrane is stretched to critical lever to cause lysis