Osmolarity and Osmotic Disturbance 2024 Lecture Notes PDF

SI2101 - LECTURE 5 Osmolarity and osmotic disturbance Leo Quinlan, Cell Physiology Research Lab FLUID COMPARTMENTS WHAT ELECTROLYTES ARE FOUND WHERE ?  What is osmolarity What is osmotic pressure What determines uid movement across cell membranes Examples of Osmotic disturbanc...

SI2101 - LECTURE 5 Osmolarity and osmotic disturbance Leo Quinlan, Cell Physiology Research Lab FLUID COMPARTMENTS WHAT ELECTROLYTES ARE FOUND WHERE ?  What is osmolarity What is osmotic pressure What determines uid movement across cell membranes Examples of Osmotic disturbance Osmolarity calculations LEARNING OUTCOMES FOR TODAY fl WHAT IS OSMOLARITY ? Simply a count of the number of dissolved particles. Also Measures effective gradient for water. Normal osmolarity approx 300mOsmolar Comparing Osmolarity Isosmotic = solutions with same osmolarity Hyperosmotic = solution with greater osmolarity Hypoosmotic = solution with lesser osmolarity  Osmoles = number of dissociated impermeable particles in solution, regardless of charge. Substances that do not dissociate (e.g. glucose), osmolarity = molarity E.g. 150mMolar Glucose = 150mOsmolar Substances that dissociate osmolarity = No. free particles X molarity. E.g. 1 M NaCl = 2 Osmolar (1 for Na, and 1 for Cl). osmolarity = osmoles per liter osmolality = osmoles per kg water CALCULATING OSMOLARITY  FLUID MOVEMENT Fluid movement is caused primarily by pressure gradients. Microscopic Osmotic differences i.e [water] differences Macroscopic Hydrostatic pressure i.e blood owing through arteries. Movement is equal to pressure gradient, the area, and the leakiness of the barriers. fl  Net diffusion of H2O across a membrane = osmosis The “concentration” of pure water is 55.5M 1M glucose solution is approximately 54.5M water. When solute (glucose) is added the actual [water] is reduced - less water molecules per unit area OSMOSIS  Diffusion of water down its concentration gradient. Most membranes freely permeable to water Water channels also exist “aquaporins” 2003, Peter Agre won the Nobel Prize for discovery. OSMOLARITY AND OSMOSIS Osmotic Pressure is the pressure required to prevent osmosis OSMOTIC PRESSURE is generated by a solution when separated from another solution by a semi-permeable membrane. The solution must consist of a solvent (H2O) which is freely permeable and at least one solute which is not.  OSMOTIC EFFECTS Isosmotic Experiment Volume = 1 nL Volume = 1 nL Volume = 1 nL Place a cell in 300 mM Sucrose 300 mOsM 300 mOsM P P 300 mM Sucrose H2O H2O 300 mM Sucrose  OSMOTIC EFFECTS Hypoosmotic Experiment Volume = 1 nL Volume = 2 nL Place a cell in 150 mM Sucrose 300 mOsM 300 mOsM P P 150 mM Sucrose H2O H2O 150 mM Sucrose  OSMOTIC EFFECTS Isosmotic Experiment Volume = 1 nL Volume = 1 nL Volume = 1 nL Place a cell in 150 mM NaCl 300 mOsM 300 mOsM P P 150 mM NaCl H2O H2O 150 mM NaCl  Calcium Chloride (CaCl₂) Solution Problem: Calculate the osmolarity of a 0.5 M CaCl₂ solution. Think; how many particles ? whats concentration of each particle Solution: CaCl₂ dissociates into three ions: one Ca²⁺ and two Cl⁻. Therefore, 1 mole of CaCl₂ produces 3 osmoles of particles. Osmolarity = Molarity × Number of particles per formula unit Osmolarity = 0.5 M × 3 = 1.5 Osm/L OSMOLARITY CALCULATIONS  Mixture of Solutes Problem: Calculate the osmolarity of a solution containing 0.2 M NaCl and 0.1 M glucose. Think; how many particles ? whats concentration of each particle Solution: Solution: NaCl dissociates into two ions: Na⁺ and Cl⁻, so 0.2 M NaCl = 0.2 M × 2 = 0.4 Osm/L. Glucose does not dissociate, so 0.1 M glucose = 0.1 Osm/L. Total osmolarity = Osmolarity of NaCl + Osmolarity of glucose Total osmolarity = 0.4 Osm/L + 0.1 Osm/L = 0.5 Osm/L OSMOLARITY CALCULATIONS  Blood Plasma; Sodium (Na⁺): 140 mM, Chloride (Cl⁻): 100 mM, Glucose: 5 mM, Potassium (K⁺): 4 mM, Urea: 5 mM Calculation: - Sodium and chloride are the primary contributors to osmolarity, and they dissociate into ions. - Sodium: 140 mM contributes 140 mOsm/L (since it dissociates into one ion). - Chloride: 100 mM contributes 100 mOsm/L. - Glucose: 5 mM contributes 5 mOsm/L (does not dissociate). - Potassium: 4 mM contributes 4 mOsm/L. - Urea: 5 mM contributes 5 mOsm/L (does not dissociate). Total osmolarity = 140 + 100 + 5 + 4 + 5 = 254 mOsm/L OSMOLARITY CALCULATIONS  Intravenous (IV) Saline Solution; Sodium Chloride (NaCl): 0.9% w/v (approximately 154 mM) Calculation: - NaCl dissociates into Na⁺ and Cl⁻, contributing two particles per formula unit. - NaCl: 154 mM × 2 = 308 mOsm/L Total Osmolarity: = 308 mOsm/L OSMOLARITY CALCULATIONS  Human Urine; Sodium (Na⁺): 50 mM, Chloride (Cl⁻): 50 mM, Urea: 200 mM, Potassium (K⁺): 30 mM Calculation: - Sodium: 50 mM contributes 50 mOsm/L. - Chloride: 50 mM contributes 50 mOsm/L. - Urea: 200 mM contributes 200 mOsm/L (does not dissociate). - Potassium: 30 mM contributes 30 mOsm/L. Total osmolarity = 50 + 50 + 200 + 30 = 330 mOsm/L OSMOLARITY CALCULATIONS  Dehydration is caused by loss of water without adequate replacement, often due to excessive sweating, diarrhea, vomiting, or insuf cient uid intake. Effects: - Increased osmolarity of blood and extracellular uid. - Water moves out of cells to balance the osmotic gradient, leading to cell shrinkage. - Dry mouth, thirst, decreased urine output, and in severe cases, confusion and organ dysfunction. Overhydration (Water Intoxication) caused by excessive water intake, often in a short period, or impaired water excretion due to kidney problems. Effects: - Decreased osmolarity of blood and extracellular uid. - Water moves into cells, causing them to swell. - headache, nausea, confusion, seizures, and in severe cases, coma. OSMOTIC DISTURBANCE fi fl fl fl  Hypernatremia caused by high sodium levels in the blood, often due to inadequate water intake, excessive salt intake, or loss of water through diarrhea or sweating. Effects: - Increased osmolarity of blood. - Water moves out of cells, causing them to shrink. - Symptoms include thirst, confusion, muscle twitching, and in severe cases, brain damage. Hyponatremia caused by low sodium levels in the blood, often due to excessive water intake, certain medications, or conditions like heart failure or kidney disease. Effects: - Decreased osmolarity of blood. - Water moves into cells, causing them to swell. - Symptoms include headache, nausea, confusion, seizures, and in severe cases, coma. OSMOTIC DISTURBANCE  Diabetic Ketoacidosis (DKA) caused by a complication of diabetes where high blood sugar levels lead to the production of ketones, causing acidosis. Effect:s; - Increased osmolarity due to high glucose and ketone levels. - Water moves out of cells to balance the osmotic gradient. - Symptoms include dehydration, frequent urination, abdominal pain, and in severe cases, coma. Syndrome of Inappropriate Antidiuretic Hormone (SIADH) caused by excessive release of antidiuretic hormone (ADH), leading to water retention. Effect: - Decreased osmolarity of blood. - Water retention leads to dilutional hyponatremia. - Symptoms include nausea, headache, confusion, and in severe cases, seizures. OSMOTIC DISTURBANCE  What is osmolarity What is osmotic pressure What determines uid movement across cell membranes Examples of Osmotic disturbance Osmolarity calculations LEARNING OUTCOMES FOR TODAY fl