1. Body Fluid Compartments Body Fluid Compartments and and Fluid Balance Fluid Balance

2. Objectives Objectives 1. Differentiate between the terms osmole, osmolarity, osmolality and tonicity. 1. Differentiate between the terms osmole, osmolarity, osmolality and tonicity. 2. List the typical value and normal range for plasma osmolality. 2. List the typical value and normal range for plasma osmolality. 3. Explain osmosis in terms of a differentially permeable membrane. 3. Explain osmosis in terms of a differentially permeable membrane. 4. Understand the concepts of osmosis and osmotic pressure. 4. Understand the concepts of osmosis and osmotic pressure. 5. Define tonicity and be able to use the terms isotonic, hypertonic, and hypotonic. 5. Define tonicity and be able to use the terms isotonic, hypertonic, and hypotonic. 6. State the water content of the body, and its physiological variations with age, fat content and gender 6. State the water content of the body, and its physiological variations with age, fat content and gender 7. Understand the distribution of body water in the various body fluid compartments. 7. Understand the distribution of body water in the various body fluid compartments. 8. Explain the principles of methods of measurement of body fluids. 8. Explain the principles of methods of measurement of body fluids. 9. List the concentration of some important solutes in intracellular and extra cellular compartments. 9. List the concentration of some important solutes in intracellular and extra cellular compartments. 10. Understand the role of osmotic pressure in the distribution of body water into compartments. 10. Understand the role of osmotic pressure in the distribution of body water into compartments.

3. Some useful information Some useful information One osmole is 1 gram molecular weight of undissociated solute. One osmole is 1 gram molecular weight of undissociated solute. Eg. 1 osmole of glucose = 180 grams of glucose, is equal to 1 osmole of glucose because glucose does not dissociate. Eg. 1 osmole of glucose = 180 grams of glucose, is equal to 1 osmole of glucose because glucose does not dissociate. 1 gram molecular weight of NaCl (58.5 gm) is equal to 2 osmole because NaCl dissociates into Na+ and Cl- (both are osmotically active). 1 gram molecular weight of NaCl (58.5 gm) is equal to 2 osmole because NaCl dissociates into Na+ and Cl- (both are osmotically active). Osmolality A solution that has 1 osmole of solute dissolved in 1 Kilogram of water Osmolality A solution that has 1 osmole of solute dissolved in 1 Kilogram of water Osmolarity A solution that has 1 osmole of solute dissolved in in 1 liter (1000 ml) of water. Osmolarity A solution that has 1 osmole of solute dissolved in in 1 liter (1000 ml) of water. Conventionally: because of low concentration, solute dissolved in mg/litre of water or Kg of H 2 O  milliOsmole (mOsm) Conventionally: because of low concentration, solute dissolved in mg/litre of water or Kg of H 2 O  milliOsmole (mOsm) Normal Osmolarity of plasma is about 300 mOsm/L Normal Osmolarity of plasma is about 300 mOsm/L -1 Mol OF Glucose solution? - 1 Mol NaCl solution? In the ECF, max contribution to Osmolalirty is by NaCl

4. Osmolarity/Osmolality Osmolarity/Osmolality Is a measure of the total number of dissolved particles in a solution Ionic composition of the ICF fluid is different from that of ECF But Osmolarity of ICF is equal to that of ECF.

5. Concept of osmotic pressure Concept of osmotic pressure H2OH2O H2OH2O Solute Semi-permeable membrane Osmosis: Diffusion of H 2 O Across semi permeable membrane From high H 2 O concentration to low H 2 O concentration. In tissues - via lipid bilayer -Through water channels (acquaporins) Osmotic pressure is the pressure which is applied at the membrane to oppose osmosis Movement of H2O Osmotic pressure is directly proportional To the osmolarity (solute concentration)

6. Concept of hydrostatic pressure Concept of hydrostatic pressure Pressure = 2 mmHg Pressure = 30 mmHg

10. ECF also includes lymph, CSF, synovial fluid, aqueous & vitreous humor, endolymph & perilymph and fuild present in pleural, pericardial and peritoneal cavities

11. Constitution of Extra and Intra cellular fluids

12. Distribution of important ionic and organic constituents