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

2. Water gain must = water loss Water gain must = water loss

4. Rate of formation of metabolic water is not regulated Source of metabolically formed water

5. Osmolarity of plasma is about 300 mOsm/L Osmolarity of plasma is about 300 mOsm/L (Measured by a method called “Freezing Point Depression) (Measured by a method called “Freezing Point Depression) TONICITY is Osmolarity in relation to that of plasma. It has the ability to change the VOLUME of a cell TONICITY is Osmolarity in relation to that of plasma. It has the ability to change the VOLUME of a cell Isotonic solution: same osmolarity as of plasma Isotonic solution: same osmolarity as of plasma Hypertonic solution Hypertonic solution Hypotonic solution? Hypotonic solution?

6. Osmotic equilibrium is maintained rapidly between ICF and ECF  Isotonic fluid gain: e.g Intravenous infusion of isotonic saline (0.9 % NaCl, 5% glucose solution)  Isotonic fluid loss: Hemorrhage No net fluid shift occur

7. What happens ? Water moves into the cells from ECF until osmotic equilibrium is achieved. Pronounced swelling of neurons leads to brain dysfunction Swelling of muscle leads to muscle weakness. Hypertension and edema caused by expansion of plasma volume. What Causes this? Over hydration: Renal failure with inability to excrete diluted urine Excessive drinking (transient) Increase in ADH secretion Water intoxication: condition of over hydration, hypotonicity and cellular swelling from excess water.

8. What happens ?  Water moves out of the cells to ECF until osmotic equilibrium is achieved  Cells shrink as water leaves them  Neurons dehydration causes disturbances in brain function manifested as mental confusion to coma. What Causes this? Dehydration due to:  Insufficient water intake  Excessive water loss (vomiting or diarrhea)  Diabetes Insipidus (deficiency of ADH) Accumulation of high levels of osmotically active solutes (urea in kidney failure)

9. Tonicity & RBC Tonicity & RBC

10. Rate of formation of metabolic water is not regulated to maintain homeostasis Water gain is regulated mainly by drinking through thirst mechanism 2% decrease in body mass due to fluid loss causes mild dehydration Baroreceptor

13. Dye-dilution metod (Indicator-dilution)

14. Measurements of various body volumes Total body water  use of a substance which when inserted in to the blood, will spread evenly through out all the body compartments. Total body water  use of a substance which when inserted in to the blood, will spread evenly through out all the body compartments. Substances used i. Radio active water Substances used i. Radio active water ii. Antipyrine –because it is lipid soluble ii. Antipyrine –because it is lipid soluble Extra cellular volume  Substance should disperse easily through water/plasma but NOT enter cells Extra cellular volume  Substance should disperse easily through water/plasma but NOT enter cells Substances used I Radioactive Na, Inulin Substances used I Radioactive Na, Inulin These rapidly spread through out extra cellular space  30-60 min These rapidly spread through out extra cellular space  30-60 min Extra cellular volume is also called SODIUM space or INULIN space Extra cellular volume is also called SODIUM space or INULIN space ICF = TBW-Extra cellular volume ICF = TBW-Extra cellular volume

15. Plasma & blood volumes Plasma & blood volumes Plasma Volume  Substance must stay INSIDE blood compartment after it is injected in to the blood stream Plasma Volume  Substance must stay INSIDE blood compartment after it is injected in to the blood stream Evans Blue (Dye) is the best choice Evans Blue (Dye) is the best choice Blood volume = Plasma volume + hematocrit (cell volume) Blood volume = Plasma volume + hematocrit (cell volume) Then BV = Plasma Volume/ (1-Hct) Then BV = Plasma Volume/ (1-Hct) Given Plasma vol as 3 litres, and Given Plasma vol as 3 litres, and Hct as 0.45 Hct as 0.45 BV = 3/(1-0.45) = 3/0.55 BV = 3/(1-0.45) = 3/0.55 = 5.45 L = 5.45 L

16. Measurement of various body fluid compartments

17. Summary Summary 1. Osmolarity, its normal value, and osmotic 1. Osmolarity, its normal value, and osmotic pressure pressure 2. Hydrostatic pressure 2. Hydrostatic pressure 3. Distribution of body water 3. Distribution of body water 4. Intra and extra cellular fluids and their 4. Intra and extra cellular fluids and their composition composition 5. Tonicity of plasma and learnt what is iso, 5. Tonicity of plasma and learnt what is iso, hypo and hyper tonicity hypo and hyper tonicity 6. Measurements of body fluid compartments 6. Measurements of body fluid compartments