BODY FLUID COMPARTMENT AND FLUID BALANCE

1. BODY FLUID COMPARTMENT AND FLUID BALANCE

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

3. The osmosis, diffusion, filtration and reabsoption provide for continual exchange of water and solutes (electrolytes) among different body compartments Yet, the volume of the fluid in different body compartments remains remarkably stable

4. Dynamics of capillary exchange (Starling’s Law of capillaries)

5. Concentration of important solutes in ICF, ECF

6. Sources of body water gain and loss Body fluid volume remains constant because water loss is equal to water gain

7. Sourse of metabolic water Rate of formation of metabolic water is not regulated

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

9. Regulation of water and solute loss This is mainly done by the kidneys

10. 27_table_01

11. Osmolality vs Osmolarity • One osmole is 1 gram molecular weight of undissociated solute. • Thus, 180 grams of glucose, which is 1 gram molecular weight of glucose, is equal to 1 osmole of glucose because glucose does not dissociate. • Therefore, 1 gram molecular weight of NaCl (58.5 gm) is equal to 2 osmole because NaCl dissociates into Na+ and Cl- (and both are osmotically active). • A solution that has 1 osmole of solute dissolved in 1 Kilogram of water is said to have an Osmolalityof 1 osmole per kilogram. • A solution that has 1 osmole of solute dissolved in 1 liter (1000 ml) of water is said to have an Osmolarityof 1 osmole per liter.

12. Principle of Osmosis Osmosis is the net movement of water molecules through a selectively permeable membrane During osmosis water molecules pass through a selectively permeable membrane in two ways (1) through the lipid bilayer and (2) through aquaporins (aqua = water) channels.

13. Osmolarity Is a measure of the total number of dissolved particles in a solution Ionic composition of the ICF fluidisdifferent from that of ECF But Osmolarity of ICF is equal to that of ECF.

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

15. ECF IS HYPERTONIC • 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)

16. ECF IS HYPOTONIC 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.

17. Movement of water between body fluid compartments

18. Measurement of fluid volumes in the different body compartments Dye-dilution metod (Indicator-dilution)

19. 27_table_02