ADVANCED PHYSIOLOGY FLUID & ELECTROLYTES Part 1 Instructor Terry Wiseth

1. ADVANCED PHYSIOLOGYFLUID & ELECTROLYTESPart 1Instructor Terry Wiseth

2. FLUID ELECTROLYTE HOMEOSTASIS • In a healthy individual fluid volume and electrolyte concentrations are maintained within strict homeostatic limits through the interaction of several organ systems

3. FLUID ELECTROLYTE HOMEOSTASIS • Total body water (TBW) can be divided by cell membranes into two main compartments: • 1) Extracellular fluid (ECF) • fluid outside cells • 1/3 of total body water • 2) Intracellular fluid (ICF) • fluid inside cells • 2/3 of total body water

4. FLUID ELECTROLYTE HOMEOSTASIS • The ECF is further divided into: • 1) Blood plasma (80%) • 2) Interstitial fluid (20%) • These two ECF compartments are separated by a capillary membrane

5. FLUID COMPARTMENTS • Effectively there are three compartments • 1) Intracellular • 2) Interstitial • 3) Plasma

6. FLUID COMPARTMENTS cell CYTOPLASM PLASMA (intracellular) (extracellular) INTERSTITIAL FLUID capillary

7. ELECTROLYTES • Dissolved ions in the: • Cell, interstitial fluid, blood • Potassium (K) • Sodium (Na) • Calcium (Ca) • Magnesium (Mg) • Chlorine (Cl) • Bicarbonate (H2CO3) • Proteins (Pr)

8. ELECTROLYTES • There are three key concepts in consideration of fluid and electrolyte management: • 1) Cell Membrane Permeability • 2) Osmolarity • 3) Electroneutrality

9. ELECTROLYTES • Cell Membrane Permeability • Refers to the ability of a cell membrane to allow certain substances to pass freely • Other substances like charged ions (Na+) cannot cross the membrane and are trapped on one side of it H2O Na+ H2O H2O H2O Na+ H2O Na+ H2O Na+ Na+ H2O Na+ Na+ H2O Na+

10. ELECTROLYTES • Osmolarity is a property of particles in solution • If a substancecan dissociate insolution, it willcontribute to theosmolarity of thesolution

11. ELECTROLYTES • The principle of Electroneutrality means that the overall number of positive and negative charges balances • For instance, in conditions like renal tubular acidosis where HCO3- is lost, chloride is retained Cl-

12. ELECTROLYTES • When the body is “In fluid balance” it means that the various body compartments (cells, tissues, organs) contain the required amount of fluids to carry out normal bodily functions

13. ELECTROLYTES • Fluid balance and electrolyte balance are inseparable • In a healthy individual, the volume of fluid in each compartment remains stable

14. ELECTROLYTES • Loss of electrolytes can have serious consequences for the body • In severe dehydration, the loss of electrolytes can result in circulatory problems such as tachycardia (rapid heart beat) and problems with the nervous systemsuch as loss ofconsciousnessand shock

15. ELECTROLYTES • Electrolytes serve three general functions: • 1) Maintain normal metabolism • 2) Maintain proper fluid movement between compartments • 3) Maintain the acid-base balance

16. ELECTROLYTE COMPOSITION OF PLASMA AND INTERSTITIAL FLUID

17. ELECTROLYTES

18. ELECTROLYTES PLASMA INTERSTITIAL FLUID

19. Na+ Cl- IONS AND MOLECULES • Ions are charged atoms • ex: Na+, Cl-, Mg++ • Molecules are formed when two or more atoms or ions are combined • ex: H2O, C6H12O6, NaCl

20. MOVEMENT OF BODY FLUIDS • Fluid moves between the compartments of the body through various mechanisms • Substances leave and enter capillaries via three mechanisms: • 1) Vesicular transport • 2) Diffusion • 3) Bulk flow

21. MOVEMENT OF BODY FLUIDS • Vesicular transport and diffusion are associated with the movement of solutes (electrolytes)

22. MOVEMENT OF BODY FLUIDS • Bulk flow is the most important process for the maintenance of relative volumes (fluids) of blood and interstitial fluid • Bulk flow involves the movement of both solvent (fluids) and solute into the interstitial space

23. MOVEMENT OF IONS AND MOLECULES • Ions and molecules pass through membranes by: • Simple Diffusion • Passage through channels • Facilitated Diffusion • Active Transport (Na-K pump)

24. CELL MEMBRANE

25. FLUID COMPARTMENTS • Describes the distribution of water in the body • Fluid compartments are separated by semipermeable membranes • Capillary wall separates the plasma and the interstitial fluid • Cell membrane separates the cytoplasm and interstitial fluid

26. FLUID COMPARTMENTS PLASMA CAPILLARY WALL CELL MEMBRANE INTERSTITIAL FLUID CYTOPLASM

27. FLUID SHIFTS • Fluid shifts may occur as the result of disease or injury

28. FLUID SHIFTS • Accumulations of fluids in a tissue or in a body cavity is called third space compartment • Ex: liver disease may lead to significant accumulations of fluid in the peritoneal cavity • Represents a fluid loss as it is trapped

29. FACTORS CONTROLLING EXCHANGES OF FLUIDS • 1) Diffusion • 2) Filtration • 3) Hydrostatic Pressure • 4) Osmotic (Oncotic) Pressure

30. DIFFUSION • Water, small molecules and ions • Movement of molecules from areas of higher concentration to areas of lower concentration

31. FILTRATION • Net flow of water is due to overall effect of pressure on both sides of a membrane • Fluid is filtered out of capillaries in response to changes in: • 1) Hydrostatic Pressures • 2) Oncotic (Osmotic) Pressures H2O H2O H2O H2O H2O H2O H2O H2O H2O

32. HYDROSTATIC PRESSURE (HP) • Fluid pressure • Ex: blood pressure in the capillaries 6 4 H2O H2O H2O H2O 8 6 H2O H2O H2O H2O H2O H2O H2O H2O

33. HYDROSTATIC PRESSURE (HP) • Fluid pressure • Ex: blood pressure in the capillaries • Ex: pressure exerted by interstitial fluid 8 6 H2O H2O H2O H2O H2O 6 4 H2O H2O H2O H2O H2O H2O H2O

34. HYDROSTATIC PRESSURE IN PLASMA • Blood Pressure at Arterial end of capillaries is 30 mm Hg • Blood Pressure at Venous end of capillaries is 10 mm Hg • Difference in pressure forces fluid out of plasma to the interstitial fluid

35. HYDROSTATIC PRESSURE IN INTERSTITIAL FLUID • Hydrostatic pressure in interstitial space is - 6 mm Hg • Supplies a pulling force (suction) drawing fluid out of the capillaries • The lymphatic system drains interstitial fluid creating a negative interstitial pressure

36. OSMOTIC (ONCOTIC) PRESSURE • Drawing force resulting from the pressure created by presence of protein dissolved in: • Cytoplasm • Plasma • Interstitial fluid • Pressure which develops when there is net movement of water across a membrane (osmosis)

37. OSMOTIC (ONCOTIC) PRESSURE • Pressure created is directly proportional to solute concentration • Thus osmotic pressure is dependent on the concentration of urea, glucose, amino acids, electrolytes and proteins • Oncotic pressure definespressures which are the resultof protein concentration differences

38. Capillary ONCOTIC PRESSURE IN PLASMA • Oncontic pressure at the arterial end of capillaries is 28 mm Hg • Oncotic pressure of interstitial fluid is 5 mm Hg • Due to a higher protein concentration in plasma Pr- Pr- Pr- Pr- Pr- Pr- H2O H2O Pr- Pr- Pr- Pr- Pr- Pr- Pr- Pr- Pr- Pr- Pr- Pr- Pr- Pr- Pr- H2O H2O H2O H2O H2O

39. Capillary ONCOTIC PRESSURE PROTEIN (OP) INTERSTITIAL FLUID PROTEIN (OP) H2O H2O Opposing oncotic pressure (OP) inside and outside of a capillary. A higher protein concentration in plasma as compared to interstitial fluid, thus it has a greater oncotic pressure

40. Capillary CAPILLARY-INTERSTITIAL FLUID EXCHANGES • Hydrostatic and osmotic (oncotic) pressures create opposing inward and outward forces on the capillary Hydrostatic Pressures Osmotic Pressures

41. Capillary OUTWARD FORCES • Arterial end of capillary exerts hydrostatic pressure (30 mm Hg) 30 Hydrostatic Pressures

42. Capillary OUTWARD FORCES • Interstitial fluid oncotic pressure (5 mm Hg) • Negative interstitial fluid pressure (-6 mm Hg) • Total outward pressure 41 mm Hg 5 30 Osmotic Pressures Hydrostatic Pressures 6 Interstitial Fluid (Pull)

43. Capillary INWARD FORCES • Plasma oncotic pressure (28 mm Hg) 28 Osmotic Pressures

44. Capillary INWARD FORCES • Net outward filtration of 13 mm Hg results in plasma fluid loss • 41 mm Hg - 28 mm Hg = 13 mm Hg 5 30 Osmotic Pressures Hydrostatic Pressures 6 28 Osmotic Pressures Interstitial Fluid (Pull)

45. Opposing forces that influence fluid shifts across the capillary wall. The net effect is outflow of fluid (41 - 28) with a net pressure of 13 Arterial end of capillary 30 mm Hg (HP) 28 mm Hg (OP) - 6 mm Hg (HP) 5 mm Hg (OP) Interstitial fluid Total pressure drawing fluid out Inward drawing force

46. ABNORMAL CAPILLARY DYNAMICS • Loss of protein and fluid from plasma to interstitial fluid is provided a return to the circulatory system by way of the lymphatic system

47. ABNORMAL CAPILLARY DYNAMICS • Increased capillary fluid loss occurs when there is: • 1) Increased Capillary Hydrostatic Pressure • 2) Increased Interstitial Fluid Oncotic Pressure • 3) Decreased Plasma Oncotic Pressure • Accumulations of fluid in interstitial spaces is called edema

48. CONDITIONS FOR EDEMA Capillary Increased HP OP - HP OP Interstitial fluid Increased capillary Hydrostatic Pressure (HP)

49. CONDITIONS FOR EDEMA Capillary Decreased OP HP - HP OP Interstitial fluid Decreased plasma Oncotic Pressure (loss of protein)

50. CONDITIONS FOR EDEMA Capillary OP HP Increased OP - HP Interstitial fluid Increased Oncotic Pressure in interstitial fluid