1. FLUIDS AND ELECTROLYTES

2. Body Fluid Composition Water – largest body component –55-65% total body weight Solutes –dissolved in body water

3. Solutes –Electrolytes Cations – positive –Sodium (Na+) –Potassium (K+) –Calcium (Ca +2 ) Anions – negative –Chloride (Cl-) –Bicarbonate (HCO 3 -) –Phosphate (HPO 4 -) –Non-electrolytes Proteins Urea Glucose Oxygen (O 2 ) Carbon dioxide (CO 2 )

4. Body Maintains Charge and Osmolality Body fluids –Electrically neutral –Osmotically maintained Specific # solute molecules per volume fluid Homeostasis of charge, osmolality maintained by –Ion transport –Water movement between fluid compartments –Kidney function

5. Units of Solute Measurement (A Review) MW (molecular weight) = sum of weights of atoms mEq (milliequivalents) = MW (in mg) / valence –Valence = # charges of ion Na+ valence = 1 Cl- valence = 1 Ca +2 valence = 2 –Allows comparisons of charge # of solutes in fluids, without molecular wts Important to monitor overall charge of body fluids mOsm (milliosms) = # particles in solution –Particles = atoms or molecules, charged or uncharged –Measures concent of overall # of solute particles in fluid Important to monitor overall concentrations of body fluids

6. Fluid Compartments ICF = IntraCellular Fluid –Inside cells –65% total body weight ECF = ExtraCellular Fluid –Not inside cells –35% total body weight –Further divided 

7. ECF – cont’d –IVF = IntraVascular Fluid In blood vessels 8% total body weight –ISF = InterStitial Fluid Bathes cells + lymph 25% of total body weight

8. Movement of Body Fluids (WATER FOLLOWS SALT!) Solutes may be in higher concentration on one side of the cell membrane Fluid (water) can move to equilibrate concentration and/or charge on both sides of the membrane

9. Definitions Diffusion = net movement of particles (solutes) down concentration gradient to establish equilibrium between two sides of membrane –Passive (no energy needed) –Assisted (energy must be added by the cell) Osmosis = diffusion of water –Freely passes through cell membranes.

10. Movement of Body Fluids – cont’d ICF to ECF –Osmolality changes in ICF not rapid Cell strives to maintain fluid and ion concentrations Cell very dependent on relatively constant water/solute amounts –BUT if ECF osmolality changes so water moves among compartments, both compartments affected and equilibrated over time

11. Movement of Body Fluids – cont’d IVF to ISF to IVF –Happens constantly due to changes in fluid pressures and osmotic forces at arterial and venous ends of the capillaries –Necessary to move oxygen and nutrients toward metabolizing cells, and wastes and carbon dioxide away from metabolizing cells

13. Movement of Body Fluids – cont’d Arteriolar end of the capillary: –Highest fluid pressure force -- Blood Hydrostatic Pressure (BHP) Pressing out against the capillary walls Direction toward cells Encourages movement out Due to fluid pressures and heart contractions –Colloid Osmotic Pressure (COP) Lower pressure at arteriolar end Pulls inward from capillary wall Encourages fluid to stay inside Due to large proteins, cells in capillary (too large to move through capillary walls, so remain in the capillary), can’t leave the bloodstream –Overall at arteriolar end of capillary, BHP > COP Greater force encouraging fluid out of capillary than encouraging fluid to stay inside capillary So fluid (from heart; oxygenated; w/ nutrients) encouraged to move toward metabolizing cells

14. Movement of Body Fluids – cont’d At the venous end of the capillary: –BHP decreased Fluid “lost” from vessel Don’t have same high fluid pressure pushing against vessel walls –COP stays the same Same amt large proteins, blood cells –Now rel higher pressure “pulling in” away from cells –Overall at venous end of capillary, COP > BHP Greater force encourages fluid into capillary than encourages fluid out of capillary Overall, fluid (from around cells; containing wastes and CO 2 ) encouraged to move into capillary –Now returned to lungs to excrete CO 2 and to kidneys to excrete wastes

16. Movement of Body Fluids – cont’d ECF to environment –Fluid intake = fluid output Intake is -- water, food, beverages Output -- urine, feces, sweat and water vapor

17. Regulation of Body Water Works through ADH (AntiDiuretic Hormone) If there is –Decreased amount water in the body, or –Increased amount Na+ in the body, or –Increased blood osmolality So the blood is too concentrated, or –Decreased circulating blood volume All of these lead to:

18. ADH Release – cont’d Stim’n hypothalamic osmoreceptors,  Release ADH, and Stimulation of thirst response –Thirst response  increased drinking Overall, water volume within the body increases

19. ADH – cont’d ADH works at kidney –  incr’d permeability of kidney tubules to water –  incr’d reabsorption of water from kidney tubules back into blood vasculature Water WOULD have been released to urine So water is conserved, not excreted

21. ADH – cont’d Overall: –Incr’d water consumption, and –Incr’d water conservation, so –Incr’d amt water in body Relieves decr’d water, decr’d circulation blood volume –Decr’d blood osmolality Relieves increased body Na+, increased blood osmolality Note: the various conditions leading to ADH release can all be caused by different dysfunctions or traumas, but are all related physiologically –If either hemorrhage (decr’d blood volume) or sweating (decr’d water in body)  decr’d fluid available  decr’d IVF  decr’d blood pressure Compensation: body tries to increase fluids in body –If endocrine disorder  incr’d Na+  incr’d blood osmolality Compensation: body tries to increase fluids to bring blood osmolality back to normal range (since body can’t n;ormalize osmolality through solute amount) So if sodium LOAD has doubled to 290 mEq/L: if fluid VOLUME can double, will now have 290 mEq/2L, which = 145 mEq/L (normal sodium CONCENTRATION is 145 mg/L)

22. ADH – cont’d Note: conditions  ADH release, regardless of cause, related physiologically –Hemorrhage (decr’d blood volume) or sweating (decr’d water in body)  decr’d fluid available  decr’d IVF  decr’d blood pressure Compensation: body tries to increase fluids in body –Endocrine disorder  incr’d Na+  incr’d blood osmolality Compensation: body tries to increase fluids (body can’t normalize osmolality through solute amount) Ex: Na+ LOAD doubled (290 mEq/L); by doubling fluid VOLUME  290 mEq/2L= 145 mEq/L (normal sodium CONCENTRATION is 145 mg/L)

23. Important Cations Contributing to Body Fluid Osmolality Sodium (Na+) –About 90% ECF cations –Normal range = 136-145 mEq/L in ECF –Pairs with Cl-, HCO 3 - to neutralize charge –Low in ICF (~10 mEq/L) –Most impt ion in regulating water balance

24. Sodium – cont’d –Regulation in ECF -- Renal tubule reabsorption, modulated by hormones: Aldosterone –Rel’d from adrenal gland when body senses decr’d Na+ load –Works at renal tubule to incr renal tubule reabsorption of Na+ Renin/angiotensin –Affects aldosterone release (also controls Na+ reabsorption) Natriuretic hormone –Works at kidney –  decr’d renal reabsorption of Na+

25. Potassium Major INTRAcellular cation ICF concentration = 150-160 mEq/L Lower in ECF (3.5-4.5 mEq/L) –K+ concentration INSIDE cells approximates Na+ concentration OUTSIDE –Na+ concentration INSIDE cells approximates K+ concentration OUTSIDE –Body keeps electrical charge constant in ICF and ECF, but uses diff cations inside/outside cells Cell moves two cations differently, uses each differently –Overall cells strive to maintain high K+ inside and high Na+ outside

26. Potassium – cont’d Why keep K+ high inside and Na+ high outside cells? –Resting membrane potential in neurons, muscles Na+, K+ move into/out of these cells  depolarization  action potential If imbalanced, can  neurological, muscle contraction problems REMEMBER: heart is an important muscle!

28. Potassium – cont’d K+ also important: –Regulates fluid, ion balance inside the cell Sim to Na+ regulation outside the cell –pH regulation K+ can move across the cell membrane for H+ when H+ is in excess (body fluids are too acidic) Regulation of body K+ is through the kidney –Aldosterone regulates K+ If body senses decr’d K+ in plasma  aldosterone release Works at kidney tubule  incr’d reabsorption of K+ from tubule back to blood (similar to Na+ mechanism) –Insulin  increased K+ taken up by cells So K+ must be monitored in diabetic patients

29. Isotonic Alterations Volume of fluid changes, but numbers and types of electrolytes remain at normal levels (Table 4-5) –Loss  volume depletion (hypovolemia); occurs with Hemorrhage Severe wound drainage Excess sweating Burns Third spacing

30. Hypovolemia – cont’d –Fluid lost from blood vessels, but remains in body –Receptors in the vessels sensitive to pressure –Interpreted as fluid loss, so decr’d ECF volume  Decr’d urine output Weight loss (through fluid weight) Can  hypovolemic shock –Symptoms of hypovolemia Decr’d blood pressure Incr’d heart rate

31. Hypervolemia Excess body fluid; occurs with: –Excessive IV fluids –Overproduction aldosterone Why should this lead to hypervolemia? –Some drugs (ex: cortisol) –With incr’d ECF volume  Weight gain (fluid weight) Diluted urine Incr’d blood pressure Can also  edema

32. Edema -- ECF Isotonic Volume Excess Accum’n isotonic fluid in interstitial space (incr’d ISF) Forces that favor incr’d ISF also favor edema: –Incr’d BHP, if Chronic hypertension Venous obstruction Water retention –Decr’d COP if Not enough proteins/cells in the blood: –Protein synthesis disorders of liver –Blood cell disorders  decreased # of blood cells

33. Edema – cont’d –Increased capillary permeability, which can occur with Trauma Inflammation Decreased lymph drainage with –Blocked lymph node –Surgical removal of lymph vessels –REMEMBER: ISF drains into lymph vessels, which returns ISF to the bloodstream

34. Edema – cont’d Clinical –Pitting –Weight gain (water weight) –Neck vein distension –Incr’d blood pressure Treatment –Treat underlying conditions (tumor, blood cell disorder, etc.) –Relieve symptoms

35. Electrolyte Imbalances (Table 4-6): Sodium Hypernatremia (a hypertonic imbalance) –Plasma Na+ > 145 mEq/L –Too much Na+ or too little water –“Tonicity”: # of solute particles in solution Hypertonic -- high amt solute Hypotonic = dilute –Characteristics of hypernatremia:  movement of water from ICF to ECF, so –Cells dehydrate  –Overall incr’d ECF vol (at expense of the cell vol)

36. Sodium Imbalances – cont’d Hypernatremia – cont’d –Due to Admin hypertonic IV sol’ns Oversecretion aldosterone Loss of pure water Long term sweating w/ chronic fever Respiratory infection  water vapor loss Diabetes  polyuria Insufficient water ingested

37. Sodium Imbalances – cont’d Hypernatremia – cont’d –Clinical Thirst Lethargy Neurological dysfunction (dehydration of brain cells) –Treatment Lower serum Na+ Use isotonic salt-free IV fluid (5% glucose) to replace body water; returns Na+ concentration to normal levels

38. Sodium Imbalances – cont’d Hyponatremia –Overall Na+ decr ECF –Two types Depletional: Too little Na+ Dilutional: Too much water –Causes of each type Depletional (Na+ lost out of body or insufficient) –Diuretics –Chronic vomiting –Chronic diarrhea »Though electrolytes loss –Decr’d aldosterone –Decr’d Na+ intake

39. Sodium Imbalances – cont’d Hyponatremia – cont’d Dilutional –Renal dysfunction w/ incr’d hypotonic fluid intake –Excessive sweating  increased thirst  intake excessive pure water Syndrome of Inappropriate ADH (SIADH)  impaired renal excretion of water Excessive beer drinking (???) –Clinical Neurological symptoms –Now improper Na+ concentration outside cell  improper depolarization/action potential/neuron conduction –Seizures possible –Treatment Restrict water, or Administer Na+

40. Electrolyte Imbalances: Potassium Hypokalemia –Characteristics Serum K+ < 3.5 mEq/L Beware if diabetes: –Insulin plays a role in K+ into the cell –Ketoacidosis  incr’d H+ in ECF (so ECF too highly + charged) »H+ enters cells »Body tries to equilibrate + charges by moving K+ out of cells »Now ECF high in K+ (lost through urine) »Overall whole body K+ deficit

41. Potassium Imbalances – cont’d Hypokalemia – cont’d –Causes Decr’d K+ intake (rare) Incr’d K+ loss –With chronic diuretics, g.i. disturbance –Acid/base imbalance  K+ out of cells into ECF, then lost through urine Clinical –Neuromuscular disorders –Cardiac arrest REMEMBER: Na+/K+ gradient for proper action potentials in neurons/muscles –Treatment Increase K+ intake BUT slowly to avoid abrupt Na+/K+ gradient change

42. Potassium Imbalances – cont’d Hypokalemia – cont’d Clinical –Neuromuscular disorders –Cardiac arrest –REMEMBER: body maintains Na+/K+ gradient for proper action potentials in neurons/muscles so proper neuron/muscle function –Treatment Increase K+ intake BUT must be increased slowly to avoid abrupt Na+/K+ gradient change

43. Potassium Imbalances – cont’d Hyperkalemia –Serum K+ > 5.5 mEq/L –Importance/causes/when to check Renal disease (kidney regulates K+) Massive cellular trauma –High intracellular K+ is released into ECF Insulin deficiency –Insulin plays a role in K+ uptake into cells Addison’s disease  altered aldosterone secretion Decr’d blood pH (high blood acidity) –  H+ into cells –  K+ out of cells  ECF –  High K+ in ECF –BUT over time K+ will be lost to urine  overall decrease in body K+

44. Potassium Imbalances – cont’d Hyperkalemia – cont’d –Clinical Muscle weakness, paralysis Change in ECG pattern –Treatment Insulin + glucose  K+ taken into the cells (out of ECF) Bicarbonate – buffers H+ ions if hyperkalemia due to acidosis Ca+2 counteracts K+ effects on heart