Chapter 21 Water, Electrolyte, and Acid-Base Balance

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Chapter 21 Water, Electrolyte, and Acid-Base Balance

  1. 1. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 21 Lecture PowerPoint
  2. 2. 2402 Anatomy and Physiology II Chapter 21 Susan Gossett [email_address] Department of Biology Paris Junior College
  3. 3. Hole’s Human Anatomy and Physiology Twelfth Edition Shier  Butler  Lewis Chapter 21 Water, Electrolyte, and Acid-Base Balance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  4. 4. 21.1: Introduction <ul><li>The term balance suggests a state of equilibrium </li></ul><ul><li>For water and electrolytes that means equal amounts enter and leave the body </li></ul><ul><li>Mechanisms that replace lost water and electrolytes and excrete excesses maintain this balance </li></ul><ul><li>This results in stability of the body at all times </li></ul><ul><li>Keep in mind water and electrolyte balance are interdependent </li></ul>
  5. 5. 21.2: Distribution of Body Fluids <ul><li>Body fluids are not uniformly distributed </li></ul><ul><li>They occupy compartments of different volumes that contain varying compositions </li></ul><ul><li>Water and electrolyte movement between these compartments is regulated to stabilize their distribution and the composition of body fluids </li></ul>
  6. 6. Fluid Compartments <ul><li>Of the 40 liters of water in the body of an average adult, about two-thirds is intracellular fluid and one-third is extracellular fluid </li></ul><ul><li>An average adult female is about 52% water by weight, and an average male about 63% water by weight </li></ul>Extracellular fluid (37%) Intracellular fluid (63%) 40 38 36 34 32 30 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 Liters Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  7. 7. Total body water Interstitial fluid Plasma Lymph Transcellular fluid Extracellular fluid (37%) Membranes of body cells Intracellular fluid (63%) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  8. 8. Body Fluid Composition <ul><li>Extracellular fluids are generally similar in composition including high concentrations of sodium, calcium, chloride and bicarbonate ions </li></ul><ul><li>Intracellular fluids have high concentrations of potassium, magnesium, phosphate, and sulfate ions </li></ul>Ion concentration (m Eq/L) 20 30 50 60 70 80 90 100 1 10 120 130 140 Relative concentrations and ratios of ions in extracellular and intracellular fluids 150 40 10 0 14:1 Ratio (Extracellular: intracellular) Na + 1:28 K + 5:1 Ca +2 1:19 Mg +2 26:1 Cl  3:1 HCO 3  1:19 PO 4  3 1:2 SO 4  2 Extracellular fluid Intracellular fluid Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  9. 9. Movement of Fluid Between Compartments <ul><li>Two major factors regulate the movement of water and electrolytes from one fluid compartment to another </li></ul><ul><ul><li>Hydrostatic pressure </li></ul></ul><ul><ul><li>Osmotic pressure </li></ul></ul>Interstitial fluid Capillary wall Transcellular fluid Lymph Plasma Serous membrane Intracellular fluid Cell membrane Lymph vessel Fluid leaves plasma at arteriolar end of capillaries because outward force of hydrostatic pressure predominates Fluid returns to plasma at venular ends of capillaries because inward force of colloid osmotic pressure predominates Hydrostatic pressure within interstitial spaces forces fluid into lymph capillaries Interstitial fluid is in equilibrium with transcellular and intracellular fluids Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  10. 10. 21.3: Water Balance <ul><li>Water balance exists when water intake equals water output </li></ul><ul><li>Homeostasis requires control of both water intake and water output </li></ul>
  11. 11. Water Intake <ul><li>The volume of water gained each day varies among individuals averaging about 2,500 milliliters daily for an adult: </li></ul><ul><ul><li>60% from drinking </li></ul></ul><ul><ul><li>30% from moist foods </li></ul></ul><ul><ul><li>10% as a bi-product of </li></ul></ul><ul><ul><li>oxidative metabolism of </li></ul></ul><ul><ul><li>nutrients called water of </li></ul></ul><ul><ul><li>metabolism </li></ul></ul>Water in beverages (1,500 mL or 60%) Average daily intake of water Water lost in sweat (150 mL or 6%) Total output (2,500 mL) Average daily output of water (a) (b) Total intake (2,500 mL) Water in moist food (750 mL or 30%) Water of metobolism (250 mL or 10%) Water lost in feces (150 mL or 6%) Water lost through skin and lungs (700 mL or 28%) Water lost in urine (1,500 mL or 60%) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  12. 12. Regulation of Water Intake
  13. 13. Water Output <ul><li>Water normally enters the body only through the mouth, but it can be lost by a variety of routes including: </li></ul><ul><ul><li>Urine (60% loss) </li></ul></ul><ul><ul><li>Feces (6% loss) </li></ul></ul><ul><ul><li>Sweat (sensible perspiration) (6% loss) </li></ul></ul><ul><ul><li>Evaporation from the skin (insensible perspiration) </li></ul></ul><ul><ul><li>The lungs during breathing </li></ul></ul><ul><ul><li>(Evaporation from the skin and the lungs is a 28% loss) </li></ul></ul>
  14. 14. Regulation of Water Output
  15. 15. 21.4: Electrolyte Balance <ul><li>An electrolyte balance exists when the quantities of electrolytes the body gains equals those lost </li></ul>Urine Electrolyte intake Fluids Feces Electrolyte output Foods Perspiration Metabolic reactions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  16. 16. Electrolyte Intake <ul><li>The electrolytes of greatest importance to cellular functions release sodium, potassium, calcium, magnesium, chloride, sulfate, phosphate, bicarbonate, and hydrogen ions </li></ul><ul><li>These ions are primarily obtained from foods, but some are from water and other beverages </li></ul>
  17. 17. Regulation of Electrolyte Intake <ul><li>Ordinarily, a person obtains sufficient electrolytes by responding to hunger and thirst </li></ul><ul><li>A severe electrolyte deficiency may cause salt craving </li></ul>
  18. 18. Electrolyte Output <ul><li>The body loses some electrolytes by perspiring typically on warmer days and during strenuous exercise </li></ul><ul><li>Some are lost in the feces </li></ul><ul><li>The greatest output is as a result of kidney function and urine output </li></ul>
  19. 19. Regulation of Electrolyte Output <ul><li>The concentrations of positively charged ions, such as sodium (Na + ), potassium (K + ) and calcium (Ca +2 ) are of particular importance </li></ul><ul><li>These ions are vital for nerve impulse conduction, muscle fiber contraction, and maintenance of cell membrane permeability </li></ul>Aldosterone is secreted Adrenal cortex is signaled Potassium ion concentration increases Renal tubules increase reabsorption of sodium ions and increase secretion of potassium ions Sodium ions are conserved and potassium ions are excreted Calcium ion concentration decreases Calcium ion concentration returns toward normal Normal phosphate concentration is maintained Addition of phosphate to bloodstream Renal tubules conserve calcium and increase secretion of phosphate Parathyroid glands are stimulated Parathyroid hormone is secreted Intestinal absorption of calcium increases Activity of bone-resorbing osteoclasts increases Increased phosphate excretion in urine Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  20. 20. 21.1 Clinical Application Water Balance Disorders
  21. 21. 21.2 Clinical Application Sodium and Potassium Imbalances
  22. 22. 21.5: Acid-Base Balance <ul><li>Electrolytes that ionize in water and release hydrogen ions are acids </li></ul><ul><li>Substances that combine with hydrogen ions are bases </li></ul><ul><li>Acid-base balance entails regulation of the hydrogen ion concentrations of body fluids </li></ul><ul><li>This is important because slight changes in hydrogen ion concentrations can alter the rates of enzyme-controlled metabolic reactions, shift the distribution of other ions, or modify hormone actions </li></ul>
  23. 23. Sources of Hydrogen Ions Aerobic respiration of glucose Anaerobic respiration of glucose Incomplete oxidation of fatty acids Oxidation of sulfur-containing amino acids Hydrolysis of phosphoproteins and nucleic acids Carbonic acid Lactic acid Acidic ketone bodies Sulfuric acid Phosphoric acid H + Internal environment Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  24. 24. Strengths of Acids and Bases <ul><li>Acids: </li></ul><ul><ul><li>Strong acids ionize more completely and release more H + </li></ul></ul><ul><ul><li>Weak acids ionize less completely and release fewer H + </li></ul></ul><ul><li>Bases: </li></ul><ul><ul><li>Strong bases ionize more completely and release more OH - </li></ul></ul><ul><ul><li>Weak bases ionize less completely and release fewer OH - </li></ul></ul>
  25. 25. Regulation of Hydrogen Ion Concentration <ul><li>Either an acid shift or an alkaline (basic) shift in the body fluids could threaten the internal environment </li></ul><ul><li>Normal metabolic reactions generally produce more acid than base </li></ul><ul><li>The reactions include cellular metabolism of glucose, fatty acids, and amino acids </li></ul><ul><li>Maintenance of acid-base balance usually eliminates acids in one of three ways: </li></ul><ul><ul><li>Acid-base buffer systems </li></ul></ul><ul><ul><li>Respiratory excretion of carbon dioxide </li></ul></ul><ul><ul><li>Renal excretion of hydrogen ions </li></ul></ul>
  26. 26. <ul><li>Bicarbonate buffer system </li></ul><ul><ul><li>The bicarbonate ion converts a strong acid to a weak acid </li></ul></ul><ul><ul><li>Carbonic acid converts a strong base to a weak base </li></ul></ul><ul><ul><li>H + + HCO 3 -  H 2 CO 3  H + + HCO 3 - </li></ul></ul><ul><li>Phosphate buffer system </li></ul><ul><ul><li>The monohydrogen phosphate ion converts a strong acid to a weak acid </li></ul></ul><ul><ul><li>The dihydrogen phosphate ion converts a strong base to a weak base </li></ul></ul><ul><ul><li>H + + HPO 4 -2  H 2 PO 4 -  H + + HPO 4 -2 </li></ul></ul><ul><li>Protein buffer system </li></ul><ul><ul><li>NH 3 + group releases a hydrogen ion in the presence of excess base </li></ul></ul><ul><ul><li>COO - group accepts a hydrogen ion in the presence of excess acid </li></ul></ul>Acid-Base Buffer Systems
  27. 27.
  28. 28. <ul><li>The respiratory center in the brainstem helps regulate hydrogen ion concentrations in the body fluids by controlling the rate and depth of breathing </li></ul><ul><li>If body cells increase their production of CO 2 … </li></ul>More CO 2 is eliminated through lungs Rate and depth of breathing increase Respiratory center is stimulated Cells increase production of CO 2 CO 2 reacts with H 2 O to produce H 2 CO 3 H 2 CO 3 releases H + Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Respiratory Secretion of Carbon Dioxide
  29. 29. <ul><li>Nephrons help regulate the hydrogen ion concentration of body fluids by excreting hydrogen ions in the urine </li></ul>High intake of proteins Increased concentration of H + in urine Increased secretion of H + into fluid of renal tubules Increased concentration of H + in body fluids Increased metabolism of amino acids Increased formation of sulfuric acid and phosphoric acid Concentration of H + in body fluids returns toward normal Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Renal Secretion of Hydrogen Ions
  30. 30. <ul><li>Various regulators of hydrogen ion concentration operate at different rates </li></ul><ul><li>Acid-base (chemical) buffers function rapidly </li></ul><ul><li>Respiratory and renal (physiological buffers) mechanisms function more slowly </li></ul>Phosphate buffer system Protein buffer system First line of defense against pH shift Second line of defense against pH shift Chemical buffer system Physiological buffers Bicarbonate buffer system Respiratory mechanism (CO 2 excretion) Renal mechanism (H + excretion) Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Time Course of pH Regulation
  31. 31. 21.6: Acid-Base Imbalances <ul><li>Chemical and physiological buffer systems ordinarily maintain the hydrogen ion concentration of body fluids within very narrow pH ranges </li></ul><ul><li>Abnormal conditions may disturb the acid-base balance </li></ul>7.35 Survival range Normal pH range pH scale 7.45 8.0 7.0 6.8 7.8 Acidosis Alkalosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  32. 32. Acidosis <ul><li>Acidosis results from the accumulation of acids or loss of bases, both of which cause abnormal increases in the hydrogen ion concentrations of body fluids </li></ul><ul><li>Alkalosis results from a loss of acids or an accumulation of bases accompanied by a decrease in hydrogen ion concentrations </li></ul>pH rises pH drops Increased concentration of H + pH scale 7.4 Acidosis Alkalosis Decreased concentration of H + Accumulation of acids Loss of bases Loss of acids Accumulation of bases Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  33. 33. Acidosis <ul><li>Two major types of acidosis are respiratory acidosis and metabolic acidosis </li></ul>Accumulation of CO 2 Respiratory acidosis Decreased rate and depth of breathing Obstruction of air passages Decreased gas exchange Accumulation of nonrespiratory acids Metabolic acidosis Excessive loss of bases Kidney failure to excrete acids Excessive production of acidic ketones as in diabetes mellitus Prolonged diarrhea with loss of alkaline intestinal secretions Prolonged vomiting with loss of intestinal secretions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  34. 34. Alkalosis <ul><li>Respiratory alkalosis develops as a result of hyperventilation </li></ul><ul><li>Metabolic alkalosis results from a great loss of hydrogen ions or from a gain in bases, both accompanied by a rise in the pH of blood </li></ul>Excessive loss of CO 2 Hyperventilation Decrease in concentration of H 2 CO 3 Decrease in concentration of H + Respiratory alkalosis • Anxiety • Fever • Poisoning • High altitude Loss of acids Net increase in alkaline substances Metabolic alkalosis Gastric drainage Vomiting with loss of gastric secretions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
  35. 35. Important Points in Chapter 21: Outcomes to be Assessed <ul><li>21.1: Introduction </li></ul><ul><li>Explain the balance concept. </li></ul><ul><li>Explain the importance of water and electrolyte balance. </li></ul><ul><li>21.2: Distribution of Body Fluids </li></ul><ul><li>Describe how body fluids are distributed in compartments. </li></ul><ul><li>Explain how fluid composition varies among compartments and how fluids move from one compartment to another. </li></ul><ul><li>21.3: Water Balance </li></ul><ul><li>List the routes by which water enters and leaves the body. </li></ul><ul><li>Explain the regulation of water input and water output. </li></ul>
  36. 36. Important Points in Chapter 21: Outcomes to be Assessed <ul><li>21.4: Electrolyte Balance </li></ul><ul><li>List the routes by which electrolytes enter and leave the body. </li></ul><ul><li>Explain the regulation of the input and the output of electrolytes. </li></ul><ul><li>21.5: Acid-Base Balance </li></ul><ul><li>Explain acid-base balance. </li></ul><ul><li>Identify how pH number describes the acidity and alkalinity of a body fluid. </li></ul><ul><li>List the major sources of hydrogen ions in the body. </li></ul><ul><li>Distinguish between strong acids and weak acids. </li></ul><ul><li>Explain how chemical buffer systems, the respiratory system, and the kidneys keep the pH of body fluids relatively constant. </li></ul>
  37. 37. Important Points in Chapter 21: Outcomes to be Assessed <ul><li>21.6: Acid-Base Imbalances </li></ul><ul><li>Describe the causes and consequences of increase or decrease in body fluid pH. </li></ul>
  38. 38. Quiz 21 Complete Quiz 21 now! Read Chapter 22.

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