chapter 21 water, electrolyte, and acid-base balance

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  • 1. Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Chapter 21 Lecture PowerPoint

2. 2402 Anatomy and Physiology II Chapter 21 Susan Gossett [email_address] Department of Biology Paris Junior College 3. Holes Human Anatomy and Physiology Twelfth Edition ShierButlerLewisChapter21 Water, Electrolyte, and Acid-Base Balance Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 4. 21.1: Introduction

  • The term balance suggests a state of equilibrium
  • For water and electrolytes that means equal amounts enter and leave the body
  • Mechanisms that replace lost water and electrolytes and excrete excesses maintain this balance
  • This results in stability of the body at all times
  • Keep in mind water and electrolyte balance are interdependent

5. 21.2: Distribution of Body Fluids

  • Body fluids are not uniformly distributed
  • They occupy compartments of different volumes that contain varying compositions
  • Water and electrolyte movement between these compartments is regulated to stabilize their distribution and the composition of body fluids

6. Fluid Compartments

  • 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
  • An average adult female is about 52% water by weight, and an average male about 63% water by weight

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. 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. Body Fluid Composition

  • Extracellular fluids are generally similar in composition including high concentrations of sodium, calcium, chloride and bicarbonate ions
  • Intracellular fluids have high concentrations of potassium, magnesium, phosphate, and sulfate ions

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. Movement of FluidBetween Compartments

  • Two major factors regulate the movement of water and electrolytes from one fluid compartment to another
    • Hydrostatic pressure
    • Osmotic pressure

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. 21.3: Water Balance

  • Water balance exists when water intake equals water output
  • Homeostasis requires control of both water intake and water output

11. Water Intake

  • The volume of water gained each day varies among individuals averaging about 2,500 milliliters daily for an adult:
    • 60% from drinking
    • 30% from moist foods
    • 10% as a bi-product of
    • oxidative metabolism of
    • nutrients called water of
    • metabolism

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. Regulation of Water Intake 13. Water Output

  • Water normally enters the body only through the mouth, but it can be lost by a variety of routes including:
    • Urine (60% loss)
    • Feces (6% loss)
    • Sweat (sensible perspiration) (6% loss)
    • Evaporation from the skin (insensible perspiration)
    • The lungs during breathing
    • (Evaporation from the skin and the lungs is a 28% loss)

14. Regulation of Water Output 15. 21.4: Electrolyte Balance

  • An electrolyte balance exists when the quantities of electrolytes the body gains equals those lost

Urine Electrolyte intake Fluids Feces Electrolyte output Foods Perspiration Metabolic reactions Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 16. Electrolyte Intake

  • The electrolytes of greatest importance to cellular functions release sodium, potassium, calcium, magnesium, chloride, sulfate, phosphate, bicarbonate, and hydrogen ions
  • These ions are primarily obtained from foods, but some are from water and other beverages

17. Regulation of Electrolyte Intake

  • Ordinarily, a person obtains sufficient electrolytes byresponding to hunger and thirst
  • A severe electrolyte deficiency may cause salt craving

18. Electrolyte Output

  • The body loses some electrolytes by perspiring typically on warmer days and during strenuous exercise
  • Some are lost in the feces
  • The greatest output is as a result of kidney function and urine output

19. Regulation of Electrolyte Output

  • The concentrations of positively charged ions, such as sodium (Na + ), potassium (K + ) and calcium (Ca +2 ) are of particular importance
  • These ions are vital for nerve impulse conduction, muscle fiber contraction, and maintenance of cell membrane permeability

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. 21.1 Clinical Application Water Balance Disorders 21. 21.2 Clinical Application Sodium and Potassium Imbalances 22. 21.5: Acid-Base Balance

  • Electrolytes that ionize in water and release hydrogen ions are acids
  • Substances that combine with hydrogen ions are bases
  • Acid-base balance entails regulation of the hydrogen ion concentrations of body fluids
  • 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

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. Strengths of Acids and Bases

  • Acids:
    • Strong acids ionize more completely and release more H +
    • Weak acids ionize less completely and release fewer H +
  • Bases:
    • Strong bases ionize more completely and release more OH -
    • Weak bases ionize less completely and release fewer OH -

25. Regulation of Hydrogen Ion Concentration

  • Either an acid shift or an alkaline (basic) shift in the body fluids could threaten the internal environment
  • Normal metabolic reactions generally produce more acid than base
  • The reactions include cellular metabolism of glucose, fatty acids, and amino acids
  • Maintenance of acid-base balance usually eliminates acids in one of three ways:
    • Acid-base buffer systems
    • Resp

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