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chapter 21 electrolyte balance
 

chapter 21 electrolyte balance

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water and electrolyte balance

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    chapter 21 electrolyte balance chapter 21 electrolyte balance Presentation Transcript

    • 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. 1
    • 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 2
    • 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 3
    • Fluid Compartments Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 40 38 36 Extracellular fluid (37%) 34 32 30 28 26 24 22 20 Liters • 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 18 16 14 12 Intracellular fluid (63%) 10 8 6 4 2 0 4
    • Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Total body water Interstitial fluid Plasma Membranes of body cells Intracellular fluid (63%) Lymph Transcellular fluid Extracellular fluid (37%) 5
    • Body Fluid Composition • Intracellular fluids have high concentrations of potassium, magnesium, phosphate, and sulfate ions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Relative concentrations and ratios of ions in extracellular and intracellular fluids 150 140 Extracellular fluid 130 Intracellular fluid 120 110 100 Ion concentration (m Eq/L) • Extracellular fluids are generally similar in composition including high concentrations of sodium, calcium, chloride and bicarbonate ions 90 80 70 60 50 40 30 20 10 0 Na+ Ratio K+ Ca+2 Mg+2 Cl− HCO3− PO4−3 SO4−2 14:1 1:28 5:1 1:19 26:1 3:1 1:19 1:2 (Extracellular: intracellular) 6
    • Movement of Fluid Between Compartments • Two major factors regulate the movement of water and electrolytes from one fluid compartment to another • Hydrostatic pressure • Osmotic pressure Fluid leaves plasma at arteriolar end of Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Capillary wall Plasma Interstitial fluid Transcellular fluid Serous membrane capillaries because outward force of hydrostatic pressure predominates Fluid returns to plasma at venular ends of capillaries because inward force Lymph of colloid osmotic vessel pressure predominates Lymph Intracellular fluid Cell membrane Hydrostatic pressure within interstitial spaces forces fluid into lymph capillaries Interstitial fluid is in equilibrium with transcellular and intracellular fluids 7
    • 21.3: Water Balance • Water balance exists when water intake equals water output • Homeostasis requires control of both water intake and water output 8
    • 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Water of metobolism (250 mL or 10%) Average daily output of water Water lost in sweat (150 mL or 6%) Water lost in feces (150 mL or 6%) Water in moist food (750 mL or 30%) Water lost through skin and lungs (700 mL or 28%) Average daily intake of water Total intake (2,500 mL) Total output (2,500 mL) Water in beverages (1,500 mL or 60%) (a) Water lost in urine (1,500 mL or 60%) (b) 9
    • Regulation of Water Intake 10
    • 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) 11
    • Regulation of Water Output 12
    • 21.4: Electrolyte Balance • An electrolyte balance exists when the quantities of electrolytes the body gains equals those lost Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Foods Fluids Metabolic reactions Electrolyte intake Electrolyte output Perspiration Feces Urine 13
    • 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 14
    • Regulation of Electrolyte Intake • Ordinarily, a person obtains sufficient electrolytes by responding to hunger and thirst • A severe electrolyte deficiency may cause salt craving 15
    • 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 16
    • 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Potassium ion concentration increases Calcium ion concentration decreases Parathyroid glands are stimulated Adrenal cortex is signaled Parathyroid hormone is secreted Aldosterone is secreted Renal tubules conserve calcium and increase secretion of phosphate Intestinal absorption of calcium increases Renal tubules increase reabsorption of sodium ions and increase secretion of potassium ions Sodium ions are conserved and potassium ions are excreted Activity of bone-resorbing osteoclasts increases Increased phosphate excretion in urine Addition of phosphate to bloodstream Calcium ion concentration returns toward normal Normal phosphate concentration is maintained 17
    • 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 18
    • Sources of Hydrogen Ions Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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 19
    • 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- 20
    • 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 • Respiratory excretion of carbon dioxide • Renal excretion of hydrogen ions 21
    • Acid-Base Buffer Systems • Bicarbonate buffer system • The bicarbonate ion converts a strong acid to a weak acid • Carbonic acid converts a strong base to a weak base H+ + HCO3-  H2CO3  H+ + HCO3• Phosphate buffer system • The monohydrogen phosphate ion converts a strong acid to a weak acid • The dihydrogen phosphate ion converts a strong base to a weak base H+ + HPO4-2  H2PO4-  H+ + HPO4-2 • Protein buffer system • NH3+ group releases a hydrogen ion in the presence of excess base • COO- group accepts a hydrogen ion in the presence of excess acid 22
    • 23
    • Respiratory Secretion of Carbon Dioxide • The respiratory center in the brainstem helps regulate hydrogen ion concentrations in the body fluids by controlling the rate and depth of breathing • If body cells increase their production of CO2… Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Cells increase production of CO2 CO2 reacts with H2O to produce H2CO3 H2CO3 releases H+ Respiratory center is stimulated Rate and depth of breathing increase More CO2 is eliminated through lungs 24
    • Renal Excretion of Hydrogen Ions • Nephrons help regulate the hydrogen ion concentration of body fluids by excreting hydrogen ions in the urine Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. High intake of proteins Increased metabolism of amino acids Increased concentration of H+ in urine Concentration of H+ in body fluids returns toward normal Increased secretion of H+ into fluid of renal tubules Increased formation of sulfuric acid and phosphoric acid Increased concentration of H+ in body fluids 25
    • Time Course of Hydrogen Ion Regulation • Various regulators of hydrogen ion concentration operate at different rates • Acid-base (chemical) buffers function rapidly • Respiratory and renal (physiological buffers) mechanisms function more slowly Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Bicarbonate buffer system First line of defense against pH shift Chemical buffer system Phosphate buffer system Protein buffer system Second line of defense against pH shift Respiratory mechanism (CO2 excretion) Physiological buffers Renal mechanism (H+ excretion) 26
    • 21.6: Acid-Base Imbalances • Chemical and physiological buffer systems ordinarily maintain the hydrogen ion concentration of body fluids within very narrow pH ranges • Abnormal conditions may disturb the acid-base balance Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Acidosis Alkalosis pH scale 6.8 7.0 7.35 7.45 7.8 8.0 Normal pH range Survival range 27
    • Acidosis • 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 • Alkalosis results from a loss of acids or an accumulation of bases accompanied by a decrease in hydrogen ion concentrations Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Loss of bases Accumulation of acids Increased concentration of H+ Acidosis pH drops pH scale 7.4 pH rises Alkalosis Decreased concentration of H+ Loss of acids Accumulation of bases 28
    • Acidosis • Two major types of acidosis are respiratory acidosis and metabolic acidosis Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Kidney failure to excrete acids Excessive production of acidic ketones as in diabetes mellitus Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Decreased rate and depth of breathing Obstruction of air passages Decreased gas exchange Accumulation of CO2 Accumulation of nonrespiratory acids Metabolic acidosis Excessive loss of bases Respiratory acidosis Prolonged diarrhea with loss of alkaline intestinal secretions Prolonged vomiting with loss of intestinal secretions 29
    • Alkalosis • Respiratory alkalosis develops as a result of hyperventilation • 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 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. • Anxiety • Fever • Poisoning • High altitude Gastric drainage Vomiting with loss of gastric secretions Hyperventilation Loss of acids Excessive loss of CO2 Decrease in concentration of H2CO3 Net increase in alkaline substances Decrease in concentration of H+ Respiratory alkalosis Metabolic alkalosis 30