Chapter 21 Lecture PowerPoint
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Hole’s Human Anatomy and Physiology Twelfth Edition
Shier Butler Lewis Chapter 21 Water, Electrolyte, and Acid-Base Balance
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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
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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
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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
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Total body water Interstitial fluid Plasma Membranes of body cells
Intracellular fluid (63%)
Lymph Transcellular fluid Extracellular fluid (37%)
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Body Fluid Composition • Extracellular fluids are generally similar in composition including high concentrations of sodium, calcium, chloride and bicarbonate 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)
• Intracellular fluids have high concentrations of potassium, magnesium, phosphate, and sulfate ions
90 80 70 60 50 40 30 20 10 0 Ratio
Na+
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)
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Movement of Fluid Between Compartments • Two major factors regulate the movement of water and electrolytes from one fluid compartment to another • Hydrostatic pressure Fluid leaves plasma • Osmotic pressure at arteriolar end of
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Capillary wall
Plasma
Interstitial fluid
Fluid returns to plasma at venular ends of capillaries because inward force Lymph of colloid osmotic vessel pressure predominates Lymph
Transcellular fluid
Serous membrane
capillaries because outward force of hydrostatic pressure predominates
Intracellular fluid Cell membrane
Hydrostatic pressure within interstitial spaces forces fluid into lymph capillaries Interstitial fluid is in equilibrium with transcellular and intracellular fluids
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21.3: Water Balance • Water balance exists when water intake equals water output • Homeostasis requires control of both water intake and water output
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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
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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)
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Regulation of Water Intake
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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)
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Regulation of Water Output
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21.4: Electrolyte Balance • An electrolyte balance exists when the quantities of electrolytes the body gains equals those lost Copyright Š The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Foods
Fluids
Metabolic reactions
Electrolyte intake
Electrolyte output
Perspiration
Feces
Urine 14
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
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Regulation of Electrolyte Intake • Ordinarily, a person obtains sufficient electrolytes by responding to hunger and thirst • A severe electrolyte deficiency may cause salt craving
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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
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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
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21.1 Clinical Application Water Balance Disorders
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21.2 Clinical Application Sodium and Potassium Imbalances
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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
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Sources of Hydrogen Ions
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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
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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-
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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 24
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 25
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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…
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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
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Renal Excretion of Hydrogen Ions • Nephrons help regulate the hydrogen ion concentration of body fluids by excreting hydrogen ions in the urine Copyright Š 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
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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
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Bicarbonate buffer system
First line of defense against pH shift
Chemical buffer system
Phosphate buffer system
Protein buffer system
Respiratory mechanism (CO2 excretion) Second line of defense against pH shift
Physiological buffers Renal mechanism (H+ excretion)
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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
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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
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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
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Acidosis • Two major types of acidosis are respiratory acidosis and metabolic acidosis
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Kidney failure to excrete acids
Excessive production of acidic ketones as in diabetes mellitus
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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
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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+
Metabolic alkalosis Respiratory alkalosis
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Important Points in Chapter 21: Outcomes to be Assessed 21.1: Introduction Explain the balance concept. Explain the importance of water and electrolyte balance. 21.2: Distribution of Body Fluids Describe how body fluids are distributed in compartments. Explain how fluid composition varies among compartments and how fluids move from one compartment to another. 21.3: Water Balance List the routes by which water enters and leaves the body. Explain the regulation of water input and water output.
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Important Points in Chapter 21: Outcomes to be Assessed 21.4: Electrolyte Balance List the routes by which electrolytes enter and leave the body. Explain the regulation of the input and the output of electrolytes. 21.5: Acid-Base Balance Explain acid-base balance. Identify how pH number describes the acidity and alkalinity of a body fluid. List the major sources of hydrogen ions in the body. Distinguish between strong acids and weak acids. Explain how chemical buffer systems, the respiratory system, and the 35 kidneys keep the pH of body fluids relatively constant.
Important Points in Chapter 21: Outcomes to be Assessed 21.6: Acid-Base Imbalances Describe the causes and consequences of increase or decrease in body fluid pH.
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Quiz 21 Complete Quiz 21 now! Read Chapter 22. 37