1 chapter 21 water, electrolyte, and acid-base balance d- water and electrolyte balance anatomy and...

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1 Chapter 21 Water, Electrolyte, and Acid-Base Balance D- water and electrolyte balance Anatomy and Physiology Slide 2 2 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 (Called what?) This results in stability of the body at all times Keep in mind water and electrolyte balance are interdependent Slide 3 3 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 Slide 4 4 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 (Why do men have more water than women?) 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. Slide 5 5 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. Slide 6 6 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 14:1Ratio (Extracellular: intracellular) Na + 1:28 K+K+ 5:1 Ca +2 1:19 Mg +2 26:1 Cl 3:1 HCO 3 1:19 PO 43 1:2 SO 42 Extracellular fluid Intracellular fluid Copyright The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Slide 7 7 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 (Define each) 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. Water balance exists when water intake equals water output Homeostasis requires control of both water intake and water output Slide 8 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 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. Slide 9 9 Regulation of Water Intake Slide 10 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 totals a 28% loss) Slide 11 11 Regulation of Water Output Slide 12 12 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. Slide 13 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 Ordinarily, a person obtains sufficient electrolytes by responding to hunger and thirst A severe electrolyte deficiency may cause salt craving Slide 14 14 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 Slide 15 15 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. Slide 16 16 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 Slide 17 17 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. Slide 18 18 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 - Slide 19 19 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 These 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 Slide 20 20 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 + + HCO 3 - H 2 CO 3 H + + HCO 3 - 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 + + HPO 4 -2 H 2 PO 4 - H + + HPO 4 -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 Slide 21 21 Slide 22 22 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 CO 2 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. Slide 23 23 Renal Excretion of Hydrogen Ions Nephrons help regulate the hydrogen ion concentration of body fluids by excreting hydrogen ions in the urine 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. Slide 24 24 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 buffer