Chapter 21 *. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.

21.1: Introduction The term balance suggests a state of constancy 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

21.2: Distribution of Body Fluids p.811 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

Fluid Compartments An average adult female is about 52% water by weight, and an average male about 63% water by weight There are about 40 liters of water (with its dissolved electrolytes) in the body, distributed into two major compartments: Intracellular fluid – 63% - fluid inside cells Extracellular fluid – 37% - fluid outside cells Interstitial fluid Blood plasma Lymph Transcellular fluid – separated from other extracellular fluids by epithelial layers Cerebrospinal fluid Aqueous and vitreous humors Synovial fluid Serous fluid Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 40 38 36 34 Extracellular fluid (37%) 32 30 28 26 24 22 Liters 20 18 16 Intracellular fluid (63%) 14 12 10 8 6 4 2

Did You Know This?????? Total body water Interstitial fluid Plasma Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Total body water Interstitial fluid Plasma Lymph Intracellular fluid (63%) Membranes of body cells Transcellular fluid Extracellular fluid (37%)

Body Fluid Composition Extracellular fluids are generally similar in composition including high concentrations of sodium, calcium, chloride and bicarbonate ions Blood plasma has more proteins than interstitial fluid or lymph 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 1 10 100 90 80 Ion concentration (m Eq/L) 70 60 50 40 30 20 10 Na+ K+ Ca+2 Mg+2 Cl- HCO3- PO4-3 SO4-2 Ratio 14:1 1:28 5:1 1:19 26:1 3:1 1:19 1:2 (Extracellular: intracellular)

Movement of Fluid Between Compartments Two major factors regulate the movement of water and electrolytes from one fluid compartment to another Hydrostatic pressure (The pressure exerted by a fluid at equilibrium at a given point within the fluid, due to the force of gravity.) Osmotic pressure Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Fluid leaves plasma at arteriolar end of capillaries because outward force of hydrostatic pressure predominates Capillary wall Plasma Fluid returns to plasma at venular ends of capillaries because inward force of colloid osmotic pressure predominates Interstitial fluid Lymph vessel Hydrostatic pressure within interstitial spaces forces fluid into lymph capillaries Lymph Transcellular fluid Intracellular fluid Interstitial fluid is in equilibrium with transcellular and intracellular fluids Serous membrane Cell membrane

21.3: Water Balance p. 814 Water balance exists when water intake equals water output Homeostasis requires control of both water intake and water output

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. Average daily intake of water Average daily output of water Water lost in sweat (150 mL or 6%) Water of metobolism (250 mL or 10%) 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%) Total intake (2,500 mL) Total output (2,500 mL) Water in beverages (1,500 mL or 60%) Water lost in urine (1,500 mL or 60%) (a) (b)

Regulation of Water Intake The primary regulator of water intake is thirst.

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)

Regulation of Water Output The osmoreceptor-ADH mechanism in the hypothalamus regulates the concentration of urine produced in the kidney.

21.1 Clinical Application p. 808 Water balance disorders Dehydration Water intoxication edema

See “water intoxication” articles posted on blog

Death By Water Intoxication RANCHO CORDOVA, Calif. (Associated Press) -- A woman who competed in a radio station's contest to see how much water she could drink without going to the bathroom died of water intoxication, the coroner's office said Saturday. A preliminary investigation found evidence "consistent with a water intoxication death," said assistant Coroner Ed Smith Death By Water Intoxication California Woman Dies Shortly After Participating in Radio Stunt

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. Metabolic reactions Foods Fluids Electrolyte intake Electrolyte output Perspiration Feces Urine

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, and some are by-products of metabolism

Regulation of Electrolyte Intake Ordinarily, a person obtains sufficient electrolytes by responding to hunger and thirst A severe electrolyte deficiency may cause salt craving

Salt Cravings The adrenal glands help the body respond to changes caused by stress and emotions. Not getting enough sleep, stress, poor nutrition, trauma or pregnancy are just a few of the reasons adrenal exhaustion can occur. This could make you crave salt. Mineral Deficiency Poor nutrition, starvation diets, fasting or diets lacking green leafy vegetables and whole grains could cause a mineral deficiency (particularly magnesium) and make you crave salt. Electrolyte Imbalance Electrolytes help control the regulation of fluids in the body. Poor nutrition or drinking too much water—which could flush minerals from your system—can cause an electrolyte imbalance, making you crave salt.

Electrolyte Output The body loses some electrolytes by perspiring (more 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

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 Sodium ions account for nearly 90% of the positively charged ions in extracellular fluids

Regulation of Electrolyte Output 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 Intestinal absorption of calcium increases Renal tubules conserve calcium and increase secretion of phosphate Renal tubules increase reabsorption of sodium ions and increase secretion of potassium ions Activity of bone-resorbing osteoclasts increases Increased phosphate excretion in urine Addition of phosphate to bloodstream Sodium ions are conserved and potassium ions are excreted Calcium ion concentration returns toward normal Normal phosphate concentration is maintained

21.2 Clinical Application P. 811 Sodium and Potassium Imbalances

21.5: Acid-Base Balance p.811 Acids are electrolytes that ionize in water and release hydrogen ions Bases are substances that combine with hydrogen ions 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 pH number indicates the degree to which a solution is acidic or basic (alkaline). The more acid the solution, the lower its pH The more alkaline the solution, the higher its pH

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

Strengths of Acids and Bases Strong acids ionize more completely and release more H+ Ex: HCl Weak acids ionize less completely and release fewer H+ Ex: H2CO3 Bases: Strong bases ionize more completely and release more OH- or other negative ions Weak bases ionize less completely and release fewer OH- or other negative ions

Regulation of Hydrogen Ion Concentration p.812 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

Chemical Buffer Systems p.812 Chemical buffer systems are in all body fluids and are based on chemicals that combine with excess acids or bases. 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

Respiratory Excretion of Carbon Dioxide p.814 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. 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… 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

Renal Excretion of Hydrogen Ions p.814 Increased concentration 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 Concentration of H+ in body fluids returns toward normal Increased metabolism of amino acids Increased concentration of H+ in urine Increased formation of sulfuric acid and phosphoric acid Increased secretion of H+ into fluid of renal tubules Increased concentration of H+ in body fluids

Time Course of pH Regulation p.815 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 Respiratory mechanism (CO2 excretion) Second line of defense against pH shift Physiological buffers Renal mechanism (H+ excretion)

21.6: Acid-Base Imbalances p. 815 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 35 Survival range

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. Accumulation of acids Loss of bases Increased concentration of H+ Acidosis pH drops pH scale 7.4 pH rises Alkalosis Decreased concentration of H+ Loss of acids Accumulation of bases

Acidosis p.816 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 nonrespiratory acids Metabolic acidosis Accumulation of CO2 Excessive loss of bases Respiratory acidosis Prolonged diarrhea with loss of alkaline intestinal secretions Prolonged vomiting with loss of intestinal secretions

Net increase in alkaline substances Alkalosis p.817 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 Gastric drainage Vomiting with loss of gastric secretions • Fever • Poisoning • High altitude 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

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.

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 center, and the 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.