Chapter 26 Fluid, Electrolytes, and Acid/Base Balance Lecture 17

1. Marieb’s Human Anatomy and Physiology Marieb w Hoehn Chapter 26 Fluid, Electrolytes, and Acid/Base Balance Lecture 17

2. Lecture Overview • Overview • Fluid (water) balance • Compartments • Body fluid composition • Intercompartmental fluid shifts • Electrolyte balance • Acid-base balance • Buffer systems • Acidosis and alkalosis

3. Overview • Our survival depends upon maintaining a normal volume and composition of • Extracellular fluid (ECF) • Intracellular fluid (ICF) • Ionic concentrations and pH are critical • Three interrelated processes • Fluid balance (How does water move from one place to the other? ) • Electrolyte balance (What is an electrolyte?) • Acid-base balance (What is normal pH?)

4. Water Content of the Human Body Of the 40 liters of water in the body of an average adult male: - one-third (15L) is extracellular - two-thirds (25L) is intracellular Figure from: Hole’s Human A&P, 12th edition, 2010

5. Fluid Compartments Figure from: Hole’s Human A&P, 12th edition, 2010 ‘Compartments’ commonly behave as distinct entities in terms of ion distribution, but ICF and ECF osmotic concentrations are identical (about 290-300 mOsm/L). Why?

6. Osmolarity and Milliequivalents (mEq) • Recall that osmolarity expresses total solute concentration of a solution • Osmolarity (effect on H2O) of body solutions is determined by the total number of dissolved particles (regardless of where they came from) • The term ‘osmole’ reflects the number of particles yielded by a particular solute (milliosmole, mOsm, = osmole/1000) • 1 mole of glucose (180g/mol) • 1 mole of NaCl (58g/mol) • Osmolarity = #moles/L X # particles yielded • An equivalent is the positive or negative charge equal to the amount of charge in one mole of H+ • A milliequivalent (mEq) is one-thousandth of an Eq • Number of Eq = molecular wt. / valence -> 1 osmole of particles -> 2 osmoles of particles

7. Body Fluid Ionic Composition ECF major ions: - sodium, chloride, and bicarbonate ICF major ions: - potassium, magnesium, and phosphate (plus negatively charged proteins) Figure from: Hole’s Human A&P, 12th edition, 2010 You should know these chemical symbols and charges (valences) of ions

8. Movement of Fluids Between Compartments Figure from: Hole’s Human A&P, 12th edition, 2010 Water moves between mesothelial surfaces: peritoneal, pleural, and pericardial cavities as well as the synovial membranes. It also moves between the blood and CSF and through the fluids of the eye and ear Net movements of fluids between compartments result from differences in hydrostatic and osmotic pressures

9. Fluid (Water) Balance Figure from: Hole’s Human A&P, 12th edition, 2010 * urine production is the most important regulator of water balance (water in = water out)

10. Water Balance and ECF Osmolarity • Regulation of water intake • increase in osmotic pressure of ECF → osmoreceptors in hypothalamic thirst center → stimulates thirst and drinking (water! ) • Regulation of water output • Obligatory water losses (must happen) • insensible water losses (lungs, skin) • water loss in feces • water loss in urine (min about 500 ml/day) • increase in osmotic pressure of ECF → ADH is released • concentrated urine is excreted • more water is retained • LARGE changes in blood vol/pressure → Renin and ADH release

11. Fluid Imbalance Figure from: Saladin, Anatomy & Physiology, McGraw Hill, 2007

12. Dehydration and Overhydration • Dehydration (removing only H2O) • osmotic pressure increases in extracellular fluids • water moves out of cells • osmoreceptors in hypothalamus stimulated • hypothalamus signals posterior pituitary to release ADH • urine output decreases • Overhydration (adding only H2O) • osmotic pressure decreases in extracellular fluids • water moves into cells • osmoreceptors inhibited in hypothalamus • hypothalamus signals posterior pituitary to decrease ADH output • urine output increases Severe thirst, wrinkling of skin, fall in plasma volume and decreased blood pressure, circulatory shock, death ‘Drunken’ behavior (water intoxication), confusion, hallucinations, convulsions, coma, death

13. Electrolyte Balance Figure from: Hole’s Human A&P, 12th edition, 2010 • Electrolyte balance is important since: • It regulates fluid (water) balance • Concentrations of individual electrolytes can affect cellular functions Na+: major cation in ECF (plasma: 136-142 mEq/L; Avg ≈ 140) K+: major cation in ICF (plasma: 3.8-5.0 mEq/L; Avg ≈ 4.0)

14. Regulation of Osmolarity Figures from: Martini, Anatomy & Physiology, Prentice Hall, 2001 Recall: [Na+]  Osmolarity Osmolarity is regulated by altering H2O content ** Osmolarity = Amt of solute / volume of H2O

15. Fluid Volume Regulation and [Na+] Volume is regulated by altering Na+ content Figures from: Martini, Anatomy & Physiology, Prentice Hall, 2001 Estrogens are chemically similar to aldosterone and enhance NaCl absorption by renal tubules Glucocorticoids can also enhance tubular reabsorption of Na+

16. Summary Table of Fluid and Electrolyte Balance You should understand this table

17. Potassium Balance Figure from: Hole’s Human A&P, 12th edition, 2010 • Potassium loss generally occurs via the urine. The rate of tubular secretion of K+ varies with: • Changes in the [K+] in the ECF • Changes in pH • Aldosterone levels Remember that Na+ can be exchanged forH+or K+ in the nephron tubules

18. Calcium Balance Figure from: Hole’s Human A&P, 12th edition, 2010 [Ca2+] in ECF is about 5 mEq/L

19. Strengths of Acids and Bases • Strong acids ionize more completely and release more H+ • Weak acids ionize less completely and release fewer H+(**allows them to act as buffers) • Strong bases ionize more completely and bind more H+ • Weak bases ionize less completely and bind fewer H+

20. Sources of Hydrogen Ions Figure from: Hole’s Human A&P, 12th edition, 2010 Some H+ is also absorbed from the digestive tract

21. Regulation of Hydrogen Ion Concentration • 1. chemical acid-base buffer systems (physical buffers) • first line of defense • can tie-up acids or bases, but cannot eliminate them • act in seconds • 2. respiratory excretion of carbon dioxide • a physiological buffer (can eliminate excess acid indirectly via CO2) • minutes • 3. renal excretion of hydrogen ions • a physiological buffer (can eliminate excess metabolic acids directly, e.g., keto-, uric, lactic, phosphoric) • hours to a day

22. Acid-Base Buffer Systems • Bicarbonate System • the bicarbonate ion converts a strong acid to a weak acid • carbonic acid converts a strong base to a weak base • an important buffer of the ECF (~ 25 mEq/L) • H+ + HCO3-↔ H2CO3 ↔ CO2 + H2O Strong acid Weak acid • Phosphate 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- Strong acid Weak acid

23. Acid-Base Buffer Systems Protein Buffer System ICF, plasma proteins, Hb Most plentiful and powerful chemical buffer system • COOH group releases hydrogen ions when pH rises NH2 group accepts hydrogen ions when pH falls - Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

24. Respiratory Excretion of Carbon Dioxide Figure from: Hole’s Human A&P, 12th edition, 2010 A physiological buffer system

25. Renal Excretion of Hydrogen Ions Figure from: Hole’s Human A&P, 12th edition, 2010 *The kidney is most powerful and versatile acid-base regulating system in the body

26. Buffering Mechanisms in the Kidney Note that secretion of H+ relies on carbonic anhydrase activity within tubular cells Net result is secretion of H+ accompanied by the (1)retention of HCO3- (2) Production of new HCO3- Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001

27. Summary of Acid-Base Balance Figure from: Hole’s Human A&P, 12th edition, 2010 (Seconds) Know this slide! (Minutes) (Hours-Days)

28. Acidosis and Alkalosis If the pH of arterial blood drops to 6.8 or rises to 8.0 for more than a few hours, survival is jeopardized • Classified according to: • Whether the cause is respiratory (CO2), or metabolic (other acids, bases) • Whether the blood pH is acid or alkaline Figure from: Hole’s Human A&P, 12th edition, 2010

29. Acidosis Figure from: Hole’s Human A&P, 12th edition, 2010 (hypopnea) Respiratory acidosis Metabolic acidosis Nervous system depression, coma, death

30. Alkalosis Figure from: Hole’s Human A&P, 12th edition, 2010 Respiratory alkalosis Metabolic alkalosis Nervousness, tetany, convulsions, death

31. Acidosis and Alkalosis • What would be the indications of acidosis and alkalosis in terms of changes in pH and PCO2? pH and HCO3-? • How would the body try to compensatefor • Acidosis • Respiratory • Metabolic • Alkalosis • Respiratory • Metabolic See Handout: Marieb, Human Anatomy & Physiology, Pearson, 2004

32. Flow chart for Acidosis/Alkalosis Three things to check: 1) pH – 7.35-7.452) pCO2 – 35-45 mm Hg3) HCO3- - 22 – 26 mEq/L pH   acidosis alkalosis  pCO2  HCO3-  pCO2 HCO3- respiratory metabolic respiratory metabolic Norm HCO3- Norm pCO2 Norm HCO3- Norm pCO2 HCO3-  pCO2  HCO3-  pCO2 No Comp Comp No Comp Comp No Comp Comp No Comp Comp

33. Review • There are two major fluid compartments of the body • Intracellular • About 2/3 of body’s fluid • Includes the fluid within cells • Major ions: K+, Mg2+, PO43-, Proteins • Extracellular • About 1/3 of body’s fluid • Includes interstitial fluid, plasma, lymph, and transcellular fluid • Major ions: Na+, Cl-, HCO3-

34. Review • There are two major forces affecting movement of fluid between compartments • Hydrostatic Pressure • Osmotic Pressure • Fluid balance • Amount of water you take in is equal to the amount of water you lose to the environment • Intake of water in food/drink is the most important source of fluid • Kidney regulation of water is the most important regulator of water loss

35. Review • Electrolyte balance • Balance: Gains and losses of every electrolyte are equal • Electrolyte balance is important because • It directly affects water balance • Electrolyte concentrations affect cell processes • Na+ (aldosterone, ADH, ANP) • Increased [Na+ ] in ECF -> ↑ ADH, ↑ ANP • Decreased [Na+ ] in ECF ->  ADH, ↑ aldosterone • K+ ([K+] in plasma, aldosterone) • Increased [K+ ] in ECF -> increased secretion, ↑ aldosterone • Decreased [K+ ] in ECF -> decreased secretion,  aldosterone,

36. Review • Electrolyte balance (cont’d) • Ca2+ (PTH, calcitriol, calcitonin) • Increase in ECF -> calcitonin promotes bone deposition • Decrease in ECF -> PTH , calcitriol • ↑ intestinal absorption • ↑ bone resorption •  Ca2+ secretion, ↑ PO43- secretion • Acid-base balance • Production of H+ is exactly offset by the loss of H+ • Major mechanisms of maintaining • acid-base (chemical) buffer systems: HCO3-, PO43-, protein • respiratory excretion of carbon dioxide • renal excretion of hydrogen ions

37. Review • Acidosis (pH < 7.35) • Excessive H+ in the plasma • Respiratory acidosis • Metabolic acidosis • Alkalosis (pH > 7.45) • Insufficient H+ in the plasma • Respiratory alkalosis • Metabolic alkalosis • Compensations

38. Review