Chapter 26 Fluid, Electrolytes, and Acid-Base Balance Lecture 17 Part 2b: Acid-Base Balance Marieb’s Human Anatomy and Physiology Ninth Edition Marieb  Hoehn

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

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

4 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 CO 2 ) 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

5 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 + + HCO 3 - ↔ H 2 CO 3 ↔ CO 2 + H 2 O 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 + + HPO 4 -2 ↔ H 2 PO 4 - Strong acidWeak acid Strong acidWeak acid

6 Acid-Base Buffer Systems Protein Buffer System ICF, plasma proteins, Hb NH 2 group accepts hydrogen ions when pH falls COOH group releases hydrogen ions when pH rises - Figure from: Martini, Anatomy & Physiology, Prentice Hall, 2001 Most plentiful and powerful chemical buffer system

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

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

9 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 HCO 3 - FigureS from: Martini, Anatomy & Physiology, Prentice Hall, 2001 Buffering Mechanisms in the Kidney Production of new HCO 3 - (2)

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

11 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: 1.Whether the cause is respiratory (CO 2 ), or metabolic (other acids, bases) 2.Whether the blood pH is acid or alkaline Figure from: Hole’s Human A&P, 12 th edition, 2010

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

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

14 Acidosis and Alkalosis What would be the indications of acidosis and alkalosis in terms of changes in pH and P CO2 ? pH and HCO 3 - ? How would the body try to compensate for –Acidosis Respiratory Metabolic –Alkalosis Respiratory Metabolic See Handout: Marieb, Human Anatomy & Physiology, Pearson, 2004

15 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