Unit III: Homeostasis Acid-Base Balance

1. Unit III: HomeostasisAcid-Base Balance Chapter 24: pp 895-903

2. Acid-Base Balance • Important part of homeostasis • metabolism depends on enzymes, and enzymes are sensitive to pH Eliminatescarbon dioxide Active tissues continuously generate acids: carbonic acid, lactic acid, fatty acids, phosphoric acids. Hydrogen ions are secreted into the urine causing an average pH of 6.0 Normalplasma pH(7.35–7.45) Tissue cells Buffer Systems short-term pHstability.

3. Acids and Bases • Determined by the solution’s hydrogen (H+) ions. • Acids • strong acids ionize freely, markedly lower pH • Bases • strong bases bind H+ ions, markedly raise pH Normal pH of the ECF:7.35 to 7.45. pH falls below 7.35Acidosis pH rises above 7.45Alkalosis Extremelyacidic Extremelybasic • (+) H+ ions (-)  • to solution pH

4. Buffers • Resist changes in pH • Physiological buffer • regulates output of acids, bases or CO2 • Chemical buffer • restore normal pH rapidly • Buffer Systems occur in Intracellular fluid (ICF) Extracellular fluid (ECF) Carbonic Acid–Bicarbonate Buffer System Phosphate BufferSystem Protein Buffer Systems Found in ECF and ICF Found in ICF and urine Found in the ECF Amino acidbuffers(All proteins) Plasmaproteinbuffers Hemoglobinbuffer system(RBCs only)

5. Bicarbonate Buffer System • Optimum pH = 6.1 • Kidneys and lungs have a pH of 7.4 • to raise pH, kidneys excrete H+ and lungs excrete CO2 • to lower pH, kidneys excrete HCO3- Additionof H Start BICARBONATE RESERVE BICARBONATE BUFFER SYSTEM Response to Acidosis NaHCO3 CO2 H2O HCO3  Na CO2 H2CO3 H  HCO3 Lungs Generationof HCO3 Otherbuffersystemsabsorb H KIDNEYS Secretionof H Alkalosis: ↓respiratory rate = ↑CO2 carbonic acid Response to Alkalosis: Conserve H+ Secrete HCO3-

6. Phosphate Buffer System • H2PO4-  HPO42- + H+ • Optimum pH of 6.8

7. Protein Buffer System • Acidic side groups can release H+ • -COOH  -COO- + H+ • Amino side groups can bind H+ • -NH2 + H+ -NH3+ Start Increasing acidity (decreasing pH) Normal pH(7.35–7.45)

8. Respiratory Control of pH • Neutralizes 2 to 3 times as much acid as chemical buffers • Collaborates with bicarbonate system • ↑CO2 and ↓pH stimulate pulmonary ventilation • While an ↑pH inhibits pulmonary ventilation

9. Renal Control of pH • Most powerful buffer system (but slow response) • Renal tubules secrete H+ into tubular fluid • Bicarbonate, ammonia, and phosphate buffers • Excreted in urine • Limiting pH of 4.5 Tubularfluid ECF Renal tubule cells CO2H2O CO2 CO2 Carbonicanhydrase Na H H2CO3 H H HCO3 HCO3 Cl H HCO3 Cl Na

10. Acid-Base Balance Responses to Acidosis Respiratory compensation ↑ respiratory rate IncreasedPCO2 Renal compensation H ions are secreted andHCO3 ions are generated. Combined Effects Respiratory Acidosis ↓ PCO2 Buffer systems other than thecarbonic acid–bicarbonatesystem accept H ions. ↑ PCO2 = ↓ plasma pH ↓H and ↑HCO3 HOMEOSTASISRESTORED HOMEOSTASISDISTURBED HOMEOSTASIS Hypoventilationcauses ↑ PCO2 Plasma pHreturns to normal Start Normal acid-base balance

11. Disorders of Acid-Base Balances • Acidosis – causes confusion, disorientation, and coma • Respiratory acidosis - rate of alveolar ventilation falls behind CO2 production • Metabolic acidosis -  production of organic acids, ingestion of acidic drugs, or loss of base • Alkalosis – causes muscle spasms, convulsions, or respiratory paralysis • Respiratory alkalosis - CO2 eliminated faster than it is produced • Metabolic alkalosis – overuse of bicarbonates or loss of acid

12. Compensation for pH Imbalances • Respiratory compensation • hypercapnia ( CO2) stimulates pulmonary ventilation • hypocapnia reduces pulmonary ventilation • Renal compensation • effective for imbalances of a few days or longer • acidosis causes  in H+ secretion • alkalosis causes bicarbonate secretion