Unit III: Homeostasis Acid-Base Balance Chapter 24: pp

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

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 pH Extremely acidic Extremely basic pH falls below 7.35 Acidosis pH rises above 7.45 Alkalosis  (+) H+ ions (-)  to solution

− Buffer Systems Intracellular fluid (ICF)Extracellular fluid (ECF) occur in Phosphate Buffer System Protein Buffer Systems Carbonic Acid– Bicarbonate Buffer System Found in ICF and urine Found in ECF and ICF Found in the ECF Hemoglobin buffer system (RBCs only) Amino acid buffers (All proteins) Plasma protein buffers Buffers Resist changes in pH Physiological buffer –regulates output of acids, bases or CO 2 Chemical buffer –restore normal pH rapidly

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 CO 2 –to lower pH, kidneys excrete HCO 3 - Addition of H  Start CO 2 CO 2  H 2 O H 2 CO 3 HH  HCO 3  Lungs HCO 3   Na  NaHCO 3 Generation of HCO 3  BICARBONATE BUFFER SYSTEM BICARBONATE RESERVE Other buffer systems absorb H  KIDNEYS Secretion of H  Alkalosis: ↓respiratory rate = ↑CO 2  carbonic acid Response to Alkalosis: Conserve H + Secrete HCO 3 - Response to Acidosis

Phosphate Buffer System H 2 PO 4 -  HPO H + Optimum pH of 6.8

Protein Buffer System Acidic side groups can release H + -COOH  -COO - + H + Amino side groups can bind H + -NH 2 + H +  -NH 3 + Start Normal pH (7.35–7.45) Increasing acidity (decreasing pH)

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

Tubular fluid Renal tubule cells ECF HH HH HH HH Na  CO 2 HCO 3  H 2 CO 3  HCO 3  CO 2  H 2 O Cl  Carbonic anhydrase Renal Control of pH Most powerful buffer system (but slow response) 1.Renal tubules secrete H + into tubular fluid Bicarbonate, ammonia, and phosphate buffers 2.Excreted in urine Limiting pH of 4.5

Acid-Base Balance Increased P CO 2 ↑ P CO 2 = ↓ plasma pH Respiratory Acidosis Responses to Acidosis Combined Effects Respiratory compensation Renal compensation ↓ P CO 2 ↓H  and ↑HCO 3  ↑ respiratory rate H  ions are secreted and HCO 3  ions are generated. Buffer systems other than the carbonic acid–bicarbonate system accept H  ions. HOMEOSTASIS DISTURBED HOMEOSTASIS RESTORED Hypoventilation causes ↑ P CO 2 Plasma pH returns to normal Start Normal acid- base balance HOMEOSTASIS

Disorders of Acid-Base Balances Acidosis – causes confusion, disorientation, and coma –Respiratory acidosis - rate of alveolar ventilation falls behind CO 2 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 - CO 2 eliminated faster than it is produced –Metabolic alkalosis – overuse of bicarbonates or loss of acid

Compensation for pH Imbalances Respiratory compensation –hypercapnia (  CO 2 ) 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