Lecture Notes on Acid-Base Balance

Introduction

• Topic: Acid-base balance
• Importance: Key for university exams and entrance preparation
• Focus: General concepts of acid-base regulation

Key Terminologies

1. pH

• Definition: Negative logarithm of hydrogen ion concentration
• Relationship: Inversely related to hydrogen ion concentration
• Normal Range: 7.35 to 7.45
  • Acidosis: pH < 7.35
  • Alkalosis: pH > 7.45

2. Acids

• Examples: Hydrochloric acid (HCl), Carbonic acid (H2CO3)
• Strong Acid: Completely ionizes (e.g., HCl)
• Weak Acid: Incompletely ionizes (e.g., H2CO3)

3. Bases

• Function: Accept protons
• Examples: Bicarbonate (HCO₃⁻), Ammonia (NH₃)

4. Buffers

• Definition: Solutions that resist pH changes
• Components: Weak acid + strong base or weak base + strong acid
• Buffering Capacity: Amount of acid/alkali needed to change pH of one liter solution by one unit

5. Alkali Reserve

• Definition: Bicarbonate concentration
• Normal Range: 22 to 26 mmol/L
• Function: Overcomes body-generated acids

6. pKa

• Definition: pH at which acid is half ionized
• Importance: Most effective when close to body pH (7.4)

Henderson-Hasselbalch Equation

• Formula: pH = pKa + log([Base]/[Acid])
• Application: Relates pH, pKa, and concentrations of base (bicarbonate) and acid (carbonic acid)

Regulation of pH in Extracellular Fluid

Defense Mechanisms

1. Blood Buffers (Immediate acting)
   • Bicarbonate Buffer
   • Phosphate Buffer
   • Protein Buffer
2. Respiratory System (Temporary)
   • Methods: Hyperventilation & hypoventilation, Hemoglobin
3. Renal Mechanism (Permanent)
   • Mechanisms: Excretion of H+ ions, Reabsorption of bicarbonate, Excretion of titrable acids, Excretion of ammonium ions

Blood Buffer Systems

• Bicarbonate Buffer
  • Ratio: 20:1 (Bicarbonate to Carbonic acid)
  • pKa: 6.1
• Phosphate Buffer
  • Ratio: 4:1 (Disodium acid phosphate to Sodium dihydrogen phosphate)
  • pKa: 6.8
• Protein Buffer
  • Active Group: Histidine imidazole
  • pKa: 6.1

Respiratory Regulation

• Mechanisms:
  • Hypoventilation/Hyperventilation: Adjusts CO₂ levels
  • Hemoglobin: Transports CO₂ and O₂ to balance pH

Renal Regulation

• Mechanisms:
  1. Excretion of H+ ions
  2. Reabsorption of bicarbonate
  3. Excretion of titrable acids
  4. Excretion of ammonium ions

Acid-Base Disorders

• Parameters:
  • pH: Normal 7.35-7.45
  • Bicarbonate: Normal 22-26 mmol/L
  • pCO2: Normal 35-45 mmHg
• Disorders:
  • Metabolic Acidosis: Decreased bicarbonate
  • Metabolic Alkalosis: Increased bicarbonate
  • Respiratory Acidosis: Increased pCO2
  • Respiratory Alkalosis: Decreased pCO2

Conclusion

• Overview of acid-base balance mechanisms
• Upcoming: Detailed discussion on disorders of acid-base balance

• Note: Important for academic exams and entrance tests.