Acid-Base Balance

Importance

• Key topic for university exams and entrance preparation.

Key Terminologies

pH

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

Acids

• Examples: Hydrochloric acid (HCl) and Carbonic acid (H2CO3)
  • Strong Acid: HCl, donates protons and ionizes completely.
  • Weak Acid: H2CO3, ionizes incompletely.

Bases

• Examples: Bicarbonate and Ammonia, accept protons.
• Converted to carbonic acid and ammonium ions.

Buffers

• Definition: Solutions resisting pH change.
• Components: Weak acid + strong base or weak base + strong acid.
• Buffering Capacity: Amount of acid or alkali required to change pH by one unit in 1 liter of buffer solution.

Alkali Reserve

• Definition: Bicarbonate concentration (24 mmol/L) to counter body acids.
• Normal Range: 22-26 mmol/L.

pKa Value

• Definition: pH at which an acid is half ionized.
• Effectiveness: Most effective if near body pH (7.4).

Henderson-Hasselbalch Equation

• Formula: pH = pKa + log (base/acid)
• Components:
  • Base: Bicarbonate (HCO3)
  • Acid: Carbonic acid (H2CO3)
• Regulation:
  • Metabolic: Controls bicarbonate (numerator).
  • Respiratory: Controls carbonic acid (denominator).

Regulation of pH

Systems

1. Blood Buffer System
   • Immediate response.
   • Types:
     • Bicarbonate buffer (most important in extracellular fluid).
     • Phosphate buffer.
     • Protein buffer.
2. Respiratory System
   • Not permanent.
   • Mechanisms:
     • Hypoventilation and hyperventilation.
     • Hemoglobin.
3. Renal System
   • Permanent mechanism.
   • Mechanisms:
     • Excretion of H+ ions.
     • Reabsorption of bicarbonate.
     • Excretion of titratable acids.
     • Excretion of ammonium ions.

Blood Buffer Systems

Bicarbonate Buffer

• Ratio: 20:1, bicarbonate to carbonic acid.
• Importance: Due to quantity (alkali reserve) and physiological control.

Phosphate Buffer

• Active Range: Wide due to multiple pKa values.
• Intracellular Importance: Most potent buffer.

Protein Buffer

• Mechanism: Histidine imidazole group active.

Respiratory Regulation

Mechanisms

1. Ventilation
   • Acidosis: Lungs expel CO2, decreases carbonic acid.
   • Alkalosis: Retain CO2, increases carbonic acid.
2. Hemoglobin
   • CO2 + H2O forms carbonic acid, dissociates, and is neutralized by hemoglobin.

Renal Regulation

Mechanisms

1. H+ Ion Excretion
   • Occurs in proximal convoluted tubule.
2. Bicarbonate Reabsorption
   • Involves concentration gradient movement.
3. Titrable Acid Excretion
   • In distal convoluted tubule.
4. Ammonium Ion Excretion
   • Glutamine converted to NH3, combines with H+ to form ammonium.

Acid-Base Disorders

Parameters

1. pH
   • Normal: 7.35 - 7.45
   • Acidosis: pH < 7.35
   • Alkalosis: pH > 7.45
2. Bicarbonate Level
   • Normal: 22-26 mmol/L
   • Metabolic Acidosis/Alkalosis: Changes in bicarbonate.
3. Partial Pressure of CO2
   • Normal: 35-45 mmHg
   • Respiratory Acidosis/Alkalosis: Changes in CO2.

Diagnosis

• Correspondence with pH indicates primary defect.
• Remaining parameter indicates compensatory mechanism.

Conclusion

• Discussion of acid-base disorders to continue in future lectures.