Acid-Base Balance Lecture Notes

Introduction

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

Key Terminologies

pH

• Definition: Negative logarithm of hydrogen ion concentration.
• Normal Range: 7.35 to 7.45
  • < 7.35 = Acidosis

  • 7.45 = Alkalosis

Acids

• Strong Acid Example: Hydrochloric acid (HCl) - Fully ionizes.
• Weak Acid Example: Carbonic acid (H2CO3) - Incompletely ionizes.

Bases

• Definition: Accept protons.
• Examples: Bicarbonate (HCO3-) and Ammonia (NH3).

Buffers

• Function: Resist changes in pH.
• Composition: Weak acid and its strong base, or vice versa.
• Buffer Capacity: Amount of acid or alkali needed to change pH by one unit in 1L of solution.

Alkali Reserve

• Definition: Bicarbonate concentration, normal value 24 mmol/L.
• Importance: Overcomes synthesized body acids.

pKa Value

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

Henderson-Hasselbalch Equation

• Formula: pH = pKa + log(Base/Acid)
• Components:
  • Base: Bicarbonate (HCO3-)
  • Acid: Carbonic acid (H2CO3)
  • Regulation
    • Metabolic regulation affects the numerator.
    • Respiratory regulation affects the denominator.

Regulation of pH in Extracellular Fluid

Defense Systems

1. Blood Buffer (Immediate Action)
   • Bicarbonate buffer
   • Phosphate buffer
   • Protein buffer
2. Respiratory System (Intermediate Mechanism)
   • Hypoventilation and Hyperventilation
   • Hemoglobin
3. Renal System (Permanent Mechanism)
   • Excretion of H+ ions
   • Reabsorption of bicarbonate
   • Excretion of titrable acids
   • Excretion of ammonium ions

Blood Buffer Systems

• Bicarbonate Buffer: Ratio of bicarbonate to carbonic acid (20:1)
• Phosphate Buffer: Ratio of disodium phosphate to sodium dihydrogen phosphate (4:1)
• Protein Buffer: Albumin and hemoglobin

Respiratory Regulation

Mechanisms

1. Hypo/Hyperventilation
   • Acidosis: Blow out CO2 to decrease carbonic acid and correct pH.
   • Alkalosis: Retain CO2 to increase carbonic acid and correct pH.
2. Hemoglobin
   • Tissue Level: CO2 converts to carbonic acid.
   • Lung Level: Oxygenated hemoglobin releases H+ to form carbonic acid.

Renal Regulation

Mechanisms

1. Excretion of H+ Ions: Via proximal convoluted tubule
2. Bicarbonate Reabsorption: No net H+ excretion
3. Excretion of Titrable Acids: Formation of sodium dihydrogen phosphate
4. Excretion of Ammonium Ions: Formation from NH3

Acid-Base Disorders

Parameters

• pH: Normal 7.35 to 7.45
• Bicarbonate Level: Normal 22 to 26 mmol/L
• Partial Pressure of CO2: Normal 35 to 45 mmHg

Disorder Types

• Metabolic Acidosis: Decrease in bicarbonate
• Metabolic Alkalosis: Increase in bicarbonate
• Respiratory Acidosis: Increase in CO2
• Respiratory Alkalosis: Decrease in CO2

Diagnosis

• Primary Defect: Parameter that corresponds with pH change.
• Compensatory Mechanism: Adjusts the remaining parameters.

Conclusion

• Next Discussion: Detailed exploration of metabolic and respiratory disorders related to acid-base balance.