Lecture 3: Acid-Base Balance and Buffer Systems

Importance of Acid-Base Balance

• Controlled by regulating hydrogen ion concentration.
• Critical in maintaining protein structures; proteins can be denatured by changes in pH.
• Normal plasma pH range: 7.35 to 7.45 (slightly alkaline).
• Deviations from this range can cause significant health problems.

Causes of Blood Acidification

• High protein diets.
• Utilizing fat as an energy source can lead to ketoacidosis (ketone body buildup).

Mechanisms for pH Regulation

1. Buffer Systems
2. Exhalation of Carbon Dioxide
3. Excretion of Hydrogen Ions by Kidneys

Buffer Systems

• Prevent drastic pH changes by converting strong acids/bases into weak acids/bases.
• Three main buffer systems:
  • Protein Buffer System
    • Mostly intracellular; plasma proteins also involved.
    • Proteins are amphoteric (can act as both weak acids and bases).
    • Carboxyl groups release H+ when pH rises; amino groups bind H+ when pH falls.
  • Carbonic Acid-Bicarbonate Buffer System
    • Buffers blood pH; forms carbonic acid (H2CO3) from CO2 and H2O.
    • Carbonic acid dissociates into H+ and bicarbonate (HCO3-).
    • Lungs can expel CO2; kidneys excrete H+ or bicarbonate.
  • Phosphate Buffer System
    • Important in plasma and erythrocytes.
    • Converts between dihydrogen phosphate (H2PO4-) and monohydrogen phosphate (HPO4^2-).
    • Binds H+ in acidic conditions; releases H+ in basic conditions.

Role of Respiratory and Renal Systems

• Secondary defense systems when buffer systems are overwhelmed.
• Respiratory System:
  • Regulates pH by varying CO2 exhalation.
  • Increased exhalation raises pH (more alkaline); decreased exhalation lowers pH (more acidic).
• Renal System (Kidneys):
  • Excretes H+ into urine; reabsorbs bicarbonate.
  • Produces new bicarbonate.
  • Critical in removing large amounts of H+.
  • Renal failure can quickly lead to acidosis.

pH Regulation Process

• Chemoreceptors detect changes in blood pH.
• Increased H+ from lower pH stimulates the respiratory center.
• More CO2 exhaled, reducing carbonic acid, increasing pH.
• Kidneys secrete H+ and reabsorb bicarbonate, further adjusting pH.

Effects of pH Imbalance

• Acidosis (pH < 7.35)
  • Depresses the central nervous system; slows synaptic transmissions.
• Alkalosis (pH > 7.45)
  • Causes over-excitability.

Lecture Goals

• Describe the protein, phosphate, and carbonic acid-bicarbonate buffer systems.
• Explain how lungs and kidneys maintain proper pH levels.
• Define acidosis and alkalosis.

These notes provide a concise overview of the acid-base balance mechanisms and are aimed at aiding the understanding of physiological pH regulation processes.