Regulation of Bicarbonate/Carbonic Acid Buffer System

Respiratory Compensation

• Respiratory compensation is fast and reaches maximal capacity in 24 hours
• Changes in ventilation affect the denominator (respiratory) component of the H-H equation

Combined Regulation of the HCO-3 / H2CO3 Buffer System

• The ultimate aim of regulation is to maintain a ratio of 20 Bicarbonate : 1 Carbonic Acid
• At this ratio, arterial blood pH = 7.40 ± 0.05
• Kidneys regulate the metabolic component (HCO-3)
• Lungs regulate the respiratory component (H2CO3)
• Regulation also includes compensation for excess or deficiency of the other

Disturbances in Acid-Base Balance

• There are four types of acid-base disturbances:
  • Metabolic acidosis
  • Metabolic alkalosis
  • Respiratory acidosis
  • Respiratory alkalosis

Metabolic Acidosis

• Happens due to:
  • Build-up of acid in blood
  • Excess HCO3- loss by excretion via kidney or diarrhea
• Results in:
  • Low HCO3- in blood
  • Disruption of HCO3-/ H2CO3 ratio
• The body tries to maintain the HCO3-/ H2CO3 ratio of 20:1 to keep the pH 7.40

Kidney Regulation of Bicarbonate

• Kidneys regulate the metabolic (HCO3-) component
• Depending on the acid-base status, kidneys may:
  • Excrete HCO3- in urine
  • Reabsorb HCO3- partially or completely
  • Synthesize HCO3- by renal tubules
• Changes introduced by the kidneys affect the numerator of the H-H equation
• HCO3- synthesis, excretion, or reabsorption involves the Na - H+ exchange mechanism by the kidney tubules

Lung Regulation of H2CO3

• Lungs regulate the respiratory (H2CO3) component
• Regulation is mainly by ventilation, i.e., Hypoventilation or Hyperventilation
• In hypoventilation:
  • CO2 is retained
  • pCO2 in alveolar spaces ↑
  • H2CO3 in the blood ↑
• In hyperventilation:
  • CO2 is exhaled "blown off"
  • pCO2 in alveolar space ↓
  • H2CO3 in the blood ↓

Terminology

• Homeostasis is the state of internal balance to maintain physical and chemical conditions by living systems
• Acid is a molecule or ion capable of donating a proton (H+)
• Base is a substance that dissociates in aqueous solution to form hydroxide ions OH−
• Buffers are substances that maintain a constant pH by neutralizing the effects of hydrogen ions
• pH is a measure of how acidic/basic water is or a measure of the concentration of hydrogen ions in an aqueous solution
• pK is the pH value at which a chemical species will accept or donate a proton

This quiz covers the regulation of the bicarbonate/carbonic acid buffer system, including the ultimate aim of maintaining a specific ratio to maintain arterial blood pH.