Acid-Base Homeostasis
Lesson focus - Define normal blood pH, explain how H⁺ affects pH, compare the body's buffer systems, differentiate the roles of the lungs and kidneys, and identify the four types of acid-base imbalances.
pH
- Normal blood pH is 7.35–7.45
- Increased H⁺ will lower pH
The body removes H⁺ by three mechanisms:
- Buffer systems
- Exhaling CO₂
- Kidney excretion of H⁺ in urine
Buffer Systems
Buffer systems prevent drastic changes in the pH of body fluids by converting strong acids and bases into weak acids and bases.
| Buffer system | Key components / action |
|---|---|
| Protein buffer system | Albumin and hemoglobin |
| Carbonic acid–bicarbonate buffer system | Excess CO₂ is exhaled from the lungs |
| Phosphate buffer system | Enables excess H⁺ to be excreted through urine |
Exhalation of CO₂
Factors affecting CO₂ elimination:
- Rate of breathing (respiratory rate)
- Depth of breathing (tidal volume)
Chemoreceptors respond to changes in pH to bring the body back to homeostasis.
Kidney Excretion of H⁺
Intercalated Cells
Intercalated cells are epithelial cells associated with the regulation of acid-base homeostasis in the distal segments of the kidney tubule.
- Excrete excess H⁺ when pH is too low
- Excrete excess HCO₃ when pH is too high
Collecting Duct Buffers
Collecting duct buffers filter any other H⁺:
- HPO₄ (monohydrogen phosphate) binds to H⁺ to form H₂PO₄ (dihydrogen phosphate)
- NH₃ (ammonia) binds to H⁺ to form NH₄ (ammonium)
Ammonium and dihydrogen phosphate are excreted in the urine.
Acid-Base Imbalances
The four key acid-base imbalances are:
| Imbalance | Origin |
|---|---|
| Respiratory acidosis | Respiratory (lungs / CO₂) |
| Respiratory alkalosis | Respiratory (lungs / CO₂) |
| Metabolic acidosis | Metabolic |
| Metabolic alkalosis | Metabolic |
Review
- pH
- Buffer systems
- Exhalation of CO₂
- Kidney excretion of H⁺
- Acid-base imbalances