Overview
This lecture explains how buffers—especially the bicarbonate buffering system—maintain blood pH within a narrow range by balancing hydrogen ion concentration.
Blood pH and Its Importance
- Normal blood pH ranges from 7.35 to 7.45.
- Blood becomes too acidic if pH drops below 7.35 and too alkaline if above 7.45.
- pH is determined by the concentration of hydrogen ions (H⁺) in the blood.
Buffer Function and Mechanism
- Buffers resist drastic changes in pH by managing hydrogen ion concentration.
- If there are too many H⁺ ions, buffers reduce them; if too few, buffers release more.
- An acid donates H⁺ ions; a base accepts or "mops up" H⁺ ions.
The Bicarbonate Buffering System
- The main biological buffer is the bicarbonate system involving carbonic acid (H₂CO₃) and bicarbonate ion (HCO₃⁻).
- Carbonic acid (H₂CO₃) can donate H⁺ ions, forming bicarbonate ion (HCO₃⁻).
- The chemical reaction: CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻.
- This is a reversible reaction influenced by CO₂, H₂O, HCO₃⁻, and H⁺ levels.
Role of Lungs and Kidneys
- The lungs manage CO₂ levels, affecting the left side of the buffer equation.
- The kidneys manage HCO₃⁻, affecting the right side.
- Respiratory imbalances affect CO₂; metabolic (kidney) imbalances affect HCO₃⁻.
Physiological Reactions and Breathing
- Accumulation of CO₂ (e.g., holding breath) increases H⁺ and lowers pH.
- Excess H⁺ ions prompt the body to increase breathing rate to expel CO₂ and raise pH.
- Breathing patterns can indicate blood pH levels.
Key Terms & Definitions
- Buffer — a substance that resists changes in pH by managing H⁺ ions.
- pH — a measurement of hydrogen ion concentration in a solution.
- Acid — a substance that donates H⁺ ions.
- Base — a substance that accepts/binds H⁺ ions.
- Carbonic Acid (H₂CO₃) — a weak acid in the bicarbonate buffer system.
- Bicarbonate Ion (HCO₃⁻) — a weak base formed when carbonic acid donates an H⁺ ion.
Action Items / Next Steps
- Review the chemical equilibrium: CO₂ + H₂O ⇌ H₂CO₃ ⇌ H⁺ + HCO₃⁻.
- Watch previous videos on calculating pH for deeper understanding.