Overview
This lecture covers the bicarbonate buffer system and how it maintains blood pH balance through respiratory and metabolic mechanisms, including compensation strategies when imbalances occur.
pH Scale Basics
- pH scale ranges from 1 (acidic) to 14 (basic); normal blood pH is approximately 7.
- High pH indicates low hydrogen ion concentration (basic condition).
- Low pH indicates high hydrogen ion concentration (acidic condition).
- Acidic substances have more hydrogen ions; basic substances have fewer hydrogen ions.
The Bicarbonate Buffer Equation
- The equation balances CO2 (acidic) on the left with hydrogen ions (acidic) and bicarbonate (basic) on the right.
- Left side represents lung function: lungs decrease acid by increasing respiration to expel CO2.
- Right side represents kidney function: kidneys decrease acid by excreting hydrogen ions and secreting bicarbonate.
- Bicarbonate acts as a base in the bloodstream to neutralize excess acid.
Respiratory Imbalances
- Respiratory issues occur when lungs cannot maintain proper CO2 levels.
- Respiratory Acidosis: Lungs fail to expel enough CO2, causing acid buildup.
- Kidneys compensate by secreting bicarbonate (base) and eliminating excess hydrogen ions.
- Respiratory Alkalosis: Excessive breathing expels too much CO2, reducing acid levels.
- Kidneys compensate by reabsorbing bicarbonate and retaining hydrogen ions.
Metabolic Imbalances
- Metabolic issues occur when kidneys cannot properly regulate hydrogen ions and bicarbonate.
- Metabolic Acidosis: Kidneys fail to secrete enough hydrogen or bicarbonate; bicarbonate gets consumed buffering excess hydrogen.
- Lungs compensate by increasing respiration rate to expel more CO2.
- Metabolic Alkalosis: Kidneys secrete too much hydrogen or bicarbonate, raising pH.
- Lungs compensate by decreasing respiration rate to retain CO2.
Compensation Mechanisms
- Lungs adjust quickly (minutes) by changing breathing rate; kidneys adjust slowly (hours to days).
- When CO2 is abnormal, the problem is respiratory in origin.
- When bicarbonate is abnormal, the problem is metabolic in origin.
- When both CO2 and bicarbonate are abnormal, compensation is occurring.
- Full compensation achieved when pH returns to normal range despite abnormal CO2/bicarbonate levels.
Summary of pH Imbalances
| Condition | pH | CO2 | Bicarbonate | Compensation |
|---|
| Respiratory Acidosis | Low | High | High | Kidneys secrete bicarbonate |
| Respiratory Alkalosis | High | Low | Low | Kidneys reabsorb bicarbonate |
| Metabolic Acidosis | Low | Low | Low | Lungs increase breathing |
| Metabolic Alkalosis | High | High | High | Lungs decrease breathing |
Key Terms & Definitions
- pH: Measure of hydrogen ion concentration; scale from 1 (acidic) to 14 (basic).
- Acidosis: Condition where blood pH drops below normal due to excess acid.
- Alkalosis: Condition where blood pH rises above normal due to excess base.
- Compensation: Process where one system (lungs or kidneys) adjusts to correct imbalance caused by the other.
- Bicarbonate (HCO3-): Base component of buffer system that neutralizes excess hydrogen ions.
- CO2: Acidic component eliminated by lungs through respiration.