Acid-Base Balance: The Bicarbonate System and Compensation
Blood pH is held in a narrow range by a buffer whose two components are controlled separately: carbon dioxide by the lungs and bicarbonate by the kidneys. Because one is fast and the other slow, a disturbance in one can be partly offset by the other.
What a learner can do afterwards
- Classifies a disturbance as respiratory or metabolic from pH, carbon dioxide and bicarbonate together.
- Explains which organ compensates and roughly how quickly.
- Says why a compensated result still shows the original disturbance.
1 · Read
Blood pH sits slightly alkaline near 7.4, guarded because even small drifts change how proteins fold and work. The bicarbonate buffer soaks up acid or base in seconds: carbon dioxide plus water forms carbonic acid, which splits into hydrogen ions and bicarbonate, and the reaction runs both ways. The lungs own the carbon dioxide side and adjust it within minutes, while the kidneys own the bicarbonate side over days.
To classify a disorder, read pH with both gases together. Carbon dioxide off first means the lungs started it, so it is respiratory. Bicarbonate off first means metabolism or the kidneys started it, so it is metabolic. Low pH with high carbon dioxide reads as respiratory acidosis, while low pH with low bicarbonate reads as metabolic acidosis.
The other system then compensates but never overshoots. The lungs answer a metabolic disorder by changing breathing within minutes, and the kidneys answer a respiratory disorder by tuning bicarbonate over hours to days. Compensation pushes pH back toward normal yet stops short, so a compensated sample still betrays the original problem.
Read pH first for acid or base, then ask which value moved with it to name the source, and which moved against it to spot compensation.
Name the starter from the matching value, and expect the other organ to answer partway.
2 · Watch
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