Biology
Acid-Base Balance Disorders and Compensatory Mechanisms
Quick fact
The body's pH balance must stay between 7.35 and 7.45; even a drop to 7.0 can be fatal.
Why this is interesting
Your blood must stay in an incredibly narrow pH range—just a few decimal points—or your body's enzymes start to fail. So what happens when that balance is threatened?
Read the full explanation
Understanding Acid-Base Balance Disorders and Compensatory Mechanisms
Think of your blood as a carefully balanced swimming pool. The pH measures how acidic or basic the water is. Your body likes to keep that pH between 7.35 and 7.45—slightly basic. Too much acid (low pH) is called acidosis; too little acid (high pH) is alkalosis. To maintain this balance, your body uses two main systems: the lungs and the kidneys. The lungs act like a fast vent—they can blow off carbon dioxide (an acid) within minutes. The kidneys are the slow, powerful filter—they can excrete acid or retain bicarbonate over hours or days. When something upsets the balance, the body kicks in to compensate, but it's not instant. That's why understanding the timing is key.
A deeper explanation
There are four primary disturbances. Respiratory acidosis occurs when you breathe too slowly or insufficiently, causing carbon dioxide (CO₂) to build up. Carbon dioxide combines with water to form carbonic acid, lowering pH. The kidneys compensate by holding onto bicarbonate and excreting acid. Respiratory alkalosis occurs when hyperventilation blows off too much CO₂, raising pH; the kidneys excrete more bicarbonate to compensate. Metabolic acidosis is caused by a loss of bicarbonate or a gain of acid (like lactic acid), lowering pH; the lungs compensate by breathing deeper and faster to blow off CO₂. Metabolic alkalosis is caused by a gain of bicarbonate or loss of acid (like from vomiting), raising pH; the lungs compensate by breathing slower to retain CO₂. The key is that these compensations never fully restore the pH to normal—they just bring it closer. That's why blood gas analysis shows a primary problem and a secondary response, guiding treatment.