If the primary acid-base disturbance is metabolic in nature, which system will respond to shift the pH toward normal?

• A. Digestive system
• B. Respiratory system
• C. Circulatory system
• D. Nervous system

Answer: (B)

When the primary problem is metabolic, the body’s first line of adjustment comes from the respiratory system. Metabolic disturbances change the amount of hydrogen ions or bicarbonate in the blood, and the lungs can alter pH quickly by changing ventilation. By increasing breathing (hyperventilation), the body blows off carbon dioxide, which shifts the carbonic acid–bicarbonate balance to form less hydrogen ions and raise pH toward normal. If the disturbance were metabolic alkalosis, the body would do the opposite and slow breathing to retain CO2. The kidneys can also compensate, but that is a slower, long-term adjustment.