KEY POINTS

Acid-Base Regulation

1. Relative constancy of the body's pH is essential because metabolism requires enzymes that operate at an optimal pH.

2. Hydrogen ion concentration is measured as pH.

3. An acid can donate a hydrogen ion, and a base can accept a hydrogen ion.

4. Buffers are combinations of salts and weak acids that prevent major changes in pH.

5. Hemoglobin and bicarbonate are the most important blood buffers.

6. The first defense against a change in blood pH is provided by the blood buffers, but the lungs and kidneys must ultimately correct the hydrogen ion load.

7. Changes in ventilation can rapidly change carbon dioxide tension and therefore alter pH.

8. Metabolic production of fixed acids requires that the kidneys eliminate hydrogen ions and conserve bicarbonate.

9. Intracellular pH is regulated by buffers and ion pumps.

Acid-Base Disturbances

1. Acid-base abnormalities accompany many diseases, and the restoration of normal blood pH should be a consideration in the treatment of any disease.

2. Respiratory acidosis is caused by the accumulation of carbon dioxide, which decreases blood pH.

3. Respiratory alkalosis is caused by the loss of carbon dioxide, which increases blood pH.

4. Metabolic acidosis is caused by the accumulation of fixed acids or the loss of buffer base, which decreases blood pH.

5. Metabolic alkalosis is caused by the excessive elimination of hydrogen ions or by the intake of base, such as bicarbonate, which increases blood pH.

6. Respiratory compensations for acid-base abnormalities occur rapidly; renal compensations occur over several hours.

7. Hydrogen and potassium ions are interrelated in acid-base homeostasis.

8. The diagnosis of acid-base disturbances depends on interpretation of measurements of arterial blood pH and carbon dioxide tension, from which bicarbonate concentration and total buffer base are calculated.

9. Over the years, many terms have been used to explain acid-base balance.