The respiratory system maintains the pH of the blood by the bicarbonate buffer system.

The bicarbonate buffer system exists in the blood as an acid-base homeostatic mechanism involving the balance of carbonic acid, bicarbonate ion, and carbon dioxide to maintain pH in the blood

When the pH of the blood decreases the concentration of hydrogen ions in the blood increase, this causes the equation above to move towards the left as it is in equilibrium. As the concentration of hydrogen ions increases, this causes the equilibrium to shift to the left resulting in more carbon dioxide being produced as a result. Additionally, increased hydrogen ions in the blood results in signals being sent to the brain to increase the respiratory rate. Increasing the respiratory rate results in more carbon dioxide being exhaled, causing the equilibrium to favour the creation of carbon dioxide and removal of hydrogen ions from the blood increasing the pH.

Conversely, when hydrogen ions decrease in the blood or more bicarbonate ions are present, the pH has reduced this results in a decreased respiratory rate resulting in less carbon dioxide being exhaled. This increases hydrogen ions concentration in the blood, reducing the pH of the blood.

Practice Questions

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MCAT Official Prep (AAMC)

Sample Test B/B Section Question 15

Key Points

• The increase in hydrogen ion concentration in the blood reduces pH and increases the respiration rate. This increases blood pH by reducing hydrogen ion concentration.

• The decrease in hydrogen ion concentration in the blood increases pH and increases the respiration rate exhaling more carbon dioxide; this decreases blood pH.

Key Terms

Buffer: a molecule that regulates pH change

Homeostatic: maintaining internal conditions 

Hydrogen ions: H⁺ ions are hydrogen atoms with no electrons, commonly found in acids

Equilibrium: in a reversible reaction when the concentration of the reactants and products are constant.