[Campbell Biology P.995] A person begins exercising intensely. Based on Figure 42.28 and the... | Practice Question

A person begins exercising intensely. Based on Figure 42.28 and the accompanying text, what is the correct sequence of events that occurs to restore blood pH homeostasis?

  • A: Increased H+ → Decreased pH → Medulla detects pH drop → Increased breathing rate → Decreased CO2 → Increased pH.
  • B: Increased O2 → Increased pH → Medulla detects pH rise → Decreased breathing rate → Increased CO2 → Decreased pH.
  • C: Increased CO2 → Increased pH → Carotid arteries detect pH rise → Decreased breathing rate → Increased CO2 → Decreased pH.
  • D: Decreased CO2 → Decreased pH → Medulla detects pH drop → Decreased breathing rate → Increased CO2 → Increased pH.

Explanation

Intense exercise increases metabolic activity, producing more CO2. CO2 reacts with water to form carbonic acid H2CO3 , which dissociates into H+ and HCO3-, lowering the blood pH. This decrease in pH is detected by sensors in the medulla and major blood vessels. In response, the medulla increases the depth and rate of breathing, which expels more CO2, thereby reducing H+ concentration and raising the pH back to normal.