During exercise, blood Carbon dioxide levels increase as a result of muscle cell activity. This makes blood more acidic, which disrupts pH homeostastisis. Place the following events in order.

1. The amount of Carbon dioxide exhaled increases.
2. The blood becomes more acidic, and the pH decreases below the set point.
3. The brainstem detects a pH change.
4. Blood pH returns to the set point.
5. The brainstem signals muscles in the diaphragm and rib cage.
6. The breathing rate increases.
7. Blood carbon dioxide levels increase.