Question

Which of the following events increase respiration and which decrease respiration?

Answer 1

The change in P_O2 and PC_O2 levels in the alveoli is sensed by the nerve endings that activate or inactivate respiratory center. The central chemoreceptors in the medulla oblongata respond primarily to increased carbon dioxide levels rather than the decreased oxygen levels. Increased carbon dioxide levels results in increased rate of respiration.

The changes in P_O2 is mainly sensed by the peripheral chemoreceptors located in the aortic bodies and carotid bodies. The decreased partial pressure of oxygen (lower than 50% of the normal) stimulate the respiratory center and thus, increase the rate of respiration.

During hyperventilation (increased rate of respiration), the carbon dioxide is exhaled out at a higher rate. This reduces the partial pressure of carbon dioxide and increases the oxygen level. So, after a period of hyperventilation, it takes longer time to reach the PC_O2 that is enough to decrease the rate of respiration. Thus, the rate of respiration decreases after hyperventilation.