Practice Questions: Answers -- Respiratory Regulation


1. A. The medullary respiratory center is essential for automatic breathing and its destruction would cause breathing to cease.

2. C. The Hering-Breuer reflex is initiated by activation of stretch receptors in the lungs.

3. A. Activation of the RAS causes a general increase in respiratory ventilation.

4. B. Breath holding is limited by the increase in Pa-CO2 to the level where involuntary breathing overcomes voluntary breath holding. Hyperventilation before holding ones breath lowers the starting Pa-CO2 permitting a longer breath holding time. Decrease in blood pH is not a correct answer, although decrease in CSF pH would have been correct had it been one of the choices.

5. D. The most important receptors in chemical regulation of ventilation by carbon dioxide are the hydrogen ion receptors in the medulla, since the pH of CSF and brain interstitial fluid are controlled by blood PCO2 as CO2 readily crosses the blood-brain barrier.