AEMCA Practice Exam

What is the primary function of stretch receptors in the lungs?

1. To facilitate gas exchange

2. To signal the need for expiration

3. To constrict bronchial passageways

4. To increase lung capacity

The correct answer is: To signal the need for expiration

The primary function of stretch receptors in the lungs is indeed to signal the need for expiration. These receptors, which are located in the smooth muscle of the airways and lungs, are sensitive to changes in lung volume. During inhalation, when the lungs expand, these stretch receptors are activated and send signals to the brain, specifically to the respiratory centers. This activation helps in the regulation of breathing by providing feedback about the extent of lung inflation. When the stretch receptors are stimulated, they play a crucial role in the Hering-Breuer reflex, which helps to prevent over-inflation of the lungs. This feedback process signals the central nervous system to initiate expiration, allowing carbon dioxide-rich air to be expelled and preparing the lungs for the next inhalation. Thus, the stretch receptors perform a vital role in maintaining a balanced and efficient respiratory cycle. In contrast to the correct answer, facilitating gas exchange primarily involves the alveoli and their close association with capillaries, while constricting bronchial passageways relates more to the action of various inflammatory mediators or autonomic control rather than a direct function of stretch receptors. Increasing lung capacity is typically achieved through physical training and adaptation rather than through the action of these receptors during normal respiration.