Over-inflation of lung is prevented by?
**Over-inflation of Lung is Prevented by the Hering-Breuer Inflation Reflex**
**Core Concept**
The Hering-Breuer inflation reflex is a physiological mechanism that prevents over-inflation of the lungs by inhibiting lung inflation when the lungs reach a certain volume. This reflex is mediated by stretch receptors in the bronchi and bronchioles, which are activated when the lungs expand beyond a certain point.
**Why the Correct Answer is Right**
When the lungs expand, the stretch receptors in the bronchi and bronchioles are activated, sending signals to the brainstem via the vagus nerve. These signals inhibit the inspiratory neurons in the medulla, resulting in cessation of inspiration and prevention of further lung inflation. This reflex helps to prevent over-inflation of the lungs and maintain a normal tidal volume.
**Why Each Wrong Option is Incorrect**
* **Option A:** This is not a correct answer as the Hering-Breuer inflation reflex is specifically related to lung inflation, not expiration.
* **Option B:** This option is incorrect as the stretch receptors are not responsible for initiating inspiration, but rather for inhibiting it when the lungs are over-inflated.
* **Option C:** This option is incorrect as the Hering-Breuer inflation reflex is a separate mechanism from the chemoreceptor reflex, which is responsible for regulating breathing in response to changes in blood pH and CO2 levels.
**Clinical Pearl / High-Yield Fact**
The Hering-Breuer inflation reflex is an important mechanism for maintaining normal tidal volumes and preventing over-inflation of the lungs, particularly in infants and young children. It is also relevant in the context of respiratory diseases such as chronic obstructive pulmonary disease (COPD), where lung hyperinflation is a common feature.
**Correct Answer: C. Hering-Breuer inflation reflex**