About normal expiration, TRUE/FALSE are: 1. At the end of normal expiration air in the lung is ERV 2. Chest wall has a tendency to move outward which is balanced by inward recoil of alveoli 3. In expiratory pleural pressure is equal to alveolar pressure 4. Muscle that elevates the chest cage are classified as muscle of expiration
**Core Concept**
Normal expiration occurs passively in a relaxed individual, without any conscious effort. It is a function of the elastic recoil of the lungs and chest wall, which helps to maintain the balance between the outward recoil of the chest wall and the inward recoil of the lungs.
**Why the Correct Answer is Right**
During normal expiration, the diaphragm and other accessory muscles of respiration relax, allowing the lungs to deflate due to their elastic recoil. At the end of expiration, the lung volume is equal to the residual volume (RV), which is the volume of air left in the lungs after a maximal exhalation. The residual volume is approximately equal to the expiratory reserve volume (ERV), which is the additional volume of air that can be exhaled after a normal expiration. The chest wall, on the other hand, tends to move outward due to its elastic recoil, but this is balanced by the inward recoil of the alveoli, which is greater than the outward recoil of the chest wall. During expiration, the pleural pressure is greater than the alveolar pressure, which is negative with respect to atmospheric pressure. Muscle that elevate the chest cage, such as the diaphragm, are actually accessory muscles of inspiration, not expiration.
**Why Each Wrong Option is Incorrect**
**Option A:** This statement is incorrect because at the end of normal expiration, the lung volume is equal to the residual volume (RV), not the expiratory reserve volume (ERV).
**Option B:** This statement is incorrect because the chest wall has a tendency to move outward due to its elastic recoil, but this is balanced by the inward recoil of the alveoli, not the other way around.
**Option C:** This statement is incorrect because during expiration, the pleural pressure is greater than the alveolar pressure, not equal to it.
**Option D:** This statement is incorrect because muscles that elevate the chest cage, such as the diaphragm, are actually accessory muscles of inspiration, not expiration.
**Clinical Pearl / High-Yield Fact**
The diaphragm is a dome-shaped muscle that separates the chest cavity from the abdominal cavity. During inspiration, the diaphragm contracts and moves downward, increasing the volume of the chest cavity and allowing air to enter the lungs.
**Correct Answer:** **A**. At the end of normal expiration air in the lung is ERV