Pleural pressure at the end of respiration is ?
**Core Concept**
Pleural pressure is the pressure within the pleural space, the thin gap between the lungs and the chest wall. It plays a crucial role in regulating lung expansion and ventilation during breathing. The pressure varies throughout the respiratory cycle due to changes in lung volume and chest wall movement.
**Why the Correct Answer is Right**
During inspiration, the diaphragm and intercostal muscles contract, increasing the volume of the thoracic cavity. This increase in volume decreases pleural pressure, making it more negative relative to atmospheric pressure. As a result, the lung expands, and air enters the lungs. At the end of inspiration, the diaphragm and intercostal muscles relax, and the pleural pressure returns to its equilibrium value, which is approximately equal to the atmospheric pressure. This is because the increased lung volume from inspiration is maintained by the elastic recoil of the lungs and the chest wall.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because pleural pressure at the end of respiration is not equal to atmospheric pressure during inspiration. The increased lung volume from inspiration is maintained by the elastic recoil of the lungs and the chest wall.
* **Option B:** This option is incorrect because pleural pressure at the end of respiration is not equal to the pressure in the alveoli. While the alveolar pressure can be similar to pleural pressure during quiet breathing, it is not the same at the end of respiration.
* **Option D:** This option is incorrect because pleural pressure at the end of respiration is not equal to the pressure in the pulmonary veins. The pressure in the pulmonary veins is primarily determined by the left atrial pressure and is not directly related to the pleural pressure.
**Clinical Pearl / High-Yield Fact**
It's essential to remember that pleural pressure is a key determinant of lung expansion and ventilation. During mechanical ventilation, changes in pleural pressure can lead to lung overdistension or atelectasis, highlighting the importance of proper ventilator settings.
**Correct Answer: C. Atmospheric pressure.**