Question

Lungs do not collapse between breaths and some air always remains in the lungs which can never be expelled because

• A. there is a negative pressure in the lungs
• B. there is a negative intrapleural pressure pulling at the lung walls
• C. there is a positive intrapleural pressure
• D. pressure in the lungs is higher than the atmospheric pressure

Answer 1

The Correct Option is B

Correct Answer: 

There is a negative intrapleural pressure pulling at the lung walls.

Detailed Explanation:

The lungs are located within the thoracic cavity and are surrounded by a thin, fluid-filled space called the intrapleural cavity, which lies between the two layers of the pleura — the visceral pleura (covering the lungs) and the parietal pleura (lining the thoracic wall).

Under normal conditions, the pressure in the intrapleural space is slightly negative compared to the atmospheric pressure. This negative pressure is crucial because:

• It creates a suction force that keeps the lungs expanded and closely adhered to the chest wall.
• It prevents the lungs from recoiling completely even after expiration, ensuring that the lungs don’t collapse.
• It allows a certain volume of air called the residual volume to always remain inside the lungs. This air cannot be exhaled, even with forceful breathing.
• This residual air keeps the alveoli (tiny air sacs in the lungs) open and functional for gas exchange even between breaths.

If for any reason this negative intrapleural pressure is lost — such as in the case of injury causing air to enter the pleural space (a condition called pneumothorax) — the lungs may collapse due to their natural elastic recoil.

Therefore, it is the negative intrapleural pressure that plays a key role in keeping the lungs inflated and preventing their collapse.