Question

Inspiration occurs when the pressure within the lungs is

• A. less than the atmospheric pressure
• B. greater than the atmospheric pressure
• C. equal to the atmospheric pressure
• D. none of the above

Answer 1

The correct option is A less than the atmospheric pressure

Inspiration is a process in which air is drawn into the lungs. During inspiration, the diaphragm and the external intercostal muscles contract because of which the chest expands.
Due to the expansion of the thoracic cavity (chest cavity) the volume inside the lungs increases. It is known from Boyle’s law that for a gas at a constant temperature the volume is inversely proportional to the pressure. So when the volume increases, the pressure decreases and goes below the atmospheric pressure. Thus, during inspiration the pressure within the lungs is less than that of the atmospheric pressure. As a result of which the air moves into the lungs from the atmosphere.
On the other hand, expiration takes place when the pressure inside the lungs is greater than the atmospheric pressure.