Question

Which of the following statements is true?

• A. During inspiration, the diaphragm stretches and the intrathoracic pressure is lower than atmospheric pressure.
• B. During Inspiration, the diaphragm relaxes and the intrathoracic pressure is higher than atmospheric pressure.
• C. During expiration, the diaphragm stretches and increases the volume of the thoracic cavity.
• D. Intercostal muscles are used in normal breathing.

Answer 1

The correct option is A

During inspiration, the diaphragm stretches and the intrathoracic pressure is lower than atmospheric pressure.

During inspiration, the dome shaped diaphragm stretches and become flat and increases the size of the thoracic chamber. As a result the pressure in the thorax is reduced to less than atmospheric pressure. Air, therefore, enters into the lungs. Statement B is just opposite of statement A and it is false. Statement C also states the opposite of what happens during expiration. Statement D is false because intercostal muscles are used to expand the ribcage during heavy breathing and not during normal breathing.