Question

To generate pressure gradients to facilitate expiration and inspiration, the human body uses the intercostal muscles and

• A. Alveolar sacs
• B. Bronchi
• C. Primary, secondary and teritary bronchioles
• D. Diaphragm

Answer 1

Answer: (D)

Diaphragm

During inspiration, inspiratory muscles, namely diaphragm and the intercostal muscles contract. Contraction of the diaphragm results in increase in the size of the thoracic cavity. Contraction of the intercostal muscles elevates the ribs and sternum. This results in the expansion of lungs. This results in the decrease of the lung pressure. The air moves from the regions of high pressure to low pressure. During expiration, the diaphragm and intercostal muscles relax. The relaxation of diaphragm results in decrease in the size of thoracic cavity. Relaxation of itnercostal muscles lowers the ribs and sternum. The pressure of the air inside the lungs increases and the air goes out.

Thus, the correct answer is option D.