Question

In the given mechanism, diaphragm, sternum and intercostal muscles work together to _____ the thoracic volume and thereby pulmonary volume. This leads to ____ in intra-pulmonary pressure to slightly_____ the atmospheric pressure, causing expiration.
Select the correct sequence of words to complete the above paragraph.

• A. decrease, decrease, below
• B. increase, decrease, above
• C. decrease, increase, above
• D. increase, increase, below

Answer 1

Answer: (C)

During inspiration, the contraction of external intercostal muscles lifts up the ribs and the sternum to increase thoracic volume. The given diagram shows expiration process. The relaxing diaphragm and intercostal muscles return to their normal positions which reduce the thoracic volume and thereby the pulmonary volume. This leads to an increase in intrapulmonary pressure to slightly above the atmospheric pressure causing the expulsion of air from the lungs, i.e., expiration.