Question

In the given diagram, what A, B and C depicts?

• A. A-Air goes inside to lungs, B-Ribs and sternum returned to original, position, C-Diaphragm contracted
• B. A-Air expelled from lungs, B-Ribs and sternum returned to original position, C-Diaphragm relaxed and arched upward
• C. A-Air expelled from lungs, B-Ribs and sternum goes upward, C-Diaphragm relaxed and arched upward
• D. A-Air goes inside to lungs, B-Ribs and sternum goes upward, C-Diaphragm relaxed and arched upward

Answer 1

The correct option is B A-Air expelled from lungs, B-Ribs and sternum returned to original position, C-Diaphragm relaxed and arched upward

Inspiration or inhalation is the process of bringing air from outside the body into the lungs due to the difference in pressure gradient between the lungs and the atmosphere.
When air enters the lungs, the diaphragm contracts toward the abdominal cavity, thereby increasing the space in the thoracic cavity for accommodating the inhaled air with simultaneous contraction of the external intercostal muscles. This causes the ribs and the sternum to move out, thereby increasing the volume of the thoracic chamber in the dorsoventral axis.

Now, as a result of this increase, the intra-pulmonary pressure becomes lesser than the atmospheric pressure. This causes the air from outside the body to move into the lungs.

Expiration occurs due to reverse movements of the ribs and diaphragm. The external intercostal muscles relax and thus the ribs becomes depressed. The diaphragm is relaxed and moves upward to its original position. Thus the thoracic cavity becomes small and lungs are compressed, which forces air out of the lungs.
The diagram given in the question is of expiration.

A – Air Expelled from Lungs
B – Ribs and sternum returned to the original position
C – Diaphragm relaxed and arched upward