Question

Describe the steps in breathing.

Answer 1

1. Inspiration: During inspiration, the atmospheric air is taken into the lungs. It occurs due to the pressure gradient formed between the lungs and the atmosphere. It is an active process in which the diaphragm becomes flat and goes downward, the external intercostal muscles contract so the ribs and sternum move upward and outward. This leads to an increase in the thoracic volume and a decrease in the pressure of the thorax and the lungs. To equalize the low pressure inside the lungs, air from the atmosphere rushes into the lungs. This is an inspiration.
2. Expiration: During expiration, the thorax contracts causing air to be exhaled. The diaphragm relaxes and is pushed upwards. It becomes dome-shaped. The intercostal muscles also relax pulling the rib cage inward and downward. This causes a decrease in thoracic volume and leads to an increase in pressure in the thorax and the lungs as compared to the atmospheric pressure. So air from the lungs rushes out. This is expiration.