Question

Explain the process of expiration.

Answer 1

Expiration: 

1. The exit of air (CO₂) from the lungs is called expiration or exhalation. 

2. It involves: 

• Relaxation of the muscles of the diaphragm, As a result, the diaphragm moves upwards & resumes dome shape. 
• Contraction of internal intercostal muscles and relaxation of external intercostal muscles. As a result, the ribs move inward & backwards i.e. posterior – the dorsal movement of the ribs. 
• The above changes in the factors cause a decrease in the thoracic volume but the thoracic pressure is increased. Hence, due to increased pressure air comes out of the lungs. 

Note: The breathing rate in adult human beings is 12 to 20 per minute.