Question

Explain inhalation - exhalation cycle in humans.

Answer 1

Breathing

It is the process by which air is moved in and out of the lungs. It occurs in the following two steps:

1. Inhalation or inspiration
2. Exhalation or expiration

Inhalation

It is the process through which air moves into the lungs. It involves the following steps:

• Due to the contraction of intercostal muscles between the ribs, the rib cage moves upward and outward.
• The diaphragm becomes flat and presses down towards the abdominal cavity.
• This results in the increase of volume in the thoracic cavity which decreases the air pressure in the lungs compared to the atmospheric pressure. Hence, air rushes inside the lungs.

Exhalation

It is the process through which air moves out of the lungs. It involves the following steps:

• There is no contraction of intercostal muscles between the ribs but relaxation takes place.
• The diaphragm becomes relaxed and hence attains its original dome shape.
• This results in the decrease of volume in the thoracic cavity which increases the air pressure within the lungs as compared to the atmosphere. Therefore, air rushes out of the lungs.