The Process of Breathing :
Breathing involves the ribs, the intercoastal muscles, lungs and the diaphragm. Breathing process is carried out in two phases :
• Inhalation or Inspiration
• Exhalation or Expiration.
Inhalation : To make inhalation possible the intercoastal muscles contract and lift the ribs upward and outward. The diaphragm muscle also contracts and flattens. These movements increase the size of chest cavity; as a result the pressure inside the lungs decreases. As the pressure outside the lungs is greater and the air moves into the lungs.
Exhalation: When breathing out, the muscles relax, the ribs go back to their normal unexpanded position, and the diaphragm springs back into place. With the chest activity back to its normal size, the pressure inside the lungs increases and is greater than the atmospheric pressure. As a result the air moves out of the lungs through nose or mouth.