First step is Intake of Oxygen to the lungs through
nostrils. While breathing (inhalation) Diaphragm contracts and
moves downward. Air passed through the bronchioles reaches alveolar
sac in alveoli.
Exchange of gases - another step is exchange of gases
to the tissues and cells by the help of blood vessels and
Cappilleries. Oxygen is diffused into the bloodstream and reached
the required locations. From there deoxygenated blood is carried
back to the alveoli.
Exhalation of carbon dioxide - Carbon dioxide is
exhaled through the nostrils this process is known as Expiration.
During this Diaphragm relaxes volume of thoracic cavity decreases.
Insufficient amount of oxygen in lungs. Which initiates for the
inhalation.