Respiration is the process by which energy is released from food in our body. The function of respiratory system is to breathe in oxygen for respiration producing energy from food, and to breathe out carbon dioxide. With the help of lungs gases are exchanged between the blood and the air.

Respiration: The process of releasing energy by the oxidation of food is known as respiration. The process of respiration involves intake of oxygenated air into the cells for breaking the food and releasing energy.
Mechanism of respiration:
i. Air is drawn into the body through the nostrils. 
ii. The air from the nasal cavity passes to the pharynx, which leads to the trachea, through a slit called glottis.
iii. The trachea runs down the neck and divides into two bronchi, which lead into the lungs and further divide into smaller bronchioles. The smallest bronchioles terminate into alveoli. 
iv. The walls of the alveoli are thin and covered by blood capillaries to facilitate the exchange of gases in the lungs.
v. In the alveoli, the exchange of gases takes place, CO2​ from the blood is replaced with O2​ and CO2​ is removed out of the body.

vi. In humans, for the process of respiration, air is drawn into the lungs by the process of breathing.
When an individual inhales, the diaphragm moves down, and the chest cavity expands and the oxygen rich air is drawn into the lungs. When the individual exhales, the diaphragm relaxes and the chest cavity moves back to its relaxed position and the carbon dioxide rich air is expelled out of the body.