The Repiratory Tract is an essential collection of organs that allow for the absorption of oxygen into the blood and the removal of CO2 from it. It allows for the ventilation of atmospheric air into the lungs, where gas exchange occurs, and the removal of waste gases that diffuse from the blood to be released into the atmosphere. This is essential for complex life as oxygen is used in oxidative phosphorylation, which produces ATP from pyruvate. ATP is essential in many processes in the body - e.g. Muscle Contraction, Active transport.
The respiratory tract is segmented into two main sections, the Upper Respiratory tract and the lower. The upper is made of the nasal cavity which flows through to the pharynx, then the larynx, followed by the lower respiratory tract whch comprises of the trachea which divides into the bronchi, the bronchioles and finally the alveoli. These act as a tree like structure of branching and increasingly complex and intricate structures. The increasing concentration of smaller and smaller structures leads eventually in the alveoli to a very large surface area where diffusion is optimised, and gas exchange can occur quickly.