To explain normal functioning of the respiratory system, it is best to know that the respiratory system in human beings is comprised of the upper respiratory tract that consists of the nasal passages, pharynx and the larynx. The lower respiratory tract is composed of the trachea, the primary bronchi and the lungs. The primary function of the respiratory system is to supply oxygen to the blood in the body. Oxygen is delivered to all parts of the body. The respiratory system does this while breathing is taking place. During the process of breathing, one inhales oxygen and exhales carbon dioxide. This exchange of gases within the thoracic cavity takes place at the alveoli within the body.