Anatomy and physiology
This chapter covers some fundamental aspects of the respiratory tract, and describes the structure and function of both the upper and lower airways, processes by which air is moved from the external environment to the gas exchange area of the lungs, and some of the aspects of the normal respiratory tract which are affected by the more common respiratory diseases. Its functions in terms of respiration are to facilitate the uptake of oxygen; eliminate carbon dioxide; and maintain the pH of the blood. Conventionally the tract is divided into upper and lower parts. The upper tract is composed of the mouth, nasal passages, and behind these a wide tube termed the pharynx. This receives inhaled air from the nose and mouth and accordingly is termed the naso- and oropharynx, respectively.