The Respiratory System

The respiratory system can be divided into upper and lower respirator tracts. The upper respiratory tract consists of the nasal and oral cavities, paranasal sinuses, the pharynx, and larynx. Tissues of the nasal and oral cavities and paranasal sinuses warm and moisten incoming air. The pharynx or throat is a muscular tube where the nasal and oral cavities open posteriorly. The epiglottis remains open during breathing, allowing air from the pharynx into the larynx. Air passing through the larynx enters the lower respiratory tract via the trachea. The trachea bifurcates, or splits, into the right and left bronchi. The bronchi enter the lung and continue to bifurcate into smaller segments. The smallest, terminal structures of the respiratory system are the alveolar sacs. The alveoli are tiny air sacs that allow for the re-oxygenation of the blood.