Structures of the Pulmonary System
- The pulmonary system consists of the lungs, airways, chest wall, and pulmonary and bronchial circulation.
- Air is inspired and expired through the conducting airways, which include the nasopharynx, oropharynx, trachea, bronchi, and bronchioles to the sixteenth division.
- Gas exchange occurs in structures beyond the sixteenth division: the respiratory bronchioles, alveolar ducts, and the alveoli. Together these structures compose the acinus.
- The chief gas-exchange units of the lungs are the alveoli. The membrane that surrounds each alveolus and contains the pulmonary capillaries is called the alveolocapillary membrane.
- The gas-exchange airways are served by the pulmonary circulation, a separate division of the circulatory system. The bronchi and other lung structures are served by a branch of the systemic circulation called the bronchial circulation.
- The chest wall, which contains and protects the contents of the thoracic cavity, consists of the skin, ribs, and intercostal muscles, which lie between the ribs.
- The chest wall is lined by a serous membrane called the parietal pleura; the lungs are encased in a separate membrane called the visceral pleura. The area where these two pleurae come into contact and slide over one another is called the pleural space.