makes the respiratory membrane that is only about 0.5 millimeters thick. It is through this membrane that gas exchange occurs.
LUNG ANATOMY The lung contains aspects of both the respiratory and conducting zones. Its main function is to participate in the exchange of oxygen for carbon dioxide in the process of pulmonary respiration. The gas exchange area is large—about 70 square meters in area. This is necessary for the most efficient exchange of gases with each breath. The lungs themselves are paired and connected to the trachea by the right and left mainstem bronchi. The lower border of the lungs is the diaphragm—a muscular structure involved in the action of “breathing in.” The lungs are completely enclosed by a pleural lining. The right lung is larger but shorter than the left lung. The left lung is smaller to make room in the left chest for the heart. The lungs consist of lobes separated by large fissures. There are three lobes to the right lung and two lobes to the left lung. Each lobe is divided into multiple bronchopulmonary segments. Each segment gets air from its own tertiary bronchus and each has its own artery. A pulmonary lobule is a subdivision of a segment. It is formed when the bronchi turn into bronchioles. There is an interlobular septum consisting of connective tissue that separates the lobules from one another. The lungs need to be highly vascularized to be available for gas exchange. There are two types of vessels in the lungs: those that participate in the gas exchange and those that supply oxygenated blood to the lung tissue. The pulmonary circulation starts with the pulmonary artery leading out of the right ventricle. It carries deoxygenated blood to smaller and smaller vessels until a single arteriole and a single venule drain a single pulmonary lobule. They ultimately form a pulmonary capillary network that surrounds the different alveoli. Together, the capillary wall and the alveolar wall form the respiratory membrane. The oxygenated blood leaves the veins via the hilum.
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