Gross Anatomy of the Lungs

of elastic walls. The stretched walls allow for excellent gas exchange. The alveoli are connected to each other by alveolar pores, which help maintain the pressure equalized throughout the lungs.

There are three types of cells that make up the alveoli. Type I alveolar cells are squamous epithelial cells, making up 97 percent of the surface area of the cells. They are highly gas-permeable. Type II alveolar cells secrete pulmonary surfactant, which is made from protein and phospholipids. The mobile cells are the alveolar macrophages, which are phagocytic and remove pathogens and debris.

The type I alveolar cell has a thin elastic membrane associated with it. It borders the endothelial lining of the capillaries—all together making the respiratory membrane (the alveolar cell, the basement membrane, and the endothelial cell). Together, these are thin enough at half a micrometer so that simple diffusion of oxygen and carbon dioxide can happen.

GROSS ANATOMY OF THE LUNGS

The lungs are pyramidal in shape and are paired organs, connected only by the trachea and bronchi. The diaphragm is located inferior to the lungs and is the main structure that is involved in the work of breathing. The right lung is shorter than the left and has three lobes, while the left lung has two lobes and a lingula that overlies part of the heart. There is a cardiac notch on the left side to fit the heart up next to the lungs.

The apex of the lungs is on the top, while the base of the lung is on the bottom. The costal surface is the part near the ribcage and the mediastinal surface faces the midline of the body. The mediastinal surface contains the hilum, which contains the main vessels entering and leaving the heart. Figure 7 depicts the main anatomy of the lungs:

Figure 7.

The three lobes of the lungs are the superior, middle, and inferior lobes. The two lobes of the lungs are the superior and inferior lobes. The lungs are also divided into bronchopulmonary segments, which consist of a tertiary bronchus, its artery, and the parenchyma that they supply. In some cases, there can be disease of a bronchopulmonary segment that necessitates its removal, which can be accomplished without damaging other segments. A lobule is a section of lung that is supplied by a bronchiole; an interlobar segment divides each lobule.

The lung has a blood supply called the pulmonary circuit or pulmonary circulation. We will talk more about that in a minute. The blood supply starts as deoxygenated blood that becomes oxygenated as part of the gas exchange process. All vessels end and leave the heart via the hilum.

The parasympathetic and sympathetic nervous system are involved in the innervation of the heart. The parasympathetic nervous system leads to bronchoconstriction, while the sympathetic nervous system leads to bronchodilation. The cough reflex and the