Emphysema is a condition of the lung characterized by permanent enlargement of the air spaces distal to the ter-minal bronchiole. This enlargement is caused by chronic obstruction of airflow, most often because of narrowing of the bronchioles, and is accompanied by destruction of the alveolar wall (Fig. F19.3.1). Thus, significant area for gas exchange is lost in this disease. Emphysema is relatively common; it is seen in about half of all autopsies and is eas-ily recognized. Pathologists identify several types of em-physema. The severity of the disease is clinically more important, however, than recognition of the specific type. Emphysema is often caused by chronic inhalations of foreign particulate material such as coal dust, textile fibers, and construction dust. The most common cause, however, is cigarette smoking. The destruction of the alveolar wall may be associated with excess lysis of elastin and other structural proteins in the alveolar septa. Elastase and other proteases are derived from lung neutrophils, macrophages, and monocytes. A specific genetic disease, 1-antitrypsin deficiency, causes a particularly severe form of emphy-sema in both heterozygous and homozygous individuals and/or chronic obstructive pulmonary disease (COPD). It is usually fatal in homozygotes if untreated, but its sever-ity can be reduced by supplying the enzyme inhibitor ex-ogenously. FIGURE F19.3.1 • Photomicrographs of emphysema and pneumonia. a. This photomicrograph from the lung of an individual with emphysema shows the partial destruction of interalveolar septa, resulting in permanent enlargement of the air spaces. Note that the changes in the lung parenchyma are accompanied by thickening of the wall of the pulmonary vessels (arrows) and the presence of numerous cells within the air spaces. These cells are the alveolar macrophages and are shown at higher magnification in Figure 19.20. 240. b. This photomicrograph is from the lung of an individual in the early stages of acute pneumonia (inflammation of the lung). Note that the air spaces are filled with exudate containing white blood cells (mainly neutrophils), red blood cells, and fibrin. The capillaries in the alveolar septum are enlarged and congested with red blood cells. Pathologists recognize this stage as the red hepatization stage of the pneumonia. At this stage, the affected portion of the lung on gross examination appears red (because of enlarged capillaries), firm (because of the lack of air spaces), and heavy (because of the presence of exudate within the alveoli); the term hepatization stems from the tissue’s resemblance to the liver. 240. Inset. Part of an alveolus at a higher magnification. Note the enlarged, congested capillary within the alveolar septum. The air space is filled with neutrophils and red blood cells. The lower right corner shows early organization of the intra-alveolar exudate; observe that the developing fibrin network contains entrapped neutrophils and several red blood cells. 420. aaaaa bbbbb  FOLDER 19.3 Clinical Correlation: Emphysema and Pneumonia
The lung has both pulmonary and bronchial circulations.
The pulmonary circulation supplies the capillaries of the alveolar septum and is derived from the pulmonary artery that leaves the right ventricle of the heart. The branches of the pulmonary artery travel with those of the bronchi and bronchioles and carry blood down to the capillary level at the alveoli. This blood is oxygenated and collected by pulmonary venous capillaries that join to form venules. They ultimately form the four pulmonary veins that return blood to the left atrium of the heart. The pulmonary venous system is located at a distance from the respiratory passages at the periphery of the bronchopulmonary segments.