Pulmonary lymphatic spaces are located within the bronchovascular bundles, interlobular septa, and the pleura. Interlobular septa are connective tissue structures that extend from the visceral pleura into portions of underlying lung, and they contain lymphatic spaces in addition to veins. Pulmonary veins course separately from arteries and are located within interlobular septa (see Figures 10.19 and 10.20). (B) Higher magnification view of the RB shows its discontinuous smooth muscle layer, as well as the smooth muscle bundles (arrows) that are present at the mouth of the adjacent AD.Īlveolar spaces may contain scattered alveolar macrophages, but numerous macrophages within contiguous alveoli are abnormal. (A) A respiratory bronchiole (RB) is seen adjacent to a pulmonary artery in this field, and it opens into alveolar ducts (AD). A few macrophages are scattered within the airspaces.įIGURE 1.2 Normal lung. Distinct alveolar lining cells are not visible. (B) Higher magnification of the alveolated parenchyma shows thin, membranous, alveolar septa containing only scattered nuclei mainly from capillary endothelium. Note that the artery and the bronchiole are similar in size. (A) At low magnification, a terminal bronchiole (TB) is seen adjacent to a pulmonary artery. Alveolar lining cells are generally not visible in normal lung, and when prominent are indicative of prior injury or interstitial lung disease.įIGURE 1.1 Normal lung. They may appear hyperplastic in emphysema.Īlveolar septa are thin, membranous structures within which only scattered nuclei, mostly from endothelial cells, can be seen ( Figure 1.1B). Smooth muscle bundles protrude along the interstitium at the mouth of alveolar ducts and are present along the wall of alveolar ducts ( Figure 1.2B). Small collections of chronic inflammation, bronchial-associated lymphoid tissue (BALT), are common in the walls of bronchioles and by themselves are not a significant abnormality. Respiratory bronchioles are partially lined by ciliated respiratory tract epithelium and open up into alveolar ducts ( Figure 1.2). Terminal (membranous) bronchioles contain a full lining of ciliated respiratory tract epithelium and have a continuous smooth muscle layer in their walls ( Figure 1.1). This relationship helps one to confirm that a particular blood vessel is an artery, and it also confirms bronchiolocentricity of an inflammatory process if the affected bronchiole is destroyed (see Figures 6.23 and 6.24). Pulmonary arteries and bronchioles course together, and are similar in size ( Figure 1.1).
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