Type I alveolar cell

Capillary endothelial

Figure 18-1. (A) Light micrograph of an intcralveolar septum. The junction of three alveoli (alv) are shown. The area within the box shows the blood-air barrier, which separates the blood (erythrocyte within the capillary) and air within the alveolus. (B) Electron micrograph of boxed area in A shows the components of the blood-air barrier: the type I pneumocyte (borders the air interface), the basal lamina, and rhe capillary endothelial (borders the blood interface). The surfactant layer covering the type I pneumocyte is not shown. Note the histologic layers that air must traverse to get to rhe erythrocyte. (B: Reprinted with permission from Faw-cett DW: A Textbook of Histology, 12th ed. New York, Chapman Hall, 1994, p 723. Courtesy of P. Gehr.)

B. Type II pneumocyte (Figure 18-2; see II R 2)

Figure 18-2. Electron micrograph of type II pneumocytes that secrete surfactant. Nore the lamellar bodies (arrows). (Reprinted with permission from Stahlman MT, Gray ME, Whitsett JA. The ontogeny and distribution of surfactant protein B in human fetuses and newborns. J Histochem Cytochem 40 (10): 1471-1480, 1992.)

Figure 18-2. Electron micrograph of type II pneumocytes that secrete surfactant. Nore the lamellar bodies (arrows). (Reprinted with permission from Stahlman MT, Gray ME, Whitsett JA. The ontogeny and distribution of surfactant protein B in human fetuses and newborns. J Histochem Cytochem 40 (10): 1471-1480, 1992.)

Figure 18-3. (A) Light micrograph of hyaline membrane disease due to respiratory distress syndrome (i.e., deficiency of surfactant). Note the air-filled bronchioles and alveolar ducts that are widely dilated. They are lined by a homogenous hyaline material consisting of fibrin and necrotic cells. In addition, there is acclcctasis or collapse of more distal alveoli. (B) Light micrograph of squamous cell carcinoma. Nore the irregular nests (asterisk) of squamous cell carcinoma. In some nests, kcratinization is present (arrow). (C) Light micrograph of cystic fibrosis. A bronchus that is filled with a thick mucus and inflammatory cells is shown (arrow). Smaller bronchi may be completely plugged by rhis material. In addition, surrounding the bronchus there is a heavy lymphocyte infiltration (asterisk). (Reprinted with permission from East Carolina University, School of Medicine, Department of Pathology slide collection.)

C. Hyaline membrane disease (Figure 18-3; see VI A 1), squamous cell carcinoma (see VI B 1), cystic fibrosis (see VI C)

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