Figure 1816

Electron micrograph of a type II alveolar cell. The type II alveolar cell has a dome-shaped apical surface with a number of short microvilli at its periphery and a relatively smooth-contoured apical center. The lateral cell margins are overlain to a variable degree by the type I

• Surfactant protein C (SP-C), which represents only 1% of the total mass of surfactant protein. Along with SP-B, SP-C aids in orientation of DPPC within the surfactant and maintenance of the thin film layer within the alveoli.

• Surfactantprotein D (SP-D), a primary protein involved in host defense. It binds to various microorganisms (e.g., Gram-negative bacteria) and to lymphocytes. SP-D participates in a local inflammatory response as the result of acute lung injury and with SP-A modulates an allergic response to various inhaled antigens.

The alveolar septum is the site of the air-blood barrier

The air-blood barrier refers to the cells and cell products across which gases must diffuse between the alveo

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