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Alveolar histology
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Two kinds of cells with very different jobs live in the wall of the alveolus, the little air sac of the lung. The first are called type I pneumocytes, and they're squamous, meaning flattened, so thin they bring to mind a sheet of clear plastic stretched over a surface. That thinness isn't a minor detail: it's what lets them form much of the barrier separating the air inside the alveolus from the blood running along the other side.
The others are the type II pneumocytes, and they aren't there to build the wall. Their job is to make and release pulmonary surfactant, the substance the lung needs to have on that surface. So in the very same place you find the cell that serves as an ultra-thin partition alongside the cell that produces and secretes surfactant.
In brief
Type I pneumocytes are extremely thin, flat cells. Their shape lets them form most of the barrier between the air in the alveoli and the blood.
A type I cell stretches across a thin barrier, while a type II cell supplies surfactant to the surface.
Type II pneumocytes make and release pulmonary surfactant.
Sources (1)
- StatPearls, NCBI BookshelfHistology, Alveolar CellsPublished
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