Medical Definition of Pneumocyte

  • Medical Author:
    William C. Shiel Jr., MD, FACP, FACR

    Dr. Shiel received a Bachelor of Science degree with honors from the University of Notre Dame. There he was involved in research in radiation biology and received the Huisking Scholarship. After graduating from St. Louis University School of Medicine, he completed his Internal Medicine residency and Rheumatology fellowship at the University of California, Irvine. He is board-certified in Internal Medicine and Rheumatology.

Pneumocyte: One of the cells lining the alveoli (the air sacs) in the lung.

The alveoli are, in fact, lined with two types of cells termed the type 1 and type 2 pneumocytes:

  • Type 1 pneumocyte: The cell responsible for the gas (oxygen and carbon dioxide) exchange that takes place in the alveoli. It is a very large thin cell stretched over a very large area. This type of cell is susceptible to a large number of toxic insults and cannot replicate itself.
  • Type 2 pneumocyte: The cell responsible for the production and secretion of surfactant (the molecule that reduces the surface tension of pulmonary fluids and contributes to the elastic properties of the lungs). The type 2 pneumocyte is a smaller cell that can replicate in the alveoli and will replicate to replace damaged type 1 pneumocytes.

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Last Editorial Review: 1/25/2017

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