Terminal Respiratory Unit

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Histological section of the lung stained with H&E, showing the terminal respiratory unit. Alveolar air spaces are separated by thin septa containing capillaries. Type I pneumocytes form most of the alveolar lining, while Type II pneumocytes with rounded nuclei are interspersed and responsible for surfactant secretion. Alveolar macrophages (dust cells) are present within the air spaces. The respiratory membrane (air-blood barrier) is visible where capillary endothelium and alveolar epithelium meet. The image illustrates the structural components of the alveolus and the gas-exchange interface.
Histology Image
University of Tasmania, J. Chapman

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