FAWCETT / GEHR / SCIENCE PHOTO LIBRARY. FAWCETT / GEHR / SCIENCE PHOTO LIBRARY.
Scanning electron micrograph (SEM) of a section of the human lung, showing the network of alveolar ducts and alveoli (air sacs) that form the final divisions of the bronchial tree - the trunk of which is the trachea, the windpipe. Alveoli are numerous (millions per lung) with adjacent ones sharing the same blood capillary & connective tissue septum. It is here that the exchange of oxygen and carbon dioxide with the blood circulation occurs. The specimen was prepared using a fixative to prevent the delicate alveoli and terminal bronchioles from collapsing.
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