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thumbnail lung h&e 1.25x thumbnail lung h&e 10x
thumbnail lung h&e 20x thumbnail lung h&e 40x

The lungs of the mouse are covered by visceral pleura and, like the lungs of the rat, consist of an undivided left lung and a right lung divided into four lobes (see Diagram of Respiratory System – Dissected). The primary bronchi, the bifurcation of the trachea, are the only bronchi in the mouse that contain cartilage and are lined by respiratory epithelium, a ciliated pseudostratified columnar epithelium interspersed with goblet cells. Subsequent branches of the bronchial tree are the smaller intrapulmonary bronchi, the terminal bronchioles, and the respiratory brochioles. As the airways get smaller their epithelium becomes more simplified and their walls become thinner with less connective tissue and smooth muscle; the smaller bronchi are lined by ciliated simple columnar epithelium, while the terminal and respiratory brochioles are lined by cuboidal epithelium. The respiratory brochioles are joined to thin-walled gas exchange areas lined by alveolar epithelium: alveolar ducts, alveolar sacs (clusters of alveoli), and alveoli. Alveolar epithelium consists of squamous type I cells and cuboidal type II cells. Separating the alveoli are interalveolar septa, connective tissue sheets that contain a capillary bed and are covered by alveolar epithelium. The mouse lung is characterized by the presence of cardiac muscle in the pulmonary veins.

The 1.25X micrograph of the lung depicts the branching of an intrapulmonary bronchus into bronchioles. The 10X micrograph shows the presence of blood vessels, a pulmonary artery and a pulmonary vein, close to a bronchus. The 10X and 20X micrographs display in increasing detail the gas exchange areas: alveolar ducts, alveolar sacs, and bronchi, which are adjacent to blood vessels and surrounded by alveoli. The 40X micrograph shows details of the ciliated simple columnar epithelium of a bronchus and the alveolar epithelium of alveoli.

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