Page 672 - Atlas of Histology with Functional Correlations

In the bronchiole (17), pseudostratified columnar ciliated epithelium with

occasional goblet cells lines the lumen. The lumen shows mucosal folds (18)
caused by the contractions of the surrounding smooth muscle (19) layer.
Bronchial glands and cartilage plates are not present, and the bronchiole (17) is
surrounded by the adventitia (16). In this illustration, a lymphatic nodule (15)
and a vein (15) adjacent to the adventitia (16) accompany the bronchiole (17).

The terminal bronchioles (8, 10) exhibit mucosal folds (10) and are lined
with a columnar ciliated epithelium without goblet cells. A thin layer of lamina
propria, smooth muscle (11), and adventitia surrounds the terminal bronchioles
(8, 10).

The respiratory bronchioles (12, 22) with alveoli outpocketings are
connected to the alveolar ducts (13, 20) and the alveoli (23). In these
bronchioles (12, 22), the epithelium is low columnar, or cuboidal, and may be
ciliated in the proximal portion of the tubules. A thin connective tissue layer
supports the smooth muscle, the elastic fibers of the lamina propria, and the

blood vessels (21). The alveoli (12) in the walls of the respiratory bronchioles
(12, 22) appear as small evaginations, or outpockets.

Each respiratory bronchiole (12, 22) divides into several alveolar ducts (13,
20) that are lined with alveoli (23) that open into the alveolar duct. Clusters of

alveoli (23) that surround and open into alveolar ducts (13, 20) are called
alveolar sacs (24). In this illustration, a plane of section passes from a terminal
bronchiole (8) to the respiratory bronchiole and into alveolar ducts (20).

The pulmonary vein (9) and pulmonary artery (9) branch as they
accompany the bronchi and bronchioles into the lung. Small blood vessels are

also seen in the connective tissue trabeculae (25) that separate the lungs into
different segments.

The serosa (14) or visceral pleura surrounds the lungs. It (14) consists of a
thin layer of pleural connective tissue (14a) and a simple squamous layer of

pleural mesothelium (14b).

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