Page 552 - Atlas of Histology with Functional Correlations

The submucosa (3) is a wide layer of moderately dense irregular connective

tissue with some adipose tissue (12). The mucous acini of esophageal glands
proper (2) are in the submucosa (3) at intervals throughout the length of the
esophagus. The excretory ducts (10) of these glands (2) pass through the
muscularis mucosae (1c) and the lamina propria (1b) to open into the esophageal
lumen. The dark-staining ductal epithelium of the glands merges with the

stratified squamous surface epithelium (1a) of the esophagus (see Fig. 14.3).
Numerous blood vessels (11) are found in the submucosa (3).

Located inferior to the submucosa (3) is the muscularis externa (4),
composed of two muscle layers, an inner circular muscle layer (4a) and the

outer longitudinal muscle layer (4b), whose muscle fibers are shown here
sectioned in a transverse plane. A thin layer of connective tissue (13) lies
between the inner circular muscle layer (4a) and the outer longitudinal muscle
layer (4b).

In humans, the muscularis externa (4) in the upper third of the esophagus

consists of striated skeletal muscles. In the middle third of the esophagus, the
inner circular layer (4a) and the outer longitudinal layer (4b) exhibit a mixture of
both smooth muscle and skeletal muscle fibers. In the lower third of the

esophagus, only smooth muscle is present.

The adventitia (5) consists of a loose connective tissue layer that blends
with the adventitia of the trachea and the surrounding structures. Adipose tissue
(14), large blood vessels, an artery and a vein (15), and nerve fibers (6) are
numerous in the connective tissue of the adventitia (5).

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