This is a cross section of an esophagus from a rat. Although
few details are visible at this very low magnification, you can see
that it is a muscular tube lined with epithelium. You're seeing
it here cut at about midlevel. The dorsal side is at the top of
the image. The lumen (L) is surrounded by the tunica mucosa (M) consisting of keratinized stratified squamous epithelium.The tunica submucosa (S) is seen as a space, an artifact of preparation. The tunica muscularis (TM) contains skeletal and smooth muscle fibers at this point.
The plicated nature of the epithelium is obvious, even at this
magnification. The esophagus has to be distensible to permit
the swallowing of a fairly large bolus of food, and the mucosa is
therefore "puckered" when the muscle of the tube hasn't been
stretched. Although you can't see them here, there are small
glands in the submucosal layer that help to lubricate the food bolus
in its passage. The contractions of the tunica muscularis push
the food along its short journey to the stomach and these are
controlled by an amazingly complex array of nerve fibers. The act
of swallowing is a sort of high speed peristalsis, partially
voluntary in nature, and very tightly controlled.
Rat esophagus; H&E stain, paraffin section, 20x
