Page 396 - Anatomy and Physiology of Farm Animals, 8th Edition

Anatomy of the Digestive System / 381

thickening of the muscle that constitutes a mucosa of the simple stomach is glandular.
Exclusive of the esophageal region, the
functional sphincter, the cardiac sphincter.
VetBooks.ir This muscle is especially well developed in Grossly, the mucosa here is thrown into
prominent gastric folds that allow the
the horse, where its strength and configura­
tion make it difficult or impossible for the stomach volume to expand to accommo­
horse to vomit. date meals. On the microscopic level, the
The cardia and pylorus are quite close columnar epithelium of the tunica mucosa
together, giving the stomach a J shape. This undulates in deep infoldings that create
arrangement results in a very short con­ depressions called gastric pits.
cave side between the cardia and pylorus, A transition from the stratified squa­
known as the lesser curvature, and a much mous epithelium of the esophageal region
longer convex side, the greater curvature. to columnar epithelium in the glandular
The large bulge near the cardia is the fun- part of the stomach demarcates the begin­
dus. In the horse, the fundus is enlarged to ning of the cardiac gland region. This
create a blind sac, the saccus cecus, the transition is grossly obvious in the horse,
mucosa of which is stratified squamous where it is called the margo plicatus.
and nonglandular. The porcine stomach The cardiac glands that give this region
features a similar albeit smaller outpocket­ its name are short, branched tubular glands
ing called the gastric diverticulum; the whose major secretory product is mucus.
mucosa of this feature of the pig stomach is The equine cardiac gland region is small,
of the typical glandular, columnar type. but it covers nearly half of the interior of
The body of the stomach is the expan­ the porcine stomach.
sile part that is defined externally by the The fundic gland region lines much of
greater curvature. The size of the gastric the interior of the stomach (and certainly
body is determined largely by the degree of more than just the fundus). The typical
filling. It narrows as the stomach arcs gland is the fundic gland (also called the
ventrad and to the right, becoming the gastric gland proper). Fundic glands are
pyloric region. A very strong sphincter, simple tubular glands that open into
the pylorus, regulates the outflow of the the gastric pits, where they discharge their
stomach in this region. In the pig (and in secretions.
the equivalent region of the ruminant The pyloric gland region corresponds
stomach), the pylorus features a muscular more or less to the pyloric region of the
and fatty enlargement, the torus pylori- simple stomach. The pyloric glands are
cus. Its function is unknown. histologically similar to the cardiac glands,
The tunica muscularis of the stomach and like them, they secrete mucus.
features three discontinuous layers of Enteroendocrine cells are scattered
smooth muscle: an outer longitudinal, a throughout the mucosa of the glandular
middle circular, and an inner oblique layer. stomach. These secrete hormones that
The lumen of the simple stomach fea­ affect the secretory and muscular activity
tures several histologically distinct regions of the gut and its accessory organs (e.g.,
whose names are similar to the gross parts of liver and pancreas).
the stomach but that unfortunately do not
directly correspond to these (Fig. 20‐9).
Immediately surrounding the cardia is an Ruminant Stomach
area of stratified squamous epithelium called
the esophageal region. This nonglandular The ruminant stomach is actually a single
region is limited in swine but is expanded in stomach modified by marked expansion of
the horse, in which it lines the saccus cecus. the esophageal region into three distinct
It is the esophageal region of the stomach and voluminous diverticula, the rumen,
that is so dramatically expanded in rumi­ reticulum, and omasum, collectively
nants, where it lines the forestomach. known as the forestomach. These are lined