neurons of the plexus can be visualized by silver
impregnation techniques. It can be shown that the plexuses consist of aggregates of nerve cells
in the form of small parasympathetic ganglia. 4. Serosa or Adventitia The serosa consists of a thin layer of loose connective tissue covered by a simple squamous epithelium (mesothelium). Serosa is present in the parts of the intestinal tract that are present in
the peritoneal cavity. The regions of the intestinal
tract that are not present in the peritoneal cavity
are held in place by an outer layer of loose
connective tissue (adventitia). ESOPHAGUS The esophagus is a straight muscular tube
connecting the oral cavity to the stomach. The
esophagus contains the four basic layers
common to the rest of the digestive tract. The esophagus is lined with stratified squamous epithelium (without keratin). The lamina propria near the stomach contains
mucus-secreting esophageal cardiac glands. Mucus-secreting esophageal glands are present in the submucosa. (This is the only site in the intestinal tract, apart from the duodenum, where
exocrine glands are present in the submucosa.) The muscularis in the upper third of the esophagus is composed of striated muscle cells
(non-voluntary muscle). In the mid-region of the
esophagus the muscularis has a mixture of
striated muscle and smooth muscle. The muscles
of the lower third of the esophagus are only
smooth muscle. The outermost layer of the esophagus consists of
adventitia, apart from a small portion of the
esophagus that extends into the peritoneal cavity
(serosa). STOMACH The stomach is a very muscular organ in which
acid secretions and digestive enzymes contribute
to the digestion of food. From a histological
viewpoint the stomach can be divided into two
major histological regions: Fundus and Body Pylorus FUNDUS and BODY These are lined with a homogeneous simple columnar epithelium consisting of mucus- secreting cells. Mucus secreted by these cells