By definition, peristalsis is the waves of contraction seen in tubelike organs; propels
substances along the tract. Though peristalsis is confined only to the esophagus, it is
necessary to understand the beginnings of food, before it enters the esophagus. After
mastication occurs, food enters the pharynx. The Pharynx is the passageway through which
many tubes run from the mouth and the nose to the upper body. Some of these tubes are the
nasopharynx, which runs oxygen to the lungs, and the oropharynx, which also runs oxygen to
the lungs. Masticated food is not passed to the longs by the actions of the epiglottis.
The epiglottis is a membrane, which covers the entrance to the nasopharynx. By covering
the entrance to the nasopharynx, food is forced to enter the esophagus.
After food passes through the pharynx, it enters the esophagus. The
esophagus, also known as the gullet, runs from the pharynx to the diaphragm, to the top of
the stomach. The Esophagus is about 25 cm (10 inches). The esophagus is really a large
muscle, which pushes food down to the stomach. The walls of the esophagus are lined with
four layers of thin tissue. These membranes are the mucosa, the submucosa, the muscularis
externa, and the serosa.
The mucosa is the inner most layer. It is a moist membrane that lines
the cavity of the esophagus. The mucosa consists of a small amount of connective tissue as
well as the surface epithelium. The mucosa is also lined with a very thin layer of smooth
muscle tissue. After the esophagus ends, the mucosa continues, but is extended by a
friction resisting membrane of stratified squamos epithelium layer.
The submucosa is the second layer of tissue, which lies within the
esophagus. The submucosa is a soft connective tissue layer. The submucosa contains lymph
nodules, nerve endings, lymphatic vessels, and blood vessels.
The muscularis externa lies within both the submucosa as well as the
mucosa. The muscularis externa is mainly constituted of two different types of smooth
muscle cells. The muscularis externa is made of the longitudinal layer of smooth muscle
cell as well as the circular layer of smooth muscle cell.
The final layer of tissue within the esophagus is the serosa. The
serosa is the innermost layer of tissue within the esophagus. The serosa is made up of a
single flat layer of serous fluid producing cells. There are two serous fluid producing
cells types, the visceral peritoneum as well as the parietal peritoneum.
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