Esophagus

The esophagus conveys food from the pharynx to the stomach by means of peristaltic waves which begin as a result of the swallowing reflex. The inner wall of the esophagus is lined with stratified squamous epithelium. It shows up as large purple on your slide. Notice that the cells at the base of this epithelial layer are cuboidal. This is the region where mitosis occurs. As new cells are produced they are pushed nearer the surface and become flattened. The most superficial cells are worn off the surface by material moving down the esophagus. What is the function of this epithelium? Why is the stratified squamous epithelium found in this portion of the digestive tract?

External to the epithelial layer is loose connective tissue. It often stains orange-red and contains ducts of the large submucosal glands. The ducts and glands appear dark purple. On some slides you may be able to trace a duct from gland to surface, but as in this image, you will generally only see a thin-walled cavity lined with purple-staining cells. Why?

At the base of the mucosa (just internal to the "purple" glands in the submucosa) lies the muscularis mucosa (not labeled). This is composed of thin tracts of smooth muscle fibers and is difficult to recognize on these slides. Remember that the epithelial layer, the connective tissue and the muscularis mucosa comprise the mucosa.

The submucosa is the next layer toward the outside and contains the submucosal glands. These large purple-staining glands produce mucus which lubricates the esophagus. A layer of loose connective tissue is found external to the glands (orangish in color). This is still submucosa.

Below the glandular layer you can see the muscularis mucosa and below this the submucosa. The easiest place to observe these two layers is in the folds. While you should be able to distinguish the muscularis mucosa here, it is similar in appearance to surrounding tissues in these preparations.

The muscularis layer differs from the other regions of the gut by having three layers of muscle rather than two. This allows for a churning motion. (All three layers are not found in all regions of the stomach). Can you relate muscle complexity to function in the different regions of the stomach?

Outside the muscularis is the serosa. The serosa is an area of loose connective tissue. A layer of simple squamous epithelium covers the serosa and is continuous with the membranes of the mesenteries. The mesenteries are also continuous with the outer layers of the small and large intestine.