The esophagus is a muscular tube transporting partially digested food from the pharynx to the stomach. As are all organs opening to the exterior, the esophagus is composed of four tunics: mucosa; submucosa; muscularis externa; and adventitia (because the esophagus does not protrude into an internal body cavity). 10x
The mucosa of the esophagus is lined with stratified squamous moist epithelium to protect the organ from the partially digested food. Mucous glands are located in the lamina propria in some regions, particularly near the gastro-esophageal junction and sometimes in the upper third. The muscularis mucosae is limited or absent in the upper third, but forms a developed layer in the lower two-thirds of the esophagus.
The submucosa possesses compound tubulo-acinar glands, called esophageal glands proper, scattered along the length of the esophagus. These glands, not present in this image, lubricate the esophagus during food transport.
Muscularis externa >
Because swallowing is a voluntary action, muscularis externa in the upper one-third of the esophagus is composed of skeletal muscle. Both skeletal and smooth muscle are located in the muscularis externa in the middle third (shown here), and only smooth muscle is found in this tunic in the lower one-third.
The esophagus is attached to the posterior body wall and does not protrude into an internal body cavity, so the outermost tunic of this organ is an adventitia of connective tissue.