Digestive System II: Lower Alimentary Tract

Esophagus

The mucous membrane of the esophagus (oesophagus) is covered by stratified squamous nonkeratinized epithelium. The lamina propria is composed of loose connective tissue with lymphatic elements that form occasional lymphatic follicles. The muscularis mucosae is remarkably thick and it is formed by longitudinally arranged smooth muscle bundles. The underlying submucosa is composed of dense irregular connective tissue with occasional ganglion cells and nerve fibers (Meissner’s plexus). Tunica muscularis externa is composed of inner circular and outer longitudinal layers and it is quite unusual since it contains skeletal muscle in the upper third of the esophagus that is mixed with smooth muscle in the middle third while the distal part of the muscularis externa is composed of smooth muscle only. Elements of myenteric (Auerbach’s) plexus are abundant between the muscle layers. Outside, the esophagus is covered by loose connective tissue tunica adventitia, only the lowermost abdominal part has serosal coverage. Esophageal glands are mucous tubuloalveolar glands. Proper esophageal glands are scattered throughout the entire length of the submucosa (submucosal glands), while glands in the lamina propria (mucosal glands) are restricted to the cardiac region (esophageal cardiac glands) and to the proximal part of the esophagus.