The wall of the digestive tract consists of four tissue layers surrounding a hollow lumen. The innermost layer of the digestive tract is the mucosa. In the oral cavity and esophagus, the mucosa is abrasion-resistant stratified squamous epithelium. From the stomach to the anus, the mucosa is simple columnar epithelium.
The submucosa is connective tissue that lies deep to the mucosa. The muscularis has inner circular and outer longitudinal layers of muscle throughout the digestive tract. The stomach has a third, oblique layer of muscle in its muscularis that aids in mixing. The outermost layer is an adventitia that attaches to surrounding tissues or a well-defined epithelial serosa.
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