The digestive system consists of a long muscular tube, extending from mouth to anus, and a large number of associated glands which secrete substances that aid food digestion. The digestive tube is generally made up of four structurally and functionally distinct layers: the mucosa, the submucosa, the muscularis and the serosa. The mucosa, which is in contact with the contents of the lumen, is constructed to resist abrasion and to perform secretory and absorptive functions. The muscular layer which serves to propel the food through the tube is attached to the mucosa by way of the submucosa, a loose connective tissue layer. The serosa is called the adventitia when it is not covered by mesothelium. The serosa or adventitia carries blood vessels and nerves into the wall of the digestive tract.

Learning Objectives:

• Recognize the major features histological and physiological features of oral mucosa.
• Understand the relationship between structure and function in the esophagus.
• Recognize specific cell types in the lining of the stomach and their roles.

Let's start with the oral cavity.