Gastrointestinal System I


Learning objectives

1. Know how the fundamental organization of the GI tract is modified along its course from the esophagus through large intestine.

2. Know the cell types in the mucosa of the GI tract and their function.

The digestive system consists of the oral cavity, the pharynx, the alimentary tract (canal), and the anal canal. There are both intrinsic and extrinsic glands, which may secrete digestive enzymes or mucus to facilitate the digestion and transport of ingested food. The intrinsic glands lie within the mucosa or submucosa of their organ of origin. The extrinsic glands communicate with their organ of origin through ducts. The extrinsic digestive glands are the major salivary glands including the parotid, sublingual and submandibular (submaxillary) glands; the pancreas; and the liver. These glands will be discussed in the following lab.

Organs of the digestive tract typically have 4 concentric coats. Proceeding outward from the lumen these are: (1) the mucosa (mucous membrane), (2) the submucosa, (3) the muscularis (muscularis externa), and (4) the adventitia or serosa. (Refer to diagram below).

1. The mucosa has three components: (a) the epithelium and its underlying basement membrane; (b) a thin underlying layer of loose, cellular connective tissue, the lamina propria; and © a relatively thin layer of smooth muscle, the muscularis mucosae. The latter may consist of both circular and longitudinally arranged layers.

2. The submucosa is composed of a layer of dense, irregularly arranged connective tissue that contains nervous tissue (the submucosal plexus of Meissner), as well as blood vessels.

3. The muscularis externa consists of at least 2 layers of smooth muscle; an inner circular and outer longitudinal layer. Connective tissue, separating the muscle layers, contains nerves (myenteric plexus of Auerbach) and blood vessels.

4. The outermost layer of adventitia consists of a thin layer of loose connective tissue; where the digestive system is covered by peritoneum the adventitial layer is called the serosa.

Lab activities

  1. Oral Cavity
  2. Esophagus
  3. Stomach
  4. Small Intestine
  5. Large Intestine
  6. Electron Micrographs
  7. Questions
  8. Answers