What are the functions of each of the four tissue layers of the GI tract?

Answer 1

The digestive tract contains four major tissue layers—the mucosa, submucosa, muscularis, and serosa.
The mucosa, often called the mucosal lining, produces secretions such as enzymes and hormones needed for digestion. A layer of connective tissue called the submucosa surrounds the mucosal layer.
The submucosa contains a rich supply of blood vessels, delivering nutrients and oxygen to the inner mucosal layer and the muscularis. These blood vessels also circulate most of the nutrients absorbed from the small intestine away from the GI tract. The submucosa contains lymphatic vessels that are filled with lymph. Lymph aids in the circulation of dietary fat away from the GI tract. The submucosa also contains a network of nerves, which regulate the release of GI secretions from cells making up the mucosal lining.
The muscularis typically consists of two layers of smooth muscle—an outer longitudinal layer and an inner circular layer. The movement of the muscularis promotes mixing of the food mass with digestive secretions and keeps food moving through the entire length of the GI tract.
The serosa secretes a fluid that lubricates the digestive organs, preventing them from adhering to one another. In addition, much of the GI tract is anchored within the abdominal cavity by a membrane that is continuous with the serosa.