Four layers of the Alimentary Canal (GI) Tract

The four layers of the alimentary canal starting with the innermost layer.

1.     The mucosa is formed by epithelium and a small amount of connective tissue, comes into direct contact with food passing through the canal. It secretes mucus that protects and lubricates the lining.

2.     The submucosa is composed of loose connective tissue, blood vessels, and many nerve endings. The blood vessels carry away the nutrients that are absorbed, and the nerve endings stimulate the muscle fibers so that the food is continually moving by peristalsis.

3.     The muscularis externa consists of a circular band and a longitudinal band of visceral muscles; is the thickest of the four layers. Main function: peristalsis.

4.     The serosa is continuous with the mesentery, the connective tissues that attach to the posterior body wall and hold the digestive organs in their proper position.