The gastrointestinal tract is necessary for an organism to ingest, digest, absorb and effieciently excrete food matter. There is a general pattern that runs throughout the wall of the GI tract. The 4 concentric layers of the wall are the mucosa (innermost), submucosa, muscularis externa and adventitia (outermost):
- The mucosa is the only layer that has direct contact with food and is responsible for absorption. In some areas, for example the small intestine, the mucosa can be folded into villi for increased surface area for absorption.
- The submucosal layer of the GI tract contains nerves, lymphatics and blood vessels. It is composed of dense irregular connective tissue.
- Muscalaris externa contains 2 muscle layers: the inner circular muscle and the outer longitudinal muscle. Together, these 2 muscle layers work antagonistically to push food along the GI tract one way in a wave movement called peristalsis. The inner circular muscle allows food to travel in a unidirectional manner by preventing food from returning back up the GI tract.
- Adventitia (serosa) is made up of epithelium and forms a serous membrane. The serous membrane secretes important digestive enzymes such as amylase (important in breakdown of starch)
Although the thckness and main functions of the layers may vary throughtout the GI tract, the basic function and layer order remains the same
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