The walls of the stomach consist of four layers, similar to other parts of the gastrointestinal tract. These layers, starting from the innermost layer, are named mucosa, sub-mucosa, muscularis externa, and the serosa.
The mucosa consists mainly of the gastric glands that secrete the digestive juices. It is covered by a layer of columnar epithelial tissue. The sub-mucosa consists of dense connective tissue and has blood vessels, lymphatic vessels, and nerves running through it. The sub-mucosa supports the mucosa and allows it to move in a flexible manner during peristalsis.
Peristalsis is the contraction and relaxation of the stomach muscles to physically breakdown food and propel it forward. These contractions are created by the muscular wall of the stomach which consists of inner circular and outer longitudinal smooth muscle. The outermost layer of the stomach wall, the serosa consists of an epithelial layer and connective tissue which connects to the surrounding organs. The mucosa and the sub-mucosa are present as folds termed rugae. When the stomach is distended with food, the rugae are flattened out and appear smooth.
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