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The gastrointestinal wall of the gastrointestinal tract is made up of four layers of specialised tissue. From the inner cavity of the gut outwards, these are:
The mucosa is the innermost layer of the gastrointestinal tract. It surrounds the lumen of the tract, and comes into direct contact with digested food. The mucosa itself is made up of three layers: the epithelium, where most digestive, absorptive and secretory processes occur; the lamina propria, a layer of connective tissue, and the muscularis mucosae, a thin layer of smooth muscle.
The submucosa contains nerves including the submucous plexus , blood vessels and elastic fibres with collagen, that stretches with increased capacity but maintains the shape of the intestine.
The muscular layer surrounds the submucosa. It comprises layers of smooth muscle in longitudinal and circular orientation that also helps with continued bowel movements and the movement of digested material out of and along the gut. In between the two layers of muscle lies the myenteric plexus.