The digestive system includes the gastrointestinal tract, which starts at the mouth, where food and fluids are taken into the body and ends at the anus, where the final waste products are eliminated in the feces.
The gastrointestinal tract consists of all structures derived from the primitive gut tube and distal to the esophagus.
As such the gastrointestinal tract includes the stomach, small intestine, large intestine and those accessory structures that have formed from that part of the gut (liver, gallbladder, pancreas, hepatopancreatic duct, anal tonsils).
The accessory organs contribute needed materials for the breakdown and processing of the food entering the system.
The gastrointestinal tract (GI) is bordered by a layer of epithelial cells (with glands) sitting on a lamina propria (or basement membrane), comprising the mucosa and adjacent to the sub-mucosa, which is penetrated by blood capillaries, lymphatics and nerves.
Beneath the mucosa and sub-mucosa are two layers of smooth muscle, lying in longitudinal and transverse directions, to allow contractions and peristalsis,
The stomach contains the same tissue layers as are found in the esophagus, small intestine and colon, with some important variations in the secretions and structure of the mucosa layer.
The surface of the mucosa is a layer of simple columnar epithelial cells called surface mucous cells.
The mucosa contains a lamina propria (areolar connective tissue) and a muscularis mucosae (smooth muscle).
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Within the stomach, but particularly in the small intestine, the surface area of the mucosa is greatly increased. The mucosal and sub-mucosal layer is folded into microscopic villi on the surface of larger folds or ridges.
The main functions of the gastrointestinal system consist of digestion and absorption.
What is gastrointestinal tract (GI)?
