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The stomach is a muscular, hollow organ in the upper gastrointestinal tract of humans and many other animals, including several invertebrates.The stomach has a dilated structure and functions as a vital organ in the digestive system.
The stomach is a distensible organ and can normally expand to hold about one litre of food. [22] This expansion is enabled by a series of gastric folds in the inner walls of the stomach. The stomach of a newborn baby will only be able to expand to retain about 30 ml.
This structure consists of connective tissue covered by a simple squamous epithelium, called the mesothelium, which reduces frictional forces during digestive movements. The intraperitoneal regions include most of the stomach, first part of the duodenum, all of the small intestine, caecum and appendix, transverse colon, sigmoid colon and rectum ...
Whilst the muscularis externa is similar throughout the entire gastrointestinal tract, an exception is the stomach which has an additional inner oblique muscular layer to aid with grinding and mixing of food. The muscularis externa of the stomach is composed of the inner oblique layer, middle circular layer, and the outer longitudinal layer.
Diagram of the alkaline mucous layer in the stomach with mucosal defense mechanisms. The gastric mucosa is the mucous membrane layer of the stomach, which contains the gastric pits, to which the gastric glands empty. In humans, it is about one mm thick, and its surface is smooth, soft, and velvety.
The pyloric gland is found in the pyloric region, the remaining 20 per cent of the stomach. The pyloric glands are mainly in the pyloric antrum. The pyloric gland secretes gastrin from its G cells. Pyloric glands are similar in structure to the oxyntic glands but have hardly any parietal cells.
Gastric pits are indentations in the stomach which denote entrances to 3-5 tubular gastric glands. [1] [2] They are deeper in the pylorus than they are in the other parts of the stomach. The human stomach has several million of these pits which dot the surface of the lining epithelium.
The function of the GI tract is to process ingested food by mechanical and chemical means, extract nutrients and excrete waste products. The GI tract is composed of the alimentary canal, that runs from the mouth to the anus, as well as the associated glands, chemicals, hormones, and enzymes that assist in digestion.