In humans, the<unk>  lies between the oesophagus and the duodenum (the first part of the small intestine). It is in the left upper quadrant of the abdominal cavity. The top of the<unk>  lies against the diaphragm. Lying behind the<unk>  is the pancreas. A large double fold of visceral peritoneum called the greater omentum hangs down from the greater curvature of the<unk> . Two sphincters keep the contents of the<unk>  contained; the lower oesophageal sphincter (found in the cardiac region), at the junction of the oesophagus and<unk> , and the pyloric sphincter at the junction of the<unk>  with the duodenum. The<unk>  is surrounded by parasympathetic (stimulant) and sympathetic (inhibitor) plexuses (networks of blood vessels and nerves in the anterior gastric, posterior, superior and inferior, celiac and myenteric), which regulate both the secretory activity of the<unk>  and the motor (motion) activity of its muscles. Because it is a distensible organ, it normally expands to hold about one litre of food. The<unk>  of a newborn human baby will only be able to retain about 30 millilitres. The maximum<unk>  volume in adults is between 2 and 4 litres. Sections Body of<unk>  2. Fundus 3. Anterior wall 4. Greater curvature 5. Lesser curvature 6. Cardia 9. Pyloric sphincter 10. Pyloric antrum 11. Pyloric canal 12. Angular incisure 13. Gastric canal 14. Rugae In classical anatomy the human<unk>  is divided into four sections, beginning at the cardia. * The cardia is where the contents of the esophagus empty into the<unk> . * The fundus () is formed in the upper curved part. * The body is the main, central region of the<unk> . * The pylorus () is the lower section of the<unk>  that empties contents into the duodenum. The cardia is defined as the region following the "z-line" of the gastroesophageal junction, the point at which the epithelium changes from stratified squamous to columnar. Near the cardia is the lower oesophageal sphincter. Recent research has shown that the cardia is not an anatomically distinct region of the<unk>  but a region of the oesophageal lining damaged by reflux. Anatomical proximity The<unk>  bed refers to the structures upon which the<unk>  rests in mammals. These include the tail of the pancreas, splenic artery, left kidney, left suprarenal gland, transverse colon and its mesocolon, and the left crus of diaphragm, and the left colic flexure. The term was introduced around 1896 by Philip Polson of the Catholic University School of Medicine, Dublin. However this was brought into disrepute by surgeon anatomist J Massey. Blood supply left and right gastric artery, left and right gastroepiploic artery and short gastric artery. The lesser curvature of the human<unk>  is supplied by the right gastric artery inferiorly and the left gastric artery superiorly, which also supplies the cardiac region. The greater curvature is supplied by the right gastroepiploic artery inferiorly and the left gastroepiploic artery superiorly. The fundus of the<unk> , and also the upper portion of the greater curvature, is supplied by the short gastric arteries, which arise from the splenic artery. Microanatomy Wall The gastrointestinal wall of the human<unk> . Like the other parts of the gastrointestinal tract, the human<unk>  walls consist of a mucosa, submucosa, muscularis externa, subserosa and serosa. The inner part of the lining of the<unk> , the gastric mucosa, consists of an outer layer of column-shaped cells, a lamina propria, and a thin layer of smooth muscle called the muscularis mucosa. Beneath the mucosa lies the submucosa, consisting of fibrous connective tissue. Meissner's plexus is in this layer interior to the oblique muscle layer. Outside of the submucosa lies another muscular layer, the muscularis externa. It consists of three layers of muscular fibres, with fibres lying at angles to each other. These are the inner oblique, middle circular, and outer longitudinal layers. The presence of the inner oblique layer is distinct from other parts of the gastrointestinal tract, which do not possess this layer.<unk>  contains the thickest muscularis layer consisting of three layers, thus maximum peristalsis occurs here. * The inner oblique layer: This layer is responsible for creating the motion that churns and physically breaks down the food. It is the only layer of the three which is not seen in other parts of the digestive system. The antrum has thicker skin cells in its walls and performs more forceful contractions than the fundus. * The middle circular layer: At this layer, the pylorus is surrounded by a thick circular muscular wall, which is normally tonically constricted, forming a functional (if not anatomically discrete) pyloric sphincter, which controls the movement of chyme into the duodenum. This layer is concentric to the longitudinal axis of the<unk> . * Auerbach's plexus (myenteric plexus) is found between the outer longitudinal and the middle circular layer and is responsible for the innervation of both (causing peristalsis and mixing). The outer longitudinal layer is responsible for moving the bolus towards the pylorus of the<unk>  through muscular shortening. To the outside of the muscularis externa lies a serosa, consisting of layers of connective tissue continuous with the peritoneum. Glands Histology of normal fundic mucosa. Fundic glands are simple, branched tubular glands that extend from the bottom of the gastric pits to the muscularis mucosae; the more distinctive cells are parietal cells. H&E stain. Histology of normal antral mucosa. Antral mucosa is formed by branched coiled tubular glands lined by secretory cells similar in appearance to the surface mucus cells. H&E stain. The mucosa lining the<unk>  is lined with a number of these pits, which receive gastric juice, secreted by between 2 and 7 gastric glands. Gastric juice is an acidic fluid containing hydrochloric acid and the digestive enzyme pepsin. The glands contains a number of cells, with the function of the glands changing depending on their position within the<unk> . Within the body and fundus of the<unk>  lie the fundic glands. In general, these glands are lined by column-shaped cells that secrete a protective layer of mucus and bicarbonate. Additional cells present include parietal cells that secrete hydrochloric acid and intrinsic factor, chief cells that secrete pepsinogen (this is a precursor to pepsin- the highly acidic environment converts the pepsinogen to pepsin), and neuroendocrine cells that secrete serotonin. Glands differ where the<unk>  meets the esophagus and near the pylorus. Near the junction between the<unk>  and the oesophagus lie cardiac glands, which primarily secrete mucus. They are fewer in number than the other gastric glands and are more shallowly positioned in the mucosa. There are two kinds - either simple tubular with short ducts or compound racemose resembling the duodenal Brunner's glands. Near the pylorus lie pyloric glands located in the antrum of the pylorus. They secrete mucus, as well as gastrin produced by their G cells. Gene and protein expression About 20,000 protein coding genes are expressed in human cells and nearly 70% of these genes are expressed in the normal<unk> . Just over 150 of these genes are more specifically expressed in the<unk>  compared to other organs, with only some 20 genes being highly specific. The corresponding specific proteins expressed in<unk>  are mainly involved in creating a suitable environment for handling the digestion of food for uptake of nutrients. Highly<unk> -specific proteins include GKN1, expressed in the mucosa; pepsinogen PGC and the lipase LIPF, expressed in chief cells; and gastric ATPase ATP4A and gastric intrinsic factor GIF, expressed in parietal cells.
Stomach
Large intestine
Small intestine
Gastrointestinal tract
Heart
Liver
Lung
Venom