Human Digestive system - Anatomy-of-the-human-stomach
A digestive pouch between the oesophagus and the duodenum, which stores food, secretes gastric juice (that kills ingested bacteria and initiates protein digestion) and, by wave-like contractions, churns and releases its contents into the duodenum at a controlled rate. Its size and position in humans is related to body build, but varies within the same individual with posture (standing, lying down) and contents (empty, full). It is divided into the cardiac region around the cardiac orifice (where the oesophagus opens into it), the fundus (the region above the level of the cardiac orifice), the body, and the pylorus, which opens into the duodenum at the pyloric orifice. Its most fixed parts are the cardiac and pyloric orifices, the latter remaining closed except for the periodic release of the stomach contents into the duodenum. In anatomy, the stomach is an organ of the gastrointestinal tract involved in the second phase of digestion, following mastication. The stomach!!!s primary function is to break down large molecules into smaller ones using hydrochloric acid so that they can be absorbed from the small intestine. The stomach is generally a highly acidic environment with a pH range of 1 to 4 depending on food intake and other factors. The stomach!!!s interior can secrete 2 to 3 litres of gastric fluid per day.
Anatomy of the human stomach
The stomach lies between the esophagus and the duodenum (the first part of the small intestine). It is on the left side of the abdominal cavity, the fundus of the stomach lying against the diaphragm. Lying beneath the stomach is the pancreas, and the greater omentum hangs from the greater curvature. The stomach is divided into four sections, each of which has different cells and functions. The sections are:
1) Cardiac region, where the contents of the esophagus empty into the stomach
2) Fundus, formed by the upper curvature of the organ
3) Body, the main central region, and
4) Pylorus or antrum, the lower section of the organ that facilitates emptying the contents into the small intestine.
Two smooth muscle valves, or sphincters, keep the contents of the stomach contained. They are the:
1) Cardiac or esophageal sphincter, dividing the tract above, and
2) Pyloric sphincter, dividing the stomach from the small intestine. In humans, the stomach has a volume of about 50 mL when empty.
Vessels and nerves
Arteries: The arteries supplying the stomach are the left gastric, the right gastric of the common hepatic, and the left gastroepiploic, right gastroepiploic and short gastric branches of the lienal (splenic artery). Contrary to popular belief, you have more nerve endings in your stomach than in your head.
Histology of the human stomach
Like the other parts of the gastrointestinal tract, the stomach walls are made of a number of layers. The submucosa lies under this and consists of fibrous connective tissue, separating the mucosa from the next layer, the muscularis externa. The muscularis in the stomach differs from that of other GI organs in that it has three layers of muscle instead of two. The epithelium of the stomach forms deep pits, called fundic or oxyntic glands. The secretion of pepsinogen prevents self-digestion of the stomach cells. Further up the pits, parietal cells produce gastric acid and intrinsic factor. Near the top of the pits, closest to the contents of the stomach are goblet cells which form the mucus gel layer above the mucosa which help protect the stomach from self-digestion. The muscularis externa is made up of three layers of smooth muscle.
Control of secretion and motility
The movement and the flow of chemicals into the stomach are controlled by both the autonomic nervous system and by the various digestive system hormones. The hormone gastrin causes an increase in the secretion of HCl, pepsinogen and intrinsic factor from parietal cells in the stomach. It also causes increased motility in the stomach. Gastrin is released by G-cells in the stomach to distenstion of the antrum, and digestive products. In a different and rare manner, secretin, produced in the small intestine, has most effects on the pancreas, but will also diminish acid secretion in the stomach. Gastric inhibitory peptide (GIP) and enteroglucagon decrease both gastric acid and motility. Other than gastrin, these hormones all act to turn off the stomach action. The stomach needs only to push food into the small intestine when the intestine is not busy. While the intestine is full and still digesting food, the stomach acts as storage for food