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The wall of the stomach consists of four coats: an outer serous coat; a muscular coat, made up of longitudinal, circular, and oblique muscle fibers; a submucous coat; and a mucous coat or membrane forming the inner lining. The muscles account for the stomach's ability to expand when food enters it. The muscle fibers slide over one another, reducing the thickness of the wall while increasing its area. When empty, the stomach has practically no cavity at all, since its walls are pressed tightly together; when full it holds about 1.4 liters.
The stomach muscles perform another function. When food enters the stomach, they contract in rhythm and their combined action sends a series of wavelike contractions from the upper end of the stomach to the lower end. These contractions, known as peristalsis, mix the partially digested food with the stomach secretions and ingested liquid until it has the consistency of a thick soup; the contractions then push it gradually by small aliquots into the small intestine.
The stomach is usually emptied of its digested contents in 1 to 4 hours; the time may be longer, however, depending on the amount and type of food eaten. Foods rich in carbohydrates leave it more rapidly than proteins, and proteins more rapidly than fats. The stomach may continue to contract after it is empty; such contractions stimulate nerves in its wall and may cause hunger pangs.
The mucous membrane lining the stomach contains innumerable gastric glands; their secretion, gastric juice, contains enzymes, mucin, and hydrochloric acid. Enzymes help to split the food molecules into smaller parts during digestion. The physiologic action of mucin is not fully understood. Hydrochloric acid aids in dissolving the food before the enzymes begin working on it.
The diagnosis and treatment of stomach disorders has changed markedly with the development of endoscopy. This benign procedure permits direct examination and biopsy of the stomach and has sharply increased the accuracy of diagnosis and, as a result, the effectiveness of medical therapy. In addition, the development of whole new families of medications that reduce gastric acid secretion (such as cimetidine) and increase gastric motility (such as metoclopramide) have decreased the need for surgery for peptic ulcer disease.
Surgery of the stomach has become increasingly conservative with a better understanding of that organ's physiology. Instead of the resections that were once done routinely for peptic ulcer disease, sophisticated procedures, such as the supraselective vagotomy, that can decrease acid secretion without resection of the stomach are available. Even so, resection may still be needed for more severe cases of ulcer disease, for such complex entities as Zollinger-Ellison syndrome, and for malignancies.
stomach/stom·ach/ (stum´ak) the musculomembranous expansion of the alimentary canal between the esophagus and duodenum, consisting of a cardiac part, a fundus, a body, and a pyloric part. Its (gastric) glands secrete the gastric juice which, when mixed with food, forms chyme, a semifluid substance suitable for further digestion by the intestine. stom´achalstomach´ic
Synonym(s): gaster [TA] , ventriculus (1) .
stomach(stum'ak) [Gr. stomachos, mouth, gullet, opening]
It is below the diaphragm to the right of the spleen, partly under the liver. It is composed of an upper fundus, a central body, and a distal pylorus. It has two openings: the upper cardiac orifice opens from the esophagus and is surrounded by the lower esophageal (cardiac) sphincter. The lower pyloric orifice opens into the duodenum and is surrounded by the pyloric sphincter. The wall of the stomach has four layers. The outer serous layer (visceral peritoneum) covers almost all of the organ. The muscular layer just beneath it has three layers of smooth muscle: an outer longitudinal layer, a medial circular layer, and an inner oblique layer. The submucosa is made of connective tissue that contains blood vessels. The mucosa is the lining that contains the gastric glands, simple tubular glands of columnar epithelium that secrete gastric juice. Chief cells secrete pepsinogen; parietal cells secrete hydrochloric acid and the intrinsic factor; mucous cells secrete mucus; G cells secrete gastrin.
The stomach is a reservoir that permits digestion to take place gradually; emptying of the stomach is under both hormonal and nervous control. Secretions and motility are increased by parasympathetic impulses (vagus nerves) and decreased by sympathetic impulses. The presence of food stimulates the production of the hormone gastrin, which increases the secretion of gastric juice. Protein digestion begins in the stomach; pepsin digests proteins to peptones. Hydrochloric acid converts pepsinogen to active pepsin and has little effect on unemulsified fats except those of cream. The intrinsic factor in gastric juice combines with vitamin B12 (extrinsic factor) to prevent its digestion and promote its absorption in the small intestine. Little absorption takes place in the stomach because digestion has hardly begun, but water and alcohol are absorbed.
bilocular stomachHourglass stomach.
cow horn stomach
foreign bodies in the stomach
stomachThe bag-like organ lying under the DIAPHRAGM in the upper right part of the ABDOMEN into which swallowed food passes, by way of the OESOPHAGUS. The stomach has an average capacity of about 1.75 l and secretes hydrochloric acid and the protein-digesting enzyme PEPSIN.
stomachthat part of the vertebrate gut system which follows the oesophagus, is expanded to form a chamber, and whose walls secrete pepsinogen giving rise to PEPSIN, RENNIN (in young mammals) and hydrochloric acid from the OCYNTIC CELLS. A major function of the stomach is the mechanical churning of the food by means of a muscular wall. Gastric secretions also include mucin, which lubricates the food mass that is passed, a little at a time, to the SMALL INTESTINE via the PYLORIC SPHINCTER.
stomachthe part of the alimentary tract just below the diaphragm. Colloquially: abdomen, belly. See also alimentary, digestion.
Patient discussion about stomach
Q. Stomach ulcer or bad heartburn? hi. i am not sure if this is just heartburn or maybe i have an ulcer. for the last 7 months i have been getting really severe pains in my stomach (between my chest and my belly button). my upper back gets sharp pains and my stomach bloats out like I’m 8 months pregnant!!!. i have tried to take antacids for this but nothing works. i don’t know what else to do. it scares me sometimes because i have no idea what it is. My mom thinks it could be an ulcer. the pain lasts for a good 4 to 5 hours and i cant even sit down because the pain hurts so bad. can anyone tell me what this might be?????
Q. 10 weeks pregnant, stomach pain. My sister is 10 weeks pregnant and she is suffering from stomach pain from week 5 until now. I am Just wondering is it normal to have stomach pain when pregnant? and dose it go away after 12 weeks? This is her first pregnancy so please educate us.
Q. Ive been having problems with my stomach bloating and it is very tender and sore what could it be?
Is the pain relieved by defecation? Do you have also diarrhea or constipation? If so, these features may suggest IBS (http://www.nlm.nih.gov/MEDLINEPLUS/ency/article/000246.htm)
Anyway, stomach problems can also result from serious, albeit usually rare, conditions, so consulting a doctor may be wise in this situation.