stomach full explanation

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"Gastric" redirects here, for the sauce flavouring see Gastrique The stomach is a muscular, hollow, dilated part of the digestion system which functions as an important organ of the digestive tract in some animals, including vertebrates, echinoderms, insects (mid-gut), and molluscs. It is involved in the second phase of digestion, following mastication (chewing).The stomach is located between the esophagus and the small intestine. It secretes protein-digesting enzymes called protease and strong acids to aid in food digestion, (sent to it via oesophageal peristalsis) through smooth muscular contortions (called segmentation) before sending partially digested food (chyme) to the small intestines.

The word stomach is derived from the Latin stomachus which is derived from the Greek word stomachos, ultimately from stoma (st?µa), "mouth". The words gastro- and gastric (meaning related to the stomach) are both derived from the Greek word gaster

                            Role in digestion

Bolus (masticated food) enters the stomach through the oesophagus via the oesophageal sphincter. The stomach releases proteases (protein-digesting enzymes such as pepsin) and hydrochloric acid, which kills or inhibits bacteria and provides the acidic pH of two for the proteases to work. Food is churned by the stomach through muscular contractions of the wall called peristalsis – reducing the volume of the fundus, before looping around the fundus and the body of stomach as the boluses are converted into chyme (partially digested food). Chyme slowly passes through the pyloric sphincter and into the duodenum of the small intestine, where the extraction of nutrients begins. Depending on the quantity and contents of the meal, the stomach will digest the food into chyme anywhere between forty minutes and a few hours. The average human stomach can comfortably hold about a litre of food.

Gastric juice in the stomach also contains pepsinogen and prorennin. Hydrochloric acid activates these inactive forms of enzymes into active forms which are pepsin and renin (proteases). Rennin digests the milk protein Caesinogen (soluble) into caesin (insoluble) thus curdling the milk. Pepsin breaks down proteins into polypeptides.

                         Anatomy of the stomach

The stomach lies between the esophagus and the duodenum (the first part of the small intestine). It is on the left upper part of the abdominal cavity. The top of the stomach lies against the diaphragm. Lying behind the stomach is the pancreas. The greater omentum hangs down from the greater curvature.Two sphincters keep the contents of the stomach contained. They are the esophageal sphincter (found in the cardiac region, not an anatomical sphincter) dividing the tract above, and the Pyloric sphincter dividing the stomach from the small intestine.
The stomach is surrounded by parasympathetic (stimulant) and orthosympathetic (inhibitor) plexuses (networks of blood vessels and nerves in the anterior gastric, posterior, superior and inferior, celiac and myenteric), which regulate both the secretions activity and the motor (motion) activity of its muscles.
In adult humans, the stomach has a relaxed, near empty volume of about 45 to 75 ml. Because it is a distensible organ, it normally expands to hold about one litre of food,but can hold as much as two to three litres. The stomach of a newborn human baby will only be able to retain about 30 ml.
 

                                      Sections

The stomach is divided into four sections, each of which has different cells and functions. The sections are:
cardia:Where the contents of the esophagus empty into the stomach.
fundus:Formed by the upper curvature of the organ.
Body or corpus:The main, central region.
pylorus:The lower section of the organ that facilitates emptying the contents into the small intestine.
 

 

                                Blood supply to stomach