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The stomach is a muscular, hollow, dilated part of the digestive system which functions as an important organ of the digestive tract in many animals, including vertebrates, echinoderms, insects (mid-gut), and molluscs. It is involved in the second phase of digestion, following mastication (chewing). In most vertebrates, the stomach is located between the esophagus and the small intestine. It secretes protein-digesting enzymes called proteases and gastric acid to aid in food digestion, through smooth muscular contractions before sending partially digested food (chyme) to the small intestines. ==Structure== The stomach lies between the esophagus and the duodenum (the first part of the small intestine). It is in the left upper part of the abdominal cavity. The top of the stomach lies against the diaphragm. Lying behind the stomach is the pancreas. A large double fold of visceral peritoneum called the greater omentum hangs down from the greater curvature of the stomach. Two sphincters keep the contents of the stomach contained; the lower esophageal sphincter (found in the cardiac region), at the junction of the oesophagus and stomach, and the pyloric sphincter at the junction of the stomach with the duodenum. 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 milliliters.〔( BBC news article )〕 Because it is a distensible organ, it normally expands to hold about one litre of food. The stomach of a newborn human baby will only be able to retain about 30 milliliters. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Stomach」の詳細全文を読む スポンサード リンク
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