The digestive system consists of the alimentary canal and the accessory organs of digestion. The alimentary canal is the continuous system of hollow organs running from the oral cavity (mouth) to the anus. There are various accessory organs, commencing with the salivary glands and also including the liver, gall bladder and pancreas. Collectively, the alimentary canal and accessory organs carry out the functions of digestion, absorption and excretion.

Mechanical digestion begins in the mouth with mastication, the chewing action of the teeth and tongue. The sublingual, submandibular and parotid salivary glands secrete saliva which lubricates the food (figure 1). The saliva also contains enzymes (such as amylase and lysozyme) which begin the chemical digestion of carbohydrates and which kill some types of bacteria. When the food is sufficiently digested in the mouth, swallowing (deglutition) commences with the tongue pushing the food towards the pharynx. The epiglottis (figure 2) closes over the entrance of the trachea to protect the lungs, and the muscles of the pharynx push the food into the esophagus. An involuntary wave of muscular contraction, peristalsis, drives the swallowed food down the esophagus and through the lower esophageal (cardiac) sphincter into the stomach.

In the stomach (figure 3), mechanical digestion continues with the muscular contractions of the stomach wall. The stomach wall also secretes enzymes, such as peptidases, and hydrochloric acid, which are particularly effective in the chemical digestion of proteins. The stomach also absorbs water and some nutrients from the partially-digested food.

From the stomach, the partially-digested food is forced through the pyloric sphincter into the first segment of the small intestine, the duodenum (figure 4). The duodenum also receives bile from the gall bladder and digestive enzymes from the pancreas. The bile helps to emulsify lipids in the partially digested food, while enzymes from the pancreas continue the digestion of protein. From the duodenum, the partially digested food, called chyme, is moved by peristalsis through the jejunum (figure 5) and ileum, and then through the ileocecal valve into the large intestine.

The cecum (figure 6) is the first portion of the large intestine and contains, on its inferior aspect, a blind pouch called the vermiform appendix. From the cecum the chyme is pushed successively through the ascending colon,transverse colon and descending colon to the sigmoid colon. As the chyme passes through the colon, water and components of the bile are reabsorbed into the bloodstream. The colon also has a rich population of bacteria which, among other tasks, produce vitamin K. The chyme, partially solidified and enriched with bacteria, forms the feces which are moved from the sigmoid colon into the rectum (figure 7) and finally passed by defecation through the anus.

English - Japanese Glossary

alimentary canal: 消化管 (shoukakan); anus: 肛門 (koumon); appendix:虫垂 (chuusui); ascending colon: 上行結腸 (jyoukoukecchou); cecum: 盲腸 (mouchou); descending colon: 下行結腸 (kakoukecchou); digestive system: 消化器; (shoukaki); duodenum: 十二指腸 (juunishichou); esophagus: 食道 (shokudou); gall bladder: 胆嚢 (tannou); ileocecal valve: 回盲弁 (kaimouben); ileum: 回腸 (kaichou); jejunum: 空腸 (kuuchou); large intestine: 大腸 (daichou); liver: 肝臓 (kanzou); oral cavity; 口腔 (koukou); pancreas:膵臓 (suizou); pharynx: 咽頭 (intou); pyloric sphincter: 幽門 (yuumon) ; rectum: 直腸 (chokuchou); salivary glands: 唾液腺 (daekisen); small intestine: 小腸 (shouchou); stomach: 胃 (i); teeth: 歯 (ha); tongue: 舌 (shita); transverse colon: 横行結腸 (oukoukecchou)