Write an explanatory note on Human Digestive System.
ANS : Human digestive system consists of alimentary canal and accessory digestive glands. Alimentary canal consists of mouth, buccal cavity, pharynx, oesophagus, stomach, small intestine, colon, rectum and anus. Accessory digestive glands are salivary glands, liver and pancreas. They secrete digestive juices.
The alimentary canal begins with mouth which is located at the anterior end between two lips. The mouth opens into the buccal cavity which lies between the upper and lower jaws.
The muscular tongue at the floor of the buccal cavity helps in digestion of food.
The upper and lower jaws have four kinds of teeth. (1) Incisors for cutting (2) Cannines for tearing (3) Premolars and (4) Molars for chewing and grinding.
The posterior region of buccal cavity is called pharynx which opens into the oesophagus. The oesophagus opens into the stomach which is situated on the left side of the abdomen. The inner wall of the stomach secretes gastric juices. The stomach opens into the duodenum through pyloric valve which is guided by sphincter muscle.
The proximal region of small intestine is called duodenum. It is U-shaped and receives the secretion of liver and pancreas through a common bile duct. The middle region of small intestine is called jejunum and the distal region is called ileum.
Ileum is about 7 m long. The inner wall of the small intestine has long fingerlike projections called villi. These increase the surface area for absorption. The small intestine opens into the large intestine. There is a projection called vermiform appendix at the junction of two intestines.
The large intestine opens into the rectum which, in turn, opens out by anus. The anus is guarded by sphincter muscles.
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