Read the text to find out about a) the parts of the digestive system b) their characteristic features.
The digestive system includes the alimentary canal (a tube that extends from the mouth to the anus), oral structures and accessory digestive glands.
The major function of the digestive system is to provide nutrients to the body tissues. Digestion involves mechanical and chemical activities. The mechanical part of digestion involves tearing, grinding and mixing food with enzymes. Chemical digestion is done by various digestive enzymes.
The oral cavity is responsible for the grasping, grinding, and moistening of food. The structures of the oral cavity include lips, cheeks, teeth, tongue, palate, and salivary glands.
The esophagus is a muscular tube that moves food from the pharynx to the stomach. There are two muscle layers in the esophagus. These muscle layers, when they contract and relax, help in the movement of food by peristalsis.
The stomach is a muscular, hollow, dilated part of the digestive system, which functions as an important organ of the digestive tract. In most vertebrates, the stomach is located between the esophagus and the small intestine. It secretes protein-digesting enzymes and gastric acid to aid in food digestion.
The small intestine is the longest part of the alimentary canal and the site of most enzymatic digestion and absorption of nutrients. The subdivisions include the duodenum, the jejunum and the ilium.
The caecum is a pouch marking the division between the small intestine and the large intestine. The cecum contains bacteria that break down plant material. In mammals, the cecum varies considerably in size, depending on the animals diet.
The large intestine includes the colon and the rectum. For mammals, the entire large intestine is an important instrument in the conservation of water. Another function of the large intestine is to consolidate the feces. The rectum temporarily stores the feces until it is released through the anus.
There are four accessory glands of the digestive system and they are the salivary glands, the pancreas, the liver and the gallbladder.
The salivary glands in mammals are exocrine glands that produce saliva. They also secrete amylase, an enzyme that breaks down starch into glucose.
The pancreas is both an endocrine gland (producing several important hormones, including insulin, glucagon, and somatostatin), as well as an exocrine gland, secreting pancreatic juice containing digestive enzymes that pass to the small intestine.
The liver plays a major role in metabolism and has a number of functions in the body, including glycogen storage, decomposition of red blood cells, plasma protein synthesis, and detoxification. It produces bile, which aids in digestion, via the emulsification of lipids.
The gallbladder is a small non-vital organ, which aids in the digestive process and stores bile.
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