基医专外学消化系统215秋.pptVIP

Digestive system 授课教师：张纪周 Email：zhangjz@ QQ:274806408 Professional English * The digestive system, also called the gastroin testinal or alimentary canal. The primary functions of the digestive system are: ingestion - the entry of food into the body; digestion - the physical and chemical breakdown of food into nutrients that can be used by the bodys cells; absorption - the passage of these nutrients from the gastrointestinal tract into the bloodstream; and elimination - the excretion of solid waste materials that cannot be absorbed into the blood. * Ana tomically, the digestive system consists of a 30-foot long, mucous membrane-lined tube beginning with the mouth, where food enters the body, and ending with the anus, where solid waste is excreted. The digestive system is composed of 9 main organs: mouth, pharynx, esophagus, stomach, small intestine, large intestine, liver, gallbladder and pancreas. The liver, gallbladder, and pancreas are also called accessory organs of the digestive system. Although food does not pass through these organs, they aid in the processing of food and nutrients. The organs of the digestive system are described in the paragraphs below. * The oral cavity. The process of digestion begins in the mouth, also called the buccal cavity, which is the opening through which food enters the body. The mouth has the ability to mechanically reduce the size of the food that is placed in it. The lips form the opening to the mouth, while the cheeks or bucca (buccae) form the borders of the oral cavity. The structures within the oral cavity including the teeth, tongue, and palate, are involved in the chewing (mastication) and swallowing (deglutition) of food. They also play a role in speech. * The teeth are used to cut, tear, and crush food into smaller pieces. They are classified mainly by their shapes and locations. Incisors and cuspids are in front of the mouth; molars are in the back. Each tooth consists of a mass of nerves and blood vessels, ca