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Read the text again and get ready to speak on the structure of the diges-tive system using the pictures and anatomical terms
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HOW THE BODY USES FOOD
The body needs energy to maintain all its functions. The body breaks food down into its nutrients through the process of digestion. Digestion begins in the mouth. As food is being chewed, saliva moistens the particles. The saliva begins to break down starchy parts of food. After the food is swallowed, it passes through the esophagus, a tube that leads into the stomach which is a hollow, sac-like organ connected to the esophagus and the duodenum. The stomach consists of layers of muscle and nerves that continue the breakdown of food which begins in the mouth. In the stomach, the food is thoroughly mixed with a digestive juice. The juice, called gastric juice, speeds up the digestion of food.
The partly digested food, called chyme, passes from the stomach into the small intestine. First, food enters the duodenum, the first part of the small intestine. It then enters the jejunum and then the ileum (the final part of the small intestine). In the small intestine, other juices complete the process of digestion. They break down the food into molecules that pass through the walls of the intestine and into the bloodstream.
The blood distributes the nutrients to cells and tissues throughout the body. There the nutrients are broken down to produce energy or are used to rebuild tissues or to regulate chemical processes. Some of the nutrients are stored in the body, and others are used over and over again. But most of the nutrients undergo chemical changes as they are used in the cells and tissues. These chemical changes produce waste products, which go into the bloodstream.
Some of the wastes are carried to the kidneys, which filter the wastes out of the blood. The body expels these wastes in the urine. The liver also filters out some wastes and concentrates them into a liquid called bile. Bile is stored in the gall bladder until it is needed to aid in the process of digestion. Then the gall bladder empties bile into the small intestine. From there, any remaining bile passes into the large intestine, along with those parts of the food that could not be digested in the small intestine. The liver (located under the rib cage in the right upper part of the abdomen), the gallbladder (hidden just below the liver), and the pancreas (beneath the stomach) are not part of the alimentary canal, but these organs are essential to digestion.
So, after passing through the small intestine, food passes into the large intestine which consists of cecum (the appendix is connected to the cecum), colon (ascending, transverse, descending) sigmoid colon and rectum. The rectum ends in the anus. The large intestine absorbs water and small amounts of minerals from waste material. This material, along with bacteria present in the large intestine, becomes the final waste product, the feces, and it is eliminated from the body.
III. Post – reading activities
Date: 2015-09-18; view: 763; Нарушение авторских прав