Structures of the digestive system he digestive

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Structures of the Digestive System he digestive process begins in the mouth. Ingestion, the first T stage of the process, is the taking of food into the body. Structures involved in ingestion include your teeth, salivary glands, and tongue. These structures are shown in Figure 17.1 on page 444. Teeth. The primary function of the teeth is to break the food you eat into smaller pieces. (MAS-tuh-KAY-shuhn) is the process of chewing, which prepares food to be swallowed. Salivary glands. The salivary glands in the mouth produce the first digestive juices used in the digestive process. Saliva produced by these glands contains an enzyme that begins to break down the starches and sugars in food into smaller par- ticles. Saliva also lubricates food, making it easier to swallow. Tongue. The tongue forms chewed food into a size and shape that can be swallowed. As you swallow, muscular contractions force food into the pharynx, or throat. The uvula, a small flap of muscular tissue at the back of the mouth, closes the opening to the nasal passages. The epiglottis, the flap of tissue covering the throat, closes the opening to the trachea, or windpipe, to prevent food from entering the respiratory system. The Esophagus When food is swallowed, it enters the esophagus, the muscular tube about 10 inches long that connects the pharynx with the stomach. Food is moved through the esophagus, stomach, and intestines by a process called (PER-uh-STAWL-suhs), a series of involuntary muscle contractions that move food through the digestive tract. The action of peristalsis is like a wave moving through the muscle to push food and fluid through each hollow organ. The peristaltic action begins as soon as food is swallowed and enters the esophagus. A sphincter muscle at the entrance to the stomach allows food to move from the esophagus into the stomach. peristalsis Mastication Your salivary glands respond to the smell of foods before you begin to eat. How does saliva help in the digestion process? 443 Lesson 1 The Digestive System Respect. Making healthful choices about what you eat and how you eat is a demonstration of responsibility and respect for your body. Using food to cope with emotions or to relieve bore- dom can lead to overeating or indigestion. Follow the Dietary Guidelines and the Food Guide Pyramid to be sure that you are getting the right balance of nutrients each day. Take time to eat slowly to help your body digest foods properly.
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444 Chapter 17 Digestive and Urinary Systems The Stomach The stomach is a hollow, saclike organ enclosed in a muscular wall. These flexible muscles allow the stomach to expand when you eat. The stomach, shown in Figure 17.2, has three tasks in digestion. Mixing foods with gastric juices. are secretions from the stomach lining that contain hydrochloric acid and pepsin, an enzyme that digests protein. Hydrochloric acid in the stomach kills bacteria taken in with food and creates an acidic environment for the pepsin to do its work. The hydro- chloric acid is strong enough to dissolve metal. Mucus produced
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