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The Digestive System (Ch. 15 Sections 2 and 3) 1. Functions of the digestive system: a. digestion--breaks down food into usable molecules b. absorption--absorbs molecules into the blood and carries it to the body c. elimination--wastes are eliminated THE MOUTH:--digestion begins here 2. mechanical digestion: in the mouth it occurs when biting and chewing 3. chemical digestion: chemicals in saliva begin breaking down food in the mouth 4. saliva: fluid in the mouth that begins chemical digestion ***bolus: wet mass of food and saliva 5. enzymes: proteins that speed up chemical reactions in the body THE ESOPHAGUS— 6. epiglottis: flap of tissue that seals off the windpipe (trachea) when swallowing 7. esophagus: muscular tube connecting the mouth to the stomach 8. peristalsis: involuntary muscle contractions that keep food moving in one direction; it occurs in the esophagus, stomach, and intestines THE STOMACH— 9. stomach: J-shaped muscular pouch in the abdomen 10. mechanical digestion: most mechanical digestion occurs in the stomach; muscles contract to churn the food 11. chemical digestion: **digestive juice contains the enzyme pepsin **pepsin works best in an acid environment **pepsin breaks proteins into short chains of amino acids **hydrochloric acid is the stomach acid that helps pepsin work **chyme—soupy mass of food that moves from the stomach to the small intestine SMALL INTESTINE— 12. small intestine: most chemical digestion and absorption take place here 13. liver: largest organ; produces bile----bile flows from the liver to the gallbladder (food does not pass through the liver) 14. bile: substance that breaks up fat particles; this is a mechanical process, not a chemical process 15. gallbladder: stores bile; after eating, bile passes from the gallbladder to the small intestine through a tube (food does not pass through the gallbladder) 16. pancreas: triangular shaped organ between the stomach and small intestine; produces enzymes that flow into the small intestine and help break down starches, proteins, and fats (food does not pass through the pancreas) 17. villi: finger-like structures covering the small intestines; villi absorb nutrients and pass them on to blood vessels LARGE INTESTINE— 18. large intestine: contains helpful bacteria; material entering the large intestine contains water and undigested food----the water is absorbed into the bloodstream, and remaining material gets ready for elimination 19. rectum: short tube at the end of the large intestine; waste material is compressed into solid form 20. anus: muscular opening at the end of the rectum; waste exits the body here