Digestive System Unit 6.11 (6 th Edition) Chapter 7.11 (7 th Edition) 1
Learning Objectives Identify the major organs of the digestive system. Explain the locations and functions of three organs in the mouth that aid in the breakdown of food. Explain two functions of the salivary glands. Describe how gastric juices act on food in the stomach. Explain how food is absorbed into the body by the villi in the small intestine. Describe three functions of the large intestine. Explain the main functions of the liver. Explain the role of the pancreas in food digestion. Explain the major diseases of the digestive system. 2
Fun Facts About the Digestive System The average human produces ~ 2 Liters of saliva in a day (that s a lot of spit). The human stomach can expand up to four times its normal size. The small intestine is at least 20 feet long. The large intestine is ~ 5 feet long (but is much wider than the small intestine). Food stays in your stomach for 1-4 hours. Within the colon, a typical person harbors more than 400 distinct species of bacteria. The liver is the largest organ (other than skin) and performs more than 500 functions. 3
Digestive System Overview Also Called Gastrointestinal System responsible for physical and chemical breakdown of food moves food into bloodstream so it can be used by cells & tissue Alimentary Canal long, muscular tube that begins at mouth pharynx esophagus stomach small & large intestines anus Accessory Organs salivary glands tongue teeth liver gallbladder pancreas 4
The Mouth and Teeth Mouth also called buccal cavity receives food as it enters the body food is tasted, broken down physically by teeth also lubricated and partially digested by saliva and swallowed Teeth physically break down food by chewing and grinding (mastication) Tongue muscular organ that contains special receptors called taste buds allow tastes of sweet, salt, sour, and bitter also aids in chewing and swallowing food Hard Palate bony structure that forms roof of mouth separates mouth from nasal cavities Soft Palate separates mouth from from nasopharynx uvula hangs from middle of soft palate and prevents food from entering nasopharynx during swallowing 5
Salivary Glands, Bolus, & Esophagus Salivary Glands produce liquid saliva saliva lubricates mouth during speech and chewing moistens food so that it can be swallowed easily saliva contains enzyme that speeds up chemical reactions salivary amylase enzyme begins chemical breakdown of carbs Bolus food after it is chewed and mixed with saliva when bolus is swallowed, it enters pharynx (throat) pharynx carries air to trachea and food to esophagus when bolus is swallowed, epiglottis closes over larynx (voice box) prevents it from entering respiratory tract & forces into esophagus Esophagus muscular tube behind the trachea receives bolus from pharynx and carries it to stomach relies on peristalsis (wavelike involuntary muscle movement) to move food forward 6
The Stomach Stomach enlarged part of alimentary canal receives food from esophagus rugae (folds) that line stomach disappear as it expands with food Cardiac Sphincter circular muscles between esophagus and stomach closes after food enters stomach prevents food from going back up esophagus Pyloric Sphincter circular muscle between stomach and small intestine keeps food in stomach until ready for small intestine food usually stays in stomach for 1-4 hours Chyme name given to semifluid food in stomach converted by gastric juices containing HCl & enzymes HCl kills bacteria, absorption, & activates pepsin enzyme lipase enzyme starts chemical breakdown of fats pepsin starts protein digestion rennin (in infants only) aids in milk digestion 7
Small Intestine Small Intestine coiled section of alimentary canal that is ~ 20 feet in length 1 inch in diameter and divided into 3 sections (1) Duodenum first 9-10 inches of small intestine bile from gallbladder and liver and pancreatic juice enters through ducts (2) Jejunum approximately 8 feet in length middle section of small intestine (3) Ileum final 12 feet of small intestine connects with large intestine at the cecum ileocecal valve separates ileum and cecum prevents food from returning to ileum 8
Intestinal Digestion In the Small Intestine process of digestion is completed and products absorbed into blood enzymes maltase, sucrase, and lactase break down sugars peptidase enzymes complete digestion of proteins steapsin enzyme digests fats bile from liver and gallbladder physically breaks down (emulsifies) fats Enzymes from Pancreatic Juice Complete Digestion pancreatic amylase or amylopsin act on sugars trypsin and chymotripsin act on proteins lipase or steapsinact on fats Villi fingerlike projections that line the walls of the small intestine blood capillaries absorb digested nutrients and carry them to liver they are stored in liver or circulated to body cells lacteals absorb most of digested fats and carry them to thoracic duct in lymphatic system when food has completed travel through small intestine, only waste and indigestible materials and excess water remain 9
Large Intestine Large Intestine final section of the alimentary canal (5 feet long, 2 inch diameter) absorbs water and any remaining nutrients stores indigestible materials before they are eliminated from body forms &absorbs some B-complex vitamins and vitamin K transportation of waste products out of alimentary canal divided into 3 main sections (1) cecum first section and is connected to ileum of small intestine contains a small projection called vermiform appendix (2) colon ascending colon continues up right side from cecum to lower part of liver transverse colon extends across abdomen below liver and stomach and above small intestine descending colon extends down left side of body and connects with signmoid colon (S-shaped section that joins with rectum (3) rectum final 6-8 inches of large intestine storage area for indigestibles and wastes fecal material leaves the rectum through the anus as stool 10
Accessory Organs Liver largest gland in the body located under diaphragm and URQ of abdomen secretes bile (used to emulsify fats in digestive tract) stores sugar in form of glycogen glycogen converted to glucose and released into blood when more blood sugar is needed stores iron, certain vitamins, and cholesterol produces heparin (prevents blood clotting) and clotting agents detoxifies substances such as alcohol and pesticides destroys bacteria that have been taken into blood from intestine Gallbladder small, muscular sac under liver & attached by connective tissue stores and concentrates bile that it receives from liver gallbladder contracts when bile is needed to emulsify fats Pancreas glandular organ located behind stomach produces pancreatic juices which contain enzymes to digest food produces insulin to secrete in bloodstream to regulate metabolism of carbohydrates to convert glucose into energy 11
Diseases & Abnormal Conditions Appendicitis inflammation of appendix (LRQ pain) Cholecystitis inflammation of gallbladder Cirrhosis chronic destruction of liver cells (hepatitis, alcoholism, poor nutrition) Constipation pain from fecal matter remaining in colon too long causes excessive reabsorption of water Diarrhea frequent, watery stool (infection, stress, diet, irritated colon, and toxins) Diverticulitis inflammation of diverticula (pouches in intestinal lining) Hemorrhoids painful dilated or varicose veins of rectum and/or anus Hepatitis viral inflammation of liver Hernia rupture when internal organ pushes through a weakened area Pancreatitis inflammation of the pancreas where enzymes digest the pancreas itself Ulcer open sore on lining of digestive tract 12