Copyright Pearson Prentice Hall Biology Copyright Pearson Prentice Hall

38–2 The Process of Digestion Photo Credit: © Fred Hossler/Visuals Unlimited Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall What are the organs of the digestive system? Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The digestive system includes: mouth (pharynx) esophagus stomach small intestine large intestine Other structures add secretions to the digestive system and aid in digestion. (ie. salivary glands, pancreas, and liver) Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Digestive System Mouth Pharynx Salivary glands Esophagus Liver Stomach The digestive system includes the mouth, pharynx, esophagus, stomach, small intestine, and large intestine. Because the pancreas and most of the gallbladder are behind other organs, their locations are indicated by dotted lines. Pancreas Gallbladder Large intestine Small intestine Rectum Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Mouth What is the function of the digestive system? To convert foods into simpler molecules - these can be absorbed/used by the cells of the body Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Mouth The Mouth Chewing begins mechanical digestion - physical breakdown of food into smaller pieces Teeth: cut, tear, and crush food into small pieces Salivary glands: secrete saliva - which moistens food and makes it easier to chew Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Mouth Saliva: - helps ease the passage of food - begins the process of chemical digestion - contains amylase - enzyme that breaks down sugars Saliva also contains lysozyme - an enzyme that fights infection Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Esophagus The Esophagus Food tube which connects mouth to the stomach Food is moved along by contractions called peristalsis - these contractions squeeze food into the stomach Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Esophagus Esophagus Bolus Peristalsis Muscles contracted Stomach Muscles in the walls of the esophagus contract in waves. Each wave pushes the chewed clump of food, or bolus, in front of it. Eventually, the bolus is pushed into the stomach. The cardiac sphincter: closes the esophagus after food has passed into the stomach. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Stomach The Stomach Continues mechanical and chemical digestion Alternating contractions of three smooth muscle layers churn food Food can stay in stomach 2-6 hours! Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Stomach Chemical Digestion The stomach lining has millions of gastric glands that release substances into the stomach. Some glands produce mucus, which lubricates and protects the stomach wall. Other glands produce hydrochloric acid, which makes the stomach contents very acidic. Other glands produce pepsin, an enzyme that digests protein. Pepsin and hydrochloric acid begin protein digestion Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Stomach Digestive enzymes break down foods and make nutrients available to the body. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Stomach Mechanical Digestion  The stomach churns to produce a mixture known as chyme Chyme flows into the small intestine through the pyloric valve between the stomach and small intestine. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Small Intestine The Small Intestine Chyme is pushed into the duodenum - the first of three parts of the small intestine - where most digestive enzymes enter the intestine Important Note: Most chemical digestion and absorption of food occurs in the small intestine Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Small Intestine Accessory Structures of Digestion Liver Bile duct Pancreas Gallbladder Pancreatic duct Duodenum Accessory structures, including the liver and pancreas, add secretions to the digestive system. The pancreas secretes enzymes that help break down carbohydrates, proteins, and fats. To rest of small intestine Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Small Intestine Accessory Structures of Digestion Pancreas: produces enzymes that break down all foods produces sodium bicarbonate - a base that neutralizes stomach acid Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Small Intestine Liver: Produces bile. Bile dissolves droplets of fat - this helps enzymes to break down fat Bile is stored in the gallbladder Copyright Pearson Prentice Hall

Absorption in the Small Intestine The small intestine is adapted for the absorption of nutrients. Villi - cover the inner surface of the small intestine - provide enormous surface area for absorption Copyright Pearson Prentice Hall

Absorption in the Small Intestine Villus Small intestine Circular folds Epithelial cells Villi Capillaries Lymph vessel The lining of the small intestine consists of folds that are covered with tiny projections called villi. Within each villus there is a network of blood capillaries and lymph vessels that absorb and carry away nutrients.  Vein Artery Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall The Large Intestine The Large Intestine - also known as the colon - removes water from the chyme. -water is absorbed quickly - leaving undigested materials behind (feces) Concentrated waste material passes through the rectum and is eliminated from the body Copyright Pearson Prentice Hall

Digestive System Disorders Stomach acids sometimes damage the lining - producing a hole in the stomach wall - known as a peptic ulcer - most ulcers are caused by a bacteria( H. pylori ) Other digestive disorders include diarrhea and constipation Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 38–2 Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 38–2 Food is moved through the esophagus into the stomach by air pressure. muscle contractions. gravity. swallowing. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 38–2 A gland that has both endocrine and exocrine functions is the liver. spleen. pancreas. gallbladder. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 38–2 The enzyme in saliva that begins the digestion of starch is amylase. pepsin. lysozyme. peptidase. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 38–2 Stomach muscles contract to churn and mix stomach fluids and food, producing a mixture known as chyme. amylase. bile. acid. Copyright Pearson Prentice Hall

Copyright Pearson Prentice Hall 38–2 Absorption of vitamins, minerals, and digested food molecules takes place in the stomach. small intestine. large intestine. duodenum. Copyright Pearson Prentice Hall

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