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Chapter 3 Digestion and Absorption Chapter Outline I. Taste and Smell: The Beginnings of Our Food Experience A. The chemosenses (Figure 3.1) Key terms: digestion, absorption, chemosenses, olfactory cells, gustatory cells, common chemical sense, essential fatty acid, cephalic phase responses II. The Gastrointestinal Tract. *The GI tract is a tube that can be divided into regions: the mouth, esophagus, stomach, small intestine, large intestine, and rectum. A. Organization of the GI tract (Figure 3.2). *Digestion and absorption of the nutrients in foods occur at various sites along the GI tract. B. A closer look at gastrointestinal structure Key terms: gastrointestinal tract, excretion, mucosa, submucosa, circular muscle, longitudinal muscle, serosa III. Overview of Digestion: Physical and Chemical Processes. *Digestion involves both physical processes (e.g., chewing, peristalsis, segmentation) and chemical processes (e.g., the hydrolytic action of enzymes). A. The physical movement and breaking up of food B. The chemical breakdown of food Key terms: sphincter, chyme, peristalsis, segmentation, enzyme, catalyze, hydrolysis IV. Overview of Absorption. *Absorption is the movement of molecules across the lining of the gastrointestinal tract and into circulation. A. The four roads to nutrient absorption (Figure 3.7). *Four mechanisms are involved in nutrient absorption: passive diffusion, facilitated diffusion, active transport, and endocytosis. Key terms: lumen, passive diffusion, concentration gradient, amino acid, facilitated diffusion, active transport, endocytosis, pinocytosis, pragocytosis V. Assisting Organs. *The pancreas and gallbladder secrete material into the small intestine to help with digestion. A. Salivary glands B. Liver C. Gallbladder D. Pancreas Key terms: emulsifier, salivary glands, liver, bile, enterohepatic circulation, gallbladder, cholecystokinin (CCK), pancreas VI. Putting It All Together: Digestion and Absorption A. Mouth. *In the mouth, food is mixed with saliva for lubrication. Salivary amylase begins the digestion of starch. B. Stomach (Figure 3.11). *Secretions from the stomach lower the pH of stomach contents and begin the digestion of proteins. 1. Nutrient digestion in the stomach 2. Nutrient absorption in the stomach C. Small intestine (Figure 3.13). *Most chemical digestion and nutrient absorption occur in the small intestine. 1. Nutrient digestion in the small intestine 2. Absorptive structures of the small intestine (Figure 3.14) 3. Nutrient absorption in the small intestine D. Large intestine (Figure 3.15). *Electrolytes and water are absorbed from the large intestine. Remaining material, waste, is excreted as feces. 1. Digestion in the large intestine 2. Nutrient absorption in the large intestine Key terms: amylase, lingual lipase, bolus, cecum, esophageal sphincter, esophagus, stomach, hydrochloric acid, pH, mucus, pepsinogen, gastric lipase, triglycerides, intrinsic factor, pyloric sphincter, small intestine, duodenum, jejunum, ileum, digestive secretions, secretin, villi, microvilli, lymph, lacteal, ileocecal valve, large intestine, colon, rectum VII. Regulation of Gastrointestinal Activity. *Both the nervous system and hormonal system regulate GI tract processes. A. Nervous system B. Hormonal system (Figure 3.17) Key terms: central nervous system (CNS), enteric nervous system, autonomic nervous system, gastric inhibitory peptide (GIP) VIII. Circulation of Nutrients A. Vascular system (Figure 3.18) B. Lymphatic system Key terms: vascular system, lymphatic system IX. Influences on Digestion and Absorption. *Numerous factors affect GI tract functioning, including psychological, chemical, and bacterial factors. A. Psychological influences B. Chemical influences C. Bacterial influences Key terms: gastric acid, acrolein X. Nutrition and GI Disorders (Figure 3.20). *Problems that occur along the GI tract can affect digestion and absorption of nutrients. Dietary changes are important in the treatment of GI disorders. A. Constipation B. Diarrhea C. Diverticulosis D. Heartburn and gastroesophageal reflux E. Irritable bowel syndrome F. Colorectal cancer G. Gas H. Ulcers I. Dyspepsia Key terms: constipation, diarrhea, gastroesophageal reflux, irritable bowel syndrome, flatus, ulcer, dyspepsia What About Bobbie? In this chapter, Bobbie’s fiber and fluid intakes are listed, as both are important for a healthy GI tract. The following questions could be asked at the close of the chapter in a small group setting: 1. Is there anything else Bobbie can do to boost her fluid intake? 2. Could Bobbie be at risk for digestive problems? Explain why or why not. Classroom Activities ACTIVITY 1: GI TRIVIA TRIVIA QUESTIONS This initial phase begins the digestive process. ANSWER: cephalic phase Starting in the mouth, name the three pairs of salivary glands. ANSWER: parotid, sublingual, and submaxillary What is the salivary enzyme called which breaks down starch into small sugar molecules? ANSWER: salivary amylase (ptyalin) The cells at the base of the tongue secrete an enzyme that starts fat digestion. What is this enzyme? ANSWER: lingual lipase For the food to be swallowed, it mixes with saliva and other fluids forming a moistened lump of food. What is this called? ANSWER: bolus As the bolus is swallowed, it passes over a valvelike flap of tissue that closes off the air passages. What is the flap called? ANSWER: epiglottis The bolus enters the stomach through the _________. ANSWER: esophageal sphincter Now that the bolus is in the stomach, secretions are produced to aid in digestion. Name five stomach secretions that aid in the digestive process. ANSWER: HCL, pepsin, gastric lipase, gastrin, instrinsic factor The next part in the GI tract is where the digestion of protein, fat, and nearly all carbohydrate is completed and where most nutrients are absorbed. ANSWER: small intestine Identify the order in which the parts of the small intestine appear. ANSWER: duodenum, jejunum, ileum What structures help absorb the nutrients in the small intestine? ANSWER: villi In discussing the small intestine, what part absorbs 85 percent of the water absorbed by the gut? ANSWER: jejunum Moving on to the next part of the GI tract, what valve connects the jejunum to the large intestine? ANSWER: ileocecal valve This is the part of the GI tract that contains a large population of bacteria that digest small amounts of fiber. Minimal nutrient absorption takes place here. ANSWER: large intestine Material moves through the large intestine along a portion extending from the cecum to the rectum. What is this portion called? ANSWER: colon This part of the digestive system is the largest glandular organ in the body. It produces and secretes bile, detoxifies harmful substances, and helps to metabolize carbohydrates, lipids, proteins, and micronutrients. Before we discuss this organ, can you tell me what it is called? ANSWER: liver (hepatic is the term referring to the liver) This part of the digestive system is pear-shaped and stores bile from the liver. What is this sac called? ANSWER: gallbladder This organ secretes enzymes that help break down nutrients and releases hormones, such as insulin, which regulate metabolism. What is this organ called? ANSWER: pancreas