Chapter 3 Digestion, Absorption and Transport CHAPTER SUMMARY This chapter explains digestion, absorption, and nutrient transport. Digestion is covered first; next, the anatomy of the organs is presented, followed with information about mechanical and chemical digestion. The process of digestion is covered (organ by organ) beginning in the mouth and proceeding through the distant end of the GI tract. This is followed with information about the anatomy and physiology of the accessory organs, which also influence digestion. Enzymes, hormones, and various digestive juices are covered in this section. The chapter presents information on nutrient absorption and nutrient distribution/delivery within the body. The four types of nutrient absorption are discussed and illustrated. Similarly, the lymph system, circulatory system, and nervous system are briefly mentioned in relationship to nutrient transport and digestive influences. Finally, the chapter includes information on minor and major digestive disorders, the causes, and the treatments. Special coverage is given to celiac disease, irritable bowel disease, and probiotics. CHAPTER OBJECTIVES After reading this chapter, your students will be able to: 1. Define digestion, absorption, and transport. 2. Describe the organs involved in digestion and their primary functions. 3. Explain the roles of the gallbladder, liver, and pancreas in digestion. 4. Explain the function of peristalsis and segmentation in the movement of food through the GI tract. 5. Explain the role of enzymes indigestion. 6. List the main carbohydrate-, protein-, and fat-digesting enzymes and the tissues that secrete them. Blake, Nutrition: From Science to You Instructor Manual and Resource Guide Chapter 3, Page 1 of 17
7. Identify the hormones involved indigestion, including their primary action and their source of origin. 8. Describe the four mechanisms of absorption in the small intestine. 9. Explain how the circulatory and lymphatic systems transport absorbed nutrients throughout the body. 10. Describe the symptoms and causes of the most common digestive disorders. CHAPTER OUTLINE I. What Are Digestion, Absorption, and Transport? A. The entire process of digestion, absorption, and transport is complex. 1. Digestion (the process that breaks bonds and reduces food into individual molecules) happens in the GI (gastrointestinal) tract. a. The resulting particles pass through the small intestinal wall via absorption, and are then transported through the circulatory system to the liver and tissues throughout the body. b. Nutrients that don't get digested or absorbed are excreted as waste by elimination. 2. The process of digestion, absorption, and transport, when working properly, generally goes unnoticed for about 48 hours after eating, when elimination occurs. 3. Enzymes are used by the body to accomplish digestion chemically, and actions of the teeth and muscular contractions of the GI tract accomplish digestion mechanically. 4. On occasion, the digestive process can be altered in an unfavorable way. II. What Are the Organs of the GI Tract and Why Are They Important? A. The GI tract regulates the absorption of nutrients that pass through the tract, either allowing nutrients to enter the body or pass through unabsorbed. 1. The mouth, esophagus, stomach, small intestine, and large intestine