Chapter 3 The Basics of Digestion 2012 Pearson Education Inc Objectives for Chapter 3 Define digestion absorption and nutrient transport Describe the organs involved in digestion and their primary functions Explain the roles of the gallbladder liver and pancreas in digestion Explain the function of peristalsis and segmentation in the movement of food through the GI tract Explain the role of enzymes in digestion List the main carbohydrate protein and fat digesting enzymes and the tissues that secrete them Identify the hormones involved in digestion including their primary action and their source of origin Explain the role of the small intestine villi and microvilli in digestion Explain how the circulatory and lymphatic systems transport absorbed nutrients throughout the body Describe the symptoms and causes of the most common digestive disorders Nutrition and You 2e 2012 Pearson Education Inc What Makes Eating So Enjoyable Hunger and thirst physical needs which drive how much and how often we eat Appetite another powerful drive but unreliable Influenced by food preferences and psychological stimulation May eat without being hungry or needing nourishment Nutrition and You 2e 2012 Pearson Education Inc Animation Control of Appetite Hunger and Satiety Nutrition and You 2e 2012 Pearson Education Inc We Develop a Taste for Certain Foods Taste Five basic categories Detected by at least 10 000 taste buds mostly on tongue but also throat and elsewhere in mouth Sweet tip of tongue Salty sides of tongue Sour sides of tongue Bitter back of tongue Savory umami throughout mouth not all people are sensitive to this taste sensation Nutrition and You 2e 2012 Pearson Education Inc We Develop a Taste for Certain Foods Humans share an innate preference for sweet pleasure salty electrolytes and fatty rich textures and aromas foods Sometimes food preferences and nutritional needs conflict and make changing food choices challenging Brain recognizes taste food dissolves in saliva contacts the tongue surface taste cells send nerve impulses to brain translated into taste sensations Nutrition and You 2e 2012 Pearson Education Inc Aromas and Flavors Enhance the Pleasure of Eating Both mouth and nose contribute to tasting of foods Aromas detected by olfactory cells in nasal cavity as food odors enter both nose and mouth move to back of throat and into nasal cavity Flavor refers to both taste and aroma Example Chocolate tastes sweet but its flavor is chocolate Nutrition and You 2e 2012 Pearson Education Inc What Is Digestion and Why Is It Important Digestion a multi step process of breaking down foods into absorbable components using mechanical and chemical means in the gastrointestinal GI tract Gastrointestinal tract consists of Mouth Esophagus Stomach Small and large intestines Other organs Nutrition and You 2e 2012 Pearson Education Inc What Is Digestion and Why Is It Important Main roles of the GI tract are to Break down food into smallest components Absorb nutrients Prevent microorganism or other harmful compounds in food from entering tissues of the body GI tract is about 23 feet long with extensive surface area for nutrient absorption Cells lining GI tract are replaced every three to five days Nutrition and You 2e 2012 Pearson Education Inc Animation Overview of Digestion and Absorption Nutrition and You 2e 2012 Pearson Education Inc Animation Basic Absorption Mechanisms Nutrition and You 2e 2012 Pearson Education Inc Digestion Is Mechanical and Chemical Mechanical digestion chewing grinding food to aid swallowing Peristalsis the forward rhythmic muscular contraction that moves food through GI tract Chemical digestion digestive juices and enzymes break down food into absorbable nutrients Nutrition and You 2e 2012 Pearson Education Inc Peristalsis Figure 3 1 Nutrition and You 2e 2012 Pearson Education Inc Digestion Allows Us to Absorb Nutrients from Foods After digestion nutrients are absorbed through the walls of the intestines into the body s two transport systems Circulatory system blood Lymph system Sent to the liver for processing before delivery to the body s cells GI tract is highly efficient 92 to 97 percent of nutrients from food are digested and absorbed Nutrition and You 2e 2012 Pearson Education Inc Diet Dream Drug Hope or Hype Pros and Cons of Alli Nutrition and You 2e 2012 Pearson Education Inc Diet Dream Drug Hope or Hype Pros and Cons of Alli Discussion Questions What does Alli claim to do in the body to help you lose weight What are some of the unpleasant side effects of using Alli What is the typical behavior of people using diet drugs Nutrition and You 2e 2012 Pearson Education Inc What Are the Organs of the GI Tract and Why Are They Important Digestion begins in the mouth Saliva released contains water electrolytes mucus and a few enzymes Softens lubricates dissolves food particles Bolus food mass moves into pharynx is swallowed and enters the esophagus Epiglottis closes off trachea during swallowing to prevent food from lodging in the windpipe Nutrition and You 2e 2012 Pearson Education Inc From Cells to Organs and Organ Systems Figure 3 2 Nutrition and You 2e 2012 Pearson Education Inc The Epiglottis Figure 3 3 Nutrition and You 2e 2012 Pearson Education Inc The Stomach Stores Mixes and Prepares Food for Digestion Esophagus propels food into the stomach Bolus is pushed down esophagus by peristalsis Lower Esophageal Sphincter LES at bottom of esophagus relaxes and allows food into stomach LES then closes to prevent backflow of hydrochloric acid HCl from stomach Reflux of stomach acid causes heartburn irritation of esophagus lining Nutrition and You 2e 2012 Pearson Education Inc The Stomach Stores Mixes and Prepares Food for Digestion Stomach s mechanical action churning mixes food with digestive juices for several hours Stomach produces powerful digestive secretions HCl activates enzyme pepsin enhances absorption of minerals breaks down connective tissue of meat Mucus protects stomach lining from damage Digestive enzymes intrinsic factor for vitamin B12 absorption stomach hormone gastrin Chyme semi liquid substance of partially digested food and digestive juices Nutrition and You 2e 2012 Pearson Education Inc Anatomy of the Stomach Figure 3 4 Nutrition and You 2e 2012 Pearson Education Inc The Stomach Stores Mixes and Prepares Food for Digestion Gastrin stimulates digestive activities and secretion of HCl increases gastric motility and emptying Liquids carbohydrates low fiber and