Chapter 42 Digestion and Human Nutrition

Chapter 42 Digestion and Human Nutrition - Chapter 42...

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Chapter 42 Digestion and Human Nutrition I. Types of Digestive Systems and Their Functions A. The digestive system is an internal space or tube with specialized regions for food transport, processing, and storage. 1 An incomplete digestive system (for example, in a planarian) has one opening. 2 A complete digestive system is a tube with two openings allowing food to move in one direction through the lumen. a. Animals with discontinuous feeding habits may have organs for storage. b. Ruminants (for example, cows) may eat grass continuously and have multiple stomachs to digest cellulose. B. The digestive system performs these four functions: 1 Movement is the breaking down, mixing, and transporting of ingested nutrients, and the elimination of undigested residues. 2 Secretion is the release of needed enzymes and hormones. 3 Digestion is the chemical breakdown of food matter to molecules small enough to cross the gut lining. 4 Absorption is the passage of digested nutrients into the blood and lymph. II. Human Digestive System: An Overview A. Components 1 Specialized regions include the mouth, pharynx, esophagus, stomach, small intestine, colon, rectum, and anus. 2 Accessory glands include the salivary glands, liver (with gallbladder), and pancreas. B. Gut Structure and Motility 1 The mucosa is the epithelial lining that faces the lumen of the gut; connective tissue underlies it. 2 The submucosa contains blood and lymph vessels plus nerve networks. 3 A muscle layer (longitudinal and circular) is covered with the outermost serosa. a. Muscular constrictions (sphincters) ensure the forward movement of the gut contents. b. Peristalsis contractions move the food forward; repeated segmentation contractions create an oscillating movement that mixes the food. C. Control of the Digestive System 1 Distention of the gut wall after a meal stimulates mechanoreceptors and their neurons, which respond with muscle action and enzyme secretion. 2 Four gastrointestinal hormones play roles.
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Chapter 42 Digestion and Human Nutrition - Chapter 42...

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