Advanced Nutrition and Human Metabolism, 8e - Chapter 2 PDF

Advanced Nutrition and Human Metabolism, 8e...

Advanced Nutrition and Human Metabolism, 8e Chapter 2: The Digestive System: Mechanism for Nourishing the Body ©2020 Cengage ©2020Learning. All Rights Cengage Learning. Reserved. All Rights May Reserved. notnotbebescanned, May copied scanned, copied or duplicated, or duplicated, or posted or posted to aaccessible to a publicly publicly accessible website, website, in whole in whole or in part. or in part. 1  Learning Objectives By the end of this chapter you should be able to: 2.1 Identify the organs of the digestive tract and their roles/functions in nutrient digestion and absorption. 2.2 Describe the secretions released by the digestive tract organs, including accessory organs, and factors influencing the release of these secretions. 2.3 Describe the factors influencing digestive tract motility. 2.4 Describe the structural features of the small intestine that facilitate nutrient absorption. 2.5 Identify the beneficial effects of the gut microflora. 2.6 Describe the roles of the nervous system and regulatory peptides in regulation of the digestive process. ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 2 Structures of the Digestive Tract and the Digestive and Absorptive Process 3©2020 © 2020 Cengage Cengage Learning. Learning. All All Rights Rights Reserved. Reserved. May May not not be be scanned, scanned, copied copied or or duplicated, duplicated, or or posted posted to to aa publicly publicly accessible accessible website, website, in in whole whole or or in in part. part. 3  Video: Human Digestive System Human digestive system available at How it works! (Animation) ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 4  The Structures and Processes of the Digestive Tract Main structures: − Oral cavity − Esophagus − Stomach − Small and large intestines Accessory Organs: − Pancreas − Liver − Gallbladder ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 5 The Structures and Processes of the Digestive Tract Layers of the Lumen Mucosa: Submucosa: Muscularis externa − Mucosal − Connective tissue Serosa: membrane − Blood − Flat mesothelial − Lamina propria cells − Lymphatic − Muscularis vessels mucosa − Lymphoid tissue − Submucosal plexus ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 6 The Structures and Processes of the Digestive Tract ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 7 The Structures and Processes of the Digestive Tract ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 8  The Oral Cavity Mouth and pharynx Salivary glands: − Parotid − Submandibular − Sublingual Enzymes in saliva ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 9  Knowledge Check 1 Carbohydrate digestion begins in the mouth through the action of which enzyme? ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 10  Knowledge Check 1: Answer Carbohydrate digestion begins in the mouth through the action of which enzyme? Salivary amylase ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 11  The Esophagus Moves bolus from oral cavity to stomach Swallowing: − Voluntary, pharyngeal, esophageal Peristalsis Gastroesophageal sphincter Selected disorders of the esophagus: − GERD ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 12  The Stomach Four main regions: − Cardia region − Fundus − Body − Antrum or distal pyloric Stomach muscles mix food with gastric juices to form chime: − Gastric juices facilitate digestion. ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 13  The Stomach There are three types of gastric glands, distinguished from one another by location and type of secretion. The cardiac gastric glands are located at the very beginning of the stomach; the intermediate, or true, gastric glands in the central stomach areas; and the pyloric glands in the terminal stomach portion. 14 ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part.  The Stomach Gastric glands: − Cardiac glands − The cardiac glands are found in the cardia of the stomach which is the part nearest to the heart, enclosing the opening where the esophagus joins to the stomach. Only cardiac glands are found here and they primarily secrete mucus ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 15  The Stomach Gastric glands: − Oxyntic glands − The fundic glands (or oxyntic glands), are found in the fundus and body of the stomach. They are simple almost straight tubes, two or more of which open into a single duct. Oxyntic means acid-secreting and they secrete hydrochloric acid (HCl) and intrinsic factor. ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 16  The Stomach Gastric glands: − Pyloric glands − Both the cardiac and pyloric glands secrete mucus, which coats the stomach and protects it from self-digestion by helping to dilute acids and enzymes. They are comprised of three cell types: the pyloric gland (mucous) cell, the parietal cell, and endocrine cells. ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 17  The Stomach What would happen if the gastric glands stopped producing mucus? it will lead to erosion of the inner lining of the stomach leading to acidity and ulcers. ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 18  Regulation of Gastric Secretions Three phases: − Before food reaches the stomach: Acetylcholine, gastrin Once food is in the stomach: − Stomach distension enhances gastric secretions. After food has left the stomach: − Reduction in chyme volume and pH trigger release of somatostatin ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 19  Activity Pretend that you are eating a peanut butter and jelly sandwich. Outline the route of digestion from the mouth to the large intestine. Remember to include enzymes and key and accessory organs of importance. ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 20  Accessory Organs 22 ©2020Cengage ©2020 CengageLearning. Learning.All AllRights RightsReserved. Reserved.May Maynot notbe bescanned, scanned,copied copiedor orduplicated, duplicated,or orposted postedtotoaapublicly publiclyaccessible accessiblewebsite, website,ininwhole wholeor orininpart. part. 21  The Accessory Organs The pancreas: − Ductless endocrine cells that secrete hormones into the blood − Digestive enzymes produced by acinar exocrine cells − Pancreatic juice contains the following: Water Electrolytes Bicarboante Pancreatic digestive enzymes ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 22  The Liver (1 of 2) Consists of lobes made of lobules Portal circulation Bile canaliculi Bile synthesis and function: − Bile composed of bile acids and salts, cholesterol, phospholipids and bile pigments in alkaline solution − Bile acts like detergent to emulsify. ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 23  The Liver ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 24  The Liver ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 25  The Gallbladder Concentrates and stores bile Selected disorders of the gallbladder: − Gallstones The recirculation and excretion of bile: − Most bile salts are reabsorbed. Bile circulation and hypercholesterolemia ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 26 Gallstones  The Absorptive Process Absorption begins in the duodenum and continues throughout the jejunum and ileum. Absorption is rapid — few hours Absorption methods: − Diffusion, facilitated diffusion, active transport or pinocytosis/endocytosis ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 28  The Absorptive Process Absorption begins in the duodenum and continues throughout the jejunum and ileum. Absorption is rapid — few hours Absorption methods: − Diffusion, facilitated diffusion, active transport or pinocytosis/endocyt osis ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 29  The Colon (Large Intestine) Contracts to mix materials Proximal colonic mucosal cells absorb sodium and water: − Influenced by hormones Materials dehydrated Colonic secretions: − Goblet cells secrete mucus. − Bicarbonate ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 30  Knowledge Check 2 Upon what does the mechanism of absorption depend? ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 31  Knowledge Check 2: Answer Mechanism of absorption depends on the following: 1. Solubility (fat versus water) 2. Concentration or electrical gradient 3. Size of molecule ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 32  Knowledge Check 3 Absorption of nutrients occurs primarily in the distal ileum of the small intestine. a) True b) False ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 33  Knowledge Check 3: Answer Absorption of nutrients occurs primarily in the distal ileum of the small intestine. 1. False ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 34  Digestive Disorders 33 ©2020Cengage ©2020 CengageLearning. Learning.All AllRights RightsReserved. Reserved.May Maynot notbe bescanned, scanned,copied copiedor orduplicated, duplicated,or orposted postedtotoaapublicly publiclyaccessible accessiblewebsite, website,ininwhole wholeor orininpart. part. 35  Selected Disorders of the Stomach Peptic ulcer disease: − Ulcerations or erosions in mucosa and submucosa layers of the stomach, duodenum, or lower esophagus − Common cause: Helicobacter (H) pylori − Other causes: Chronic alcohol ingestion Use of NSAIDs − H2 receptor blockers used to treat ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 36  Selected Disorders of the Pancreas Pancreatitis: − Zymogens become activated and digest pancreatic tissue − Condition can occur with excessive alcohol consumption, hypertriglyceridemia, duct blockage, viral infections, or injury. − Patient often requires partially hydrolyzed nutrients or lipase ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 37 Coordination and Regulation of the Digestive Process 36 ©2020Cengage ©2020 CengageLearning. Learning.All AllRights RightsReserved. Reserved.May Maynot notbe bescanned, scanned,copied copiedor orduplicated, duplicated,or orposted postedtotoaapublicly publiclyaccessible accessiblewebsite, website,ininwhole wholeor orininpart. part. 38 Neural Regulation and Regulatory Peptides Neural regulation: − Myenteric plexus: peristalsis, motility − Submucosal plexus: secretions, local blood flow Regulatory peptides: − Hormones − Paracrines ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 39 Regulation of Gastric Motility and Gastric Emptying Peristaltic waves propel digestive contents: − Basic electrical rhythm is initiated by pacemaker cells. Gastric emptying is affected by factors in stomach and duodenum. Dietary fat intake has an inhibitory effect on gastric emptying. ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 40  Regulatory Peptides − Ghrelin (stimulates food intake) − Leptin (increases satiety) Effects of r-metHuLeptin on weight in three children with congenital leptin deficiency. (a) Weights of child A compared with normal centiles for girls and of child B and child C compared with normal centiles for boys. Arrows indicate the start of r-metHuLeptin therapy. (b) Clinical photographs of child B before (height = 107 cm) and 24 months after r-metHuLeptin therapy (height = 124 cm) (reproduced with the permission of the child's parents). 41  Discussion What might the nutritional impact be for an individual who has undergone Roux- En-Y gastric bypass surgery for obesity treatment? ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 42  Discussion Bypass of the duodenum impairs mixing of ingested nutrients with bile acids and pancreatic enzymes leading to maldigestion. The combination of malabsorption and maldigestion, while resulting in significant weight loss, predisposes to malnutrition. ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 43  Summary Factors influencing digestion and absorption: − Dispersion and mixing of ingested food − Quantity and composition of gastrointestinal secretions − Enterocyte integrity − Expanse of intestinal absorptive area − Transit time of intestinal contents Adequate nourishment depends on a normally functioning gastrointestinal tract. ©2020 Cengage Learning. All Rights Reserved. May not be scanned, copied or duplicated, or posted to a publicly accessible website, in whole or in part. 44