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Human Biology Sylvia S. Mader Michael Windelspecht Chapter 8 Part 1 Digestive System and Nutrition Lecture Outline See separate FlexArt PowerPoint slides for all figures and tables pre-inserted into PowerPoint without notes. Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Points to Ponder 1. What are the digestive system structures and their functions? 2. Where does carbohydrate, protein, and fat digestion and absorption occur? 3. What are proteins, lipids, carbohydrates, minerals and vitamins needed for? 4. What is an essential vs. a nonessential nutrient? 5. What are the 3 accessory organs of digestion? 6. What is obesity and why is it a problem? 7. What is LDL and HDL? 8. What are the components of a healthy diet? 9. Name and explain 4 eating disorders. 8.1 Overview of digestion What are the main steps in the digestive process? Ingestion: intake of food by the mouth. Digestion: mechanically or chemically breaking down food into their subunits Movement: food must be moved along the GI tract in order to fulfill all functions. Absorption: movement of nutrients across the GI tract wall to be delivered to cell via the blood. Elimination: removal of indigestible molecules. 8.1 Overview of digestion What are the 4 major layers that make up the wall of the GI tract? Mucosa: innermost layer that produces mucus that protects the lining and also produces digestive enzymes. Sub mucosa: 2nd layer of loose connective tissue that contains blood vessels, lymphatic vessels, and nerves. Muscularis: 3rd layer made of 2 layers of smooth muscle that move food along the GI tract. Serosa: outer lining that is part of the peritoneum. 8.1 Overview of digestion Visualizing the layers of the GI tract Mucosa nerve lymph supply vessel inner mucous membrane layer modified according to the digestive organ Submucosa broad band of loose connective tissue that contains nerves, blood, and lymphatic vessels Lumen central space containing food being digested Serosa thin, outermost tissue that is the visceral peritoneum Muscularis two layers of smooth muscle artery vein 8.1 Overview of digestion An overview of the digestive system Accessory organs Salivary gland secrete saliva: contains digestive enzyme for carbohydrates Digestive tract organs Mouth teeth chew food; tongue tastes and pushes food for chewing and swallowing Pharynx passageway where food is swallowed Esophagus passageway where peristalsis pushes food to stomach Liver major metabolic organ: processes and stores nutrients; produces bile for emulsification of fats Gallbladder Stomach secretes acid and digestive enzyme for protein; churns, mixing food with secretions, and sends chyme to small intestine stores bile from liver; sends it to the small intestine Small intestine Pancreas produces pancreatic juice: contains digestive enzymes, and sends it to the small intestine; produces insulin and secretes it into the blood after eating mixes chyme with digestive enzymes for final breakdown; absorbs nutrient molecules into body; secretes digestive hormones into blood Large intestine absorbs water and salt to form feces Rectum stores and regulates elimination of feces Anus 8.1 Overview of digestion What is the pathway that food follows? 1. 2. 3. 4. 5. 6. 7. 8. Mouth Pharynx Esophagus Stomach Small intestine Large intestine Rectum Anus 8.2 First part of the digestive tract The mouth 3 pairs of salivary glands secrete salivary amylase that begins carbohydrate digestion. Tonsils at the back of the mouth and other lymphatic tissues are important in fighting disease. Contains teeth that begin the mechanical breakdown of food. The tongue is covered in taste buds and also assists in the mechanical breakdown and movement of food. The tongue forms a bolus(mass of chewed food) and moves it toward the pharynx. 8.2 First part of the digestive tract Anatomy of the mouth hard palate soft palate uvula tonsil molars (3) premolars (2) canine (1) incisors (2) 8.2 First part of the digestive tract Teeth 32 in adults used for mechanical breakdown of food (20 deciduous teeth in babies). Each tooth is made of a crown and a root. A hard covering called enamel and dentin covers the crown with an inner pulp area with nerves and blood vessels. Dental caries (cavities) occur when bacteria metabolize sugars and produce acids, so limiting sugar intake and brushing teeth reduces these. 8.2 First part of the digestive tract Anatomy of a tooth Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. enamel crown dentin pulp gum jawbone root canal root periodontal membrane cementum 8.2 First part of the digestive tract The pharynx and esophagus • Pharynx: is a cavity between the mouth and esophagus that serves as a passageway for food (and air). • Esophagus: is a long, muscular tube that carries food to the stomach. 8.2 First part of the digestive tract How do we swallow food? • Voluntary phase: – The beginning of food being swallowed from the mouth into the pharynx. • Involuntary phase: – Once the food is in the pharynx swallowing becomes a reflex action perform automatically. – The epiglottis covers the voice box to make sure food is routed into the esophagus. – Food moves down the esophagus through peristalsis (rhythmic contraction). 8.2 First part of the digestive tract How do we swallow food? Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. hard palate food bolus nasopharynx Soft palate closes off nasopharynx. soft palate bolus peristaltic wave epiglottis glottis Esophagus is closed. trachea (airway) open a. Swallowing Larynx rises and epiglottis covers glottis. esophagus opens Lower gastroesophageal esophagus spincter relaxes and food enters stomach. b. Peristalsis stomach 8.2 First part of the digestive tract Health focus: Heartburn Occurs when acids from the stomach pass into the esophagus (acid reflux). Burning sensation in the esophagus. Chronic heartburn is called gastro esophageal reflux disease (GERD). Tips for decreasing heartburn: Avoid high fat meals. Don’t overeat. Eat several small meals rather than the standard 3 larger meals each day. Exercise lightly. The stomach • The stomach is an enlarged part of alimentary canal and receives food from esophagus. • The stomach like J shape with a thick wall. • Mucous membrane lining stomach contains folds called rugae. • Folds disappear as stomach fills with food. o Its structure is divided into 4 main region: o Funds: bulge o Body : largest region o Antrum: o Pylorus : pyloric sphincters o It has two sphincters: Cardiac sphincter. Pyloric sphincter. Function of stomach store food, start digestion of proteins controls movement of chyme into the small intestine. Mixing of the food in the stomach produces Chyme. Mixing movement mainly occurs in the Antrum. Controlled emptying of gastric content into duodenum. HCl Secretion gives the stomach a pH of 2 which activates pepsin and helps kill bacteria found in food. 8.3 The stomach and small intestine Anatomy of the stomach Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. esophagus lower gastroesophageal sphincter pyloric sphincter Muscularis layer has three layers of muscle. Mucosa layer has rugae. c. Gastric pits in mucosa gastric pit SEM 3,260x lower gastroesophageal sphincter a. Stomach gastric pit gastric gland cells that secrete gastric juice b. Gastric glands pyloric sphincter d. How the stomach empties c: © Dr. Fred Hossler/Visuals Unlimited 8.3 The stomach and small intestine The small intestine Averages 6m (18 ft) in length Enzymes secreted by the pancreas into the small intestine digest carbohydrates, proteins, and fats. Bile is secreted by the gallbladder into the small intestine to emulsify fats. Digested food is absorbed through large surface area created by numerous villi (finger-like projections) and microvilli. Amino acids and sugars enter the capillaries while fatty acids and glycerol enter the lacteals (small lymph vessels). 8.3 The stomach and small intestine Anatomy of the small intestine Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Small intestine Section of intestinal wall villus lumen lacteal blood capillaries villus microvilli goblet cell lymph nodule venule lymphatic vessel Villi arteriole (villi): © Manfred Kage/Peter Arnold/Photolibrary; (microvilli):Reprinted from Medical Cell Biology, Charles Flickinger, copyright 1979, with permission from Elsevier. 8.3 The stomach and small intestine How are nutrients digested and transported out of the small intestine? carbohydrate protein pancreatic amylase + bile salts fat globules trypsin emulsification droplets peptides maltase cell of intestinal villus peptidase lipase glucose monoglycerides and free fatty acids amino acids pH = basic pH = basic pH = basic blood capillary a. Carbohydrate digestion blood capillary b. Protein digestion lymphatic capillary c. Fat digestion chylomicron 8.3 The stomach and small intestine What are the major digestive enzymes? 8.4 Three accessory organs and regulation of secretions The three accessory organs • Pancreas Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. bile canals • Liver bile branch of hepatic artery central vein common hepatic duct • Gallbladder pancreatic duct pancreas pancreatic juice gallbladder b. common bile duct duodenum a. bile duct branch of hepatic portal vein 8.4 The accessory organs and regulation of secretions The pancreas • Fished-shaped spongy organ behind the stomach • Functions of the pancreas: 1. Secretes enzymes into the small intestine • Trypsin: digests proteins. • Lipase: digests fats. • Pancreatic amylase: digests carbohydrates. 2. Secretes bicarbonate into the small intestine to neutralize stomach acids 3. Secretes insulin into the blood to keep blood sugar levels under control 8.4 The accessory organs and regulation of secretions The liver and gallbladder • Large metabolic organ that lies under the diaphragm and is made of 100,000 lobules. Function: 1. Filters blood from the GI tract thus acting to remove poisons and detoxify the blood. 2. Removes iron, vitamins A, D, E, K and B12 from the blood and stores them. 3. Stores glucose as glycogen and breaks it down to help retain blood glucose levels. 4. Makes plasma proteins and helps regulate cholesterol levels by making bile salts. 5. Makes bile that is then stored in the gallbladder to be secreted into the small intestine to emulsify fats. 6. Breaks down hemoglobin. 8.4 The accessory organs and regulation of secretions Liver disorders • Hepatitis: – Inflammation of the liver – Caused by Hepatitis A, B, and C – This can lead to liver damage, cancer and/or death • Cirrhosis: – The liver becomes fatty and eventually this tissue is replaced by fibrous scar tissue. – Seen in alcoholics and obese people. – This can lead to liver failure in which the liver cannot regenerate as fast as it is being damaged. 8.4 The accessory organs and regulation of secretions How do hormones control digestive gland secretions? gallbladder liver stomach pancreas duodenum blood vessel secretin CCK gastrin 8.5 The large intestine and defecation The large intestine • Includes the cecum, colon, rectum and anal canal • Larger in diameter but shorter than the small intestine • The cecum has a projection known as the appendix that may play a role in fighting infections • Functions to: transverse colon ascending colon small intestine descending colon 1. Absorb water to prevent dehydration. 2. Absorbs vitamins (B complex and cecum orifice of appendix vermiform appendix rectum K) produced by intestinal flora. 3. Forms and rids the body of feces through the anus. internal anal sphincter anal canal sigmoid colon external anal sphincter anus 8.5 The large intestine and defecation Disorders of the colon and rectum 1. Diarrhea: increased peristalsis and water is not reabsorbed due to either an infection or nervous stimulation. 1. Constipation: condition when feces are dry and hard that may be controlled with water and fiber. 1. Hemorrhoids: enlarged and inflamed blood vessels of the anus due to chronic constipation, pregnancy, aging, and anal intercourse. 8.6 Nutrition and weight control To understand weight and nutrition we first have to understand nutrients • Nutrients are a component of food that is needed to perform a physiological body function. • Nutrients include: Carbohydrates Proteins Lipids Minerals Vitamins