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Chapter 14 Anatomy of the Digestive System Alimentary Canal- gastrointestinal tract- Mouth- Food enters the digestive tract here, also called the oral cavity Pharynx- connection between nasal and oral cavities with esophagus/trachea, three sections: -Nasopharynx -Oropharynx -Laryngopharynx Esophagus- food tube about 10 inches long -From the esophagus to the large intestine, the alimentary canal is made up of 4 basic tissue layers: -Mucosa-Submucosa-Muscularis Externa-Serosa- 1 -Parietal peritoneum-MesenteryStomach- made up of different regions -Cardiac region-Fundus-Body-PylorusThe Stomach: -greater curvature-lesser curvature-greater and lesser omentums-also contains an oblique muscle layer, allows for churning and mixing food. -chemical breakdown of proteins begins in the stomach -gastric pits lead to gastric glands that secrete gastric juice -Intrinsic factor2 -Pepsinogen-HCl-mucus neck cells- Small Intestine- major digestive and absorption organ -extends from pyloric sphincter to ileocecal valve -averages about 6-13 feet in a living person -has three subdivisions: duodenum, jejunum, and ileum -Duodenum-Jejunum-Ileum-Majority of chemical digestion takes place in the small intestine -enzymes of the pancreas enter the small intestine by the pancreatic duct -bile enters the small intestine by the bile duct -nearly all of food absorption occurs in the small intestine 3 -three structures that increase absorptive surface area: -Microvilli-VilliLacteal-Circular folds- Large Intestine- functions in drying out indigestible food by absorbing water, eliminate feces. -has five major regions- cecum, appendix, colon, rectum, anal canal -Cecum-Appendix -Colon-RectumAnal canal- Accessory Digestive Organs Salivary Glands -Parotid, submandibular, sublingual- 4 Teeth -Deciduous teeth (baby teeth)- -Permanent teeth- Pancreas- produces enzymes that break down all categories of digestible foods Liver- digestive function is to produce bile -Bile- Gall Bladder- stores bile for use on fatty foods. Functions of the Digestive System Essential Activities of the GI tracts include 6 processes 1. Ingestion- 2. PropulsionPeristalsis5 3. Food Breakdown: 4. Food Breakdown: 5. Absorption- 6. Defecation- -Regulated by the parasympathetic division, uses mechanoreceptors and chemoreceptors located in the wall of the alimentary canal. Activities of the Mouth, pharynx, and esophagus -food breakdown, swallowing, peristalsis Activities of the Stomach -Gastric juice-Presence of food and falling pH-Food stretching stomach-Other than alcohol and aspirin, no absorption occurs in the stomach. 6 -Rippling peristalsis begins to move the chime toward the pyloric sphincter Activities of the Small Intestine -By the time the food has reached the small intestine, carbohydrate and protein digestion has begun, no fat digestion has occurred. -Brush Border Enzymes- -Intestinal Juice- -Pancreatic Juice- contains enzymes and buffers that: -End of small intestine, all that remains is water, indigestible food, and large amounts of bacteria Activities of the large intestine -Takes 12 to 24 hours, no digestive enzymes, bacteria continue to metabolize nutrients Water reabsorption occurs here: - diarrhea- constipation-Mass movements7 -Defecation reflex- Nutrition and Metabolism Nutrient- a substance in food that is used by the body to promote normal growth, maintenance, and repair. Major Nutrients: CarbohydratesLipidsProteinsWaterMinor Nutrients: VitaminsMineralsMetabolism- all chemical reactions that are necessary to maintain life. CatabolismAnabolism- 8 Carbohydrate Metabolism- preferred mechanism for cells to produce ATP, referred to as cellular respiration. -Glucose is broken down to produce CO2, H2O, and ATP -The major steps in cellular respiration are glycolysis, Krebs cycle, and the electron transport chain. Fat Metabolism- mostly takes place in the liver. -Fats are broken down into acetic acid, which is then converted to CO2, H2O, and ATP. -Fats are broken down in large quantities if glucose is not available Protein Metabolism- only occurs when glucose and fats are not available, or proteins are overabundant. -Proteins are broken down into amino acids which are oxidized. Releases ammonia and other molecules which enter the Krebs Cycle. 9 Liver in Metabolism -The liver is one of the most versatile and complex organs in the body. -Cholesterol is not used for fuel, more for structural purposes *No Heat mechanisms or developmental aspects* 10
