PowerPoint® Lecture Slides prepared by Meg Flemming Austin Community College C H A P T E R 16 The Digestive System © 2013 Pearson Education, Inc. Chapter 16 Learning Outcomes • 16-1 • Identify the organs of the digestive system, list their major functions, and describe the four layers of the wall of the digestive tract. • 16-2 • Discuss the anatomy of the oral cavity, and list the functions of its major structures. • 16-3 • Describe the structures and functions of the pharynx and esophagus, and the key events of the swallowing process. • 16-4 • Describe the anatomy of the stomach, including its histological features, and discuss its roles in digestion and absorption. © 2013 Pearson Education, Inc. Chapter 16 Learning Outcomes • 16-5 • Describe the anatomy of the small intestine, including its histological features, and explain the functions and regulation of intestinal secretions. • 16-6 • Describe the structure and functions of the pancreas, liver, and gallbladder, and explain how their activities are regulated. • 16-7 • Describe the structure of the large intestine, including its regional specializations, and list its absorptive functions. • 16-8 • List the nutrients required by the body, describe the chemical digestion of organic nutrients, and discuss the absorption of organic and inorganic nutrients. © 2013 Pearson Education, Inc. Chapter 16 Learning Outcomes • 16-9 • Describe the effects of aging on the digestive system. • 16-10 • Give examples of interactions between the digestive system and each of the other organ systems. © 2013 Pearson Education, Inc. Digestive System Basics (16-1) • Digestive tract, or gastrointestinal (GI) tract • Mouth, pharynx, esophagus, stomach, small and large intestines, rectum, anus • Accessory organs contribute to digestion • Teeth, tongue, salivary glands, gallbladder, liver, and pancreas © 2013 Pearson Education, Inc. Six Functions of the Digestive System (16-1) 1. Ingestion • Food enters mouth 2. Mechanical processing • Physical manipulation that enhances movement • Increases surface area for enzymes to work 3. Digestion • Chemical breakdown of food to absorbable size © 2013 Pearson Education, Inc. Six Functions of Digestive System (16-1) 4. Secretion • Release of water, acids, enzymes, and buffers into lumen 5. Absorption • Movement of nutrient molecules across digestive epithelium and into interstitial fluid of body 6. Excretion • Elimination of waste products © 2013 Pearson Education, Inc. Figure 16-1 The Components of the Digestive System. Major Subdivisions of the Digestive Tract Oral Cavity, Teeth, Tongue Mechanical processing, Mouth Accessory Organs moistening, mixing with of the Digestive salivary secretions System Pharynx Salivary glands Muscular propulsion of Secretion of lubricat- materials into the esophagus ing fluid containing enzymes that break Esophagus down carbohydrates Transport of materials to the stomach Liver Secretion of bile Stomach (important for lipid Chemical breakdown of digestion), storage of materials by acid and nutrients, many other enzymes; mechanical vital functions processing through muscular contractions Gallbladder Storage and Small Intestine concentration of bile Enzymatic digestion and absorption of water, organic Pancreas substrates, vitamins, and Exocrine cells secrete ions buffers and digestive Large Intestine enzymes; endocrine cells secrete Dehydration and compaction hormones of indigestible materials in preparation for elimination Anus © 2013 Pearson Education, Inc. Four Histological Layers of the GI Tract (16-1) 1. Mucosa 2. Submucosa 3. Muscularis externa 4. Serosa © 2013 Pearson Education, Inc. Mucosa (16-1) • Inner lining of lumen of GI tract • Layered epithelium, lamina propria • Stratified squamous in high physical stress organs • Rest is simple columnar with surface modifications • Ducts of secretory glands open to surface of epithelium • Villi and microvilli increase surface area • Muscularis mucosae moves mucosal folds and villi © 2013 Pearson Education, Inc. Submucosa (16-1) • Dense irregular connective tissue • Binds mucosa to muscularis externa • Contains blood vessels and lymphatics • Submucosal plexus on outer border • A neural network that can function without CNS • Regulates secretions and motility • Also has parasympathetic neurons and sensory neurons © 2013 Pearson Education, Inc. Muscularis Externa (16-1) • Inner circular and outer longitudinal layer of smooth muscle • Function to mix and propel materials • Myenteric plexus between layers of muscle • Contains parasympathetic ganglia, sensory neurons, interneurons, and sympathetic postganglionic fibers • Parasympathetic is excitatory, increases activity • Sympathetic is inhibitory, decreases activity © 2013 Pearson Education, Inc. Serosa (16-1) • Serous membrane is the peritoneum • Mesenteries • Specialized peritoneum helps to organize and stabilize GI tract, lymphatics, blood vessels, and nerves • Adventitia • Name of outer layer of oral cavity, pharynx, esophagus, and rectum © 2013 Pearson Education, Inc. Figure 16-2 The Structure of the Digestive Tract. Mesenteric artery and vein Mucosal Circular fold epithelium Lamina Mucosa Circular propria Mesentery fold Villi Mucosal glands Submucosal gland Muscularis mucosae Lymphatic vessel Mucosa Artery and vein Submucosa Submucosal plexus Muscularis Circular muscle externa layer Serosa Myenteric plexus (visceral Longitudinal peritoneum) muscle layer © 2013 Pearson Education, Inc. Movement of Digestive Materials (16-1) • Pacesetter cells in smooth muscle trigger contraction • Peristalsis • Waves of contraction initiated by circular layer, followed by longitudinal layer • Propels material down tract • Segmentation • A mixing action with no propulsion © 2013 Pearson Education, Inc. Figure 16-3 Peristalsis. Initial State Longitudinal muscle Circular muscle From To mouth anus Contraction of circular muscles behind bolus Contraction Contraction of longitudinal muscles ahead of bolus Contraction Contraction Contraction in circular muscle layer forces bolus forward © 2013 Pearson Education, Inc. Checkpoint (16-1) 1. Identify the organs of the digestive system. 2. List and define the six primary functions of the digestive system. 3. Describe the functions of the mesenteries. 4. Name the layers of the digestive tract from superficial to deep. 5. Which is more efficient in propelling intestinal contents from one place to another—peristalsis or segmentation? © 2013 Pearson Education, Inc. The Oral Cavity (16-2) • Also called the buccal cavity • Receiver of food lined with oral mucosa • Senses material before swallowing • Mechanically processes material • Lubricates material with saliva and mucus • Begins enzymatic digestion of carbohydrates and lipids • Gingivae • The gums that surround base of teeth © 2013 Pearson Education, Inc. The Oral Cavity (16-2) • Boundaries • Cheeks form lateral walls • Labia or lips are continuous with cheeks • Hard and soft palates form roof of cavity • Tongue forms the floor • Free edge of tongue is attached to floor with lingual frenulum • Oropharynx starts at base of tongue and uvula © 2013 Pearson Education, Inc. Figure 16-4 The Oral Cavity. Hard palate Soft palate Hard palate Nasal Soft palate cavity Pharyngeal tonsil Palatal Upper arches labium Entrance to (lip) auditory tube Palatine Nasopharynx tonsil Uvula Cheek Uvula Lingual Tongue Lower Palatine tonsil frenulum labium Tongue Palatal arch (lip) Gingiva Oropharynx Gingiva Vestibule Lingual tonsil Vestibule Epiglottis Hyoid bone Laryngopharynx An anterior view of the oral cavity, Sagittal section of the oral cavity as seen through the open mouth © 2013 Pearson Education, Inc. The Tongue (16-2) • Manipulates food within oral cavity • Mechanically compresses, abrades, distorts material • Assists in chewing and forming a bolus to swallow • Sensory analysis of taste, touch, temperature • Lingual tonsils • Paired lymphoid nodules at base of tongue © 2013 Pearson Education, Inc. The Salivary Glands (16-2) • Parotid • On each side of oral cavity between mandible and skin • Parotid duct empties at level of second upper molar • Sublingual • Under mucous membrane on floor of mouth • Submandibular • Lateral sides of floor of mouth © 2013 Pearson Education, Inc. Figure 16-5 The Salivary Glands. Parotid salivary gland Parotid duct Openings of sublingual ducts Lingual frenulum Opening of left submandibular duct Sublingual Submandibular Submandibular salivary gland salivary gland duct © 2013 Pearson Education, Inc. Saliva (16-2) • About 1–1.5 liters produced each day • While eating, pH rises from 6.7 to 7.5 • Contents and functions • 99.4 percent water and mucins, lubricate and reduce friction • Ions and buffers, change pH • Enzyme salivary amylase begin chemical digestion of starches © 2013 Pearson Education, Inc. The Teeth (16-2) • Perform chewing or mastication • Neck is boundary between root and crown • Enamel covers crown, requires Ca2+, phosphates, and vitamin D3 • Dentin makes up most of tooth • Pulp cavity has blood vessels and nerves through root canal • Periodontal ligament, with cementum, binds to bone © 2013 Pearson Education, Inc. Types of Teeth (16-2) • Incisors • At front, blade-shaped for cutting • Cuspids • Or canines, for tearing or slashing • Bicuspids or premolars and molars • Have flattened crowns with ridges • For crushing, mashing, and grinding © 2013 Pearson Education, Inc. Dental Succession (16-2) • Deciduous • Primary, baby or milk teeth, usually 20 in number • Periodontal ligaments and roots erode during eruption of adult teeth • Secondary