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PowerPoint® Lecture Slides prepared by Barbara Heard, Atlantic Cape Community College CHAPTER 23 The Digestive System: Part A © Annie Leibovitz/Contact Press Images © 2013 Pearson Education, Inc. Digestive System • Two groups of organs 1. Alimentary canal (gastrointestinal or GI tract) • Mouth to anus • Digests food and absorbs fragments • Mouth, pharynx, esophagus, stomach, small intestine, and large intestine © 2013 Pearson Education, Inc. Digestive System 2. Accessory digestive organs • Teeth, tongue, gallbladder • Digestive glands – Salivary glands – Liver – Pancreas © 2013 Pearson Education, Inc. Figure 23.1 Alimentary canal and related accessory digestive organs. Mouth (oral cavity) Tongue* Parotid gland Sublingual gland Submandibular gland Salivary glands* Pharynx Esophagus Stomach Pancreas* (Spleen) Liver* Gallbladder* Transverse colon Small intestine Anus © 2013 Pearson Education, Inc. Duodenum Jejunum Ileum Descending colon Ascending colon Cecum Sigmoid colon Rectum Appendix Anal canal Large intestine Digestive Processes • Six essential activities 1. 2. 3. 4. 5. 6. Ingestion Propulsion Mechanical breakdown Digestion Absorption Defecation © 2013 Pearson Education, Inc. Figure 23.2 Gastrointestinal tract activities. Ingestion Mechanical breakdown • Chewing (mouth) • Churning (stomach) • Segmentation (small intestine) Digestion Food Pharynx Esophagus Propulsion • Swallowing (oropharynx) • Peristalsis (esophagus, stomach, small intestine, large intestine) Stomach Absorption Lymph vessel Small intestine Large intestine Blood vessel Mainly H2O Feces Defecation © 2013 Pearson Education, Inc. Anus Figure 23.3 Peristalsis and segmentation. From mouth Peristalsis: Adjacent segments of alimentary tract organs alternately contract and relax, moving food along the tract distally. © 2013 Pearson Education, Inc. Segmentation: Nonadjacent segments of alimentary tract organs alternately contract and relax, moving food forward then backward. Food mixing and slow food propulsion occur. GI Tract Regulatory Mechanisms 1. Mechanoreceptors and chemoreceptors – Respond to stretch, changes in osmolarity and pH, and presence of substrate and end products of digestion – Initiate reflexes that • • © 2013 Pearson Education, Inc. Activate or inhibit digestive glands Stimulate smooth muscle to mix and move lumen contents GI Tract Regulatory Mechanisms 2. Intrinsic and extrinsic controls – Short reflexes - enteric nerve plexuses (gut brain) respond to stimuli in GI tract – Long reflexes respond to stimuli inside or outside GI tract; involve CNS centers and autonomic nerves – Hormones from cells in stomach and small intestine stimulate target cells in same or different organs to secrete or contract © 2013 Pearson Education, Inc. Figure 23.4 Neural reflex pathways initiated by stimuli inside or outside the gastrointestinal tract. External stimuli (sight, smell, taste, thought of food) Central nervous system Long reflexes Visceral afferents Internal (GI tract) stimuli Extrinsic visceral (autonomic) efferents Chemoreceptors, osmoreceptors, or mechanoreceptors Local (intrinsic) nerve plexus ("gut brain") Effectors: Smooth muscle or glands Short reflexes Gastrointestinal wall (site of short reflexes) Lumen of the alimentary canal © 2013 Pearson Education, Inc. Response: Change in contractile or secretory activity Peritoneum and Peritoneal Cavity • Peritoneum - serous membrane of abdominal cavity – Visceral peritoneum on external surface of most digestive organs – Parietal peritoneum lines body wall • Peritoneal cavity – Between two peritoneums – Fluid lubricates mobile organs © 2013 Pearson Education, Inc. Figure 23.5a The peritoneum and the peritoneal cavity. Abdominopelvic cavity Vertebra Dorsal mesentery Parietal peritoneum Ventral mesentery Visceral peritoneum Peritoneal cavity Alimentary Liver canal organ Two schematic cross sections of abdominal cavity illustrate the peritoneums and mesenteries. © 2013 Pearson Education, Inc. Peritoneum and Peritoneal Cavity • Mesentery - double layer of peritoneum – Routes for blood vessels, lymphatics, and nerves – Holds organs in place; stores fat • Retroperitoneal organs posterior to peritoneum • Intraperitoneal (peritoneal) organs surrounded by peritoneum © 2013 Pearson Education, Inc. Homeostatic Imbalance • Peritonitis – Inflammation of peritoneum – Causes by e.g., piercing abdominal wound, perforating ulcer, ruptured appendix – Peritoneal coverings stick together, localizing infection – Dangerous and lethal if widespread – Treated with debris removal and antibiotics © 2013 Pearson Education, Inc. Blood Supply • Hepatic portal circulation – Drains nutrient-rich blood from digestive organs – Delivers it to the liver for processing © 2013 Pearson Education, Inc. Histology of the Alimentary Canal • Four basic layers (tunics) – Mucosa – Submucosa – Muscularis externa – Serosa © 2013 Pearson Education, Inc. Figure 23.6 Basic structure of the alimentary canal. Intrinsic nerve plexuses • Myenteric nerve plexus • Submucosal nerve plexus Glands in submucosa Mucosa • Epithelium • Lamina propria • Muscularis mucosae Submucosa Muscularis externa • Longitudinal muscle • Circular muscle Mesentery © 2013 Pearson Education, Inc. Nerve Artery Gland in mucosa Vein Duct of gland outside Lymphatic vessel alimentary canal Serosa • Epithelium (mesothelium) • Connective tissue Lumen Mucosa-associated lymphoid tissue Mucosa • Lines lumen • Functions – different layers perform 1 or all 3 – Secretes mucus, digestive enzymes, and hormones – Absorbs end products of digestion – Protects against infectious disease • Three sublayers: epithelium, lamina propria, and muscularis mucosae © 2013 Pearson Education, Inc. Mucosa • Epithelium – Simple columnar epithelium and mucussecreting cells (most of tract) • Mucus – Protects digestive organs from enzymes – Eases food passage – May secrete enzymes and hormones (e.g., in stomach and small intestine) © 2013 Pearson Education, Inc. Mucosa • Lamina propria – Loose areolar connective tissue – Capillaries for nourishment and absorption – Lymphoid follicles (part of MALT) • Defend against microorganisms • Muscularis mucosae: smooth muscle local movements of mucosa © 2013 Pearson Education, Inc. Submucosa • Submucosa – Areolar connective tissue – Blood and lymphatic vessels, lymphoid follicles, and submucosal nerve plexus © 2013 Pearson Education, Inc. Muscularis Externa • Muscularis externa – Responsible for segmentation and peristalsis – Inner circular and outer longitudinal layers • Circular layer thickens in some areas sphincters • Myenteric nerve plexus between two muscle layers © 2013 Pearson Education, Inc. Serosa • Visceral peritoneum – Areolar connective tissue covered with mesothelium in most organs – Replaced by fibrous adventitia in esophagus – Retroperitoneal organs have both an adventitia and serosa © 2013 Pearson Education, Inc. Figure 23.6 Basic structure of the alimentary canal. Intrinsic nerve plexuses • Myenteric nerve plexus • Submucosal nerve plexus Glands in submucosa Mucosa • Epithelium • Lamina propria • Muscularis mucosae Submucosa Muscularis externa • Longitudinal muscle • Circular muscle Mesentery © 2013 Pearson Education, Inc. Nerve Artery Gland in mucosa Vein Duct of gland outside Lymphatic vessel alimentary canal Serosa • Epithelium (mesothelium) • Connective tissue Lumen Mucosa-associated lymphoid tissue Enteric Nervous System • Intrinsic nerve supply of alimentary canal – enteric neurons (more than spinal cord) • Major nerve supply to GI tract wall; control motility – Submucosal nerve plexus • Regulates glands and smooth muscle in the mucosa – Myenteric nerve plexus • Controls GI tract motility © 2013 Pearson Education, Inc. Enteric Nervous System • Linked to CNS via afferent visceral fibers • Long ANS fibers synapse with enteric plexuses – Sympathetic impulses inhibit digestive activities – Parasympathetic impulses stimulate digestive activities © 2013 Pearson Education, Inc. Functional Anatomy: Mouth • Oral (buccal) cavity – Bounded by lips, cheeks, palate, and tongue – Oral orifice is anterior opening – Lined with stratified squamous epithelium © 2013 Pearson Education, Inc. Figure 23.7a Anatomy of the oral cavity (mouth). Soft palate Palatoglossal arch Uvula Hard palate Oral cavity Palatine tonsil Tongue Oropharynx Lingual tonsil Epiglottis Hyoid bone Laryngopharynx Esophagus Trachea © 2013 Pearson Education, Inc. Sagittal section of the oral cavity and pharynx Lips and Cheeks • Contain orbicularis oris and buccinator muscles • Oral vestibule - recess internal to lips (labia) and cheeks, external to teeth and gums • Oral cavity proper lies within teeth and gums • Labial frenulum - median attachment of each lip to gum © 2013 Pearson Education, Inc. Figure 23.7b Anatomy of the oral cavity (mouth). Upper lip Gingivae (gums) Palatine raphe Hard palate Soft palate Uvula Palatine tonsil Superior labial frenulum Palatoglossal arch Palatopharyngeal arch Posterior wall of oropharynx Tongue Sublingual fold with openings of sublingual ducts Lingual frenulum Opening of Submandibular duct Gingivae (gums) Oral vestibule Lower lip Anterior view © 2013 Pearson Education, Inc. Inferior labial frenulum Palate • Hard palate - palatine bones and palatine processes of maxillae – Slightly corrugated to help create friction against tongue • Soft palate - fold formed mostly of skeletal muscle – Closes off nasopharynx during swallowing – Uvula projects downward from its free edge © 2013 Pearson Education, Inc. Digestive Processes: Mouth • Ingestion • Mechanical breakdown – Chewing • Propulsion – Deglutition (swallowing) • Digestion (salivary amylase and lingual lipase) • ~ No absorption, except for few drugs © 2013 Pearson Education, Inc. Mastication • Cheeks and closed lips hold food between teeth • Tongue mixes food with saliva; compacts food into bolus • Teeth cut and grind • Partly voluntary • Partly reflexive – Stretch reflexes; pressure receptors in cheeks, gums, tongue © 2013 Pearson Education, Inc. Deglutition • Involves tongue, soft palate, pharynx, esophagus • Requires coordination of 22 muscle groups • Buccal phase – Voluntary contraction of tongue • Pharyngeal-esophageal phase – Involuntary – primarily vagus nerve – Control center in the medulla and lower pons © 2013 Pearson Education, Inc. Figure 23.13 Deglutition (swallowing). Slide 1 Bolus of food Tongue Uvula Pharynx Bolus Epiglottis Epiglottis Glottis Trachea Esophagus 1 During the buccal phase, the upper esophageal sphincter is contracted. The tongue presses against the hard palate, forcing the food bolus into the oropharynx. 2 The pharyngeal-esophageal phase begins as the uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus. 4 Peristalsis moves food through the esophagus to the stomach. Relaxed muscles Circular muscles contract Upper esophageal sphincter 3 The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after food enters. Relaxed muscles 5 The gastroesophageal sphincter surrounding the cardial orifice opens, and food enters the stomach. Bolus of food Longitudinal muscles contract Circular muscles contract Gastroesophageal sphincter closed Gastroesophageal sphincter opens Stomach © 2013 Pearson Education, Inc. Bolus Figure 23.13 Deglutition (swallowing). Slide 2 Bolus of food Tongue Pharynx Epiglottis Glottis Trachea © 2013 Pearson Education, Inc. 1 During the buccal phase, the upper esophageal sphincter is contracted. The tongue presses against the hard palate, forcing the food bolus into the oropharynx. Figure 23.13 Deglutition (swallowing). Slide 3 Uvula Bolus Epiglottis Esophagus 2 The pharyngeal-esophageal phase begins as the uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus. © 2013 Pearson Education, Inc. Figure 23.13 Deglutition (swallowing). Upper esophageal sphincter © 2013 Pearson Education, Inc. Slide 4 Bolus 3 The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after food enters. Figure 23.13 Deglutition (swallowing). Slide 5 4 Peristalsis moves Relaxed muscles food through the esophagus to the stomach. Circular muscles contract Bolus of food Longitudinal muscles contract Gastroesophageal sphincter closed Stomach © 2013 Pearson Education, Inc. Figure 23.13 Deglutition (swallowing). Slide 5 4 Peristalsis moves Relaxed muscles food through the esophagus to the stomach. Circular muscles contract Bolus of food Longitudinal muscles contract Gastroesophageal sphincter closed Stomach © 2013 Pearson Education, Inc. Figure 23.13 Deglutition (swallowing). Slide 6 Relaxed muscles 5 The gastroesophageal sphincter surrounding the cardial orifice opens, and food enters the stomach. Circular muscles contract Gastroesophageal sphincter opens © 2013 Pearson Education, Inc. Figure 23.13 Deglutition (swallowing). Slide 7 Bolus of food Tongue Uvula Pharynx Bolus Epiglottis Epiglottis Glottis Trachea Esophagus 1 During the buccal phase, the upper esophageal sphincter is contracted. The tongue presses against the hard palate, forcing the food bolus into the oropharynx. 2 The pharyngeal-esophageal phase begins as the uvula and larynx rise to prevent food from entering respiratory passageways. The tongue blocks off the mouth. The upper esophageal sphincter relaxes, allowing food to enter the esophagus. 4 Peristalsis moves food through the esophagus to the stomach. Relaxed muscles Circular muscles contract Upper esophageal sphincter 3 The constrictor muscles of the pharynx contract, forcing food into the esophagus inferiorly. The upper esophageal sphincter contracts (closes) after food enters. Relaxed muscles 5 The gastroesophageal sphincter surrounding the cardial orifice opens, and food enters the stomach. Bolus of food Longitudinal muscles contract Circular muscles contract Gastroesophageal sphincter closed Gastroesophageal sphincter opens Stomach © 2013 Pearson Education, Inc. Bolus Tongue • Skeletal muscle • Functions include – Repositioning and mixing food during chewing – Formation of bolus – Initiation of swallowing, speech, and taste • Intrinsic muscles change shape of tongue • Extrinsic muscles alter tongue's position • Lingual frenulum: attachment to floor of mouth © 2013 Pearson Education, Inc. Tongue • Surface bears papillae – Filiform—whitish, give the tongue roughness and provide friction; do not contain taste buds – Fungiform—reddish, scattered over tongue; contain taste buds – Vallate (circumvallate)—V-shaped row in back of tongue; contain taste buds – Foliate—on lateral aspects of posterior tongue; contain taste buds that function primarily in infants and children © 2013 Pearson Education, Inc. Tongue • Lingual lipase – Secreted by serous cells beneath foliate and vallate papillae secrete – Fat-digesting enzyme functional in stomach © 2013 Pearson Education, Inc. Figure 23.8 Dorsal surface of the tongue, and the tonsils. Epiglottis Palatopharyngeal arch Palatine tonsil Lingual tonsil Palatoglossal arch Terminal sulcus Foliate papillae Vallate papilla Medial sulcus of the tongue Dorsum of tongue Fungiform papilla Filiform papilla © 2013 Pearson Education, Inc. Salivary Glands • Major salivary glands – Produce most saliva; lie outside oral cavity – Parotid – Submandibular – Sublingual • Minor salivary glands – Scattered throughout oral cavity; augment slightly © 2013 Pearson Education, Inc. Salivary Glands • Function of saliva – Cleanses mouth – Dissolves food chemicals for taste – Moistens food; compacts into bolus – Begins breakdown of starch with enzymes © 2013 Pearson Education, Inc. Salivary Glands • Parotid gland – Anterior to ear; external to masseter muscle – Parotid duct opens into oral vestibule next to second upper molar – Mumps is inflammation of parotid glands © 2013 Pearson Education, Inc. Salivary Glands • Submandibular gland – Medial to body of mandible – Duct opens at base of lingual frenulum • Sublingual gland – Anterior to submandibular gland under tongue – Opens via 10–12 ducts into floor of mouth © 2013 Pearson Education, Inc. Figure 23.9 The salivary glands. Tongue Teeth Ducts of sublingual gland Frenulum of tongue Sublingual gland Parotid gland Parotid duct Masseter muscle Body of mandible (cut) Posterior belly of digastric muscle Mylohyoid muscle (cut) Submandibular duct Anterior belly of digastric muscle Submandibular gland © 2013 Pearson Education, Inc. Mucous cells Serous cells forming demilunes Salivary Glands • Two types of secretory cells – Serous cells • Watery, enzymes, ions, bit of mucin – Mucous cells • Mucus • Parotid, submandibular glands mostly serous; sublingual mostly mucous © 2013 Pearson Education, Inc. Composition of Saliva • 97–99.5% water, slightly acidic – Electrolytes—Na+, K+, Cl–, PO4 2–, HCO3– – Salivary amylase and lingual lipase – Mucin – Metabolic wastes—urea and uric acid – Lysozyme, IgA, defensins, and a cyanide compound protect against microorganisms PLAY Animation: Rotating head © 2013 Pearson Education, Inc. Control of Salivation • 1500 ml/day • Intrinsic glands continuously keep mouth moist • Major salivary glands activated by parasympathetic nervous system when – Ingested food stimulates chemoreceptors and mechanoreceptors in mouth – Salivatory nuclei in brain stem send impulses along parasympathetic fibers in cranial nerves VII and IX • Strong sympathetic stimulation inhibits salivation and results in dry mouth (xerostomia) © 2013 Pearson Education, Inc. Teeth • Tear and grind food for digestion • Primary and permanent dentitions formed by age 21 • 20 deciduous teeth erupt (6–24 months of age) – Roots resorbed, teeth fall out (6–12 years of age) as permanent teeth develop • 32 permanent teeth – All but third molars in by end of adolescence • Third molars at 17–25, or may not erupt © 2013 Pearson Education, Inc. Classes of Teeth • Incisors – Chisel shaped for cutting • Canines – Fanglike teeth that tear or pierce • Premolars (bicuspids) – Broad crowns, rounded cusps – grind/crush • Molars – Broad crowns, rounded cusps – best grinders © 2013 Pearson Education, Inc. Figure 23.10 Human dentition. Incisors Central (6–8 mo) Lateral (8–10 mo) Canine (eyetooth) (16–20 mo) Molars First molar (10–15 mo) Second molar (about 2 yr) Deciduous (milk) teeth Incisors Central (7 yr) Lateral (8 yr) Canine (eyetooth) (11 yr) Premolars (bicuspids) First premolar (11 yr) Second premolar (12–13 yr) Molars First molar (6–7 yr) Second molar (12–13 yr) Third molar (wisdom tooth) (17–25 yr) © 2013 Pearson Education, Inc. Permanent teeth Tooth Structure • Crown - exposed part above gingiva (gum) – Covered by enamel—hardest substance in body (calcium salts and hydroxyapatite crystals) • Enamel-producing cells degenerate when tooth erupts no healing if decay or crack • Root - portion embedded in jawbone – Connected to crown by neck © 2013 Pearson Education, Inc. Tooth Structure • Canine, incisor, and premolar one root – First upper premolar often has two • First two upper molars three roots • First two lower molars two roots • Third molar roots vary; often single fused root © 2013 Pearson Education, Inc. Tooth Structure • Cement - calcified connective tissue – Covers root; attaches it to periodontal ligament • Periodontal ligament – Forms fibrous joint called gomphosis – Anchors tooth in bony socket • Gingival sulcus - groove where gingiva borders tooth © 2013 Pearson Education, Inc. Tooth Structure • Dentin - bonelike material under enamel – Maintained by odontoblasts of pulp cavity • Pulp cavity - surrounded by dentin – Pulp - connective tissue, blood vessels, and nerves • Root canal - as pulp cavity extends to root • Apical foramen at proximal end of root – Entry for blood vessels, nerves, etc. © 2013 Pearson Education, Inc. Figure 23.11 Longitudinal section of a canine tooth within its bony socket (alveolus). Enamel Dentin Crown Neck Dentinal tubules Pulp cavity (contains blood vessels and nerves) Gingival sulcus Gingiva (gum) Cement Root Root canal Periodontal ligament Apical foramen © 2013 Pearson Education, Inc. Bone Tooth and Gum Disease • Dental caries (cavities) - demineralization of enamel and dentin from bacterial action – Dental plaque (film of sugar, bacteria, and debris) adheres to teeth – Acid from bacteria dissolves calcium salts – Proteolytic enzymes digest organic matter – Prevention: daily flossing and brushing © 2013 Pearson Education, Inc. Tooth and Gum Disease • Gingivitis – Plaque calcifies to form calculus (tartar) – Calculus disrupts seal between gingivae and teeth – Anaerobic bacteria infect gums – Infection reversible if calculus removed © 2013 Pearson Education, Inc. Tooth and Gum Disease • Periodontitis (from neglected gingivitis) – Immune cells attack intruders and body tissues • Destroy periodontal ligament • Activate osteoclasts dissolve bone – Possible tooth loss; may promote atherosclerosis and clot formation in coronary and cerebral arteries – Risk factors - smoking, diabetes mellitus, oral piercing © 2013 Pearson Education, Inc.