PowerPoint ® Lecture Slides prepared by Janice Meeking, Mount Royal College C H A P T E R Copyright © 2010 Pearson Education, Inc. 23 The Digestive System: Part A

Copyright © 2010 Pearson Education, Inc. Digestive System Two groups of organs 1.Alimentary canal (gastrointestinal or GI tract) Digests and absorbs food Mouth, pharynx, esophagus, stomach, small intestine, and large intestine

Copyright © 2010 Pearson Education, Inc. Digestive System 2.Accessory digestive organs Teeth, tongue, gallbladder Digestive glands Salivary glands Liver pancreas

Copyright © 2010 Pearson Education, Inc. Figure 23.1 Mouth (oral cavity) Tongue Esophagus Liver Gallbladder Anus Duodenum Jejunum Ileum Small intestine Parotid gland Sublingual gland Submandibular gland Salivary glands Pharynx Stomach Pancreas (Spleen) Transverse colon Descending colon Ascending colon Cecum Sigmoid colon Rectum Vermiform appendix Anal canal Large intestine

Copyright © 2010 Pearson Education, Inc. Digestive Processes Six essential activities 1.Ingestion 2.Propulsion 3.Mechanical digestion 4.Chemical digestion 5.Absorption 6.Defecation

Copyright © 2010 Pearson Education, Inc. Figure 23.2 Food Ingestion Propulsion Esophagus Stomach Pharynx Mechanical digestion Chemical digestion Chewing (mouth) Churning (stomach) Segmentation (small intestine) Small intestine Large intestine Defecation Anus Feces Blood vessel Lymph vessel Absorption Swallowing (oropharynx) Peristalsis (esophagus, stomach, small intestine, large intestine) Mainly H 2 O

Copyright © 2010 Pearson Education, Inc. Figure 23.3 From mouth (b) Segmentation: Nonadjacent segments of alimentary tract organs alternately contract and relax, moving the food forward then backward. Food mixing and slow food propulsion occurs. (a) Peristalsis: Adjacent segments of alimentary tract organs alternately contract and relax, which moves food along the tract distally.

Copyright © 2010 Pearson Education, Inc. 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 Activate or inhibit digestive glands Stimulate smooth muscle to mix and move lumen contents

Copyright © 2010 Pearson Education, Inc. GI tract regulatory mechanisms 2.Intrinsic and extrinsic controls Enteric nerve plexuses (gut brain) initiate short reflexes in response to stimuli in the GI tract Long reflexes in response to stimuli inside or outside the GI tract involve CNS centers and autonomic nerves Hormones from cells in the stomach and small intestine stimulate target cells in the same or different organs

Copyright © 2010 Pearson Education, Inc. Figure 23.4 External stimuli (sight, smell, taste, thought of food) Central nervous system and extrinsic autonomic nerves Afferent impulsesEfferent impulses Long reflexes Internal (GI tract) stimuli Chemoreceptors, osmoreceptors, or mechanoreceptors Local (intrinsic) nerve plexus (“gut brain”) Effectors: Smooth muscle or glands Gastrointestinal wall (site of short reflexes) Response: Change in contractile or secretory activity Lumen of the alimentary canal Short reflexes

Copyright © 2010 Pearson Education, Inc. Peritoneum and Peritoneal Cavity Peritoneum: serous membrane of the abdominal cavity Visceral peritoneum on external surface of most digestive organs Parietal peritoneum lines the body wall Peritoneal cavity Between the two peritoneums Fluid lubricates mobile organs

Copyright © 2010 Pearson Education, Inc. Figure 23.5a Peritoneal cavity Parietal peritoneum Visceral peritoneum Ventral mesentery Abdominopelvic cavity Dorsal mesentery Vertebra Alimentary canal organ (a) Schematic cross sections of abdominal cavity illustrate the peritoneums and mesenteries. Liver

Copyright © 2010 Pearson Education, Inc. Peritoneum and Peritoneal Cavity Mesentery is a double layer of peritoneum Routes for blood vessels, lymphatics, and nerves Holds organs in place and stores fat Retroperitoneal organs lie posterior to the peritoneum Intraperitoneal (peritoneal) organs are surrounded by the peritoneum

Copyright © 2010 Pearson Education, Inc. Figure 23.5b Abdominopelvic cavity Mesentery resorbed and lost (b) Some organs lose their mesentery and become retroperitoneal during development. Alimentary canal organ Alimentary canal organ in a retroperitoneal position

Copyright © 2010 Pearson Education, Inc. Blood Supply: Splanchnic Circulation Arteries Hepatic, splenic, and left gastric Inferior and superior mesenteric Hepatic portal circulation Drains nutrient-rich blood from digestive organs Delivers it to the liver for processing

Copyright © 2010 Pearson Education, Inc. Histology of the Alimentary Canal Four basic layers (tunics) Mucosa Submucosa Muscularis externa Serosa

Copyright © 2010 Pearson Education, Inc. Figure 23.6 Glands in submucosa Submucosa Lumen Mucosa-associated lymphoid tissue Duct of gland outside alimentary canal Gland in mucosa Nerve Artery Vein Lymphatic vessel Mesentery Intrinsic nerve plexuses Myenteric nerve plexus Submucosal nerve plexus Mucosa Epithelium Lamina propria Muscularis mucosae Muscularis externa Longitudinal muscle Circular muscle Serosa Epithelium Connective tissue

Copyright © 2010 Pearson Education, Inc. Mucosa Lines the lumen Functions Secretes mucus, digestive enzymes and hormones Absorbs end products of digestion Protects against infectious disease Three sublayers: epithelium, lamina propria, and muscularis mucosae

Copyright © 2010 Pearson Education, Inc. Mucosa Epithelium Simple columnar epithelium and mucus- secreting cells Mucus Protects digestive organs from enzymes Eases food passage May secrete enzymes and hormones (e.g., in stomach and small intestine)

Copyright © 2010 Pearson Education, Inc. Mucosa Lamina propria Loose areolar connective tissue Capillaries for nourishment and absorption Lymphoid follicles (part of MALT) Muscularis mucosae: smooth muscle that produces local movements of mucosa

Copyright © 2010 Pearson Education, Inc. Submucosa and Muscularis Externa Submucosa Dense connective tissue Blood and lymphatic vessels, lymphoid follicles, and submucosal nerve plexus

Copyright © 2010 Pearson Education, Inc. Submucosa and Muscularis Externa Muscularis externa Responsible for segmentation and peristalsis Inner circular and outer longitudinal layers Myenteric nerve plexus Sphincters in some regions

Copyright © 2010 Pearson Education, Inc. Serosa Visceral peritoneum Replaced by the fibrous adventitia in the esophagus Retroperitoneal organs have both an adventitia and serosa

Copyright © 2010 Pearson Education, Inc. Figure 23.6 Glands in submucosa Submucosa Lumen Mucosa-associated lymphoid tissue Duct of gland outside alimentary canal Gland in mucosa Nerve Artery Vein Lymphatic vessel Mesentery Intrinsic nerve plexuses Myenteric nerve plexus Submucosal nerve plexus Mucosa Epithelium Lamina propria Muscularis mucosae Muscularis externa Longitudinal muscle Circular muscle Serosa Epithelium Connective tissue

Copyright © 2010 Pearson Education, Inc. Enteric Nervous System Intrinsic nerve supply of the alimentary canal Submucosal nerve plexus Regulates glands and smooth muscle in the mucosa Myenteric nerve plexus Controls GI tract motility

Copyright © 2010 Pearson Education, Inc. Enteric Nervous System Linked to the CNS via afferent visceral fibers Long ANS fibers synapse with enteric plexuses Sympathetic impulses inhibit secretion and motility Parasympathetic impulses stimulate

Copyright © 2010 Pearson Education, Inc. Mouth Oral (buccal) cavity Bounded by lips, cheeks, palate, and tongue Oral orifice is the anterior opening Lined with stratified squamous epithelium

Copyright © 2010 Pearson Education, Inc. Figure 23.7a Uvula Soft palate Palatoglossal arch Palatine tonsil Hard palate Oral cavity Tongue Lingual tonsil Oropharynx Epiglottis Hyoid bone Laryngopharynx Esophagus Trachea (a) Sagittal section of the oral cavity and pharynx

Copyright © 2010 Pearson Education, Inc. Figure 23.7b Uvula Palatine tonsil Sublingual fold with openings of sublingual ducts Tongue Upper lip Lower lip Vestibule Gingivae (gums) Hard palate Soft palate Lingual frenulum Opening of submandibular duct Palatine raphe Inferior labial frenulum Posterior wall of oropharynx Palatopharyngeal arch Superior labial frenulum Palatoglossal arch (b) Anterior view

Copyright © 2010 Pearson Education, Inc. Salivary Glands Extrinsic salivary glands (parotid, submandibular, and sublingual)

Copyright © 2010 Pearson Education, Inc. Salivary Glands Intrinsic (buccal) salivary glands are scattered in the oral mucosa Secretion (saliva) Cleanses the mouth Moistens and dissolves food chemicals Aids in bolus formation Contains enzymes that begin the breakdown of starch

Copyright © 2010 Pearson Education, Inc. Figure 23.9 Teeth Ducts of sublingual gland Sublingual gland Submandibular duct Posterior belly of digastric muscle Parotid duct Masseter muscle Body of mandible (cut) Parotid gland Tongue Submandibular gland (a) Frenulum of tongue Mylohyoid muscle (cut) Anterior belly of digastric muscle Mucous cells (b) Serous cells forming demilunes

Copyright © 2010 Pearson Education, Inc. Composition of Saliva Secreted by serous and mucous cells 97–99.5% water, slightly acidic solution containing Electrolytes—Na +, K +, Cl –, PO 4 2–, HCO 3 – Salivary amylase and lingual lipase Mucin Metabolic wastes—urea and uric acid Lysozyme, IgA, defensins, and a cyanide compound protect against microorganisms PLAY Animation: Rotatable head

Copyright © 2010 Pearson Education, Inc. Control of Salivation Intrinsic glands continuously keep the mouth moist Extrinsic salivary glands produce secretions when Ingested food stimulates chemoreceptors and mechanoreceptors in the mouth Salivatory nuclei in the brain stem send impulses along parasympathetic fibers in cranial nerves VII and IX Strong sympathetic stimulation inhibits salivation and results in dry mouth (xerostomia)

Copyright © 2010 Pearson Education, Inc. Teeth Primary and permanent dentitions are formed by age deciduous teeth erupt (6–24 months of age) Roots are resorbed, teeth fall out (6–12 years of age) as permanent teeth develop 32 permanent teeth All except third molars erupt by the end of adolescence