UNIT 8 The Digestive System Part 1 of 2 (Chapter 23)

1. UNIT 8 The Digestive System Part 1 of 2 (Chapter 23) • Digestive System Overview • Digestive Processes • Peritoneal Cavity and Peritoneum • Abdominopelvic Regions and Quadrants • Histology of the Alimentary Canal • Functional Anatomy - The Mouth, Pharynx, and Esophagus • Functional Anatomy - The Stomach • Functional Anatomy - The Small Intestine (7th edition)

2. Digestive System Overview (fig. 23.1) • ALIMENTARY CANAL (also known as the gastrointestinal tract or GI tract) - includes mouth, pharynx, esophagus, stomach, small intestine, large intestine • Accessory Digestive Organs - include teeth, tongue, salivary glands, liver, gallbladder, pancreas (7th edition)

3. Digestive Processes (fig. 23.2, 23.3) • INGESTION - food is taken into the mouth • PROPULSION - involves swallowing (voluntary) and peristalsis (involuntary); peristalsis involves progressive waves of contraction that move food along the alimentary canal • MECHANICAL DIGESTION - chewing (teeth) and churning of food (stomach); segmentation involves segments of the small intestine contracting and relaxing; this mixes food with digestive juices and increases absorption efficiency • CHEMICAL DIGESTION - breakdown of carbohydrates, proteins, and lipids • ABSORPTION - transport of material from the lumen of the alimentary canal to blood and lymph capillaries • DEFECATION - removal of indigestible material from the body as feces (7th edition)

4. Peritoneal Cavity and Peritoneum (fig. 23.5) • Peritoneum - a serous membrane • VISCERAL PERITONEUM - covers digestive organs • PERITONEAL CAVITY - a slit-like potential space • PARIETAL PERITONEUM - lines the abdominal wall • Mesenteries (fig. 23.5, 23.30) - double layer of peritoneum; hold organs in place; fat storage • DORSAL - most mesenteries including the greater omentum • VENTRAL - falciform “ligament” (liver) and lesser omentum (liver, stomach, and duodenum) • RETROPERITONEAL Organs (fig. 23.5) - some digestive organs are not contained in the abdominal or pelvic cavities; instead, they are found just outside of the cavity, behind the parietal peritoneum • fuse to dorsal abdominal wall during development • lose their mesentery • are located behind the parietal peritoneum • examples: parts of the esophagus, duodenum, colon, and rectum; the kidneys (urinary system) are also retroperitoneal (7th edition)

5. Abdominopelvic Regions and Quadrants (fig. 1.11, 1.12); this information is contained in Chapter 1 of our textbook, but it makes more sense to cover it here • Regions (fig. 1.11): umbilical region, epigastric region, hypogastric (pubic) region, right and left iliac(inguinal) regions, right and left lumbar regions, right and left hypochondriac regions *Be able to identify digestive organs or parts of digestive organs with regions; for example, the liver is contained in the right hypochondriac and epigastric regions • Quadrants (fig. 1.12): right upper quadrant, left upper quadrant, right lower quadrant, left lower quadrant *Be able to identify digestive organs or parts of digestive organs with quadrants; for example, the stomach is mostly contained in the left upper quadrant (7th edition)

6. Histology of the Alimentary Canal (fig. 23.6) • MUCOSA - innermost layer; three sub layers: • lining epithelium - absorbs nutrients and secretes mucus • lamina propria - nourishes the lining epithelium and absorbs digested nutrients; contains lymphatic tissue for protection from bacteria and other invaders • muscularismucosae - thin layer of smooth muscle • SUBMUCOSA - contains the major blood vessels, lymphatic vessels, and nerve fibers • MUSCULARIS EXTERNA - contains two layers of smooth muscle that work together to cause peristalsis and segmentation (mixing) • inner circular layer - muscle fibers orient around the circumference of the canal; “squeezes” the gut tube • outer longitudinal layer - muscle fibers orient along the length of the canal; shortens the gut tube • SEROSA - composed of the visceral peritoneum (7th edition)

7. Functional Anatomy - The Mouth, Pharynx, and Esophagus • Oral Cavity (Mouth) - fig. 23.7; composed of a thick, non-keratinized, stratified squamous epithelium to help deal with friction / “wear and tear” from ingested food and drink • ORAL ORIFICE - anterior opening • VESTIBULE - between teeth and cheeks (and lips) • LABIA - lips; formed from the orbicularisoris muscle • CHEEKS - formed from the buccinator muscles • PALATE - roof of the mouth; hard palate, soft palate, uvula, and palatine tonsils (7th edition)

8. Functional Anatomy - The Mouth, Pharynx, and Esophagus • Associated Organs of the Mouth • TONGUE (fig. 23.8) - a muscle; contains lingual tonsil and papillae • filiform papillae - “roughen” the tongue; provide friction for manipulating food • fungiform papillae, circumvallate papillae, and foliate papillae - have taste buds • SALIVARY GLANDS (fig. 23.9) - produce saliva (a combination of water, ions, mucus, and enzymes); the enzyme amylase begins the digestion of starch in the mouth • intrinsic salivary glands - keep mouth moist at all times; found in the tongue, palate, lips, and cheeks • extrinsic salivary glands (external to mouth) - secrete saliva during eating or anticipation of a meal; include the parotid, submandibular, and sublingual glands • mucous cells - sublingual glands; produce mucus; the sublingual glands contain mostly mucous cells • serous cells - produce enzymes (e.g. amylase); the parotid glands contain only serous cells *the submandibular glands have approximately equal numbers of mucous and serous cells (7th edition)

9. Functional Anatomy - The Mouth, Pharynx, and Esophagus • Associated Organs of the Mouth • DENTITION (fig. 23.10) - teeth lie in alveolar sockets of the mandible and maxillary bones • deciduous (primary) teeth (20) - include the incisors, canines (=cuspids or eyeteeth), and molars • permanent teeth (32) - include incisors, canines (=cuspids, eyeteeth), premolars (=bicuspids), molars (including “wisdom” teeth) (7th edition)

10. Functional Anatomy - The Mouth, Pharynx, and Esophagus • Associated Organs of the Mouth • tooth structure (fig. 23.11) • gingivae - gums • crown (above the gums) vs. root (below the gums) • enamel - 99% mineralized (with hydroxyapatite); hardest substance in body • dentin - like bone but harder and lacking blood vessels; not as hard as enamel • pulp cavity - contains “pulp, ” and the tooth’s blood vessels and nerves * The root canal is the portion of the cavity that is below the gum line; the pulp can die and become infected, thus requiring root canal therapy be performed on the tooth. • periodontal ligament - connects the cementum of the tooth to the alveolar bone; composed of collagen fibers (7th edition)

11. Functional Anatomy - The Mouth, Pharynx, and Esophagus • Oropharynx and Laryngopharynx (fig. 23.7) - passageway for food, fluids, and air • both are composed of non-keratinized, stratified squamous epithelium • the epiglottis helps to block the opening to the larynx and assures that food continues down the esophagus • Esophagus (fig. 23.7, 23.12) - composed of non-keratinized, stratified squamous epithelium • muscular tube that propels food to the stomach • lies directly posterior to trachea • passes through diaphragm, turns to the left, and connects to the stomach at the cardia (=cardiac region) • narrowing of the cardia at the esophagus-stomach junction helps to limit regurgitation of stomach acid back into the esophagus *at the esophagus-stomach junction (fig. 23.12b) non-keratinized, stratified squamous epithelium gives way to simple columnar epithelium in the stomach (7th edition)

12. Functional Anatomy - The Stomach • Functions • storage of food (for about 4 hours) • churning of food to turn it into a paste called chyme • secretion of the pre-enzyme pepsinogenwhich converts to the enzyme pepsin (when in an acidic environment) to begin protein digestion; protein digestion begins in the stomach • secretion of hydrochloric acid (HCl) to destroy harmful bacteria in food • very little digestion occurs in the stomach; the small intestine is the site of digestion (7th edition)

13. Functional Anatomy - The Stomach • Gross Anatomy (fig. 23.14) • inner lining composed of simple columnar epithelium • greater and lesser curvatures • longitudinal, circular, and oblique layers of muscle • cardia (cardiac region), fundus (fundic region), body, and pyloric region (including the pyloric antrum, pyloric canal, pyloric sphincter, and pylorus) • rugae - non-permanent folds that allow the stomach to stretch • pyloric sphincter - controls passage of chyme into the duodenum of the small intestine (7th edition)

14. Functional Anatomy - The Stomach • Invaginations called gastric glands increase surface area in the stomach, and contain the following types of cells: • mucous cells - secretes mucus • parietal cells - secrete hydochloric acid (HCl) • chief cells - secrete pepsinogen • enteroendocrine cells - influence digestive system target organs; e.g. gastrin regulates stomach secretion and motility (7th edition)

15. Functional Anatomy - The Small Intestine • Site of most chemical digestion and absorption • Like the stomach, the intestinal wall is lined with simple columnar epithelium • Contains villiand microvilli (fig. 23.21, 23.22) that greatly increase surface area for digestion and absorption • Composed of 3 segments: the duodenum, jejunum, and ileum (fig. 23.1, 23.20) • The duodenum is the short, c-shaped, first section of the small intestine; it receives: • chyme from the stomach • bile from the liver and gallbladder via the hepatopancreaticampulla • digestive enzymes from the pancreas via the hepatopancreaticampulla • The jejunum is the middle section of the small intestine • the ileum, the last and longest section of the small intestine; the ileum connects to the cecum of the large intestine; the ileocecal valve prevents feces from entering small intestine (fig. 23.29) (7th edition)

16. This concludes the current lecture topic • Be sure to read the next lecture topic: The Digestive System Part 2 of 2 (close the current window to exit the PowerPoint and return to the Unit 8 Startpage) (7th edition)