Human Anatomy Unit 2 DIGESTIVE SYSTEM In Anatomy Today Abdominopelvic Quadrants Abdominopelvic Regions Body Cavities Body Cavities Serous Membranes • A simple squamous epithelium and its underlying connective tissue – Produces a serous fluid – Lubricates, prevent frictional damage • Pericardial cavity – Visceral pericardium – Parietal pericardium • Pleural cavity – Visceral pleura – Parietal pleura • Abdominal cavity – Visceral peritoneum – Parietal peritoneum Components of the Digestive System Functions • Motility – ingestion – mastication – deglutition – peristalsis • Secretion – exocrine – endocrine • Digestion • Absorption Terminology • Ingestion • to take in food • Mastication • chewing (mechanical breakdown of food) • Deglutition • swallowing • Digestion • chemical breakdown of food • Absorption • passage of nutrients from the gi tract lumen to the blood • Peristalsis • Waves of smooth muscle contraction to propel food • Defecation • formation and excretion of solid waste Mucosa • Absorptive layer, large surface area • 3 major components – Mucosal epithelium • Columnar epithelium (stomach, intestines) or stratified squamous • Gastric Pits, Crypts of Leiberkuhn, Intestinal Crypts – folds in the mucosa of the small intestines, colon – source of new epithelial cells – digestive enzymes – Lamina propria • Loose CT of the mucosa, with capillaries that receive absorbed nutrients • lymphatic tissue: capillaries and lymphatic nodules involved in absorption of fat • Peyer’s Patches: aggregates of lymph nodes, significant protection against intestinal infections – Muscularis mucosa • a thin layer of smooth muscle that keeps the folds of the mucosa folded Submucosa, Muscularis Externa, Serosa • Submucosa – tissue: dense irregular CT – Submucosal plexus • nerve supply to the muscularis mucosa • Muscularis Externa – mostly a double layer of smooth muscle, propels and mixes digestive contents • circular layer: thick inner layer, muscle fibers describe a circle • longitudinal layer: thin outer layer, muscle fibers run along the length of the GI tract – Myenteric plexus: nerve supply to the muscularis externa • Serosa – loose CT + simple squamous epithelium – outer wall of the GI tract – Is the visceral peritoneum Enteric Nervous System Movement Through the Digestive Tube Mesentaries • Sheets of serous membrane that connect the parietal and visceral peritoneum – Suspends organs in the space – Provides a route for blood vessels, nerves, lymphatics • Lesser omentum • Greater omentum • Mesentery proper • Mesocolon • Transverse mesocolon • Sigmoidal mesocolon Oral Cavity The Tongue • Body • Root • Papillae • Taste buds • Frenulum Salivary Glands • Release water, lysozyme, digestive enzymes, mucus – Salivary amylase • Parotid – Pure serous – Parotid duct • Sublingual – Pure mucus – Sublingual ducts • numerous • Submandibular – Mixed serous/mucus – Submandibular ducts • numerous Teeth • Neck • Crown • Gingivae • Enamel • Dentine • Pulp cavity – Apical foramen • Periodontal ligaments • Cementum Types of Teeth Pharynx • Passageway for air, water, food • Divisions – Nasopharynx – Oropharynx – Laryngeal pharynx Swallowing Esophagus • Function – move food to the stomach • Lining epithelium – stratified squamous • Muscle layer – 1st third • skeletal muscle – 2nd third • a mixture of skeletal and smooth muscle – 3rd third • smooth muscle Esophageal Gastric Juncture Gross Anatomy of the Stomach • Lesser curvature • Greater curvature • Cardia – Cardiac orifice • Fundus • Body • Pylorus – Pyloric sphincter • Rugae Layers of the Stomach Functions of the Stomach • Functions – Food storage – Chemical digestion • Chief cells • Parietal cells – Mechanical digestion • Churning by 3 layers of smooth muscle – Kills bacteria – Moves food to SI – Hormonal regulation of digestion • G cells Histology of the Stomach • Lining epithelium – simple columnar epithelium – Mucon neck cells • Gastric glands – microscopic folds, secrete gastric juice. • Gastric pits – openings from gastric glands to gastric lumen The Small Intestine • ~ 3 meters long • Function – Digestion and absorption • Duodenum • Jejunum • Ileum • Support of the small intestine – Mesentary proper Intestinal Surface Area • Plicae circularis – macroscopic permanent folds (permanent until death) – Circular pleats like conduit • Villi – fingerlike projections • Microvilli – submicroscopic folds on apical surface of columnar cells – “brush border” Histological Organization of the Small Intestine Serosa versus Adventitia Histology of the Small Intestine • Intestinal villi • Microvilli • Goblet cells • Crypts of Lieberkühn Regions of the Colon • Ascending colon – Right colic flexure • Transverse colon – Left colic flexure • Descending colon • Sigmoid colon – Sigmoid flexure Large Intestine • Cecum – Ileal papilla – Iliocecal valve – appendix • The colon – Thin wall – Larger diameter – Haustra – Taeniae coli Appendix: an extension of lymphatic – Fatty appendices tissue near the ileocecal junction The Rectum • Last 15 cm • Anal canal • Anal columns • Internal anal sphincter • External anal sphincter Histology of The Large Intestine • Lacks villi • Abundant goblet cells • Intestinal crypts – Deeper – More goblet cells • Large lymphoid nodules • Taenia coli – Reduced longitudinal muscularis layer Accessory Glandular Digestive Organs • Liver • Gall bladder • Pancreas Anatomy of the Liver • Lobes – Left, right, caudate, quadrate • Ligaments – Falciform ligament • Liver to anterior body wall – Coronary ligament • Liver to diaphragm – Ligamentum teres hepatis (also called the round ligament) • Falciform ligament to umbilicus • Left, right hepatic ducts Liver Lobules • Functional unit of the liver • Hepatic triad – Hepatic artery – Hepatic portal vein – Bile duct • Bile canaliculi • Hepatocytes – Hepatic plates (cords) • Kupffer cells – macrophages • Central vein • Sinusoids The Gall Bladder • Fundus • Body • Neck • Stores, concentrates bile • Ducts – Left, right hepatic ducts – Common hepatic duct – Cystic duct – Common bile duct • Hepatopancreatic sphincter – Ampulla of Vater – Sphincter of Oddi The Pancreas • Head • Body • Tail • Pancreatic duct – Sphincter of Oddi • Accessory pancreatic duct – Duct of Santorini Histology of the Pancreas • Pancreatic acini – Exocrine glands – Pancreatic juice • Islets of Langerhans – Endocrine glands – Alpha cells • glucagon – Beta cells • insulin Blood Flow.