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Lecture 13 – Digestive System, Part II Dr. Siddique Introduction to Human Anatomy East Los Angeles College The Pharynx • Oropharynx and laryngopharynx – Passages for air and food – Lined with stratified squamous epithelium – External muscle layer • Consists of superior, middle, and inferior pharyngeal constrictors The Esophagus • Gross anatomy—muscular tube – Begins as a continuation of the pharynx – Joins the stomach inferior to the diaphragm • Cardiac sphincter—closes lumen to prevent stomach acid from entering esophagus The Esophagus • Microscopic anatomy – Epithelium is stratified squamous epithelium – When empty, mucosa and submucosa in longitudinal folds – Mucous glands—primarily compound tubuloalveolar glands – Muscularis externa • Skeletal muscle first third of length – Adventitia—most external layer Microscopic Structure of the Esophagus Mucosa (contains a stratified squamous epithelium) Submucosa (areolar connective tissue) Lumen Muscularis externa Circular layer Longitudinal layer Adventitia (fibrous connective tissue) (a) Cross section through esophagus (5) (b) Gastroesophageal junction, longitudinal section (85) Figure 23.16 The Stomach • Site where food is churned into chyme • Secretion of pepsin begins protein digestion – Functions under acidic conditions • Food remains in stomach approximately 4 hours • Regions of the stomach – Cardiac region – Fundus – Body – Pyloric region The Stomach Cardia Fundus Esophagus Serosa Muscularis externa Longitudinal layer Circular layer Oblique layer Body Lumen Lesser curvature Rugae of mucosa Greater curvature Duodenum (a) Pyloric canal Pyloric sphincter (valve) at pylorus Pyloric antrum Figure 23.17a The Stomach Fundus Liver (cut) Body Spleen Lesser curvature Greater curvature (b) Figure 23.17b Microscopic Anatomy of the Stomach • Muscularis has three layers – Circular and longitudinal layers and oblique layer • Epithelium is simple columnar epithelium • Mucosa dotted with gastric pits – Gastric glands—deep to gastric pits Microscopic Anatomy of the Stomach • Gastric glands of fundus and body – Mucous neck cells • Secrete a special mucus – Parietal (oxyntic) cells • Secrete hydrochloric acid and gastric intrinsic factor – Chief (zymogenic) cells • Secrete pepsinogen – Pepsinogen is activated to pepsin when it encounters acid in the gastric glands The Stomach—Microscopic Anatomy Gastric pits Surface epithelium (mucous cells) Surface epithelium Gastric pit Mucosa Submucosa (contains submucosal plexus) Mucous neck cells Parietal cell Gastric gland Lamina propria Muscularis mucosae Chief cell Oblique layer Circular layer Muscularis externa (contains myenteric Longitudinal plexus) layer Serosa Stomach wall (a) Layers of the stomach wall, longitudinal section Pepsinogen HCl Enteroendocrine cell (b) Enlarged view of gastric pits and gastric glands Pepsin Gastric pits Mucus-secreting cells Surface mucous cell Mucus neck cells Mitochondria Parietal cell HCl secreting parietal cells Gastric gland Chief cell Enzyme secreting chief cells Enteroendocrine cell (c) Location of the HCl-producing parietal cells and pepsin-secreting chief cells in a gastric gland Muscularis mucosae (d) Micrograph of the stomach mucosa, view similar to part (b) (115) Figure 23.18 The Small Intestine—Gross Anatomy • Longest portion of the alimentary canal • Site of most enzymatic digestion and absorption • Three subdivisions – Duodenum – Jejunum – Ileum • Innervation – Parasympathetic fibers from vagus nerve – Sympathetic from thoracic splanchnic nerves The Duodenum • Receives digestive enzymes and bile • Main pancreatic duct and common bile duct enter duodenum – Sphincters control entry of bile and pancreatic juices The Duodenum and Related Organs Right and left hepatic ducts of liver Common hepatic duct Cystic duct Bile duct and sphincter Accessory pancreatic duct Mucosa with folds Gallbladder Major duodenal papilla Hepatopancreatic ampulla and Duodenum sphincter Tail of pancreas Pancreas Jejunum Main pancreatic duct and sphincter Head of pancreas Figure 23.19 The Small Intestine—Microscopic Anatomy • Modifications for absorption – Circular folds (plicae circulares) • Transverse ridges of mucosa and submucosa – Villi • Finger-like projections of the mucosa • Covered with simple columnar epithelium – Microvilli • Further increase surface area for absorption Histology of the Intestinal Wall • Absorptive cells – Uptake digested nutrients • Goblet cells – Secrete mucus that lubricates chyme • Enteroendocrine cells – Secrete hormones • Intestinal crypts – Epithelial cells secrete intestinal juice The Small Intestine—Structural Features Vein carrying blood to hepatic portal vessel Muscle layers Lumen Microvilli (brush border) Circular folds Absorptive cells Villi Lacteal Goblet cell Blood capillaries (a) (b) Mucosa associated lymphoid tissue Intestinal crypt Muscularis mucosae Duodenal gland Absorptive cells Vilus Goblet cells Villi Enteroendocrine cells Venule Lymphatic vessel Submucosa (c) Intestinal crypt Figure 23.20 The Large Intestine • Digested residue contains few nutrients • Small amount of digestion by bacteria • Main functions – Absorb water and electrolytes • Mass peristaltic movements force feces toward the rectum Gross Anatomy of Large Intestine • Subdivided into – Cecum, vermiform appendix, colon, rectum, anal canal • Special features of large intestine – Teniae coli • Thickening of longitudinal muscularis – Haustra • Puckering created by teniae coli – Epiploic appendages • Fat-filled pouches of visceral peritoneum Gross Anatomy of Large Intestine • Cecum – Blind pouch – Beginning of large intestine • Vermiform appendix – Contains lymphoid tissue – Neutralizes pathogens • Colon – Divided into distinct segments • Ascending, transverse, descending, and sigmoid colon Gross Anatomy of Large Intestine • Rectum – Descends along the inferior half of the sacrum • Anal canal – The last subdivision of the large intestine – Lined with stratified squamous epithelium Gross Anatomy of Large Intestine Left colic (splenic) flexure Transverse colon Transverse mesocolon Epiploic appendages Superior mesenteric artery Descending colon Right colic (hepatic) flexure Haustrum Ascending colon IIeum Cut edge of mesentery IIeocecal valve Teniae coli Sigmoid colon Cecum Vermiform appendix Rectum Anal canal External anal sphincter (a) Figure 23.21a Gross Anatomy of Large Intestine Rectal valve Rectum Hemorrhoidal veins Levator ani muscle Anal canal External anal sphincter Internal anal sphincter Anal columns Anal valves Pectinate line Anal sinuses Anus (b) Figure 23.21b Microscopic Anatomy of Large Intestine • • • • Villi are absent Contains numerous goblet cells Intestinal crypts—simple tubular glands Lined with simple columnar epithelial tissue – Epithelium changes at anal canal • Becomes stratified squamous epithelium Mucosa of the Large Intestine Absorptive cells Lamina propria Goblet cells Intestinal crypts Muscularis mucosae Figure 23.23 The Liver • Largest gland in the body – Performs over 500 functions – Digestive function • Bile production • Stored in gall bladder – Performs many metabolic functions The Liver Sternum Nipple Bare area Liver Falciform ligament Left lobe of liver Right lobe of liver Gallbladder Round ligament (ligamentum teres) Figure 23.24 Visceral Surface of the Liver Lesser omentum (in fissure) Caudate lobe of liver Left lobe of liver Porta hepatis containing hepatic artery (left) and hepatic portal vein (right) Quadrate lobe of liver Ligamentum teres Bare area Sulcus for inferior vena cava Hepatic vein (cut) Bile duct (cut) Right lobe of liver Gallbladder (a) Figure 23.25a Visceral Surface of the Liver Hepatic portal vein Caudate lobe Hepatic veins Inferior vena cava Bare area Left lobe Ligamentum venosum in fissure Porta hepatis Right hepatic artery Left hepatic artery Right hepatic duct Left hepatic duct Cystic duct Common hepatic duct Gallbladder Fissure (b) Falciform ligament Ligamentum teres Right lobe Quadrate lobe Figure 23.25b Microscopic Anatomy of the Liver • Some functions of hepatocytes – Rough ER manufactures blood proteins – Smooth ER produces bile salts, detoxifies poisons – Peroxisomes detoxify poisons (alcohol) – Golgi apparatus packages secretory products – Mitochondria provide energy for liver processes – Glycosomes store sugar – Great capacity for regeneration Microscopic Anatomy of Liver (a) (b) Lobule Central vein Connective tissue septum Interlobular veins (to hepatic vein) Central vein Sinusoids Bile canaliculi Plates of hepatocytes Bile duct (receives bile from bile canaliculi) Fenestrated lining (endothelial cells) of sinusoids Hepatic macrophages in sinusoid walls Bile duct Portal venule Portal arteriole Portal triad Portal vein (c) Figure 23.26 The Gallbladder • Stores and concentrates bile • Expels bile into duodenum – Bile emulsifies fats • Cholecystokinin—released from enteroendocrine cells in response to fatty chyme The Gallbladder Right and left hepatic ducts of liver Common hepatic duct Cystic duct Bile duct and sphincter Accessory pancreatic duct Mucosa with folds Gallbladder Major duodenal papilla Hepatopancreatic ampulla and Duodenum sphincter Tail of pancreas Pancreas Jejunum Main pancreatic duct and sphincter Head of pancreas Figure 23.19 The Pancreas • Exocrine function – Acinar cells make, store, and secrete pancreatic enzymes – Enzymes are activated in the duodenum • Endocrine function – Produces insulin and glucagon – Regulates blood sugar The Exocrine Pancreas: Histology Diaphragm Liver Spleen Pancreas Tail Body Head Duodenum Acinar cells (b) Photomicrograph of the exocrine acinar cells of the pancreas (160) Small duct Acinar cells (a) Dissection illustrating the pancreas and its relationship to surrounding organs in the superior abdomen Basement membrane Zymogen granules Rough endoplasmic reticulum (c) Illustration of the pancreatic acinar cells Figure 23.27 Peptic Ulcers • Are erosions of the mucosa of a region of the alimentary canal • Gastric ulcers – Occur in pyloric region of the stomach • Duodenal ulcers – Occur in duodenum of the small intestine Peptic Ulcers • Caused by Helicobacter pylori • H. pylori – Acid-resistant – Binds to gastric epithelium • Induces oversecretion of acid and inflammation Peptic Ulcers Bacteria Mucosa layer of stomach (a) A gastric ulcer lesion (b) H. Pylori bacteria Figure 23.28 Disorders of the Digestive System • Intestinal obstruction – Mechanical obstructions • Adhesions, tumors, or foreign objects – Nonmechanical obstruction • Halt in peristalsis – Trauma – Intestines touched during surgery Disorders of the Digestive System • Inflammatory bowel disease – Inflammation of intestinal wall • Crohn’s disease • Ulcerative colitis • Viral hepatitis – Jaundice and flu-like symptoms – Major types—A, B, C, and G Disorders of the Digestive System • Cystic fibrosis and the pancreas – Pancreatic ducts become blocked with mucus • Clogged ducts prevent pancreatic juices from entering small intestine • Leads to malabsorption of fats and other nutrients