Lower Digestive Tract Histology PDF

LOWER DIGESTIVE TRACT Feriha Ercan, PhD. Dept. Histology&Embryology  LOWER DIGESTIVE TRACT Comprises: Stomach Small intestine (duodenum, jejunum, ileum) Large intestine (caecum, appendix, colon, rectum)  Several processes of the digestive tract (DT): Digestion of food...

LOWER DIGESTIVE TRACT Feriha Ercan, PhD. Dept. Histology&Embryology  LOWER DIGESTIVE TRACT Comprises: Stomach Small intestine (duodenum, jejunum, ileum) Large intestine (caecum, appendix, colon, rectum)  Several processes of the digestive tract (DT): Digestion of food material Absorbtion of the end products of digestion Absorbtion of ingested fluids and reabsorbtion of secreted fluid The Layers of DT: Tunica mucosa: epithelium lamina propria muscularis mucosa Tunica submucosa Tunica muscularis:Two layers of smooth muscle (3rd. Layer in stomach) Inner circular (arranged spirally) Outer longitudinal (more elongated helix) Tunica adventitia (serosa)  MUCOSA Epithelium Lamina propria: loose CT Blood & lymph vessels Glands Lymphoid nodules (MALT) Muscularis mucosae (smooth muscle) Inner circular layer Outer longitudinal layer  In sub mucosa it is impossinle. To see glands though out SUBMUCOSA garstointestinal tracts Dense, irregular fibroelastic CT layer No gland (except esophagus & duodenum) Blood & lymph vessels Meissner’s plexus (component of enteric nervous system)  A patient vists Er with stab move injury in the GI tract the parasympathetic innervation is MUSCULARIS EXTERNA damaged which layer is most likely damaged Usually inner circular & outer longitudinal SM (except esophagus) Responsible for peristaltic activity Auerbach’s myenteric plexus between SM layers Regulates activity of ME & to a limited extent, the mucosa Postganglionic parasympathetic nerve cell bodies  SEROSA & ADVENTITIA ME is enveloped by a thin CT layer that may or may not be surrounded by simple squamous epithelium of visceral peritoneum. If the region of the alimentary canal is intraperitoneal, it is invested by peritoneum, and the covering is known as the serosa. If the organ is retroperitoneal, it adheres to the body wall by dense irregular CT, and known as the adventitia. Esophagus Copyright © McGraw-Hill Companies  ESOPHAGUS ~ 25 cm Mucosa: longitudinal folds with grooves, causing lumen to appear to be obstructed Folds disappear when it is distended & lumen becomes patent  MUCOSA Epithelium Stratified squamous nonkeratinized epithelium Lamina propria Mucosal glands Muscularis mucosae Single layer of longitudinal SM fibers  SUBMUCOSA Dense, fibroelastic CT Esophageal glands proper Submucosal plexus MUSCULARIS EXTERNA & ADVENTITIA Inner circular & outer longitudinal layers Both skeletal & smooth muscle fibers Upper 1/3: mostly skeletal m. Middle 1/3: both skeletal & smooth m. Lower 1/3: only smooth m. Auerbach’s plexus: between inner circular & outer longitudinal SM layers Adventitia: until esophagus pierces diaphragm, then it is covered by serosa Trachea and Esophagus This is a normal esophagus with the usual white to tan smooth mucosa seen at the left. The gastroesophageal junction (not an anatomic sphincter) is at the center, and the stomach is at the right. The upper GI endoscopic view of the transition from str. squamous mucosa to pink columnar mucosa is seen below. This is normal esophageal squamous mucosa at the left, with underlying submucosa containing mucus glands and a duct surrounded by lymphoid tissue. The muscularis is at the right. DT Epithelial and Glandular Formations increase the surface Intrusion of folding of epithelium (villi or plicae) Inversion of epithelium to form tubular structures (pits or cripts) Formation of complex glands within or exterior to the tract lumen Localised thickenings of muscle in the bowel wall act as valves and are called sphincters. The sphincters of the DT: Esophagogastric sphincter Pyloric sphincter Ileocecal valve Internal anal sphincter Immunologic defence against antigens ingested in the digestive tract is provided by gut-associated lymphoid tissue (GALT) GALT Innervation of the Gut Intrinsic innervation: Submucosal (Meissner’s) plexus Myenteric (Auerbach’s) plexus Extrinsic innervation: Parasympathetic (stimulatory) Sympathetic (inhibitory)  STOMACH Esophagogastric sphincter Cardia Fundus Body Pylorus Pyloric sphincter Areas of the stomach  STOMACH Food is converted into chyme by the secretions of gastric mucosa Gastric mucosa secrets A dilute solution hydrochloric acid Proteolytic enzymes, mainly pepsin Rennin, gastric lipase Mucins Many hormones (gastrin etc.) Esophagus Stomach Esophagogastric junction  There are three layers of muscle in the stomach wall. Oblique muscle fibers presence as the innermost layer of the muscularis externa. When contracted the mucosa is thrown up into the longitudinal folds called rugae. The cell types of the gastric epithelium What are sturcures seen in gastric Mucous cells epithelium ? Surface mucous cells Neck mucous cells Acid producing cells (oxyntic or parietal cells) Enzyme producing cells (chief or peptic cells) Stem cells Enteroendocrine cells Gastric Mucosa can be divided into 3 histologic zones Superficial zone (Surface mucous cells, faveolae, pits, cripts) Neck zone (Stem cells, neck mucous cells) Deep zone (Glands) Cardiac mucosa Body mucosa Pyloric mucosa SZ SZ SZ NZ NZ NZ DZ DZ DZ Muscularis mucosa Muscularis mucosa Muscularis mucosa Light micrograph of gastric mucosa SEM micrograph of gastric mucosa Mucous cells  Parietal cell Chief and parietal cells Parietal cell Deep microvilli lined canaliculus HCl and intrinsic factor (bind vitamin B12, absence results in Vit B12 deficiency and consequent «pernicious anemia») Electron micrographs Chief cell Pepsinogen secreting cells CC EC CC CC EC PC CC EC: Enteroendocrine cell, CC: Chief cell; PC: Parietal cell. Electron micrographs Endocrine cells -Diffuse neuroendocrine cells (DNES) -Gastroenteropancreatic (GEP) cells -Amine Precursor Uptake and Decarboxylation (APUD) cells -Enterochromaffin cells, argentaffin Endrocrine cell IHC, light micrograph cells or argirophil cells -They have 2 types Open type Close type - Secrete gastrin, bombesin, VIP etc. Electron micrograph Gastric ulcer  SMALL INTESTINE Brunner’s gland Histology of the small intestine Plicae Transverse folds of the intestinal lining Villi Fingerlike projections of the mucosa Lacteals Terminal lymphatic in villus Intestinal glands (Cript’s of Lieberkuhn) Lined by enteroendocrine, goblet and stem cells ME: Inner circular and auter longitudinal SM Auerbach’s myenteric plexus between 2 layers Peristaltic activity Entire small intestine invested by serosa (except 2nd and 3rd parts of duodenum, which have adventitia) Small Intestine Duodenal glands Branched tubuloalveolar glands (Brunner’s glands) secrete mucus, alkaline fluid Helps neutrolize acidic chyme Secrete hormone urogastron Inhibits production of HCl by directly inhibiting parietal cells Ileum aggregated lymphoid nodules (Peyer’s patches) Jejunum Villi are tongue shaped. Absence of Brunner’s glands.  Villi Villus SEM MICROGRAPHS OF SMALL INTESTINE Enterocytes  Small Intestine Cells of the Epithelial layer Enterocytes Mucous cells (Goblet cells) Paneth cells (defensin) Endocrine cells (serotonin, enteroglukagon, somatostatin, secretin, gastrin, motilin, vasoactive intestinal peptide (VIP) Stem cells Muscular Layer Inner circular layer Outer longitudinal layer Light micrographs 1: Microvillus, 2: Apical cytoplasm, 3, 4 and 5: lateral junctions. Electron micrograph ENTEROCYTES Electron micrographs Paneth cells Produce antibacterial agent lysosyme, defensive protein-defensin-, TNF-alpha Cript of Lieberkühn GOBLET CELLS Unicellular glands Produce musinogen, whose hydrated form is mucin, a component of mucus. Electron micrographs Endocrine cell Electron micrograph M Cells (Microfold Cells) Believed to belong to mononuclear phagocyte system of cells Sample, phagocytose, transport antigens in intestinal lumen to LP Electron micrograph Copyright © McGraw-Hill Companies Gluten enteropathy Functions of the large intestine Reabsorb water and compact material into feces Absorb vitamins produced by bacteria Store fecal matter prior to defecation  LARGE INTESTINE The part of Large Intestine Cecum Ascending, transverse and descending colon Sigmoid colon Rectum The cells of Epithelial Layer Columnar cells Mucous cells (Goblet cells) Endocrine cells a:columnar cell, b: goblet cell, c: muscularis mucosa (chromogranin, substance P, somatostatin, glukagon) Stem cells Histology of the large intestine Absence of villi Presence of goblet cells Deep intestinal glands without Paneth cells a:columnar cell, b: goblet cell, c: muscularis mucosa  Apendix Mucosa Submucosa Muscular layer Adventitia 10-year-old child appendix 36-year-old man appendix  COLON LP, MM & submucosa resemble those of small intestine ME is unusual in that outer longitudinal layer is not of continuous thickness along surface; instead, most of it is gathered into 3 narrow ribbons of muscle fascicles (taeniae coli) Constant tonus maintained by taeniae coli puckers large intestine into sacculations called haustra coli. Serosa displays numerous fat-filled pouches called appendices epiploicae.. COLON Scanning electron micrograph Ulcerative colitis Hirschsprung’s disease  The rectum Last portion of the digestive tract Terminates at the anal canal Internal and external anal sphincters  ANAL CANAL submucosa circular muscle internal rectum longitudinal hemorrhoidal muscle plexus anal column junctional zone of epithelium internal anal sphincter pectinate line fibroeleastic anal canal septum external hemorrhoidal anal skin external anal plexus sphincter Stratified squamous epithelium Simple columnar epithelium Questions 1) Match the left column with the right column. I. Acid production a- Duedenum II. Mucus production b- Ileum III. Pepsinogen production c- Paneth cell IV.Defensin production d- Chief cell V. Peyer’s patch e- Goblet cell VI.Bruner’s gland f- Parietal cell a) I-d, II-e, III-f, IV-c, V-b, VI-a b) I-c, II-d, III-f, IV-e, V-b, VI-a c) I-f, II-e, III-d, IV-c, V-b, VI-a d) I- e II-f, III- c, IV-d, V-b, VI-a e) I-a, II-c, III-e, IV-d, V-b, VI-f 2) Which one of the statements written below is not true for the organ, the cell type and cell product? Organ Cell Type Cell product a) Stomach Mucous surface cell Mucus b) Stomach Mucous neck cell Mucus c) Small intestine Enterocyte Lipase d) Small intestine Neuroendocrine cell Pepsinogen e) Large intestine Goblet cell Mucus