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Histology of gastrointestinal tract

The mucose membrane lining of gastrointestinal tract is stratified squamous epithelium at the esophagus which slowly convert into simple columnar epithelium at the stomach until the anus it converts back into the stratified squamous epithelium at the lower half of the anal canal. The stratified epithelium is a wear and tear epithelium.

As it passes down from the small to large intestine, goblet cells increase because as it passes down water was absorb, goblet cells function to produce mucous.

This is just a rough idea, for better slides with more reference please PM the author at davidgqf@gmail.com.

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Histology of gastrointestinal tract

  1. 1. HISTOLOGY OF GASTROINTESTINAL TRACT By: Gan Quan Fu, PT, MSc Anatomy (Batch 3)
  2. 2. Content 1. Introduction 2. General Structure 3. Histology of: 1. Oral Cavity 2. Esophagus 3. Stomach 4. Small Intestine 5. Large Intestine 6. Appendix 7. Salivary Gland 8. Liver 9. Gall Bladder 10. Pancreas 4. Medical Application
  3. 3. Introduction Gastrointestinal Tract Digestive Tracts Oral Cavity Esophagus Stomach Small & Large Intestines Rectum Anus Associated Glands Salivary Glands Liver Gall Bladder Pancreas
  4. 4. General Structure of Digestive Tract Common Characteristics: o Hollow tube composed of a lumen whose diameter varies. o Surrounded by a wall made up of 4 principal layers: • Mucosa o Epithelial lining; A lamina propria of loose connective tissues rich in blood, lymph vessels and smooth muscle cells; Muscularis mucosae. • Submucosa o Dense connective tissues with many blood and lymph vessels. • Muscularis o Contains smooth muscle cells, divide into 2 layers; internal (circular); external (longitudinal) • Serosa o Thin layer of loose connective tissue rich in blood and lymph vessels and adipose and single squamous covering epithelium (mesothelium)
  5. 5. Oral Cavity Stratified Squamous Epithelium Keratinized Protects Oral Mucosa from damage during masticatory function. In Gingiva and Hard Palate Lamina Propria has several papillae and rest directly on bony tissue Non Keratinized Covers soft palate, lips, cheeks and floor of mouth Lamina Propria has Papillae, similar to those in dermis of skin and continuous with submucosa containing diffuse small salivary gland
  6. 6. Oral Cavity • Tongue o Papillae • Filiform • Fungiform • Foliate • Circumvallate • Pharynx • Teeth and Associate Structures o Dentin o Enamel o Pulp o Periodontium
  7. 7. Tongue • Mass of striated muscle covered by a mucous membrane. • Muscle fibers cross on another in 3 planes, they are grouped in bundles, usually separated by connective tissue. • Dorsal Surface  Irregular; Thicker epithelium; Covered anteriorly by a great number of small eminences papillae; Separated from anterior two thirds by a V-shaped boundary. • Ventral Surface  Epithelium on this surface is thinner.
  8. 8. Tongue
  9. 9. Papillae of Tongue
  10. 10. Papillae of Tongue • Filiform Papillae o Conical Shape o Numerous and present over entire surface of tongue o Their epithelium does not contain taste bud and is Keratinized. • Fungiform Papillae o Resemble mushrooms (narrow stalk and smooth surface, dilated upper part) o Contain scattered taste buds on upper surfaces o Irregularly interspersed among filiform papillae. • Foliate Papillae o Poorly developed in humans o 2 or more parallel ridges and furrows on the dorsolateral surface of tongue o Contain many taste buds
  11. 11. Papillae of Tongue • Circumvallate Papillae o 7 – 12 extremely large circular papillae whose flattened surface extend above other papillae (Papillae surrounded by deep circular furrows). o Distribute in the V region at the junction of the anterior 2/3rd and posterior 1/3rd of tongue. o The epithelium is smooth on the lateral surface of papillae o Great number of taste buds present along sides of these papillae. • Taste Buds o Onion shaped structures containing 50 – 100 cells. o Rests in Basal Lamina o Apical portion project microvilli that poke through an opening called taste pore. o 2types of cells are distinguished in relation to taste buds • Supporting or sustentacular cells • Neuroepithelial or gustatory cells
  12. 12. Taste Bud • SUSTENTACULAR OR SUPPORTING CELLS o Arranged peripherally, curved course, narrow at each end and broader in the centre appearing spindle shaped. o At both ends the cells surround small openings known as external and internal pores. • NEUROEPITHELIAL OR GUSTATORY CELLS o Distributed between the sustentacular cells long narrow, having slender red shaped form with a nucleus in the middle. o On the free surface, these cells gives rise to short hair which project into the lumen of the pit. o The substances to be tasted gets dissolved in the saliva, stimulate the hairs in the neuroepithelial cells and the impulses is conducted along the nerves (sweet, bitter, sour, salty)
  13. 13. Pharynx • Lined by Stratified non keratinized squamous epithelium in region continuous with esophagus. • Lined by ciliated pseudostratified columnar epithelium containing goblet cells in region close to nasal cavity. • Contains tonsils. • Mucosa of pharynx also has many small mucous salivary glands in its lamina propria • Compose of dense connective tissues.
  14. 14. Esophagus
  15. 15. Esophagus • Muscular Tube function to transport food stuffs from mouth to stomach • Covered by non keratinized stratified squamous epithelium. • In general same layers as rest of digestive tract. • In submucosa  groups of small mucous secreting glands (esophageal glands) secretion facilitated transport of food stuff and protects mucosa. • Lamina Propria near stomach  groups of gland (esophageal cardiac gland) secrete mucus • Distal end muscular layer  Only smooth muscle • Mid Portion  Mixture of striated and smooth muscle • Proximal end  Only striated muscle cells • Portion in peritoneal cavity covered by serosa • The other portion covered by layer of connective tissue, adventitia that blends into surrounding tissue.
  16. 16. LoweresophagusUpperesophagus
  17. 17. Stomach
  18. 18. Stomach • Mixed exocrine endocrine gland. • Divides into 4 regions: o Cardia o Fundus o Body o Pylorus • Fundus and body are identical in microscopic structure. • Mucosa and submucosa of undistended stomach lie in longitudinally directed folds known as rugae.
  19. 19. Gastric Mucosa • Consists surface epithelium invaginates to various extend into lamina propria forming gastric pits. • Lamina propria of stomach composed of loose connective tissue interspersed with smooth muscle and lymphoid cells. • Muscularis mucosae to separate mucosa from underlying submucosa • Epithelium lining the pits and covering the surfaces are simple columnar epithelium & all cells secrete alkaline mucus.
  20. 20. Gastro-esophageal Junction
  21. 21. Stomach (Cardia) • Mucosa contains simple or branched tubular cardiac glands • Terminal portion of these glands are frequently coiled, often with large lumens. • Similar in structure to cardiac glands of the terminal portion of esophagus.
  22. 22. Stomach (Fundus & Body) • Simple columnar surface epithelium extends into gastric pits into which opens into gastric glands. • Lamina propria consist of fine reticular and collagen fibres fills the spaces between the packed gastric glands. • Each gastric gland has 3 distinct region: o Isthmus o Neck o Base • Isthmus contains differentiating mucous cells and undifferentiated stem cells and parietal cells. • Neck consist of stem, mucous neck and parietal cells. • Base contains parietal and chief (zymogenia) cells. • The muscularis mucosa composed of inner circular and outer longitudinal smooth muscle.
  23. 23. Stomach (Pylorus) • Deep gastric pits into which the branched tubular pyloric glands open. • The epithelium of the mucous membrane consist of tall columnar cells which lines the deep pits and short glands. • Longer pits and shorter coiled secretory portion compare to glands in cardiac region. • The acini of pyloric glands and their ducts are in lamina prorpia. • G (Gastrin) cells are enteroendocrine cells intercalated among mucous cells of pyloric glands. • D cells secrete Somatostatin • The muscularis externa is made up of thick circular muscle to form pyloric sphincter which helps to control emptying of the stomach.
  24. 24. Small Intestine Duodenum Jejunum Ileum
  25. 25. Small Intestine • 4 layers: 1. Mucosa 2. Submucosa 3. Muscularis externa 4. Serosa • Surface area of small intestine increased by 1. Length of small intestine 2. Valves of Kerkring/ Plica Circularis 3. Villi 4. Microvilli 5. Cypts Of Lieberkuhn
  26. 26. Mucosa of Small Intestine
  27. 27. Valves of Kerkring • Also known as Plica Circulares • Permanent submucosal circular folds • Large, seen with naked eye • Prominent in duodenum & jejunum • Less marked in ileum • Significance: o Increases surface area o Slow down the passage of contents
  28. 28. Villi • Central lacteal (lymphatic vessel) • Core capillaries • Core of connective tissue • Epithelial cells – Tall columnar with striated border
  29. 29. Crypt of Lieberkuhn (Intestinal gland) • Invaginations of lining epithelium into lamina propria • Wall of crypt is lined by the following cells: 1. Columnar cells 2. Goblet cells 3. Undifferentiated stem cells 4. Paneth / Zymogen cells 5. Argentaffin cells
  30. 30. Crypt of Lieberkuhn • Absorptive columnar cells / Enterocytes o Microvilli which give it a striated border appearance • Goblet cells o Secretes mucus • Undifferenciated cells o Actively multiply, move upwards give rise to other cells
  31. 31. Crypt of Lieberkuhn • Paneth cells / Zymogen cells o Seen in deeper parts of crypts o rich in Zinc, secrete lysozyme that destroys bacteria • Endocrine cells o Seen near lower ends of crypts o Argentaffin cells o Entero-chromaffin cells o APUD cells – secrete serotonin
  32. 32. Submucosa of Small Intestine
  33. 33. Brunner’s Gland • In duodenum (Also known as duodenal glands) • Clusters of ramified, coiled tubular glands that opens into the intestinal crypts. • Cells are mucous type. • Secretions are distinctly alkaline (PH8.1 – 9.3), to protect duodenal mucous membrane from effects of acid gastric juice and to brings intestinal contents to optimum PH for pancreatic enzyme action.
  34. 34. Peyer’s Patches • Lymphoid Nodules. • Present in ileum, more prominent in terminal ileum. • In lamina propria and submucosa • Dome shaped area devoid of villi • Instead of absorptive cells, its covering epithelium consist M cells.
  35. 35. Differences between duodenum, jejunum & ileum Duodenum Jejunum Ileum Epithelium Columnar Striated border Few goblet cells Columnar Striated border goblet cells+ Columnar goblet cells++ Villi Broad Spatula Shaped Closely packed Tongue-shaped Different heights Few thin finger- shaped Lamina Propria Crypts+ No Peyer’s patches Crypts+ Diffuse infiltration of lymphocytes No Peyer’s patches Crypts+ Peyer’s patches extend into submucosa Submucosa Mucus secreting Brunner’s glands Only connective tissues and blood vessels Peyer’s patches
  36. 36. Large Intestine • Consists mucosal membrane with no folds except in its distal (rectal) portion. • No vili are present • Long intestinal glands • Great abundance of goblet and absorptive cells • Small number of enteroendocrine cells. • Fibers of outer longitudinal layer congregates in 3 thick longitudinal band (Teniae coli). • Serous layer characterized by small, pendulous protuberances composed adipose tissues (appendices epiploicae) • Mucous membrane forms a series of longitudinal folds (rectal columns of morgagni)
  37. 37. Appendix • Evagination of cecum • Small, narrow and irregular lumen caused by presence of abundant lymphoid follicles in its wall. • Although general structure similar to large intestine, it contains fewer and shorter intestinal glands and has no teniae coli.
  38. 38. Small Vs Large Intestine Small intestine Large intestine Villi 1. Crypts shallow 2. Goblet cells less 1. Absence of villi 2. Crypts deeper, More Goblet cells Longitudinal muscle coat of muscularis externa 1. Uniformly thick 1. Three bands of Taenia coli
  39. 39. Histology of Accessory Organs of GIT
  40. 40. Salivary Gland 3 pairs of salivary glands: 1. PAROTID GLAND • Purely serous (few mucous acini maybe present) 2. SUBMANDIBULAR GLAND • Mixed, Predominantly serous 3. SUBLINGUAL GLAND • Mixed, Predominantly mucous
  41. 41. General Features • Serous cells o Pyramidal in shape o Broad base resting on basal lamina o Narrow apical surface with short irregular microvilli facing lumen o Secretory cells are joined together by junctional complex and usually form spherical mass of cells called acinus • Mucous Cells o Usually cuboidal to columnar o Oval nuclei pressed towards bases of the cells o Most often organized as tubules, consisting of cylindrical arrays of secretory cells surrounding a lumen.
  42. 42. General Features • Duct System o Intralobular ducts • Intercalated Ducts o Lined by Cuboidal Epithelial Cells o Ability to differentiate into secretory or ductal cells • Striate Ducts o Radial striations seen to consist infoldings of basal plasma membrane with numerous elongated mitochondria o Drains into Interlobular Ducts o Interlobular Ducts (Excretory Ducts) • Initially lined with pseudo stratified or stratified cuboidal epithelium. • Distal parts lined with stratified columnar epithelium consisting few mucus secreting cells • Ultimately empties into oral cavity and lined by nonkeratinized-stratified squamous epithelium.
  43. 43. Characteristics • Parotid Gland o Branched acinar glands o Surrounded by a capsule from which arise numerous interlobular connective tissue septa that subdivides the gland into many lobes and lobules. o Located in the connective tissue septa between the lobules are arteriole, venule and interlobular excretory ducts. • Submandibular Gland o Presence of both serous and mucous acini. o Mucous acinus are larger than the serous. o Between the mucous cells and basement membrane are half moon shaped granules known as demilunes of Gianuzzi. • Sublingual Gland o Similar as Sub mandibular o Intralobular ducts are not as well developed as in other major salivary gland
  44. 44. Liver • Repeating hepatic lobules (Hexagonal Unit). • Central Vein in the centre of each hepatic lobule. • Portal canals (Portal Traids) in periphery the surrounding connective tissue [Branches of the hepatic artery, hepatic portal vein, bile duct, and lymph vessels seen.] • Hepatic sinusoids (dilated blood channels) contains epithelial cells and macrophages called “Kupffer cells” • The hepatic sinusoids separated from the underlying hepatocytes by subendothelial perisinusoidal space of Disse. • The major exocrine functions of hepatocytes is synthesis and release about 500-1200ml of bile per day which is delivered to the gallbladder via the bile canaliculli.
  45. 45. Gall Bladder • It consist of mucosa composed of Simple columnar epithelium and lamina propria; a layer of smooth muscle; a perimuscular connective tissue layer and a serous membrane. • Mucosa has abundant folds that are particularly evident when gall bladder is empty. • Epithelial cells are rich in mitochondria • Surrounding the bundle of smooth muscle fibres is a thick dense connective tissue containing large blood vessels  artery & vein, lymphatic and nerves. • Serosa covers entire unattached gallbladder surface
  46. 46. Pancreas • Mixed endocrine and exocrine gland • Exocrine  compound acinar gland, similar in structure to parotid gland. • Distinction between 2 glands can be made based on absence of striated ducts and presence of islets of Langerhans. • Initial portions of intercalated ducts penetrate lumens of acini. • Centroacinar cells constitude interacinar portion of intercalated duct.
  47. 47. Medical Application • Gastroesophageal Reflux Disease associated with incompetent barriers at gastroesophageal junction caused by decrease in lower esophageal sphincter tone or hiatus hernia. Reflux esophagitis develops when mucosal defenses are not sufficient to protect esophageal mucosa from acid, pepsin and bile. • Stress, ingested aspirin, NSAID or ethanol can disrupt epithelial layer in stomach lead to ulceration. Ulcer is disruption of mucosal integrity leading to an excavation due to active inflammation. Apirin and ethanol irritates mucosa partly by reducing blood flow.
  48. 48. References • Junquiera, L. C. (2005) Basic Histology text & Atlas, 11th edn. McGraw Hill, New York.
  49. 49. Thank You