1. Digestive tract Digestive tract Li Zhong Jie （李仲杰）, Ph. D School of Medicine,Zhejiang University

2. ---Digestive system: Digestive tract Digestive tract Digestive gland Digestive gland ---Digestive system function: ---Digestive system function: This system is responsible for the mechanical and chemical breakdown of food material, and for absorbing these digestive products into the blood for use as nutrients by the individual cells and tissues of the body This system is responsible for the mechanical and chemical breakdown of food material, and for absorbing these digestive products into the blood for use as nutrients by the individual cells and tissues of the body

3. The Digestive Process Ingestion Ingestion –Taking in food through the mouth Propulsion (movement of food) Propulsion (movement of food) –Swallowing – Peristalsis – propulsion by alternate contraction &relaxation Mechanical digestion Mechanical digestion –Chewing –Churning in stomach –Mixing by segmentation Chemical digestion Chemical digestion –Carbohydrates, Fat, and Proteins are broken down by enzymes. Absorption Absorption –Transport of digested end products into blood and lymph in wall of canal Defecation Defecation –Elimination of indigestible substances from body as feces

4. Chemical digestion Chemical digestion –Complex food molecules (carbohydrates, proteins and lipids) broken down into chemical building blocks (simple sugars, amino acids, and fatty acids and glycerol) –Carried out by enzymes secreted by digestive glands into lumen of the alimentary canal

5. Components of digestive tract ---oral cavity ---oral cavity ---pharynx ---pharynx ---esophagus ---esophagus ---stomach ---stomach ---small intestine ---small intestine ---large intestine ---large intestine ---rectum and anus ---rectum and anus

6. General plan of digestive tract ---Except for oral cavity and pharynx, all other organs share a similar histological plan 1.Mucosa 2.Submucosa 3.Muscularis externa 4.Adventitia from lumen (inside) out from lumen (inside) out

7. 1.Mucosa 2.Submucosa 3.Muscularis externa 4.Adventitia from lumen (inside) out from lumen (inside) out General plan of digestive tract

8. Inner layer: the mucosa* (mucous membrane) Three sub-layers – Lining epithelium – Lamina propria (may contain glands) – Muscularis mucosae (Smooth muscle) *

9. More about the mucosa Epithelium: absorbs nutrients, secretes mucus Epithelium: absorbs nutrients, secretes mucus –Continuous with ducts and secretory cells of intrinsic digestive glands (those within the wall) –Extrinsic (accessory) glands: the larger ones such as liver and pancreas Lamina propria Lamina propria –Loose connective tissue with nourishing and absorbing capillaries –Contains most of mucosa-associated lymphoid tissue (MALT) Muscularis mucosae Muscularis mucosae –Thin layer of muscle producing only local movements

10. the submucosa* * – Loose C.T. containing major blood and lymphatic vessels, glands and nerves,many elastic fibers so gut can regain shape after food passes – Loose C.T. containing major blood and lymphatic vessels, glands and nerves, many elastic fibers so gut can regain shape after food passes – Meissner’s autonomic nerve plexus

11. the muscularis externa* Two layers of smooth muscle responsible for peristalsis and segmentation Inner circular layer (circumferential) Inner circular layer (circumferential) – Squeezes – In some places forms sphincters (act as valves) Myenteric (Auerbach’s) autonomic nerve plexus Myenteric (Auerbach’s) autonomic nerve plexus Outer longitudinal layer: shortens gut Outer longitudinal layer: shortens gut *

12. Smooth muscle Muscles are spindle-shaped cells One central nucleus Grouped into sheets: often running perpendicular to each other Peristalsis No striations (no sarcomeres) Contractions are slow, sustained and resistant to fatigue Does not always require a nervous signal: can be stimulated by stretching or hormones

13. Tunica adventitia Tunica adventitia – Fibrosa or serosa (covered by mesothelium)

14. Nerves Enteric nervous system: the gut’s own Enteric nervous system: the gut’s own –Visceral plexuses within gut wall controlling the muscles, glands and having sensory info Muscularis external: Myenteric (Auerbach’s) plexus Muscularis external: Myenteric (Auerbach’s) plexus Submucosal: Meissner’s autonomic nerve plexus Submucosal: Meissner’s autonomic nerve plexus –100 million neurons! (as many as the spinal cord) Autonomic input: speeds or slows the system Autonomic input: speeds or slows the system –Parasympathetic Stimulates digestive functions Stimulates digestive functions –Sympathetic Inhibits digestion Inhibits digestion Largely automatic Largely automatic

15. outer longitudinal Nerve plexus inner circular : regulate the movement of SM * Myenteric (Auerbach’s) plexus : regulate the movement of SM

16. Esophagus Esophagus mucosa submucosa muscularis adventitia

17. Esophagus Passage way for food from the pharynx to the stomach mucosa: epithelium: stratified squamous epithelium epithelium: stratified squamous epithelium lamina propria: compact CT contain simple tubular glands lamina propria: compact CT contain simple tubular glands muscularis mucosa: longitudinal muscularis mucosa: longitudinal arranged smooth muscle arranged smooth muscle At GE junction – thin simple columnar At GE junction – thin simple columnar epithelium epitheliumsubmucosa: LCT LCT esophageal gland: mucous gland esophageal gland: mucous gland ---acidic mucin ---acidic mucin

18. Muscularis externa: inner circular and outer longitudinal inner circular and outer longitudinal upper 1/3: skeletal muscle upper 1/3: skeletal muscle middle 1/3: mixed of skeletal muscle and smooth muscle middle 1/3: mixed of skeletal muscle and smooth muscle lower 1/3: smooth muscle lower 1/3: smooth muscle Tunica adventitia: a fibrous coat of loose connective tissue a fibrous coat of loose connective tissue

19. When empty, mucosa and submucosa lie in longitudinal folds

20. Stomach ---widest part of alimentary canal ---Temporary storage and mixing – 4 hours ---digest food partially to form a semi-fluid mass, termed chyme ---absorb part of water and ions – Water, electrolytes, some drugs like aspirin and alcohol (absorbed through stomach)

21. Stomach (regions) Cardia (Cardiac junction) Cardia (Cardiac junction) – Surrounds esophageal entrance Fundic stomach defined histologically includes Fundic stomach defined histologically includes – Fundus – Body Pylorus (Pyloric junction) Pylorus (Pyloric junction) – Pylorus is continuous with the duodenum

22. Rugae: longitudinal folds on internal surface (helps distensibility) Rugae: longitudinal folds on internal surface (helps distensibility) Muscularis: additional innermost oblique layer (along with circular and longitudinal layers) Muscularis: additional innermost oblique layer (along with circular and longitudinal layers)

23. Mucosa Mucosa – Epithelium (simple columnar mucus-secreting) – Lamina propria (gastric glands of different types) – Muscularis mucosae (Smooth muscle) Submucosa Submucosa – Loose C.T. no glands Muscularis externa Muscularis externa inner oblique, middle circular, outer longitudinal inner oblique, middle circular, outer longitudinal Tunica adventitia Tunica adventitia – Mostly serosa Stomach Histology Overview

24. mucosa Rugae Rugae – Longitudinal folds of mucosa A mucosal fold contains submucosa A mucosal fold contains submucosa Gastric pits: small depressions, 3-5 gastric gland open into the bottom Gastric pits: small depressions, 3-5 gastric gland open into the bottom Diffuse lymphoid tissue and nodules may be present Diffuse lymphoid tissue and nodules may be present Gastric pit

25. Rugae in the stomach Mucosa Muscularis mucosa Submucosa Muscularis externa Rugae

26. Cross section of gastric pits Simple columnar epithelium Gastric pit Laminia propria between pits

27. ① epithelium: simple columnar epithelium surface mucous cell: surface mucous cell: -tall columnar -ovoid, basally-located nuclei -apical mucin granule -tight junction The mucus( bicarbonate- buffered mucus) is secreted on to the epithelial surface to form a barrier layer which protects it from injury by ingested substance and the stomach’s own secretion of acid and enzymes. The mucus( bicarbonate- buffered mucus) is secreted on to the epithelial surface to form a barrier layer which protects it from injury by ingested substance and the stomach’s own secretion of acid and enzymes.

28. ② lamina propria: CT contains fibroblast, LC, plasma cell, mast cell and eosinophil, smooth muscle CT contains fibroblast, LC, plasma cell, mast cell and eosinophil, smooth muscle gastric gland (fundic gland)- oxyntic gland gastric gland (fundic gland)- oxyntic gland cardiac gland: mucous gland cardiac gland: mucous gland pyloric gland: mucous gland pyloric gland: mucous gland

29. * Fundic gland - long, straight, branched or unbranched gland

30. Three part of gland: The neck The body The base Five type cells are found: Chief cells Parietal cells Mucous neck cells Stem cells Enterendocrine cells

31. Fundic gland

32. chief cell or zymogenic cell ---structure: LM: LM: columnar columnar Round, basally-located Nuclei Round, basally-located Nuclei cytoplasm: cytoplasm: /basal-basophilic /basal-basophilic /apical-zymogen granules /apical-zymogen granules

33. EM: ---RER, Golgi apparatus ---function: secret pepsinogen (the precursor of pepsin)

34. parietal cell or oxyntic cell ---structure:LM: large, pyramidal or spherical large, pyramidal or spherical round centrally-located nuclei round centrally-located nuclei eosinophilic cytoplasm eosinophilic cytoplasm

35. EM: intracellular secretory canaliculus -invaginations tubulovesicular system mitochondria Active secreting cell Resting cell

36. ---function: i.. secret hydrochloric acid (HCl) i.. secret hydrochloric acid (HCl) synthesis processes of HCl: in intracellular secretory canaliculus in intracellular secretory canaliculus H + K + -ATP pump: get H + from cell H + K + -ATP pump: get H + from cell Cl - channel: get Cl - from blood Cl - channel: get Cl - from blood H + +Cl - →HCl H + +Cl - →HCl function of HCl: pepsinogen→pepsin pepsinogen→pepsin kill the bacteria kill the bacteria

37. ii. secret intrinsic factor: ii. secret intrinsic factor: glycoprotein + Vitamin-B 12 → absorption of glycoprotein + Vitamin-B 12 → absorption of VB 12 in ileum VB 12 in ileum result in Addison’s anaemia an deficiency of VB 12

38. mucous neck cell less, neck part less, neck part pale stain in HE stain pale stain in HE stain secrete mucus secrete mucus stem cell undifferentiated cell undifferentiated cell enterendocrine cell L cell: secreting histamine, promote secretion of parietal cell L cell: secreting histamine, promote secretion of parietal cell D cell: secreting somatostatin, inhibit the secretion of parietal cell D cell: secreting somatostatin, inhibit the secretion of parietal cell

39. * Mucous-HCO 3 barrier structure : mostly of glycoproteins rich in carohydrates and bicarbonate ions mostly of glycoproteins rich in carohydrates and bicarbonate ions 0.25-0.5mm thick mucous 0.25-0.5mm thick mucous The pH of the surface is usually 0.9-1.5 The pH of the surface is usually 0.9-1.5

40. * Mucous-HCO 3 barrier function : The mucus( bicarbonate-buffered mucus) is secreted on to the epithelial surface to form a barrier layer which protects it from injury by ingested substance and the stomach’s own secretion of acid and enzymes. The mucus( bicarbonate-buffered mucus) is secreted on to the epithelial surface to form a barrier layer which protects it from injury by ingested substance and the stomach’s own secretion of acid and enzymes. HCl P H: 0.9-1.5 HCl P H: 0.9-1.5 H + + HCO 3 - → H 2 CO 3 → H 2 O + CO 2 H + + HCO 3 - → H 2 CO 3 → H 2 O + CO 2 ↑ bicarbonatase bicarbonatase acid-base neutralization acid-base neutralization

41. Epithelial transition Epithelial transition ---Stratified Squamous nonkeratinized to simple columnar ---Stratified Squamous nonkeratinized to simple columnar It is clinically important, as it is the most site of esophageal carcinoma. It is clinically important, as it is the most site of esophageal carcinoma. Cardiac Junction

42. Small intestine Duodenum – first region, only about 25cm long, Jejunum – second region is roughly 2.5m long Ileum – last region is roughly 3.5m long Primary functions Transport food from stomach to Large intestine Transport food from stomach to Large intestine Secretion of digestive enzymes to facilitate digestion of food substances Secretion of digestive enzymes to facilitate digestion of food substances Absorption of food substances into blood and lymph vessels Absorption of food substances into blood and lymph vessels Secretion of certain hormones Secretion of certain hormones

43. Small Intestine Overview Mucosa Mucosa – Epithelium (simple columnar) – Lamina propria (intestinal glands) – Muscularis mucosae (Smooth muscle) Submucosa Submucosa – loose C.T. (contain duodenal glands in the duodenum) Muscularis externa Muscularis externa inner circular, outer longitudinal inner circular, outer longitudinal Tunica adventitia Tunica adventitia – serosa (except for the duodenum)

44. 44

45. Lymph Nodules

46. Special structure of mucosa Plicae circulares Plicae circulares – Mucosa and submucosa are arranged in permanent, circular mucosal folds Intestinal villi Intestinal villi – Mucosal projections covered by epithelium and containing only lamina propria Crypt or intestinal glands Crypt or intestinal glands – Surrounded by lamina propria – Extend to the muscularis mucosae

47. Plicae circulares villi

48. Villi

49. Epithelium (Simple columnar) Epithelium (Simple columnar) – Absorptive cells Numerous, regular microvilli form striated-border Numerous, regular microvilli form striated-border Well formed junctional complex Well formed junctional complex Plicae circulares, villi and microvilli are serve to increase the surface area of the small intestine by as much as 600-fold Plicae circulares, villi and microvilli are serve to increase the surface area of the small intestine by as much as 600-fold surface coat: a layer of glycoprotein film, protect the underlying cells from mucolytic and proteolytic agent surface coat: a layer of glycoprotein film, protect the underlying cells from mucolytic and proteolytic agent – Goblet cells :secrete mucus to lubricate and protect the epithelium – Enteroendocrine cells: produce hormones

50. striated-border

51. microvilli

52. lamina propria: LCT contains network of blood and lymph capillaries LCT contains network of blood and lymph capillaries -Carbs and proteins into blood to liver via hepatic portal vein -Carbs and proteins into blood to liver via hepatic portal vein -Fat into lymph -Fat into lymph central lacteal: lymphatic vessel, lymphatic vessel, absorb fat absorb fat

53. Crypt or small intestinal gland: the invagination of epithelium into lamina propria absorptive cell absorptive cell goblet cell goblet cell endocrine cell endocrine cell stem cell stem cell Peneth cell Peneth cell

54. Peneth cell : LM: ---pyramidal in shape, locate in basal portion of the glands, in groups ---apical: acidophilic granules- contain defensin (cryptdin), Lysozyme EM: -protein-secreting cell feature Function: related to immune function, anti-bacterial activity

55. Large intestine ---Consists of: -cecum -cecum -ascending colon -transverse colon -descending colon -sigmoid colon -rectum -anal canal --- function: absorb water and ions absorb water and ions

56. Mucosa Mucosa – No villi or plicae circulares – Glands are longer than in small intestine – Single columnar epithelium contain numerous goblet cells but absorptive cells are still present – Occasional solitary lymph nodules – At anal junction there is an abrupt transition to stratified squamous non-keratinized epithelium.

57. Submucosa Submucosa – Similar to small intestine except nerve plexus are more easily found here Muscularis externa Muscularis externa – Inner circular layer is evident – Outer longitudinal layer forms three bands, the taenia coli Adventitia Adventitia – Both serosa and fibrosa are found

58. Mucosa is like the colon except Mucosa is like the colon except – Numerous lymph nodules are present in the young – These decrease with age – They break up the muscularis mucosae so that it is difficult to find – The glands are also often not very evident. Submucosa and muscularis externa are like the rest of the colon Submucosa and muscularis externa are like the rest of the colon Appendix

59. Appendix

60. Review and exercise 1. Compare the mucosal structure of stomach with that of esophagus, small intestine and large intestine. 2. Describe the fine structure and ultra-structure of the parietal cell and chief cell in the gastric gland. 3. Describe the different formation of villi and plicae in small intestine. 4. Describe the structure of mucosa of the digestive tract.

61. Thanks for your attention!