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Lect. 13b   digestive system
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Lect. 13b digestive system


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  • "Normal epithelial tissues have a constant level of death and renewal.This image shows a gland from the small bowel mucosa.You should be able to identify the epithelial cells and mucin-containing goblet cells.You can also see two mitotic figures, representing stem-cells renewing epithelium in the gland crypt."
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    • 1. Digestive System Continuation (Digestive Tract)
    • 2. Histology of the Mucosa Organ Epithelium Mouth Nonkeratinized Stratified Squamous Pharynx Nonkeratinized Stratified Squamous Esophagus Nonkeratinized Stratified Squamous Stomach Simple Columnar Small Intestine Simple Columnar Large Intestine Simple Columnar Anus Nonkeratinized Stratified Squamous
    • 3. Histology of the Mucosa Organ Folds of the epithelium Esophagus none Stomach L: Rugae, S: gastric pits Small Intestine L: Plicae circulares, Villi S: Crypts of Lieberkuhn, microvilli Large Intestine L: Haustra S: Intestinal glands
    • 4. Histology of the Submucosa Organ Specialized structures Esophagus Esophageal gland Stomach None Duodenum Brunner’s glands Ileum Peyer’s Patches Large Intestine None
    • 5. Histology of the Muscularis Organ Smooth muscle layers Esophagus 2, circular and longitudinal Stomach 3, oblique, circular, and longitudinal Small Intestine 2, circular and longitudinal Large Intestine 2, circular and longitudinal
    • 6. Histology of the Serosa Organ Serosa Esophagus Adventitia due to the fact that the esophagus is not in a cavity Stomach Visceral Peritoneum Small Intestine Visceral Peritoneum Large Intestine Visceral Peritoneum Anus Adventitia
    • 7. Esophagus • A muscular tube whose function is to transport foodstuffs from the mouth to the stomach (peristalsis) and to prevent the retrograde flow of gastric contents (esophageal sphincter). • Peristalsis - controlled by reflexes and ANS
    • 8. 3 Regions: • Proximal end - only striated (skeletal) muscle cells. • Middle portion - mixture of striated & smooth muscle cells • Distal end - only smooth muscle cells that close to the stomach, form the lower esophageal sphincter (LES).
    • 9. Clinical Significance: GERD – gastroesophageal reflux disease • Due to weakened LES; reflux of gastric contents to the esophagus. • Excessive gastric distention – Fatty meals, smoking, and beverages such as tea and coffee (with high xanthine content) also cause relaxed LES.)
    • 10. • Mucosa: Non-keratinized stratified squamous epithelium. • Submucosa: Esophageal glands (mucus- secreting) facilitates the transport of foodstuffs and protects the mucosa. • Lamina propria: Cardiac glands – near junction between esophagus and stomach (mucus-secreting)
    • 11. Esophagus , l.s.
    • 12. Esophagus
    • 13. Esophageal Gland • Mucous secreting • Similar to salivary glands • Aid lubrication of bolus • Most prominent in the upper and lower thirds of the esophagus
    • 14. Esophagus
    • 15. • Tunica muscularis (muscularis externa) • Tunica serosa – covers esophageal portion in peritoneal cavity • Tunica adventitia – covers the rest of the upper esophagus that blends into the surrounding tissue.
    • 16. STOMACH • Bean-shaped hollow muscular organ of the gastro-intestinal tract involved in the second phase of digestion • It has four anatomical parts: cardia, fundus, corpus (body) and pylorus • It has three histological distinct parts: (1) cardia, (2) the fundus and the body have the same histological properties (3) pylorus
    • 17. Epithelium • Simple columnar epithelium invaginates into the lamina propria, thereby it makes gastric pits Gastric pits (Foveolae) empties into branched tubular glands (cardiac, gastric, and pyloric) characteristic of each region of the stomach.
    • 18. Lamina Propria • loose connective tissue, which may contain many lymphocytes • all the gastric glands are located in this lamina Muscularis mucosae • well-developed, usually is composed of two sublayers • of smooth muscle cells
    • 19. stomach
    • 20. Structure of gastric glands
    • 21. Branched tubular gastric glands • cardiac -, fundic- and pyloric glands • in the three histological portions of the stomach the glands display somewhat different morphology; their products are also different Parts of a gastric gland: – 1. Isthmus – small canal (opening) – 2. Neck - passageway – 3. Base – glandular area
    • 22. The three functional regions of the stomach. The regions have different luminal secretions and patterns of smooth muscle activity indicative of their unique functions in response to food.
    • 23. A. Representation of the structure of the gastric mucosa showing a section through the wall of the stomach. B. Detail of the structure of gastric glands and cell types in the mucosa
    • 24. Cell types in the stomach Glandular Epithelium: • Simple columnar cells • Chief cells • Parietal cells • Enteroendocrine cells – G cells – D cells
    • 25. Columnar cells • All columnar cells - secrete an alkaline mucus consists primarily of water (95%), lipids, and glycoproteins, which, in combination, form a hydrophobic protective gel. • Surface epithelial cells – secretes bicarbonate into the mucous gel. • Mucous gel - pH 1 at the gastric luminal surface - pH 7 at the epithelial cell surface - the mucus firmly adherent to the epithelial surface is very effective in protection, while the superficial luminal mucous layer is more soluble, partially digested by pepsin and mixed with the luminal contents.
    • 26. Chief cells (or zymogenic cells) • Chief cells (or zymogenic cells) – most numerous cells; location: body of the gastric glands – produce pepsinogen (precursor of pepsin, proteolytic enzyme); pH optimum of pepsin = about 2 (break down collagen)
    • 27. Parietal cells (or oxyntic cells) – most frequent (in neck of the glands, reaching the lumen of the gland) situated deeper, between and below chief cells, in lower parts of the gland. – secrete the hydrochloric acid of the gastric juice. Aside from activating the pepsinogen the hydrochloric acid also effectively sterilizes the contents of the stomach. – secrete intrinsic factor, which is necessary for the resorption of vitamin B12.
    • 28. Clinical Significance • Pernicious Anemia – Vit.B12 Deficiency • This condition may result from a destruction of the gastric mucosa by e.g. autoimmune gastritis or the resection of large parts of the lower ileum, which is the main site of vitamin B12 absorption, or of the stomach. • Vitamin B12 - cofactor of enzymes which synthesize tetrahydrofolic acid, which is needed for the synthesis of DNA components. An impairment of DNA synthesis will affect rapidly dividing cell populations, among them the hematopoietic cells of the bone marrow (pernicious anemia).
    • 29. • Helicobacter pylori - so far only one type of bacteria has found which can live happily in the stomach - Unfortunately, they are involved in the pathogenesis of gastritis and gastric ulcers.
    • 30. Enteroendocrine cells • scattered, usually solitary, throughout the epithelium of the gastrointestinal tract • G cells - most frequent in the middle third of the glands; stimulate secretion of acid and pepsinogen; stimulated by nervous input, the distension of the stomach or secretagogues. • D cells - mainly in glands of the pyloric antrum; inhibit G cells and thereby acid production; stimulated by acid in the lumen of the stomach and duodenum.
    • 31. • Enteroendocrine cells (apex: microvilli) • The best characterized endocrine cells in the gastric mucosa are gastrin-producing cells (G cells) and somatostatin-producing cells (D cells).
    • 32. Stomach: Pyloric-duodenal junction
    • 33. Small Intestines
    • 34. Small intestine
    • 35. Villus Enterocytes – tall columnar cells; the main absorptive cells.
    • 36. Crypts of Lieberkühn • Simple tubular glands • in between intestinal villi e • extends through the lamina propria down to the muscularis mucosae. • secretes "intestinal juice" (about 2 liter/day), closely resembles ECF, which is rapidly reabsorbed. • The intestinal juice enzymes are enteropeptidase (or enterokinase), which activates the pancreatic enzyme trypsin, and small amounts of amylase.
    • 37. Crypts of Lieberkuhn
    • 38. Cell proliferation Small intestine mucosa – instestinal gland
    • 39. Secretory cells of Intestinal Gland • Goblet cells – produce mucin for the lubrication of the intestinal contents and protection of the epithelium. • Paneth cells – located at the bottom of the crypts; • produce antimicrobial peptides known as defensins (lysozyme), which provide the first line of defense against any disease producing microbes. involved in the control of infections (maintains normal flora)
    • 40. Other cells in the intestinal gland • Enteroendocrine cells – produce locally acting hormones which regulate gastrointestinal motility and secretion. • Enterocytes – tall columnar cells; the main absorptive cells. • Mitotic cells – stem cells; divide continuously to replenish all of the above four cells.
    • 41. • Lamina propria: similar to the lamina propria of the stomach; – with larger lymph nodules (Peyer’s patches) • Muscularis mucosae: 2 muscle layers and extends into the intestinal villi, where the smooth muscle cells form a longitudinal bundle in the center of the villi.
    • 42. Duodenum • Submucosa – (+) glands only in the (Brunner's glands). • Brunner’s gland – Secretion: mucous and slightly alkaline due to bicarbonate ions (pH 7-8). • The amount of bicarbonate is however too low to neutralize the acidic contents of the duodenal lumen. Instead, the secretion of Brunner's glands protects the duodenal mucosa - similar to the mucus which protects the gastric mucosa.
    • 43. • Submucosal glands – Brunner’s gland
    • 44. Jejunum • Plicae circulares (lined with long intestinal villi) • Surface epithelium: (+) simple columnar with goblet cells, intestinal crypts, muscularis mucosae, submucosa and muscularis externa. • Intestinal Crypts - fairly short and narrow. • Do not have Peyer’s patch
    • 45. • Plicae circularis
    • 46. Jejunum
    • 47. ILEUM ILEUM • Tall villi • Thin submucosa • Tunica serosa – well-defined (mesothelium)
    • 48. Ileum – with Peyer’s patch • Accumulations of lymphocytes are common in the mucosa of the GIT, and they occur frequently in the small intestine to facilitates their function in the immune-defense of the body against possible pathogens in the lumen of the intestine.
    • 49. Ileum
    • 50. Colon (Large Intestine/Bowel) • Constitutes the terminal part of the digestive system. • 3 main sections: cecum (including the appendix), colon, and rectum (with the anal canal) • Primary function: Reabsorption of water and inorganic salts. • Mucus - the only important secretion (lubricant for transport of the intestinal contents)
    • 51. Large Intestine: • Mucosa – Surface is relatively smooth – No plicae circulares or intestinal villi. – Crypts of Lieberkühn are present and usually longer and straighter than those of the small intestine – Goblet cells account for more of the epithelial cells than in the small intestine. • Lamina propria – very little; squeezed between the intestinal glands. • Muscularis mucosae – forms 2 smooth muscle layers
    • 52. • Submucosa: considerable amounts of fat • Muscularis externa: Different from the small intestine. Inner circular layer of muscle - forms the usual sheath around the large intestine Outer longitudinal layer - forms Tenia coli (3 flattened muscles) • Tunica Adventitia (serosa): Forms Appendices epiploicae (small pouches filled with fatty tissue) along the large bowel.
    • 53. • Thank you for taking this journey of the human body …TISSUE LEVEL ! • MS. O. HARA