HISTOLOGY Gastrointestinal & Nutrition Block GNT 223 Histology of Small and Large Intestine By Dr. Einas Yousef 2018/2019

Objectives At the end of the lecture, student should be able to: List the different parts of small intestine. Describe the microscopic structure of the three regions of the small intestine: Duodenum, Jejunum, Ileum. List the different parts of large intestine. Describe the microscopic structure of the different regions of the large intestine. Know the difference between small and large intestine. 17-10-02

Introduction Digestive system consists of digestive tract and its associated glands.

General structure of GIT The wall of the gastrointestinal tube is formed of 4 main layers: Mucosa Submucosa Muscularis externa (Musculosa) Serosa or adventitia Serosa: loose CT that is covered by a single layer of squamous mesothelial cells of peritoneum. Adventitia: loose CT that is not covered by a single layer of squamous mesothelial cells of peritoneum. 17-10-02

Small intestine Small intestine is a tightly folded tube about 6 meters long. It connects to the stomach on the top end and to the large intestine (colon) on the bottom end. It consists of three parts: A- The first part, called the duodenum, connects to the stomach. B- The middle part is the jejunum. C- The third part, called the ileum, attaches to the colon. 4/22/2019

Histology of Small Intestine Mucosa: It is characterized by the presence of large number of folds or Plicae (plica circulares or Kerckring’s valves) arranged circularly around the lumen of small intestine (this can be seen by naked eye). The surface of the plica shows numerous finger like projections called intestinal villi and simple tubular gland (crypt of Lieberkuhn) Mucous brunner’s gland secrete alkaline mucous into the lumen of duodenum to neutralize the acidic chyme to produce optimum PH for the action of pancreatic juice. Peyer’s patches: are large lymphoid follicles that are present in the lamina propria and may bulge through the muscularis mucosa into the submucosa. Present mainly in the lower part of the ileum. The villi is absent over them and they are covered by M- cells. 4/22/2019

Histology of Small Intestine Mucosa: is made of: Epithelium: covers the villi and lines the crypts. It consists of different types of cells (Next slides). Lamina Propria: loose C.T. that form the core of intestinal villi and fill the space between the crypts. It contains blood vessesls, nerves and lymphatics (Lacteals) Muscularis Mucosae: 2 layers of smooth muscle (inner circular & outer longitudinal) Submucosa: loose C.T. contains mucous Brunner’s gland in the duodenum and Peyer’s patches in the ileum. Muscularis externa (Musculosa): 2 layers of smooth muscle (inner circular & outer longitudinal) Serosa: loose CT covered with mesothelium of the peritoneum. Mucous brunner’s gland secrete alkaline mucous into the lumen of duodenum to neutralize the acidic chyme to produce optimum PH for the action of pancreatic juice. Peyer’s patches: are large lymphoid follicles that are present in the lamina propria and may bulge through the muscularis mucosa into the submucosa. Present mainly in the lower part of the ileum. The villi is absent over them and they are covered by M- cells.

Epithelium of Small Intestine 1- Absorptive columnar cells (Enterocytes) Tall columnar cells with oval basal nuclei. The apical free surface of the cell are striated due to microvilli (brush border) which increase the surface area of absorption. 2- Goblet cells: Unicellular mucous secreting glands. Scattered between absorptive cells. The apical part is distended with mucin and the basal part is cylindrical with an oval darkly stained nucleus. They secrete mucous which protects and lubricates the lining of the intestine.

Epithelium of Small Intestine 3- Paneth Cells They are only found in the bottom of the crypts. They are pyramidal cells with basal rounded nuclei. They contain apical acidophilic secretory granules and basal basophilic striations (RER). They also contain large supranuclear Golgi apparatus and numerous mitochondria. They secrete intestinal and bacteriolytic enzymes which play role in controlling the intestinal flora. Paneth cells

Epithelium of Small Intestine 4- Enteroendocrine (Argentaffin, APUD) cells Pyramidal cells with darkly stained nuclei. Site: Mainly in the base of the gastric glands and also in the small and large intestine. Function: Secretion gastrointestinal hormones such as gastrin, serotonin, endorphin and intestinal hormones (Secretin, pancreozymin and motilin) in blood. 5- Regenerative (stem) cells They are small cells with oval basal nuclei. They are located mostly basal half of the intestinal glands. They are capable of replacing all cells in the intestinal villi and crypt. APUD= amine precursor uptake and decarboxylation 4/22/2019

Histology of Small Intestine Mucous brunner’s gland secrete alkaline mucous into the lumen of duodenum to neutralize the acidic chyme to produce optimum PH for the action of pancreatic juice. Peyer’s patches: are large lymphoid follicles that are present in the lamina propria and may bulge through the muscularis mucosa into the submucosa. Present mainly in the lower part of the ileum. The villi is absent over them and they are covered by M- cells. 4/22/2019

Intestinal Villi Finger like projection of the mucous membrane. Each villous has a covering epithelium and core of loose C.T., blood and lymph vessels (Lacteal) of the lamina propria. The epithelium covering the intestinal villi consists mainly of: 1- Mature simple columnar epithelium with brush border (microvilli) (Absorptive cells). 2- Goblet cells. 3- Enteroendocrine cells. Function: They increase the surface area of absorption. 4/22/2019

Intestinal Crypt Also known as crypts of Lieberkuhn. Simple tubular glands. Present in the lamina propria reaching almost the muscularis mucosa. They open into the lumen of small intestine in between the bases of the villi. The crypt epithelium consists of: 1- Immature simple columnar epithelium with brush border (microvilli). 2- Goblet cells 3- Paneth cells: at the base of the gland. 4-Enteroendocrine (Argentaffin) cells 5- Stem cells The turnover time of intestinal epithelium is from 3-5 days Paneth cell play role in immunity of GIT by secreting substantial quantities of antimicrobial peptides and proteins. 4/22/2019

Peyer’s Patches They are large lymphoid aggregations, present in the lamina propria and may bulge through the muscularis mucosa into the submucosa. Present mainly in the lower part of the ileum. The villi is absent over them and they are covered by M- cells. The follicles are extremely rich in B- lymphocytes which differentiate into immunoglobulin producing plasma cells. Villi Peyer’s patches M- cells

Peyer’s Patches M-cells (Microfold cells): They are specialized epithelial cells overlying the lymphatic nodules. They are thin broad-dome shaped cells, they have basal cavity that is packed with intraepithelial lymphocytes and macrophages. Function: They endocytose antigens and transport them to underlying lymphocytes and macrophages, where they transport them to other compartments of the immune system.

Comparison between different parts of small intestine Duodenum Jejunum Ileum Villi shape Leaf-like Finger-like But shorter Goblet cells + ++ +++ Lymphatic tissue (Peyer’s patches) Less common Aggregated L.N. (Peyer’s patches) Glands in submucosa Present (Brunner’s mucous gland) None 4/22/2019

Functions of Small Intestine 1- Completing digestion of food delivered into it from the stomach through secretion of mucous by goblet cells and Brunner’s mucous gland. This mucous act to neutralize the acidic chyme (to produce optimum PH for the action of pancreatic enzymes). 2- Main function is absorption of the products of digestion into the blood (glucose & a.a.) and lymph (Lipids) vessels. 3- Secretion of some endocrine substances (Hormones) 4- Defense function against antigens as bacteria, performed by rich lymphatic tissue, macrophages, M-cells and by barrier that is formed by epithelial lining cells and tight junctions between them.

Morphological adaption of small intestine (to increase absorption) Increase surface area and slow down passage of intestinal content.

Large Intestine Large intestine comes after the small intestine in the digestive tract and it measures around 1.5 m in adult human. Wall of large intestine is much thinner than small intestine but its lumen is much larger. Main functions are: 1- Fluid and electrolyte absorption. 2- Secretion of mucus for lubrication and protection of intestinal lining. 3- Formation of fecal mass. 4/22/2019

Large Intestine The large intestine consists of the following: 1- Cecum and appendix 2- Colon (ascending, transverse, descending) 3- Pelvic (sigmoid) colon 4- Rectum 5- Anal canal 4/22/2019

Histology of Large Intestine All parts of large intestine except the anal canal have the following structure: 1- Mucosa: A- Epithelium: The surface epithelium is folded to form deep wide intestinal crypts. There is no intestinal villi. The epithelium is formed of two types of cells: Simple columnar epithelium with microvilli (brush border) which work mainly to absorb water. Goblet cells which secret mucous. The mucous cells increase and the absorptive cells decrease toward the anal canal.

Histology of Large Intestine B- Lamina Probria: loose C.T., Peyer’s patches. C- Muscularis mucosa: 2 layers of smooth muscle. Submucosa: loose C.T. contains blood and lymph vessels and nerve fibers Muscularis externa (Musculosa): 2 layers of smooth muscle; inner circular and outer longitudinal. The fibers of outer longitudinal layer are collected into 3 flat bands, the taenia coli Serosa: loose CT covered with mesothelium of the peritoneum. The serous coat forms little peritoneal sacs that enclose adipose tissue (Appendices epiploicae).

Comparison between small & large intestines Only the large intestine (not the small intestine) is characterized by: 1- No villi. Only crypt. 2- There is no Paneth cells. 3-Musculosa: 2 layers of smooth muscle. The fibers of outer longitudinal layer are collected into 3 flat bands, the taeniae coli. 4- Serosa: The serous coat forms little peritoneal sacs that enclose adipose tissue (Appendices epiploicae)

Vermiform Appendix The lumen is small, irregular and narrow (due to the presence of abundant lymphoid follicles in the wall. 1- Mucosa: The crypts are fewer and shorter. Epithelium: columnar, goblet, argentaffin cells, occasional Paneth and stem cells. Corium: numerous lymphoid follicles. Muscularis mucosa is not well developed and may be absent in some areas. 2- Submucosa: contains numerous lymphatic follicles. 3- Musculosa: two layers of smooth muscle. No taenia coli. 4- Serosa: completely surround the appendix. 4/22/2019

The Anal Canal It is the lower part of large intestine. It works to give passage for the feces outside the body. The differences between the anal canal and large intestine: 1- Mucosa The surface columnar epithelium of large intestine replaced by non-keratinized stratified squamous epithelium which extends 2-4 cm to become Keratinized stratified squamous epithelium of skin of the anus. No crypts No muscularis mucosa The mucous membrane of the upper half of anal canal is thrown into longitudinal folds known as Anal columns (columns of Morgagni).

The Anal Canal 2- Musculosa: The circular layer of musculosa (smooth muscle) is thickened to form internal anal sphincter. The longitudinal layer ends between the internal and external anal sphincters. External anal sphincter is formed of voluntary skeletal muscle. Anus is covered by skin having typical hairs, sebaceous glands and special sweat glans.

References Junqueira C., Carneiro J. (2005). Basic Histology, Text & Atlas, 11th ed. Gartner LP (2016). Color Textbook of Histology. 4th ed. Philadelphia: Saunders WB. Young B, O' Dowd G, Woodford P (2013). Wheater‟s Functional Histology. 6th ed. London: Churchill Livingstone. 17-11-19

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