Intestine: Small And Large Flashcards
What are the regions of the small intestine (SI)?
Duodenum-Shortest and widest
Jejunum-begins at the duodenojejunal junction
Ileum-Lower 3/5 of SI ends at the ileocecal junction
What are the functions of the small intestine?
Digestion-Principal site for digestion Absorption of nutrients Synthesis and secretion of digestive enzymes Control of microbial growth Regulation of GI via endocrine secretion
What are the unique features of the structure of the SI?
Plicae circulares
Villi
Intestinal glands
What are the characteristics of the Plicae circulares?
Permanent transverse folds with a submucosa core
Contain mucosa and submucosa
Located in the distal duodenum and proximal jejunum
Increase surface absorption
What are the characteristics of the villi?
Evagination of the mucosa projecting into the lumen
Found strictly in SI
Core made of lamina propria
No submucosa
What are the characteristics of the intestinal glands?
Mucosal glands
Called crypts of Lieberkuhn
Invagination of the surface of the epithelium
Found throughout intestine (small and large)
Contain Paneth cells and progenitor cells
What are the characteristics of gluten enteropathy or coeliac disease?
Found in patients with hypersensitivity to gluten present in wheat, rye or barley
Due to subtotal or total atrophy of villi
Manifested as malabsorption syndrome with steatorrhea (fatty diarrhea with unabsorbed lipids) and weight loss
What are the mucosal cells of the SI?
1-Cells of the surface epithelium are: Enterocytes, goblet cells, M cells, enteroendocrine cells,and intraepithelial lymphocytes
2-Cells of the crypts of Lieberkuhn: Paneth cells and progenitor cells
What are the characteristics of the enterocytes?
Intestinal absorptive cells, most predominant cells
Columnar cells
Possess microvilli forming brush border
Possess tight junctions forming a barrier between lumen and intercellular compartment
What are the functions of the enterocytes?
Absorption of nutrients
Production of digestion enzymes for final stage of digestion of carbohydrates and proteins within glycocalyx
Digestion of lipids
Transcytosis of IgA
What are the characteristics of the lipids digestion?
Lipids are broken down into MAG and FFA within lumen
MAG and FFA absorbed into cells and re-synthesized into TAG by SER
TAG transported into golgi and coated with protein
Chylomicron= TAG coated with protein
Chylomicron transported out to lymphatics and not blood due to size
What are the characteristics of the transcytosis of IgA?
IgA synthesized by plasma cells in the lamina propria
IgA binds to receptors and transported to apex of enterocytes
IgA released into lumen
IgA protects mucosa by regulating microbial growth
The intestinal flora is responsible for regulation of IgA receptors
What are the characteristics of the goblet cells?
Unicellular mucous glands with narrow base and wide apex
Apex contains mucinogen granules giving the frothy appearance of the cytoplasm
The nucleus is small, triangular and heterochromatic
Increase in numbers from duodenum to terminal part of ileum
Produce mucus
What are the characteristics of M-cells?
Antigen transporting cells located over lymphoid follicles
Convey microorganisms from lumen to lymphoid follicles via endocytosis by carrier vesicles
Hollow dome shaped with microfolds on apical surface and deep invaginations and pockets on basal surface
What are the characteristics of enteroendocrine cells?
Have the same structure as the enteroendocrine cells in the stomach with basally placed granules
Found anywhere in the epithelium
Function in GI regulation
What are the characteristics of the intraepithelial lymphocytes?
Specialized T cells blood derived
Provide mucosal immunity
What are the characteristics of the Paneth cells?
Found at the bottom of the crypts of Lieberkuhn
Contain eosinophilic granules in apical portion
Play important role in regulation of normal bacterial growth
What are the characteristics of the progenitor cells?
Undifferentiated cells found in crypts of Lieberkuhn
Serve as replacement cells for all surface epithelium cells except intraepithelial lymphocytes
What are the characteristics of the lamina propria of the SI?
Loose CT with large number of immune cells forming GALT or MALT
What are the types of GALT?
Diffuse lymphoid tissue found throughout SI made of leukocytes and macrophages
Scattered lymphoid follicles- Packed B cells found in duodenum and jejunum
Peyer’s patch- Aggregated lymphoid follicles in the anti mesenteric side found in the ileum
What is lymphoma?
Also called MALToma Common cancer of SI Characterized by diffuse thickening of the wall infiltrating lymphocytes Occurs in proximal SI Incurable Long survival through chemotherapy
What is the blood supply of the lamina propia?
Consists of capillary loops into villus from arterioles of the submucosal vascular plexus
Returns to the same plexus
Collects soluble nutrients like AA and sugars bit not chylomicra
What are the characteristics of the lymphatics of the lamina propria?
Each villus has a central blind ended lymphatic capillary called lacteal
Lacteal drains into larger lymphatic vessels within submucosa
Lacteal transports chylomicra
What are the layers of the submucosa of the SI?
Dense CT
Vascular plexus
Meissner’s plexus
Brunner’s glands- found only in duodenum, branched tubular, have alkaline secretion to neutralize gastric acid
What are the characteristics of the other layers of SI?
Muscularis externa is similar with 2 layers separated by Auerbach plexus
Adventitia in most of the duodenum
Serosa in proximal 1st segment and distal 4th segment of duodenum,in jejunum and ileum
How to differentiate the 3 parts of the SI?
Duodenum has submucosal glands, and few goblet cells
Jejunum has the tallest villi
Ileum has the most goblet cells, has Peyer’s patches and short villi
What are the regions of the large intestine (LI)?
Cecum with the vermiform appendix containing aggregated lymphatic follicles
Colon - only area with teniae coli
Rectum containing prominent transverse rectal folds
What are the functions of the large intestine?
Reabsorption of water and electrolytes
Elimination of waste and undigested food
What are the characteristics of the large intestine?
General structure in similar to the rest of the GI
Mucosa has no villi
Cells of the crypts of Lieberkuhn are similar to the SI except do not have Paneth cells
Abundant goblet cells presence
Teniae coli which are thickened bands in the outer longitudinal layer of colon and not appendix or rectum
Serosa has omental appendices which are small fatty projections
What is adenocarcinoma?
Most common cancer of larger intestine
Typically found in colon or rectum
Most common in patients with adenomatous polyps or ulcerative colitis
Total resection of tumor is the treatment of choice
