GI 3-4 Flashcards
Small Intestine
Longest component of alimentary canal; 3 portions duodenum, jejunum, ileum; serves to digest food, absorb nutrients, secrete enzymes, control microbial growth and regulate GI function
Structure of SI
mucosa, submucosa, muscularis externa, and serosa/adventitia; UNIQUE: PLICA CIRCULARES; Mucosa contains villi
Duodenum
shortest and widest part of SI; Brunner’s glands, least goblet cells
Jejunum
begins at DJ junciton and gradually changes its character to become ileum; tallest villi, prominent lacteals
Ileum
lower 3/5 of SI ending at Ileocecal junction; most goblet cells; Peyer’s patches and shorter villi
What system regulates GI function?
endocrine secretion by enteroendocrine cells
Where are plicae most numerous?
Distal duodenum and proximal jejunum
What is the role of plicae?
Increase surface area
What is the most unique feature of mucosa of the SI?
Villi: all mucosa (no submucosa); loose CT of lamina propria; role is to increase SA more; found on columnar cells of surface epithelium; atrophty is found in coeliac diasease
Gluten enteropathy/Coeliac disease
found in patients with hypersensitivity to gluten and caused by total or subtotal atrophy of the villi in the SI. Results in malabsorption syndrome characterized by weight loss, steatorrhea.
Surface epithelium of SI
simple columar: does not change between villi and intervilli; includes enerocytes which absorb nutrients, produce digestive enzymes, break down lipids, and transcytose IgA to protect mucosa.
Enterocytes
Tall columnar cells with numerous microvilli on apical surface forming brush border to increase SA. They are bound by tight and anchoring junctions to create a barrier between intestinal lumen and epithelial intercellular component.
What is digested in the glycocalyx of enterocytes
proteins and carbs
What happens to lipids in the SI and where does this occur>
broken down to monogylcerides for transport occurs in the lumen of intestine and are rebuilt into trglycerides in the smooth ER. Fat droplets then fo to the golgi to get a protein coat, becoming CHYLOMICRA which can be released into extracellular for uptake by lymph
IgA role in SI
Found in lamina propria, moved to intestinal lumen after synthesis and secretion by plasma cells. They protect mucosa by controlling microbial growth.
Goblet Cells (of SI)
unicellular mucous glands intersperesed amoung enterocytes that INCREASE IN NUMBER IN THE TERMINAL ILEUM. 1* role is to produce mucus. Narrow base, wide apex, frothy cytoplasm, mucinogen granules. Pale staining.
M-Cells
limited distribution, found in epithelium OVERLYING LYMPHOID FOLLICLES. Antigen transporters: alert invaders of lumen to the lympoid follicles. Endocytosed using carrier vesicles and delivered to basolateral membrane to be discharged into intercellular space near T-lymphocytes.
Enteroendocrine cells
same structure and function as in stomach: Mostly concentrated at base of gland. Secrete product into lamina propria. Secrete gastrointestinal hormones to regulate functioning of alimentary canal. (including gastrin, ghrelin.) Rest on basement membrane and form microvilli that reach lumen of gland. Filled with membrane bound secretory granules in basilar part of cell.
Intraepithelial Lymphocytes
unusual T-lymphocytes; dervied from progenitor cells in crypts of lieberkuhn (blood derived) and help mucosal immunity
Mucosal Glands
Crypts of Lieberkuhn; simple invaginations. Extend through muscularis mucosa. The 2 unique cells here are paneth and progenitor cells
Panteth cells
bottom of crypt of Lieberkuhn; regulate bacterial growth; numerous large eosinophilic granules in apical part containing AB enzyme lysozyme, Alpha defensins, etc; basilar ER
Progenitor Cells
mainly found in cypts of L; undifferentiated cells that replace any epithelium except lymphocytes; indentifiable as mitotic cells
Lamina Propria of the SI
loose CT with lymphoid follicles
Lyphoid Follicles
scattered throughout lamina propria; GALT; Largely identifiable as peyers patches in the ileum and consist of m-cells
Small Intestine LYMPHOMA
most common of SI, arises from B- or T- lymphocytes in lamina propria in proximal SI, wall becomes thickened and inflitrated with lymphocytes
Blood supply to SI
capillary loops from arterioles of submucosal vascular plexus and return to venules of same plexus; solubel nutrients like AA and carbs are transported by blood vessels (NOT FAT)
Lymphatics of SI
Each villus has a central blind-ended capillary called LACTEAL. These drain into larger vessels in submucosa. Transports the chylomicra (fat) ingested by enterocytes
Muscularis Mucosae or SI
several layers of smooth muscle
Submucosa of SI
Dense CT, vascular and nerve (Meissner’s) plexi; glands: BRUNNERS OF DUODENUM
Brunner’s Glands
only found in DUODENUM, mucus-producing branched tubular glands of alkaline secretion that protects the intestine by neutralizing acidic chye from stomach
Muscularis Externa of SI
inner circular and outer longitudinal layer; Auerbach’s plexi between muscle layers
Most of the duodenum is covered with ___ while the jejunum and ileum are covered with ____.
adventitia, serosa
Large Intestine
Cecum, colon, rectum, and anal canal; serves to reabsorb water and electrolytes while eliminating undigested food and waste; same comp as alimentary canal; NO VILLI
Mucosal Epithelium of LI
no villi, no paneth cells, yes progenitor cells, columnar absorber cells (enterocytes) predominate, goblet cells are MORE ABUNDANT than SI and outnumber enterocytes in rectum
Goblet Cells of the LI
MORE ABUNDANT than SI and outnumber enterocytes in rectum; procude extensive amounts of mucus to facilitate the elimination of solid waste
Adenocarcinoma
most common and malignant tumor of the LI usually in colon or rectum. Usually arise in patients with adenomatus polyps or UC. Tx- resection.
Submucosa of LI
same structure as alimentary canal
Muscularis Externa of LI
2 layers of smooth muscle: inner O and outer l; change is that the outer longitudinal layer forms 3 thickened bands called teniae coli
Serosa of LI
contain omental appendices (fatty deposits)
Colon
largest portion of LI, well expressed teniae coli
Veriform appendix
useless, has aggregated lymphatic follicles, no teniae coli
Rectum
similar mucosa to distal colon, prominent transverse rectal folds, no teniae coli
