Flashcards in 19. Histology of the Lower GI Deck (59):
What are the three main modifications of the luminal surface of the SI that increase the SA to aid absorption?
What are plicae circularies? How much increase in SA
Permenant mucosal folds in the duo, jej, and prox ilieum
Increase the surface area 2-3 fold
What are villi? How much do they increase SA?
Finger-like projections of epithelium-covered lamina propria, contain central lacteal and several capillaries
Increase the SA by 10 fold
What are microvilli?
Extensions of the epithelial cell apical plasma membrane that increase the surface area 20 fold
(increase the SA by 20 fold)
**3,000 on each epithelial cell
How much do plicae circulares, villi, and microvilli cumatively increase the SA?
What is present in the center of the villus?
Smooth muscle fibers
What are the 3 difference cells found lining the villi?
Absorptive cells (enterocytes) **
What three cells are found in the Crypts of Lieberkuhn?
What are the most abundant cells in the small intestine?
What kind of cells are absorptive cells?
Columnar epithelial cells (25 uM high with elongated nuc)
What is the principal function of enterocytes?
Terminal digestion and absorption of water and nutrients
Reesterify fatty acids into triglycerides, form chylomicrons, and transport the bulk of absorbed nutrients into the lamina propria for distribution
What are the microvilli coated in?
Glycocalyx coat made of glycosylated membrane proteins
What is the role of the glycocalyx that coats the microvilli in the SI?
Digestion of disaccharides and dipeptides into monomers for absorptiong through peptide hydrolases and diassachridases that are abundant on the apical surface
How can goblet cells be recoginzed on H and E?
Full of carbohydrate and remain unstained
**carb within goblet cells can be identified by PAS stain
What do goblet cells secrete?
Copious mucin--high MW glycoprotein macromolecules that have 20% protein and 80% carbohydrate
What happens when mucin granules are released from goblet cells?
Hydrated and expand several hundred fold in volume, lubricates and protects the intestines
What does Ki-67 stain?
The crypts of Lieberkuhn extend from the base of the villi into the:
What are the cells in the crypts of lieberkuhn?
Where are new cells for the epithelial lining of the intestine generated?
Stem cells in the crypts--migrate up the villus and are exfoliated from the tips of the vilus
The intestinal epithelium is replaced every ___ days?
How can stem cells be identified in the crypts?
Mitotic figures, since they are the only cells that are proliferating
What secretes lysozyme and defensins?
Where are paneth cells found?
Resident at the base of the crypts--do not participate in upward migration of epithelial cells
Staining of paneth cells
Stain with eosin
Phloxine-tartrazine stains the secretory granules scarlet
How can EC cells be distinguished from paneth cells?
EC cell granules on the basal side for secretion of hormones into the blood
Paneth cells have granules at the apical side for secretion into the lumen
What area of the mucosa is highly vascularized and accepts the products of absorption? Also contains lymphoid cells to protect from microbial invasion
What is the role of fibers from the muscularis mucosa that enter the vilus and extend to the tip?
Contract to cause shortening of the villus during digestion
Important for emptying of the lacteal
Lamina propria maintains an extensive immune defense system in the form of lymphoid tissue called:
Gut-Associated Lymphoid Tissue (GALT)
Though most GALT exists as individual lymphocytes in the mucosa and epithelium, what are aggregates called?
What is the structure that forms from the joining of several lymphoid nodules?
Where are Peyer's Patches most commonly found?
Ileum (some in the jej)
What layer of the SI is moderately dense CT with small numbers of adipose cells
How does the duodenal submucosa differ from the rest of the GI tract?
large numbers of BRUNNER'S GLANDS
What are Brunner's glands?
Similar to mucous acini, ascend through the muscularis mucosae layer and enter the crypts to deposit secretions into the lumen
What is the composition of the secretions from Brunner's glands in the duodenal submucosa?
Alkaline mucus that neutralized the pH of gastric chyme and protects duodenum
Epidermal growth factor, increases stem cell proliferation in the crypts
What controls secretion of fluid from the SI (2 liters a day)
Neural control from Meissner's plexus
Hormonal control from enteroendocrine cells
What nerve plexus is found between the outer and inner layers of the muscularis externa?
What are the two types of movement associated with the small intestine?
1. Mixing contractions: expose chyme to digestive juices
2. Propulsive contractions: peristaltic waves of muscle movement (transports chyme at 2cm/min)
In each day, the SI absorbes:
__ L fluid
__ g sodium
__ kg carbs/protein
__ kg fat
How do the villi of the duodenum differ from those of the jej and ileum?
Villi are broader, taller, and more numerous per unit area
What is the main distinguishing feature of the duodenum?
Brunner's glands in the submucosa
**also fewer goblet cells
How do the villi of the jejunum differ from those of the duodenum?
Narrower, shorter, sparser
**more goblet cells
How do the villi of the ileum differ from those of the jej?
Sparsest, shortest, and narrowest
What is the most distinctive feature of the ileum?
Peyer's patches in the ileum
**in the region of the Peyers patches, villi may be reduced in height or absent
How long is the large intestine? Parts?
Cecum, appendix, ascending/transverse/descending/sigmoid colon, rectum, and anus
Why is the surface of the colon relatively smooth?
Not folded into plicae circularis and villi
Though the colonic epithelium has a similar celluar composition, what cells are absent from the colonic crypts?
How do colonic crypts differ from those in the small intestine?
Highly glandular, with an abundance of goblet cells
How often is the colonic mucosa replaced?
Replaced every 6-7 days
How does the muscularis mucosae of the colon differ?
Better developed, with clear circular and longitudinal fibers
The musculars externa outer longitudinal muscles are arranged in three distinct bands called:
Creates sacculations called:
What is characteristic of appendix histology?
Masses of lymphoid tissue in the mucosa and submucosa (forms follicles with germinal centers)
Mucosal glands are more disperse
How does the rectal mucosa compare to colonic mucosa?
Crypts are deeper and goblet cells are more abundant
What transition occurs at the recto-anal junction?
Epithelium transitions from simple columnar to stratified squamous
What are crypts replaced by at the recto-anal junction?
Large circumanal glands
What are the two venous plexi that are found in the submucosa of the anal canal?
Internal hemorrhoidal plexus
External hemorrhoidal plexus
**can cause hemorrhoids in older people and pregnancy
What is the composition of the internal and external anal sphincters?
Internal: smooth muscle
External: striated muscle