Normal Histology of Small and Large Bowel - Cirillo Flashcards
What is the common purpose of each of the following modifications to the small intestine? Describe each.
Plicae Circularis
Villi
Microvilli
All aid in absorption in the small intestine by increasing the surface area (overall: 400-600 fold)
Plicae circularis: permanent mucosal folds located primarily in the duodenum, jejunum, and proximal ileum. Increase surface area by 2-3 fold.
Villi: finger-like projections of epithelium. Increase surface area 10-fold
Microvilli: extensions of epithelial cell apical plasma membrane. Increase surface area 20-fold
What is a lacteal?
Central lymphatic channel in an intenstinal villus
Name the (3) major epithelial cell types found on the intestinal villi? Which is the most abundant?
Enterocytes (most abundant)
Golbet cells (secrete mucus)
DNES cells (neuroendocrine)
What is a Paneth cell? Where is it located?
What stains might be used to identify these cells?
Paneth cells secrete lysozyme and defensins - overall purpose is to help neutralize bacterial and viral infections
These are long-lived cells that remain resident in the base of the crypts (do not migrate like other cells).
H&E (eosinophilic) or Phloxine-Tartrazine (scarlet)
Each enterocyte contains approximately how many microvilli?
What is the glycocalyx coat? What is its purpose?
~3000 microvilli per enterocyte
Glycocalyx coat: protective layer covering the microvilli made of glycosylated membrane proteins. Its overall purpose is protective but it also assists in the digestion of disaccharides and dipeptides (breakdown into monomers)
What is the purpose of Goblet cells?
How do they appear on H&E stain? Why? What might be used to better visualize them?
Secrete ‘copious’ amounts of mucin (high MW glycoprotein)
H&E stain: appear unstained (clear) due to high carbohydrate content (does not stain). Use PAS instead (stains carbohydrate)
How might one identify stem cells in the crypts of Lieberkuhn?
Look for mitotic bodies
Describe the cell populations in the upper and basal halves of the crypts of Lieberkuhn.
Upper: surface absorptive (enterocytes) and goblet cells
Basal: few goblet cells. Most cells are regnerative (stem cells), DNES cells, and Paneth cells.
Approximately how often is the epithelium of the small intestine replaced?
3-6 days
Describe the core of intestinal villi
Core = lamina propria
Highly vascularized to accept absorbed nutrients
Abundance of lymphoid cells (protection from microbial invasion)
Muscularis mucosae (inner circular and outer longitudonal smooth muscle)
Some muscle fibers extend to the tip - these contract during digestion to shorten the villus (possibly to empty the lacteal)
What is GALT?
Gut-associated lymphoid tissue
Dense aggregates of lymphoid cells within the intestinal mucosa are called what?
What is it called when several of these coalesce? How many of these are found in the gut? Where are they found?
Lymphoid nodules
Peyer’s Patches: 30-40 permanent patches found throughout the gut (principally in the ileum, some in the jejunum, few/none in the duodenum)
What is the key histological feature of the duodenum (not found anywhere else)?
What is its purpose?
Brunner’s glands
Found in the submucosa - secrete alkaline mucous that helps to neutralize gastric chyme as it enters the duodenum from the stonach
Secretions in the small intestine are principally under the control/influence of what?
Approximately how much fluid is secreted by the small intestine per day?
Submucosal (Meissner’s) plexus
~2 L/day
Describe the (2) actions of the musclaris externa
Mixing: localized contractions that churn the chyme, increasing exposure of nutrients to digestive juices
Propulsive: peristaltic waves that propel the chyme along the gut tube (~2 cm/minute)
