Flashcards in Lower GI Normal Structure/Function Deck (42):
What are the 3 divisions of the small intestine?
What is the function of the small intestine?
digest food and absorb end products
What are the plicae circulares?
permanent mucosal folds present in the duodenum, jejunum and proximal ileum that increase the surface area by 2-3X
What are the villi?
finger like projections of epithelium covered lamina propria that increase surface area by 10X
What are the microvilli?
extensions of the epithelial cell apical plasma membrane that increases surface area by 20X
What is contained within the villi lamina propria?
central lymphatic channel and capillaries
smooth muscle fibers, loose CT and lymphoid cells
What cell types are contained in the crypts of lieberkuhn?
DNES cells, stem cells, paneth cells
What cell types are contained in the SI epithelium?
enterocytes, goblet cells, DNES cells
What type of epithelium is in the SI?
What is the main function of the enterocyte?
terminal digestion and absorption of water and nutrients
-reesterify FAs into TGs, form chylomicrons, and transport the bulk of the absorbed nutrients into the lamina propria for distribution to the rest of the body
What does the glycocalyx coat over the microvilli do?
involved in digestion of disaccharides and dipeptides into monomers for adsorption through peptide hydrolases andd disaccharidases that are abundant on the apical surface
What do goblet cells secrete? What does it's product do?
lubricates and protects the intestine
What does goblet cell mucin contain?
high MW glycoprotein macromolecules
What happens to mucin after it was released?
granules become hydrated and expand several hundred fold
What is located in the upper half of the crypt of lieberkuhn?
surface absorptive and goblet cells
What is located in the basal half of the crypt?
mostly stem cells, DNES cell and paneth cells
How often is small intestine epithelium replaced in humans?
every 3-6 days
What do paneth cells secrete?
lysozyme & defensins
What do defensins do?
neutralize bacterial and viral infections
What does shortening of the villi assist with?
emptying the lacteal
What is the extensive immune defense system in the form of lymphoid tissue?
What are Peyer's patches?
a coalescence of lymphoid nodules
What are brunner's glands?
alkaline mucus that neutralizes the pH of the gastric chyme and protects the duodenum, they also contain epidermal growth factor that may be involved in stem cell proliferation in the crypts
Which enteric plexus controls secretion?
What does the auerbach's (myenteric) plexus control?
motor innervation to muscularis externa
secretomotor innervation to the mucosa
What are the two types of movements in the small intestine called?
mixing and propulsion
What are distinguishing features of the duodenum?
villi are broader, taller and more numerous per unit area
What are disinguishing features of the jejunum?
villi are narrower, shorter and sparser
more goblet cells per unit area
What are distinguishing features of the ileum?
villi are sparsest, shortest and narrowest
List the regions of the large intestine
colon (ascending, transverse, descending, sigmoid)
What does the ileocecal valve do?
prevents reflux of cecal/colonic content back into the ileum
What is the surface of the colon like?
smooth, no villi
does have crypts of lieberkuhn
What cell type is missing from the colonic crypts that is present in the crypts of the small intestine?
What are the differences between small and large intestine crypts?
crypts n the colon are longer and more glandular with an abundance of goblet cells
both have stem cells at the base of the crypts
How often is the colonic mucosa replaced?
every 6-7 days
What is the taenia coli?
muscularis externa outer longitudinal muscle arranged in three distinct bands that remain partially contracted and cause the large intestine to be puckered in o haustra coli sacculations
What are the key features of the appendix?
masses of lymphoid tissues in the mucosa and submucosa
lymphoid tissues often forms follicles with germinal centers
What is the terminal 12 cm of the GI tract called?
What is the rectal mucosa like?
similar to the colon except that the crypts are somewhat deeper and the goblet cells more abundant
What change occurs at the recto anal junction?
epithelium transitions from simple to columnar to stratified squamous
(crypts disappear just prior to this junction and are replaced by large circumanal glands
What are the two venous plexi found in the submucosa of the anal canal?
internal hemorrhoidal plexus
external hemorrhoidal plexus
*in older people and during pregnancy an increased in the size of the vessels in these plexuses can result in hemorrhoids