Histology of the SI/LI Flashcards
What are the parts of the small intestine?
duodenum, jejunum, and the ileum
what is the function of the small intestine?
principal site for digestion of food and absorption of digestion products
what are the transverse folds that are found in the small intestine lumen called? and what are they made up of?
plicae circulares (made up of mucosa with a submucosal core)
where are the plicae circulares visible?
they are visible in the jejunum, less so in the ileum
what are found on top of the plicae circulares?
intestinal villi
what are intestinal villi covered with/ what cells are found in this layer?
simple columnar epithelium of enterocytes and goblet cells
what is the core of the intestinal villi made up of?
loose connective tissue with microvasculature and a lacteal
what are lacteals important for?
they absorb lipids from the diet
what do the enterocytes have on them?
microvilli
what do enterocytes produce?
enzymes for digestion and absorption
what is the function of goblet cells?
they produce a mucus coating to shield from abrasion and bacterial invasion
what type of epithelium makes up the mucosal layer of the SI?
simple columnar epithelium
what is found within the simple columnar epithelium of the mucosal layer of the SI?
tubular intestinal glands (aka crypts)
besides the epithelium, what else makes up the mucosal layer of the SI?
the lamina propria and the muscularis mucosae
what is the submucosa of the SI made up of?
dense irregular CT with neurovasculature, lymphatics, and glands may also be present
what is the muscularis layer of the SI made up of?
inner circular and outer longitudinal layers
what is the serosa of the SI made up of?
loose CT covered by visceral peritoneum
What are the intestinal glands lined by?
simple columnar epithelium
what cells are found within the intestinal glands?
paneth cells, M cells, intestinal stem cells, and enteroendocrine cells
where do the intestinal glands open into?
the luminal surface of the intestine at the base of the villi
What do paneth cells llok like?
they are pyramidal-shaped cells at the base of the intestinal glands; they have large eosinophilic (pink staining) granules in their apical cytoplasm
what is the function of Paneth cells?
innate immunity by secreting antimicrobial substances (such as lysozymes and alpha defensins); they also regulate normal bacterial flora via antibacterial action and phagocytosis
where do intestinal stem cells reside?
in a niche at the intestinal gland base, near paneth cells
what types of cells can the intestinal stem cell repopulate?
goblet cells, enterocytes, and enteroendocrine cells
where are M cells located?
in the ileal mucosa-overlying the peyer patches
what are M cells main function?
highly specialized antigen-transporting cells
what is an example of a specific bacteria that M cells will bind to?
gram-negative bacteria (e.g. E. coli)
when looking at the duodenum, what would you expect to see in the mucosal layer?
simple columnar epithelia with scattered goblet cells
what is the hallmark for identifying the duodenum?
in the duodenum’s submucosal layer, there are duodenal glands
what is the composition of the duodenal glands in the submucosal layer?
tubuloacinar mucous glands that produce an alkaline secretion (it neutralizes acidic chyme)
when looking at the jejunum, what would you expect to see in the mucosal layer?
long-finger like villi with a villus core containing a well-developed lacteal; tubular intestinal glands; lymphoid follicles in the lamina propria
when looking at the ileum, what would you expect to see in the mucosal layer?
the villi are typically shorter than the jejunum; peyer’s patches; paneth cells found at the base of the intestinal glands
how can you tell that you are looking at the gastroduodenal junction?
the stomach lacks the submucosal glands and then the duodenum has the submucosal glands
what is the function of the LI?
absorbs water, sodium, vitamins, and minerals; will uptake sedatives, anesthetics, and steroids
what is the hallmark for identifying the large intestine on histological slides?
the intestinal glands and goblet cells; NO INTESTINAL VILLI
what cells make up the mucosal layer of the LI?
colonocytes, goblet cells, stem cells, and enteroendocrine cells
what is extensive in the mucosal layer of the colon?
the GALT- it may penetrate the submucosa
what happens to the outer longitudinal layer in the muscularis layer of the LI?
it gets organized into taeniae coli–> this forms the haustra of the LI
what is Hirschprung’s disease/ megacolon?
it is when there is aganglionosis of the distal gut tube
what causes Hirschprung’s disease?
mutations of the RET gene- normally required for migration and differentiation of NCC; so there is a failure of NCC development in both plexuses of the bowel segment
what is short-segment hirschprung’s disease?
confined to the rectosigmoid region
what is long-segment hirschprung’s disease?
it extends past the rectosigmoid region to the splenic flexure
what is the presentation of hirschprung’s disease?
constipation, poor-feeding, and progressive abdominal distention
where are the circumanal glands found?
they are large apocrine glands surrounding the anal orifice
what are the three zones of the anal canal?
the colorectal zone, the anal transition zone, and the squamous zone
what is the colorectal zone?
it is simple columnar epithelium (the upper 1/3 of the anal canal); identical to the rectum
what is the anal transitional zone?
the middle 1/3 of the anal canal; area where we have a change from our simple columnar epithelium to stratified squamous epithelium of the perianal skin
what is the squamous zone?
it is the external portion of the anal canal; the lower 1/3 of the anal canal; it is stratified squamous epithelium that is continuous with perineal skin
how does the internal anal sphincter form?
at the level of the anus, the inner circular layer thickens to form the internal anal sphincter
