Histology Of Small And Large Intestines Flashcards
Plicae circularis
Permanent folds of the mucosa and Submucosa
- most prominent in the proximal jejunum (decrease in number and size distally
- also contains villi which are in and of themselves permanent folds of mucosa only
*are absent from the proximal duodenum until after the major duodenal papillae
Villi
Are permanent folds in the mucosa layers of epithelium overlaying plicae circularis and the lamina propria
Contain lacteal ducts, lymph vessels, blood vessels and muscularis mucosae within them
Also process 3 cell types
- 1) enterocytes: absorptive columnar cells with apical microvilli and form the brush border
- 2) goblet cells: mucous cells dispersed throughout the epithelial cell layer that’s excretes mucin (hydrates mucosa layer)
- 3) enteroendocrine cells: small located cells that secrete paracrine or endocrine hormones/products (look like a “bulls eye”)
Types of epithelial cells in the small intestines
1) enterocytes:
- outside columnar cell layer that absorbs and contains microvilli (brush border)
2) goblet cells:
- secretes mucous
3) paneth cells:
- secretes lysozyme and defensins
4) enteroendocrine cells:
- paracrine and endocrine functions
5) Microfold cells: “M cells” are the main APC molecule in preyer patches
6) stem cells: pluripotent cells.that give rise to the above
Enterocytes and lipid processing steps
1) lipids metabolized in the lumen and diffuse across the plasmalemma of the microvilli
2) products move into smooth ER and resynthesized into triglycerides
3) triglycerides are processed by golgi and rough ER into chylomicrons
4) chylomicrons are released laterally and pass through basement membrane and into lacteal ducts
Duodenal (Brunner) glands
Branched tubular mucous glands found in the proximal duodenum that extend through the lamina propria layer and into the Submucosa.
- secrete alkaline mucous that neutralizes stomach acid
What are the only secretory cells found throughout the GI tract from fundus of stomach -> colon?
D-cells = somatostatin
ENS neurons secreting Vasoactive intestinal peptide (VIP)
Difference histologically between Crohn’s and celiac disease
Celiac = only damages the mucosal layer of the intestines, specifically damaging the enterocytes with inflammation
Crohn’s = damages all layers of the intestines with inflammation
Types of cells in the large intestines
1) colonocytes: functional columnar cells with microvilli that work to absorb fluid
2) goblet cells: secretes mucous
3) enteroendocrine cells: paracrine and endocrine cells
4) stem cells: pluripotent cells that transform into any of the above when needed
How does the muscularis externa differ in the colon?
Has tenia coli in the longitudinal layer of the muscularis externa
Difference between true and pseudo diverticulum
True diverticula = include all 4 layers of the intestine
False diverticula = includes mucosa and Submucosa, BUT NOT MUSCULARIS EXTERNA
What are the 3 zones of the anal canal?
1) colon-rectal zone
- looks pretty similar to the rectum in histology
- only contains simple columnar
2) anal transitional zone
- transitional layer which has rectum (simple columnar) histology and stratified squamous epithelium
- contains the pectinate line
3) squamous zone
- contains only stratified squamous epithelium that is continuous with the perianal skin.
- derived from proctoderrm but the epithelium lining is surface ectoderm
- innervation = inferior rectal nerve of the pudendal nerve
Difference between internal and external hemorrhoids
External = arises from the external rectal plexus (inferior to pectinate)
- innervated by somatic afferent neurons (pudendal nerve)
- visable and painful
Internal = arises form the internal rectal plexus (superior to pectinate)
- innervated by somatic afferent neurons (pelvic splanchnics)
- not visable and not painful
