Histology of The lower GI tract Flashcards
4 degrees of folding in SI
1) plicae circularis (mucosa and submucosa)
2) intestinal villi (folds of mucosa)
3) intestinal glands: crypts of lieberkuhn (between villi)
4) microvilli on the apical surface of enterocytes
what are enterocytes?
epithelial cells lining the lumen
plicae circularis begin in the ____ are distinct in the ____ and disappear in the ____
duodenum, jejunum, mid-ileum
intestinal glads are formed by what?
crypts of lieberkuhm are formed by invaginations of the mucosa between adjacent intestinal villi
cells of the crypts of lieberkuhn
paneth cells, absorptive cells, goblet cells, enteroendocrine cells
microvilli are what
evaginations of the apical part of the enterocytes to increase SA
-produce a brush border on the apical border of enterocytes
serosa makeup
thin layer of loose CT covered by visceral peritoneum (mesothelium)
arterioles derived from the submucosal plexus enter the mucosa of the SI and give rise to 2 capillary networks?
1) the villus capillary plexus: supplies intestinal villus and upper portion of crypts of lieberkuhn
2) pericryptal capillary plexus: supplies lower half of crypts of lieberkuhn
lacteal location
- core of the villus
- just above muscularis mucosae is the lymphatic plexus whose branches surround lymphoid nodule in the submucosa
- efferent vessels anastomose with the lacteal and exit digestive tube together with BV
Lacteal Function
convey chyle (lymph containing lipids absorbed from the meal and packaged in chylomicrons) from SI to lymphatic circulation—>thoracic duct—>systemic circulation
What is chyme?
semifluid mass of partly digested food expelled by the stomach into the duodenum
duodenum histologic features
Brunner’s glands (mucous) in submucosa
few goblet cells
leaflike villi
jejunum histologic features
well eveloped plicae circulares
irregeular villi
more goblet cells
no brunner’s glands (no glands submucosa) or peyer’s patches
ileum histologic features
many peyer’s patches in lamina propria and submucosa
finger-like villi (short)
most goblet cells
villi and crypts of lieberkuhn lined by ____ ____ ___ with 4 cell types
simple columnar epithelium
1) absorptive enterocyte cells
2) goblet cells
3) paneth cells
4) enteroendocrine cells
cells found in the crypts of lieberkuhn
PES
paneth cells, enteroendocrine cells, stem cells
microvilli on enterocyte cells contain?
intramembranous enzymes, including lactase, maltase, sucrase for digestion of carbs
lactose intolerance
no lactase present, bacteria ferment lactose which causes gas and organic acids lead to irritation and increased motility, water also stays in for diarrhea
goblet cells: cell type, location, secretory product
- columnar mucus secreting cells scattered among enterocytes of intestinal epithelium
- secretes glycoproteins (80% carbs 20% proteins) released by exocytosis
mucus from goblet cell function
forms protective gel coat to shield epithelium from abrasion and bacterial invasion, can trap bacteria, protects enterocytes
enteroendocrine cells secrete what
gastrin, secretin, CCK
gastrin
stimulates gastric motility, HCL and insulin
secretin
stimulates pancreatic bicarb secretion, enhances insulin secretion
CCK
acts on pyloric sphincter to slow emptying
-stimulates release of bile and pancreatic enzymes
paneth cells secrete
antimicrobial proteins to limit bacteria-enterocyte contact
antimicrobial proteins action and storage
kill bacteria by enzymatic degradation of the bacterial wall or by disrupting the bacterial inner membrane
-retained in intestinal mucus blanket
SI is protected from pathogens by:
GAP PIT V
Gastric juice acidity inactivates ingested microorganisms
Antimicrobial proteins from paneth cells
Peyer’s patches particip. in cell surveillance of antigens
Peristalsis prevents bacterial colonization
IgA neutralizes antigens
Tight junction barrier of intestine links adjac. enterocytes
Viscous gel-like blanket produced by goblet cells
If any of these are knocked out, then it can lead to a disease process
IBD
1) initial alteration
2) inflamm process
3) accumulation
initial alteration is infiltration of neutrophils into crypts of lieberkuhn–>destorys intestinal glands by forming crypt abscesses and atrophy and ulceration of mucosa
- inflammatory process also infiltrates submucosa and muscularis
- accumulation of lymphocytes forms aggregates of cells (granulomas)
complications of IBD
-crohn’s segments
- occlusion of intestinal lumen by fibrosis and formation of fistulas in other segments of SI
- segments affected by crohn’s disease are separated by normal stretches of intestinal segments
technique to replace bad bacteria with good bacteria and what bacteria usually is the bad one
C. Diff and use fecal microbiota transplant
large intetine histologic features
mucosa of LU lined by simple columnar epithelium from enterocytes and abundant goblet cells
enterocytes have short apical microilli
major function of enterocytes in LI
transport of ions and water
what is not found beyond the ileocecal valve?
plicae circulares and intestinal villi
what is characteristic of the mucosa of the colon
numerous openings of straight tubular glands or crypts of Lieb.
-much deeper here than in SI
have high proportion of goblet cells
main function of LI
absorption of water, sodium, vitamins, and minerals
-active transport of sodium removes water and concentrates chyme into semisolid feces
4 cell types of colon mucosa
1) simple columnar absorptive cells with SHORT apical microvilli (enterocytes)
2) stem cells
3) predominant goblet cells
4) enteroendocrine cells
regions of colon are facilitated by PM channels that are regulated by _____. and explain process
mineralocorticoids such as aldosterone inserts Na+ channels to increase absorption of Na+
glands of Lieb in LI contain what cells
goblet ells, enteroendocrine cells, stem cells
no paneth cells (may be some in cecum)
taeniae coli is formed by what
fused bundles of outer smooth muscle layer
contraction of taeniae coli and inner circular smooth muscle produces?
haustra
appendix function
may be safehouse for good bacteria
appendix most important features
thickening of its wall due to large accumulations of lymphoid tissue in lamina propria and submucosa
appendix hist features
villi absent, crypts not frequent, fatty tissue in submucosa
appendix mucularis externa
thinner than reminder of LI and outer SM layer does not aggregate into taenia coli
ano-rectal junction
simple columnar epithelium of rectal mucosa replaced by stratified squamous epithelium
formation of internal anal sphincter
inner circular layer of SM in the ano-rectal junction thickens to form the internal anal sphincter
anal region is lined by what
keratinized stratified squamous epithelium and submucosa contains sebaceous and sweat glands
gene responsible for familial polyposis and colorectal tumorigeneis
APC gene
colorectal tumor location
where it develops in the colon and then spreads bsed off lymph and venous drainage of section of colon. this determines what area it will affect next
