Normal/Abnormal Small Bowel/Colon IBD Flashcards
What are M cells?
antigen presenting cells aiding in immunosurveillance; location over lymphoid follicles –> rich in terminal ileum with peyer’s patches
In what layer of the bowel do inflammatory cells hang out?
lamina propria
An out-pouching of the distal small bowel containing all the layers (hence a true diverticulum) that occurs as a result of a “pulling” of this segment during retraction of the small bowel back into the abdominal cavity during fetal development.
Meckel’s Diverticulum
Failure of gut to retract back into peritoneal cavity; must be surgically placed back.
Omphalocele
What is atresia associated with?
trisomy 21
What is a common consequence of malrotation?
May cause subsequent “twisting” and ischemia.
Etiology of Hirschsprung’s
Failure of development of Meissner’s and Auerbach’s plexi; migration from cephalocaudal direction to normally reach fetal rectum by 12 weeks - migration problem
Hirschsprung’s Histology
lack of ganglion cells in distal portion rectum; may involve more proximal colon as well.
Presentation of Hirchsprung’s
Usually neonatal
- Failure to pass meconium
- Obstruction
- Proximal dilatation - i.e. affected segment relatively constricted.
- There is a rare, familial form associated with mutations in the RET oncogene.
Where do Meckel’s diverticula arise?
w/in 1 foot proximal of ileocecal valve
Presentation of Meckel’s diverticula?
bleeding + “appendicitis”
Are all layers present in a Meckel’s?
yes –> true diverticulum
Those changes which occur due to compromise of blood flow. These changes follow a sequence some parts of which are reversible and others not.
Ischemia
Clinical presentation of small bowel ischemia
severe, acute abdominal pain out of proportion to physical exam
Where do ischemic changes in the small bowel begin?
mucosa: most sensitive to ischemia
Features of acute small bowel ischemia
mucosal ulceration, neutrophils, edema/thumbprinting –> muscle necrosis and perforation
Features of chronic small bowel ischemia
fibrosis and stricture
Most common thrombotic source in small bowel ischemia
SMA > mesenteric vein
Causes of small bowel ischemia
thrombotic/emblic, voluvulus, adhesions, vasculitis, hypotension, vasospasm
Is there cross-feeding between arcades?
no –> not until reaching the marginal artery of drummond
Why is small bowel ischemia notable for sharp demarcations between injured/non-injured areas?
b/c of parallel arcades
What is the major factor in determining area of ischemic damage in small bowel ischemia?
size of the occluded vessel correlates with area of damage
What are thumbprints?
xray areas of edema associated with ischemia
3 grades of small bowel ischemia?
mild, moderate, severe
T/F mucosal erosions and ulcerations may be repaired after ischemia
T –> via reepithelialization
Ulceration suggests what grade of ischemia?
moderate/severe
What are the histologic features of mild small bowel ischemia?
edema, mild acute inflammatory infiltrate
In which segment of the population do volvuli occur most often?
elderly
After the gut re-enters the abdominal cavity, specific areas of the gut are “tacked” down to prevent free rotation of the gut. When these areas of “tacking down” occur in wrong areas, bands of fibrosis are formed termed ______
Ladd bands –> may aserve as a point of rotation for gut resulting in obstruction and ischemia
Which of ulcerative colitis and crohn’s disease has a genetic component?
both do but different genetic components
2 types of IBD
crohn’s and ulcerative colitis
Among which population group is incidence of IBD highest?
white/jewish in canada/europe/us
In which decade of life does IBD present?
2nd-4th
Site of involvement: CD
any where from mouth to anus, all layers, can skip areas
Site of involvement: UC
colon only, continuous w/o skipping, mucosa only
This disease is geographically unlimited with respect to the GI tract and thus affects anywhere from mouth to anus and is transmural. The disease is noncontinuous and thus may have “skip” areas. Many investigators think of this disease (or at least a subset) as a granulomatous vasculitis.
Crohn’s
Crohn’s pathology
transmural inflammation w/fibrosis/stricture/fistulae + cobblestone mucosa, linear/apthous/fissuring/knife like ulcers, creeping fat, thickened wall, non caseous granulomas, pyloric metaplasia
Tx of Crohn’s
immunosuppression/surgery if severe
Sequelae of Crohn’s
stricture/obstruction, GI cancer, malnutrition
This is a geographically restricted inflammatory disease which is mucosally limited and continuous beginning from rectum and extending proximally. The small bowel and rest of the GI tract are not affected. Cause is not known.
Ulcerative colitis
What causes stricture in Crohn’s?
muscle hypertrophy
Ulcerative colitis pathology
crypt distortion, muscularis mucosa thickening, cryptitis, hemorrhage, pseudopolymps, no strictures, loss of haustra, no granulomas
Sequelae of Ulcerative colitis
Cancer, primary sclerosing cholangitis of liver, pyoderma granulosa
Tx of Ulcerative colitis
immunosuppression, j pouch for fecal continence, surgery cures, dysplasia surveillance
Crohn’s 3 categories of pathogenesis and associated genes
- autophagy: atg16L1, IRGM, LRKK2
- intracellular bacterial sensing: NOD2
- ER stress: XBP1 and ORMDL3
Consequences of NOD2 mutations in Crohn’s
- abnormal paneth granules = decreased killing of pathogens
- defective sensing and clearance of bacteria = increased load/inflammation
- prevents p38 phosphorylation of nuclear protein for IL10
- weakened tight junctions that increase permeability to pathogens
What does NOD2 induce?
dimerizes, binds to rick –> activates NF-kB but not apoptosis
What is tubular colon?
With remission of the active inflammatory component, the colonic mucosa regenerates and repairs ulcerated areas. This repair in conjunction with disruption and distortion of the muscularis mucosa may lead to a flat appearance of the colon as shown on the left. There is a relatively normal colon to the right for comparison. This appearance is also termed a “tubular colon.”
Breach in epithelial integrity
crypt abscess
The finding of _____ on a biopsy is a very powerful feature to help diagnose IBD
crypt distortion
What must one do before making a dx of IBD?
rule out infection!
Which of Crohn’s and UC are geographically limited?
UC is geographically limited
