S.I./Colon Key Concepts Flashcards
what is the most common site of gastrointestinal ischemia?
the colon
- lesions can be continuous but are most often segmental and patchy
- mucosa is hemorrhagic and may be ulcerated
- bowel wall is thickened by edema that may involve the mucosa or extend into the submucosa and muscularis propria
what is the main cause of transmural infarction?
acute arterial obstruction
initially the tissue in intensely congested and dusky to purple-red -> later, blood-tingued mucus or frank blood accumulates in the lumen and the wall becomes edematous, thickened and rubbery
- coagulative necrosis of the muscularis propria within 1-4 days, and perforation may occur
- serositis, with purulent exudates and fibrin deosition may be prominent
transmural infarction
arterial blood continues to flow for a time, resulting in a less abrupt transition from affected to normal bowel
- propagation may lead to secondary involvement of the splanchnic bed
- ultimate result is similar to that produced by acute arterial obstruction because impaired venous drainage eventually prevents oxygenated arterial blood from entering the capillaries
mesenteric venous thrombosis
crypts may be hypoproliferative
- inflammatory infiltrates are initially absent in acute ischemia, but neutrophils are recruited within hours of reperfusion
ischemic intestine
this is accompanied by fibrous scarring of the lamina propria, and uncommonly, stricture formation
chronic ischemia
in both acute and chronic ischemia, bacterial superinfection and enterotoxin release produces what?
- resembles C. diff-associated pseudomembranous colitis
pseudomembrane formation
biopsy specimens from the second portion of the duodenum or proximal jejunum (which are exposed to highest concentration of dietary gluten) are diagnostic in what?
celiac disease
increased numbers of intraepithelial CD8 T lymphocytes (intraepithelial lymphocytosis), crypt hyperplasia, and villous atrophy
- loss of mucosal brush-border most likely leads to malabsoprtion
- increased crypt mitotic activity may limit the ability of absorptive enterocytes to fully differentiate and express proteins necessary for terminal digestion and transepithelial transport
- increased numbers of plasma cells, mast cells, and eosinophils
celiac disease
what is a sensitive (NOT specific) serologic marker of celiac disease?
increase in the number intraepithelial lymphocytes, particularly in the villus (even in the absence of epithelial damage and villous atrophy)
NOTE: combination of histology and serology is the most specific diagnosis of celiac
may occur through any weakness or defect in the wall of the peritoneal cavity, including inguinal and femoral canals, the umbilicus and sites of surgical scars
abdominal hernias
a segment of intestine that telescopes into the immediately distal segment
- most common cause of intestinal obstruction in children younger than 2 years of age
intussusception
most common at the splenic flexure, sigmoid colon and rectum (watershed zones where two arterial circulations terminate)
ischemic bowel disease
malformation of submucosal and mucosal blood vessels
- common cause of lower intestinal bleeding in those older than 60
angiodysplasia
malabsorption associated with what disease, is the result of pancreatic insufficiency
- leading to inadequate pancreatic digestive enzymes, and deficient luminal breakdown of nutrients
cystic fibrosis
immune-mediated enterophathy, triggered by the ingestion of gluten-containing grains
- malabsorptive diarrhea is due to loss of brush border surface area, including villous atrophy, and possibly deficient enterocyte maturation as a result of immune-mediated epithelial damage
celiac disease
prevalent in areas with poor sanitation
- estimated to affect more than 150 million children worldwide, may contribute to a large number of deaths
environmental enterophathy
osmotic diarrhea due to inability to break down or absorb lactose
- AR form is rare and severe, acquired form usually presents in adulthood and is common
lactase deficiency
X-linked disorder characterized by severe persistent diarrhea and autoimmune disease that is caused by mutation in FOXP3 resulting in defective function of regulatory T cells
autoimmune enteropathy
rare AR disease due to a mutation in microsomal triglyceride transfer protein that is required for enterocytes to process and secrete triglyceride-rich lipoproteins
abetalipoproteinemia
comma-shaped, flagellated, gram-neg org
- dx by stool culture since biopsy findings are nonspecific
- acute self-limited colitis
- mucosal and intraepithelial meutrophil infiltrates are prominent, particularly within superficial mucosa
- cryptitis (neutrophil infiltration of crypts)
- crypt abscess (accumulation of luminal neutrophils)
- CRYPT ARCHITECTURE IS PRESERVED
Campylobacter
up to 40% of what syndrome are associated with campylobacter infection?
Guillain-Barre syndrome
most prominent in the left colon, but ileum may be involved (due to Peyer patches)
- mucosa is hemorrhagic and ulcerated
- pseudomembranes may be present
- tropism for M cells, so aphthous-appearing ulcers may occur, similar to those seen in Crohn’s disease
Sigella infection
this sickness causes infection of Peyer patches in the terminal ileum
- enlarged, sharply delineated, plateau-like elevations up to 8cm in diameter
- draining lymph nodes enlarged
- neutrophils accumulate within the superficial lamina propria
- macrophages containing bacteria, red cells, and nuclear debris mix with lymphocytes and plasma cells in the lamina propria
- mucosal damage creates oval ulcers, oriented along the axis of the ileum, that may perforate
Typhoid fever
this sickness causes an enlarged, soft spleen with uniformly pale red plump, follicular markings and prominent phagocyte hyperplasia
- liver shows small randomly scattered foci of parenchymal necrosis in which hepatocytes are replaced by macrophage aggregates, called typhoid nodules
typhoid fever
infection of this organism preferentially involves the ileum, appendix, and right colon
- organisms multiply extracellularly in lymphoid tissue, resulting in lymph node and Peyer patch hyperplasia and bowel wall thickening
- mucosa overlying lymphoid tissue may become hemorrhagic, and aphthous-like erosions and ulcers may develop, along with neutrophil infiltrates and granulomas
Yersinia
NOTE: can be confused with Crohn disease
adherent layer of inflammatory cells and debris at sites of colonic mucosal injury
- surface epithelium is stripped down, and the superficial lamina propria contains a dense infiltrate of neutrophils and occasional fibrin thrombi within capillaries
- superficially damaged crypts are distended by a mucopurulent exudate that forms an eruption reminiscent of a volcano
C. diff-associated colitis with pseudomembranes
dense accumulation of distended, foamy macrophages in the small intestinal lamina propria
- macrophages contain periodic acid-Schiff (PAS)-positive, diastase-resistant granules that represent lysosomes stuffed with partially digested bacteria
- intact rod-shaped bacilli can also be identified by electron microscopy
- villous expansion caused by dense macrophage infiltrate imparts a shaggy gross appearance to the mucosal surface
Whipple disease
when would you see macrophages accumulating within mesenteric lymph nodes, synovial membranes of affected joints, cardiac valves, and the brain?
Whipple disease
org that secretes a preformed toxin that causes massive chloride secretion
- water follows resulting is osmotic gradient -> secretory diarrhea
Vibrio cholerae
most common bacterial enteric pathogen in developed countries, also causes traveler’s diarrhea
- most isolates are noninvaside
Campylobacter jejuni
often triggered by antibiotic therapy that allows colonization by this organism
- releases toxins that disrupt epithelial function
- associated inflammatory response includes characteristic volcano-like eruptions of neutrophils from colonic crypts that spread to form mucopurulent pseudomembranes
C. difficile