Intestine Path Flashcards
How can you differentiate the different parts of the small intestine?
duodenum - Brunner’s glands
jejunum - lacks Brunner’s and Peyer’s patches
ileum - Peyer’s patches
What increases the absorptive surface of the small intestine?
villi, microvilli, and plicae circulares (folds in submucosa)
How does the epithelial lining change in the colon and rectum?
shaped into tubular structures called crypts or glands, no villi
What do all cells in the large intestine have in common?
proper polarity - nuclei at bottom of cells
What is ischemic enterocolitis?
reduction, interruption, obstruction of blood supply
often result of decreased systemic perfusion or anatomic occlusion
Where does ischemic injury usually occur within the GI tract?
watershed areas where collateral arteries small and narrow
mostly left colon (splenic flexure)
How does ischemic enterocolitis usually resolve?
usually mild and on their own - accessory supply from retroperitoneal portions
minority are gangrenous
What are the causes of acute and chronic cases of ischemic enterocolitis?
acute - thrombi/emboli - hemorrhagic due to dual blood supply
chronic - atherosclerosis
What are the major variables in ischemic bowel dz?
severity of vascular compromise
period during which it develops
vessels affected
What are the two watershed zones?
sup and inf mesenteric arteries
inf mesenteric and hypogastric arteries
How does microvascular anatomy affect ischemic bowel dz?
intestinal capillaries run from crypt to surface and hairpin turn before emptying
allows blood to supply crypts (w stem cells) but leaves surface epithelium vulnerable to ischemic injury - look for hyperproliferative crypts w surface atrophy as morphological hallmark
What are predisposing conditions for bowel infarcts?
arterial thrombosis arterial embolism venous thrombosis obstruction non-occlussive ischemia (low flow)
What are the three categories of ischemic bowel injury?
mucosal infarct
mural infarction - mucosa and submucosa
transmural infarction - acute occlusion of major mesenteric A
What do you see with transmural bowel infarctions?
purple-red hemorrhagic, then blood in lumen and wall edematous and thickened
coagulative necrosis of muscularis propria w/i 1-4 days
possible serositis
What are the possible consequences of transmural bowel infarctions?
perf
mucosal barrier breaks down - bacteria enter circulation –> sepsis
What do the margins of ischemic damage look like in the bowel?
arterial occlusion - sharply defined
venous occlusion - less distinct
What generally causes mucosal and mural infarctions?
hypoperfusion
What do you see with mucosal or mural bowel infarcts?
often patchy lesions hemorrhagic mucosa - maybe ulcers thickened edematous bowel wall no serosal hemorrhage or serositis psuedomembranes may form
When are mucosal and mural bowel infarcts completely reversible?
as long as muscularis propria spared and hypoperfusion corrected
What is diverticulosis?
blind pouch leading off GI tract - lined by mucosa communicating with gut lumen
What is the difference between congenital and acquired diverticulosis?
congenital - have all 3 layers of bowel wall
acquired - lack or have attenuated musc. propria, mostly in sigmoid
What are examples of congenital diverticulum?
meckel, normal appendix
What are examples of acquired diverticulum?
zenker, colontic
What two influences contribute to the genesis of diverticula?
exaggerated peristaltic contractions w elevation of luminal pressure
inherent anatomy of colon - incomplete outer longitudinal muscle gathered into tenia coli and focal defects where neurovascular bundles penetrate
Why are diverticula associated with Western diets?
low fiber causes prolonged transit time and increased intraluminal pressure associated w low volume stools
What are some symptoms of diverticula?
sensation of inability to empty rectum, alternating constipation and diarrhea
What are complications of diverticula?
inflamation or inf
peritonitis, hemorrhage, perf w abscess
What other conditions can diverticula resemble?
carcinoma radiologically
appendicitis clinically
What types of bowel obstructions are there?
mechanical or functional
majority in small bowel - strangulated (surgical emergency) or not
What are the most common causes of bowel obstruction?
mechanical - adhesion, hernia, intussusception, volvulus
When do adhesions develop?
when peritonitis heals
Where do hernias most often occur?
inguinal and femoral canals
umbilicus
site of surgical scars
What is a hernia?
portions of intestine or ab fat tissue bulge out - covered by thin membrane, can become trapped or strangulated
What is intussusception?
segment of intestine invaginates into adjoining intestinal lumen - intraluminal tumor?
What is volvulus?
twisting of intestine loop around mesenteric attachment site, mostly in small bowel
What are complications of small bowel obstruction?
sepsis, intra-ab abscess, wound dehiscence, aspiration, short bowel syndrome from multiple surgeries, death
What are signs and symptoms of small bowel obstruction?
pain nausea and vomiting diarrhea then constipation fever and tachycardia previous surgery or XRT hx of malignancy
What causes Hirchsprung dz?
absence of ganglion cells - segment narrows
RET gene mutations that inactivate RET receptor kinase
What indicates diarrhea?
stool weights above 250-300 gms/day
What is the basic pathogenesis of all diarrhea?
reversal of normal net absorption of water and electrolytes to secretion - by osmotic force or active secretion
What are acute causes of diarrhea?
acute infections
drugs
food allergies
IBD
What are chronic causes of diarrhea and how long is needed to be considered chronic?
3 weeks IBD IBS chronic infections malabsorption syndromes
What is the most important mechanism of diarrhea?
malabsorption - accumulation of unabsorbed material leads to steatorrhea
will abate w fasting
What can cause malabsorption diarrhea?
giardia
celiac sprue
lactase def
What kind of diarrhea is c. difficile responsible for?
antibiotic associated diarrhea and colitis = psuedomembranous, caused by exotoxins A & B
What is celiac sprue?
immune response to glutin controlled by CD4 T cells
predisposing HLA-DQ2 and HLA-DQ8
How is celiac sprue diagnosed?
confirm by biopsy from 2nd part of duodenum - villous atrophy, lymphocytes, crypt hyperplasia
AGA or EMA antibodies present
What is Whipples dz?
systemic illness from tropheryma whippelii - arthritis, weight loss, diarrhea, encephalopathy, lymphadenopathy, steatorrhea
What are microscopic findings in whipples?
foamy macrophages in lamina propria w PAS+ organisms
