P- Small and Large Intestines Flashcards
What are the layers of the small bowel from the lumen out?
- mucosa
- lamina propria
- muscularis mucosa
- submucosa
- muscularis propria
- serosa
Describe the mucosa of the small bowel.
It consists of crypts and villi line by simple columnar epithelium.
the villi is: enterocytes(absorptive), Goblet cells (mucus), and enteroedocrine
the crypts are Paneth cells (secrete lysozomal enzymes and factors) and stem cells
What are the 3 sections of the small intestine and what are the distinguishing features of each part?
- Duodenum - Brunner’s glands (submucousal glands that secrete bicarb, pepsinogen, glycoproteins)
- Jejunum (no special features. longest part)
- Ileum - Peyer’s patches - increased mucosal lymphoid tissue which clusters into nodules
What are the layers of the colon and rectum from lumen out?
Mucosa Lamina Propria Muscularis mucosa submucosa muscularis propria serosa
Describe the mucosa of the colon and rectum.
The absorptive simple columnar epithelium has crypts and glands arranged in parallel in the lamina propria. There are no VILLI.
The cells of epithelium are :endocrine, Goblet cells, undifferentiated stem cells and columnar cells
Describe the proliferative zone of the colon mucosa.
It is located in the bottom of the crypts and scattered mitotic figures go 1/3 to 1/2 up the crypt.
As the cells move up the crypt they:
- increase cytoplasm
- decrease N/C ratio
- maintain proper polarity (nucleus at the base of the cell)
Ischemic injury can occur anywhere in the GI tract, but what are the 2 places it occurs most frequently?
It occurs most frequently at watershed areas where the collaterals are small and narrow.
- rectosigmoid junction - terminal branches of IMA
- ** splenic flexure - terminal branches of SMA
Why is the small intestine much more vulnerable to ischemia than the colon?
Because the colon can get some accessory supply and drainage from the retroperitoneal portions (ascending/descending)
What typically causes acute enterocolitis? What kind of infarct would occur?
What typically causes chronic enterocolitis?
Acute- thrombus/embolism in the celiac, SMA or IMA which can cause hemorrhagic infarct {hemorrhagic infarct is seen in organs with dual blood supply}
Chronic- gradual build up of atherosclerosis in vessels supplying the bowel
What patient population is most likely to be affected by ischemic enterocolitis?
Incidence increases with:
- age
- cardiovascular disease
- DM
What are the 3 major variables in ischemic bowel disease?
- severity of the vascular compromise
- period over which the compromise developed
- vessel involved
Why are the splenic flexure and rectosigmoid junction considered “watershed areas”?
Splenic flexure- termination of SMA, IMA
Rectosigmoid- termination of IMA, pudendal, iliac
Because the blood supply terminates here, these areas are most suceptible to injury by hypotension or hypoxemia
In addition to the major arteries to the intestines, what other blood supply is involved in intestinal circulation?
Intestinal capillaries run from the crypts alongside the glands to the surface and empty into postcapillary venules.
This protects the stem cells of the crypt so they can repopulate the surface.
The epithelium is more susceptible to ischemic injury because they are last to receive blood supply
What is a morphological signature of ischemic intestinal disease?
- surface epithelium atropy
- sloughing/necrosis of epithelium
- normal or hyperproliferative crypts
What are predisposing conditions to bowel infarcts due to arterial thrombus?
- atherosclerosis
- vasculitis
- dissecting aneurysm
- hypercoagulable states
- angiography procedures/surgery accidents
What are predisposing conditions to bowel infarcts due to arterial embolism?
- cardiac vegetations
- angiographic procedures
- aortic atheroembolism
What are predisposing conditions to bowel infarcts related to venous thrombosis?
- hypercoagulable state
- sepsis
- post-op
- vascular-invasive cancer (hepatocellular carcinoma)
- cirrhosis
- abdominal trauma
What are predisposing factors to bowel infarct related to NON-occlusive ischemia?
Anything that gives low flow
- cardiac failure
- shock
- dehydration
- vasoconstrictive drugs (cocaine)
What is the difference between a mucosal, mural and transmural infarct?
Mucosal - does not go below the muscularis mucosa (due to acute/chronic hypoperfusion)
Mural- mucosa AND submucosa (due to acute/chronic hypoperfusion)
Transmural- all layers of the wall (due to occlusion of major mesenteric artery)
Describe what you would see with transmural infarct due to an acute arterial obstruction.
What is occuring in the mucosal layer? Muscularis propria? Serosa?
- sharp demarcation between normal/ ischemic bowel
- infected bowel is intensely congested, purple/red and hemorrhagic
- wall becomes thick, edematous, rubbery
- Coag necrosis of muscularis propria in 1-4 days with the potential for perforation
- serositis- purulent exudate and fibrin deposition
A patient presents with sudden, severe abdominal pain and tenderness. They have nausea, vomiting, melena. They are progressing to shock/vascular collapse. Peristaltic sounds have diminished and they have rigidity of the abdomen. What are 4 potential things this could be?
- acute transmural infarction
- acute appendicitis
- perforated ulcer
- acute cholecystitis
Describe the difference in margins between arterial occlusion and venous occlusion causing transmural infarction of the bowel.
Arterial - sharply defined borders of ischemic area
Venous- margins are less distinct
Describe the lesions associated with mucosal and mural infarcts. What layers are involved? What parts of the bowel? What forms at the edges of the segments?
They can affect anywhere from the stomach to the anus.
The lesions can be continuous but are most often patchy and segmental.
Mucosa- hemorrhagic and ulcerated
Bowel wall is thickened with edema and can involve just the mucosa or extend down into the submucosa.
Serosa hemorrhage and serositis are ABSENT.
At the edges of the affected segments, pseudomembranes form. They are necro-inflammatory exudates overlying the mucosa.
As long as the ______________ is spared, mucosal and mural infarct lesions are completely reversible.
Muscularis propria