P- Small and Large Intestines Flashcards Preview

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Flashcards in P- Small and Large Intestines Deck (139)
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1

What are the layers of the small bowel from the lumen out?

1. mucosa
2. lamina propria
3. muscularis mucosa
4. submucosa
5. muscularis propria
6. serosa

2

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

3

What are the 3 sections of the small intestine and what are the distinguishing features of each part?

1. Duodenum - Brunner's glands (submucousal glands that secrete bicarb, pepsinogen, glycoproteins)

2. Jejunum (no special features. longest part)

3. Ileum - Peyer's patches - increased mucosal lymphoid tissue which clusters into nodules

4

What are the layers of the colon and rectum from lumen out?

Mucosa
Lamina Propria
Muscularis mucosa
submucosa
muscularis propria
serosa

5

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

6

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:
1. increase cytoplasm
2. decrease N/C ratio
3. maintain proper polarity (nucleus at the base of the cell)

7

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.

1. rectosigmoid junction - terminal branches of IMA
2.** splenic flexure - terminal branches of SMA

8

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)

9

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

10

What patient population is most likely to be affected by ischemic enterocolitis?

Incidence increases with:
1. age
2. cardiovascular disease
3. DM

11

What are the 3 major variables in ischemic bowel disease?

1. severity of the vascular compromise
2. period over which the compromise developed
3. vessel involved

12

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

13

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

14

What is a morphological signature of ischemic intestinal disease?

1. surface epithelium atropy
2. sloughing/necrosis of epithelium
3. normal or hyperproliferative crypts

15

What are predisposing conditions to bowel infarcts due to arterial thrombus?

1. atherosclerosis
2. vasculitis
3. dissecting aneurysm
4. hypercoagulable states
5. angiography procedures/surgery accidents

16

What are predisposing conditions to bowel infarcts due to arterial embolism?

1. cardiac vegetations
2. angiographic procedures
3. aortic atheroembolism

17

What are predisposing conditions to bowel infarcts related to venous thrombosis?

1. hypercoagulable state
2. sepsis
3. post-op
4. vascular-invasive cancer (hepatocellular carcinoma)
5. cirrhosis
6. abdominal trauma

18

What are predisposing factors to bowel infarct related to NON-occlusive ischemia?

Anything that gives low flow
1. cardiac failure
2. shock
3. dehydration
4. vasoconstrictive drugs (cocaine)

19

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)

20

Describe what you would see with transmural infarct due to an acute arterial obstruction.

What is occuring in the mucosal layer? Muscularis propria? Serosa?

1. sharp demarcation between normal/ ischemic bowel
2. infected bowel is intensely congested, purple/red and hemorrhagic
3. wall becomes thick, edematous, rubbery
4. Coag necrosis of muscularis propria in 1-4 days with the potential for perforation
5. serositis- purulent exudate and fibrin deposition

21

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?

1. acute transmural infarction
2. acute appendicitis
3. perforated ulcer
4. acute cholecystitis

22

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

23

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.

24

As long as the ______________ is spared, mucosal and mural infarct lesions are completely reversible.

Muscularis propria

25

What is the difference between congenital and acquired diverticulosis? What are examples of each?

1. Congenital -involves all three layers of bowel INCLUDING the muscle
- Meckel diverticulum
- normal appendix

2. Acquired- lack or have attenuated muscularis propria due to focal weakness or increased intraluminal pressure (80% in the sigmoid colon)
- Zenker diverticulum
- colonic diverticulum

26

What are the 2 influences that lead to the genesis of a diverticula?

1. exaggerated peristaltic contractions (elevated intraluminal pressure)
2. inherent anatomy - incomplete longitudinal muscle layer gathered in tenia coli and neurovascular bundles penetrating the inner circular muscle alongside tenia coli

Western diets lead to diverticula because the low fiber diet increased transit time, thus increasing #1)

27

Describe the gross morphology of diverticulosis.

1. multiple small, flask-like envaginations along the tenia coli filled with mucus or stool
2. bulging into the serosa or omental appendices
3. thickened circular muscle of the colon with "accordion" mucosal folds

28

Describe diverticulosis microscopically?

there will be an absence of muscle except for some random bundles of muscularis mucosa.

Inflammation may be present if there is obstruction or perforation. This can extend into the pericolic fat and give the appearance of colon carcinoma

29

A patient presents with cramping, discomfort, sensation of the inability to completely empty rectum. They have alternating constipation and diarrhea. What are you suspicious of and what are some of the complications associated?

Diverticulosis.

Complications:
1. diverticulitis - inflammation/infection
2. peritonitis
3. hemorrhage
4. perforation with abscess resembling a mass or forming a sinus tract
5. adhesions
6. obstruction
7. fistula to bowel/bladder

30

What is treatment for diverticula?

1. High fiber diet
2. if diverticulitis--> antibiotics
3. if peritonitis/perforation--> resection