Diseases of the Bowel and Colon

Question 1

Mostly Crypts, but no villi; numerous goblet cells

• (vs. small bowel: mostly villi)

Answer 1

Normal Colon Histology

Question 2

• Cecum
• Ascending colon
• Hepatic Flexure
• Transverse colon
• Splenic flexure
• Descending colon
• Sigmoid colon
• Rectum
• 3 layers of muscle in the muscularis externa
• Vasa recta: blood vessels that traverse wall; potential areas of weakness in the wall

Answer 2

Colon Anatomy

Question 3

Reabsorb fluids and electrolytes

Answer 3

Major task of colon

Question 4

• Celiac artery supplies the esophagus, stomach, liver, spleen, superior portion of duodenum and pancreas
• Superior mesenteric artery supplies small bowel to the transverse colon
• Inferior mesenteric artery supplies splenic flexure to upper rectum

Answer 4

GI tract arterial supply

Question 5

Persistence of herniation of abdominal viscera (and occasionally liver) into base of umbilical cord → externalized abdominal contents enveloped in sac into which the umbilical cord inserts

Answer 5

Omphalocele

Question 6

1. Ileocecal artery (distal terminal ileum, cecum, appendix)
2. Right colic artery (ascending colon; absent 2-18%)
3. Middle colic (transverse colon)

Answer 6

Branches of Superior Mesenteric Artery

Question 7

• left colic artery
• sigmoid branches
• superior rectal artery

Answer 7

Branches of Inferior Mesenteric Artery

Question 8

• Arises from the inferior mesenteric artery
• Supplies distal transverse colon, splenic flexure and descending colon
• May form collaterals with the left branch of the middle colic artery (marginal artery)

Answer 8

Left Colic Artery

Question 9

1. Formed by anastamosis of ileocolic, right colic and middle colic arteries
2. Completed by left colic artery
3. Travels along mesenteric border of colon
4. Serves as connection btw SMA and IMA circulation
5. Small vasa recta arise from this vessel and directly supply colon wall

Answer 9

Marginal Artery

Question 10

1. connects proximal SMA and the proximal IMA
2. Vital source of blood supply when occlusion of SMA or IMA
3. Dilates in response to mesenteric occlusion

Answer 10

Arc of Riolan

Question 11

• vulnerability of splenic flexure region to ischemic injury in hypotension
• splenic flexure has variable collateral circulation
• located at confluence of blood supplies of midgut and hindgut
• 50% of ppl no clearly identifiable arteries in “watershed” area: ppl rely upon vasa recta for blood supply in this area

Answer 11

“Watershed” Area

Question 12

• Branches of inferior mesenteric artery

- Branches of internal iliac artery

Answer 12

Arterial Supply of the Rectum

Question 13

• Right and proximal transverse colon drain into Superior Mesenteric Vein
• Distal transverse, descending, and sigmoid colon and most of rectum drain into Inferior Mesenteric Vein
• Anal canal venous drainage occurs via middle and inferior rectal veins into the IMV

Answer 13

Venous drainage of the colon

Question 14

Acetylcholine

Answer 14

ENS Excitatory Motor Neuron Neurotransmitter

Question 15

• nitric oxide
• ATP
• vasoactive intestinal polypeptide

Answer 15

ENS Inhibitory Motor Neuron Neurotransmitter

Question 16

• Sensation of urge to defecate, even if the bowel is empty; occurs with inflammation of the rectum

Answer 16

Tenesmus

Question 17

• Syndrome characterized by relapsing abdominal pain/discomfort (12 weeks of symptoms within 12 months)
• Associated with change in stool frequency and/or consistency
• Symptoms improve with defecation; dietary fibers may improve symptoms
• Related to disturbed intestinal motility
• NO IDENTIFIABLE PATHOLOGIC CHANGES
• Middle-aged female predominance

Answer 17

Irritable Bowel Syndrome

Question 18

• A false diverticulum, Involving herniation of only the mucosa and submucosa outward from the lumen (true diverticula involve the entire wall)
• typically occur near vasa recta (areas of weakness)
• Left-sided divertiula more common in West, right-sided predominance in East
• is frequently asymptomatic

Answer 18

Colonic Diverticula/Diverticulosis

Question 19

• Inflamed/infected diverticulum
• Most common complication of diverticulosis - Likely to occur when inspissated stool in a diverticulum interferes with emptying, i.e., obstructing fecal material
• Symptoms/signs: LLQ pain, fever, altered bowel habits, high WBC
• More significant complications including abscess, free perforation, fistulization and peritonitis can occur

Answer 19

Diverticulitis

Question 20

• Typically large volume painless bleeding (Hematochezia) in an older patient due to segmental weakening of the vasa recta as it courses over the diverticulum

Answer 20

Diverticular Hemorrhage

Question 21

Ischemic damage to the colon, usually athte splenic flexure (watershed area of the superior mesenteric artery)

• Primarily a disease of the elderly (90% of cases in patients>60 years)
• Atherosclerosis of SMA is the most common cause (most distal point of blood flow)
• Presents with postprandial pain (after eating) and weight loss

Clinical features:

• Sudden onset abdominal pain, usually LLQ
• Urge to defecate
• Passage of maroon stool
• Pain and tenderness are usually mild to moderate

Dx:

• Plain films may demonstrate “thumb-printing” (correlated to submucosal hemorrhage)
• CT may reveal mural thickening

Answer 21

Ischemic Colitis

Question 22

• Types: Viral (Rotavirus), Bacterial (E. coli, salmonella), Parasitic (giardia, ameba), Traveler’s diarrhea, Hospital acquired (Pseudomembranous colitis)
• Dx: Stool testing

Risk factors:

• recent antibiotic use (C. difficult invades after wiping out gut flora)
• Underlying colonic disease (IBD)
• Chronic enteral feeding

Answer 22

Infectious Colitis

Question 23

C. difficile infection after recent antibiotic use wipes out gut flora
- usually hospital-acquired colitis

Answer 23

Pseudomembranous colitis

Question 24

• due to hyperplasia of glands
• classically show a serrated appearance on microscopy
• Benign, with no malignant potential

Answer 24

Hyperplastic polyps

Question 25

- due to neoplastic proliferation of glands - benign, but premalignant - may progress to adenocarcinoma via the adenoma-carcinoma sequence

Answer 25

Adenomatous polyps

Question 26

- APC (tumor suppressor gene) mutations increase risk for formation of polyp - K-ras mutation leads to formation of polyp (adenoma) - P53 mutation and increased expression of COX allows for progression to carcinoma - Aspirin impedes progression from adenoma to carcinoma

Answer 26

Adenoma-carcinoma sequence

Question 27

- size - sessile growth (elevated, but flattened appearng) - Villous histology (vs. tubular)

Answer 27

Risk factors for progression from adenoma to carcinoma

Question 28

Clinical presentation: - Anemia: b/c of folate/B12 deficiency - Hematochezia - Abdominal pain - Mass - Change in bowel habits (diarrhea, constipation - Change in stool caliber May arise from: - adenoma-carcinoma sequence - Microsatellite instability

Answer 28

Colorectal Carcinoma

Question 29

- Microsatellites are repeating sequences of noncoding DNA; instability indicates defective DNA copy mechanisms - increases risk for colorectal, ovarian and endometrial carcinoma - colorectal carcinoma arises de novo via this mechanism

Answer 29

Microsatellite Instability

Question 30

- usually grows as a napkin-ring lesion - usually via adenoma-carcinoma sequence - presents with LLQ pain & blood streaked stool

Answer 30

Left-sided colorectal carcinoma

Question 31

- usually grows as a raised lesion - usually via microstatellite instability pathway - presents with iron-deficiency anemia due to occult bleeding, and vague pain

Answer 31

Right-sided colorectal carcinoma