Small Bowel

Question 1

Duodenal Atresia

Answer 1

failure of duodenum to canalize and is associated with Down syndrome causing polyhydramnios, bilious vomiting, double bubble (distension of stomach and blind loop of duodenum)

Question 2

Meckel Diverticulum

Answer 2

outpouching of all 3 layers of the bowel wall from failure of the vitelline duct to involute

seen in 2% of population, 2in long, within 2ft of ileocecal valve, presents during first 2 years of life (bleeding, volvulus, intussusception, obstruction)

Question 3

Volvulus

Answer 3

twisting of bowel along mesentery causing obstruction and disruption of blood supply (infarction)

*usually in sigmoid colon in elderly or cecum in young adults

Question 4

Intussusception

Answer 4

telescoping of proximal segment of bowel forward into distal segment (pulled by peristalsis) causing obstruction and blood supply disruption (infarction)

• children: caused by lymphoid hyperplasia in terminal ileum leading to intussusception into cecum
• adults: cause is a tumor

Question 5

Small Bowel Infarction

Answer 5

susceptible to ischemic injury which causes abdominal pain, bloody diarrhea and decreased bowel sounds

• <b>transmural infarction</b>: with thrombosis/embolism of SMA or thrombosis of mesenteric vein
• <b>mucosal infarction</b>: with marked hypotension

Question 6

Lactose Intolerance

Answer 6

decreased function of lactase (usually in brush border of enterocytes) presenting with abdominal distension and diarrhea

• undigested lactose is osmotically active
• temporary deficiency is seen after small bowel infection (lactase is highly susceptible to injury)

Question 7

Celiac Disease

Answer 7

immune-mediated damage of small bowel villi from gluten exposure (gliadin= pathologic component) associated with HLA-DQ2 and DQ8 presenting with abdominal distension, diarrhea, failure to thrive (children) or chronic diarrhea and bloating (adults)

*dermatitis herpetiformis from IgA deposition at the tips of dermal papillae

• gliadin–> deamindated by tissue transglutaminase–> presented by APCs via MHCII–> helper T cells mediate tissue damage
• lab findings: IgA Ab against endomysium, tTG or gliadin, increased incidence of IgA deficiency, flattening of villi, hyperplasia of crypts, increased intraepitherlial lymphocytes (more damage in duodenum)

*late complications: small bowel carcinoma, T-cell lymphoma

Question 8

Tropical Sprue

Answer 8

damage to small bowel villi causing malabsorption

*differs from celiac disease: in tropical regions, after infectious diarrhea, responds to antibiotics, more damage in jejunum and ileum (secondary vB12 or folate deficiency)

Question 9

Whipple Disease

Answer 9

tissue damage characterized by macrophages with Tropheryma whippelii organisms especially in small bowel lamina propria (could also involve synovium of joints, cardiac valves, lymph nodes, CNS)

1. macrophages compress lacteals
2. chylomicrons cannot be transferred from enterocytes to lymphatics
3. fat malabsorption and steatorrhea

Question 10

Abetalipoproteinemia

Answer 10

deficiency of B48 and B100 causing malabsorption (defective chylomicron formation since there is no B48) and absent plasma VLDL and LDL (since there is no B100)

Question 11

Carcinoid Tumor

Answer 11

low-grade malignancy due to proliferation of neuroendocrine cells (positive for chromogranin) which most often arises in the small bowel as a submucosal polyp-like nodule

• secretes serotonin which is released into the portal circulation and is metabolized by liver MAO into 5-HIAA which is excreted in teh urine
• metastasis of carcinoid tumor to the liver allows serotonin to bypass liver metabolism (serotonin is released into the hepatic vein and leaks into systemic circulation–> carcinoid syndrome and carcinoid heart disease