Small Bowel Disease

Question 1

preferred site of absorption of iron and folate

Answer 1

Duodenum

Question 2

90% of nutrient absorption occurs within the first 100-150 cm of jejunum, many drugs absorbed here

Answer 2

Jejunum

Question 3

site of vitamin B12 and bile salt absorption, “ileal brake” mediated by peptide YY (mechanism for slowing gastric emptying when fat reaches ileum)

Answer 3

Ileum

Question 4

• absorbs about 7 L daily (max 12 L)

Answer 4

Small bowel absorptive capacity

Question 5

• Presence of bile salts, pancreatic lipase and colipase at nearly neutral pH
• Healthy enterocytes
• Majority of dietary fat is in form of triglycerides
• Fat is emulsified by mastication and coating with phospholipid, bile acids
• TG, cholesterol and cholesterol esters, phospholipids packaged into chylomicrons and VLDL’s
  Chylomicrons secreted by the enterocyte into the lymphatic circulation
  Medium chain TG’s taken up directly into the portal circulation

Answer 5

Fat absorption requirements

Question 6

• Inability to absorb fats, leading to fatty stool

Answer 6

Steatorrhea

Question 7

• abnormal hydrolysis of nutrients

- relates more to pancreatic insufficiency

Answer 7

Maldigestion

Question 8

• abnormal mucosal absorption
• Processes other than abnormal hydrolysis of nutrients or abnormal mucosal function can lead to derangements in nutrient absorption (i.e. intestinal dysmotility)

Mech:

• Mucosal factors
• Pancreatic enzyme deficiency
• Intraluminal consumption of nutrients
• Bile acid deficiency

Answer 8

Malabsorption

Question 9

Diarrhea

• Weight loss
• Hyperphagia
• Deficiency syndromes associated with specific nutrients (vitamins A, D, Calcium, Magnesium, EK, B12, folate, iron)

Subtle manifestations:

• Abdominal distension, flatulence
• Anemia
• Kidney stones (increased oxalate absorption)
• Peripheral neuropathy
• Bone pain, osteomalacia, fractures (vit D malabsorption)
• dermatitis

Answer 9

Manifestations of Malabsorption

Question 10

In stomach: HCl acts on it to separate B12 from food

In small bowel: links to salivary R protein for transport; then is separated again

In terminal ileium: Links up to intrinsic factor, binds to ileal enterocyte and is absorbed

Answer 10

Vitamin B12 absorption

Answer 11

Small Ileal Resection

Question 12

> 100 cm resection, leading to significant reduction in luminal digestion of fats

• Result is also a secretory diarrhea (long-chain FA stimulate chloride/fluid secretion by colonocytes)
• Cholestyramine may worsen this type of diarrhea (further reduces the bile acid pool leading to worsening steatorrhea); you need the bile acids for fat absorption

Answer 12

Larger Ileal Resection

Question 13

• a bile acid sequestrant, which binds bile in the gastrointestinal tract to prevent its reabsorption

Answer 13

Cholestyramine

Question 14

• Increased oxalate absorption, with Volume depletion
• Calcium normally binds to oxalate and is excreted; calcium-bound-oxalate is not absorbed by colon
  In order to develop Oxalate stones:
• If no colon: no problem; oxalate is not absorbed
• If short bowel, but intact colon: poor fat absorption, resulting in saponification of Ca and fat; oxolate is reabsorbed in the colon, creating perfect mix for developing kidney stones

Answer 14

Malabsorption and Renal Stones

Question 15

• D-xylose is a pentose absorbed by passive diffusion (no pancreatic enzymes or bile salts required
• Previously used to distinguish malabsorption (mucosal factors) from maldigestion (pancreatic insufficiency)
• if malabsorption, D-xylose won’t be absorbed

Answer 15

D-Xylose testing

Question 16

• Malabsorbed CHO reaches intraluminal bacteria and H2 is produced, absorbed and measured in exhaled air
• Lactulose is ingested (non-absorbable CHO) to test for SBBO. Excess H2 is exhaled and measured

Answer 16

Breath Tests for Carbohydrate Malabsorption or Small Bowel Bacterial Overgrowth

Question 17

• Immune-mediated damage of small bowel villi due to gluten exposure
• assoc with HLA-DQ2 and DQ8
• Characteristic lesion: villous atrophy of small bowel mucosa
• Adherence to a gluten-free diet results in resolution of histologic and clinical findings

Clinical manifestations include:

• diarrhea, weight loss
• Vague abdominal discomfort, bloating and distension
• Growth failure and failure to thrive in children
• Life threatening malnutrition in severe cases
• Dermitits herpetiformis (small, herpes-like vesicles due to IgA deposition)

Diagnostic tests include:

• Serology: tissue transglutaminase (tTG) antibody/IgA
• Endoscopic biopsy: Rough, scalloping appearance of the small bowel

Answer 17

Celiac Disease

Question 18

• infection with Tropherymii whippelii (Red Bacilli) (treatable), causing systemic tissue damage
• Involves damage to the small bowel lamina propria
• Compression of lacteals prevents chylomicrons from being transferred from enterocytes to lymphatics
• Characterized by malabsorption, weight loss, diarrhea and abdominal pain
• CNS symptoms including dementia, cognitive changes, supranuclear ophthalmoplegia, and altered level of consciousness
• Cardiac manifestations: myocarditis and pericarditis, less commonly endocarditis; Oligoarthralgias or polyarthralgias (Arthritis Polyserositis)

Answer 18

Whipple’s Disease

Question 19

• lymphatic obstruction (primary or secondary) results in rupture of intestinal lacteals, causing leakage of protein, chylomicrons, and lymphocytes
• results in blunting of villi, fat malabsorption an diarrhea
• Primary intestinal lymphangiectasia usually presents with hypoproteinemia, edema, diarrhea, lymphocytopenia
• Secondary cases may be the result of retroperitoneal lymphadenopathy, fibrosis, pancreatitis or other processes that impair lymphatic drainage

Answer 19

Intestinal Lymphangiectasia

Question 20

• is a cause of malabsorption
• is associated with many disorders of the gut (gut dysmotility, hypochorhydria, surgery- especially with loss of ic valve, strictures,etc)
• Contributes to diarrhea and malabsorption in these patients
• Risk increases with age
• diagnose with Lactulose breath test

Answer 20

Small Bowel Bacterial Overgrowth

Question 21

• Acquired primary lactase deficency is the most common type
• Manifest by abdominal bloating, abdominal cramping, flatulence, diarrhea
• Reversible lactase deficiency commonly seen in viral gastroenteritis,and other SB diseases (ie Crohn’s)

Answer 21

Lactase Deficiency

Question 22

• Loss of 70-75% of small bowel
• can survive with 100-120 cm of small bowel without a colon; or 50 cm of small bowel with a colon
• Crohn’s disease is a major cause
• Severe fluid and electrolyte problems can arise in SBS; Patients may respond to dehydration with hypotonic fluids which can result in significant volume depletion and electrolyte derangements
• use Na/KATPase to create electrochemical gradient that favors absorption into cell

Answer 22

Short Bowel Syndrome

Question 23

• Adequate absorption unless > 75% resected
• Preserved absorption of VitB12 and bile salts
• good ileal adapatation
• normal transit

Answer 23

Jejunal Resectioning

Question 24

• Adequate calorie and fluid absorption
• Malabsorption of Vit B12 and bile salts
• poor jejunal adaptation
• Rapid intestinal transit

Answer 24

Ileal Resectioning

Question 25

Na/K ATP-ase on basolateral membrane creates gradient to draw Na in from apical membrane - Apical membrane Na-glucose cotransporter drives Na and glucose into cell - Water follows Na movement - Net result enhances water absorption

Answer 25

Na-Glucose transporter