Ileal Disease/Resection

Disease or resection of terminal ileum or congenital absence of the ileal BA transporter results in BA malabsorption and wasting in the colon. Increased hepatic synthesis can compensate for BA losses of up to 3 g/day; however, when losses exceed 3 g/day, the enterohepatic BA pool shrinks, resulting in impaired micelle formation and fat malabsorption.

Daily fecal fat excretion remains normal until greater than 100cm of ileum is resected. With less extensive resections, fat absorption is preserved, but bile acid wasting in the colon results in a secretory diarrhea.

Long-term complications of chronic bile salt wasting and fat malabsorption:

1. Renal stones. Oxalate stones occur when unabsorbed FAs within the intestinal lumen bind Ca++ with generation of free oxalate anions which pass into the colon where they are absorbed.

2. Bone disease. Impaired micelle formation results in decreased absorption of vitamin D with resulting decreased calcium absorption.

3. Gallstones. Mechanism is unknown but both cholesterol and pigment (calcium bilirubinate) stones can form.

Impaired Mixing

Surgery altering normal intestinal flow e.g. partial gastric resection with gastrojejunostomy (Billroth II anastomosis) may result in malabsorption.

1. Release of bile and pancreatic secretions distal to the site of entry of gastric contents into jejunum results in poor mixing with resulting impaired lipolysis and micelle formation.

2. Rapid transit through the jejunum contributes to nutrient malabsorption.

3. Afferent loop of bowel not in continuity with intestinal flow predisposes to bacterial overgrowth.

Category: Gastroenterology Notes