Bile Acid Reabsorption – Function and Disorders
Bile acid reabsorption is the process by which bile acids secreted into the small intestine are taken back up into the bloodstream – a key step in the enterohepatic circulation.
Things worth knowing about "Bile Acid Reabsorption"
Bile acid reabsorption is the process by which bile acids secreted into the small intestine are taken back up into the bloodstream – a key step in the enterohepatic circulation.
What Is Bile Acid Reabsorption?
Bile acid reabsorption is a physiological process in which bile acids released into the intestine during digestion are recaptured and transported back to the liver. This process forms the core of the enterohepatic circulation and allows bile acids to be reused multiple times for fat digestion.
Function of Bile Acids
Bile acids are synthesized in the liver from cholesterol and stored in the gallbladder. After a meal, they are released into the small intestine, where they emulsify dietary fats and fat-soluble vitamins (A, D, E, K), making them accessible for absorption through the intestinal wall.
Mechanism of Reabsorption
The reabsorption of bile acids takes place primarily in the terminal ileum – the final section of the small intestine. Specialized transport proteins, in particular the apical sodium-dependent bile acid transporter (ASBT), actively take up bile acids from the intestinal lumen into the epithelial cells. From there, bile acids enter the portal vein and are transported back to the liver, where they are re-secreted into bile.
Key Steps at a Glance
- Release of bile acids from the gallbladder into the small intestine
- Emulsification of dietary fats in the intestinal lumen
- Active reabsorption in the terminal ileum via ASBT transporters
- Transport through the portal vein back to the liver
- Re-uptake into liver cells and re-secretion into bile
Importance of the Enterohepatic Circulation
The body recycles bile acids up to 10 times per day through this mechanism. Only a small fraction (approximately 5%) is lost in the stool and must be replaced by new synthesis in the liver. This efficient recycling system conserves resources and maintains a stable bile acid pool.
Disorders of Bile Acid Reabsorption
When reabsorption is impaired – for example in Crohn disease affecting the terminal ileum, following surgical removal of intestinal segments (ileal resection), or in certain bowel conditions – excess bile acids reach the large intestine. There, they exert osmotic and secretory effects on the colonic mucosa, causing a condition known as bile acid diarrhea (also called bile acid malabsorption).
Possible Causes of Impaired Bile Acid Reabsorption
- Crohn disease with involvement of the terminal ileum
- Surgical resection of the ileum (e.g., due to cancer or inflammatory bowel disease)
- Radiation enteritis following abdominal radiotherapy
- Idiopathic bile acid malabsorption (no identifiable underlying cause)
Diagnosis
The SeHCAT test is commonly used to evaluate bile acid malabsorption. It involves administering a radiolabelled bile acid analogue and measuring how much is retained in the body after seven days. Low retention values indicate malabsorption. Alternatively, bile acid levels can be measured in blood or stool samples.
Treatment
Confirmed bile acid malabsorption is typically treated with bile acid sequestrants such as cholestyramine or colesevelam. These agents bind excess bile acids in the intestinal lumen and prevent them from irritating the colon. Dietary modifications – such as a low-fat diet – can also help reduce symptoms.
References
- Staels B, Fonseca VA. Bile acids and metabolic regulation. Diabetes Care. 2009;32(Suppl 2):S237–S245.
- Hofmann AF, Hagey LR. Bile acids: chemistry, pathochemistry, biology, pathobiology, and therapeutics. Cellular and Molecular Life Sciences. 2008;65(16):2461–2483.
- Walters JR. Bile acid diarrhoea and FGF19: new views on diagnosis, pathogenesis and therapy. Nature Reviews Gastroenterology and Hepatology. 2014;11(7):426–434.
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