Enterohepatic circulation

Diagram of the enterohepatic circulation

The enterohepatic circulation refers to the circulation of bile acids, bilirubin, drugs, and other substances from the liver to the bile, followed by entry into the small intestine, absorption by the enterocytes, and transport back to the liver. This process is crucial for the digestion and absorption of lipids and fat-soluble vitamins, as well as the detoxification and excretion of various substances.

Components of Enterohepatic Circulation

Bile Acids

Bile acids are synthesized in the liver from cholesterol and are secreted into the bile. They play a key role in the emulsification and absorption of dietary fats in the small intestine. After aiding in digestion, bile acids are reabsorbed in the ileum and returned to the liver via the portal vein.

Bilirubin

Bilirubin is a byproduct of the breakdown of hemoglobin from red blood cells. It is conjugated in the liver and excreted into the bile. In the intestine, bilirubin is converted into urobilinogen, some of which is reabsorbed and returned to the liver, while the rest is excreted in the feces.

Drugs and Toxins

Many drugs and toxins undergo enterohepatic circulation. After being metabolized in the liver, they are excreted into the bile and can be reabsorbed in the intestine, prolonging their presence in the body.

Physiological Importance

The enterohepatic circulation is essential for maintaining the body's homeostasis of bile acids and cholesterol. It allows for the efficient recycling of bile acids, reducing the need for de novo synthesis. This circulation also plays a role in the regulation of lipid metabolism and the detoxification of harmful substances.

Clinical Significance

Disruptions in enterohepatic circulation can lead to various medical conditions. For example, impaired reabsorption of bile acids can result in bile acid malabsorption, leading to diarrhea and malabsorption of fats. Additionally, certain liver diseases can affect the enterohepatic circulation, impacting the body's ability to process and excrete bilirubin and other substances.

Related Pages

• Liver
• Bile
• Small intestine
• Portal vein
• Cholesterol
• Bilirubin