Library · Physiology
Bile secretion
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Bile is a watery fluid that the liver makes and secretes. It is not just water: it carries bile salts, phospholipids, cholesterol, conjugated bilirubin (one of its pigments), electrolytes (mineral salts) and water.
The interesting part is where it comes from. The liver cells, the hepatocytes, have extremely fine channels between them called canaliculi, and they push bile salts into them. That push is what sets the pace: when the salts enter the canaliculus, water follows them in by osmosis, which is the movement of water toward wherever there are more dissolved substances. That is why bile comes out as a liquid and not as a paste.
Once in the ducts, other cells called cholangiocytes receive it and modify it: they dilute it a little more and make it less acidic. Together they produce about 600 milliliters of bile a day.
And little goes to waste. When bile reaches the intestine and finishes its job, most of the bile acids are reabsorbed in the ileum, the last stretch of the small intestine, and travel back to the liver to be used again. That round trip is called the enterohepatic circulation.
In brief
Bile is a watery solution secreted by the liver, mainly bile salts, phospholipids, cholesterol, conjugated bilirubin, electrolytes and water.
Hepatocytes release it into their canaliculi; that transport of conjugated bile salts is the strongest driver.
Once the salts enter the canaliculus, water follows by osmosis; cholangiocytes dilute and alkalinize it, and daily flow is around 600 milliliters.
The solute enters the tube and water follows it in.
Most bile acids are reabsorbed in the ileum and return to the liver through the enterohepatic circulation.
Sources (1)
- National Center for Biotechnology Information, StatPearls PublishingPhysiology, Bile Secretion, StatPearlsPublished
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