What is a Bile, secretion of bile and the role of bile acids in digestion

You may have been wondering; what is a bile? If you have ever killed a bird (chicken) for consumption, there is a small sac like organ attached to the liver that is normally cutted out carefully ( to prevent it from becoming bitter) that is the gall bladder that habours the bile we are about to discuss.

Bile is a complex fluid that contains water, electrolytes, and other organic molecules such as bile acids, cholesterol, phospholipids and bilirubin that flows into the small intestine through the biliary track.

You may also wonder , How much bile is secreted/produced daily? About 400-800ml of bile is secreted daily in adult human and other animals with bile.

 

Functions of bile

Okay, let’s sharply look at the functions,. Bile has two major functions viz.

Digestion and elimination of fat soluble vitamins and cholesterol

Elimination of waste products ( including bilirubin) by secretion into bile and eliminated in faece .

Production of bile

Bile is produced by liver cells (hepatocytes) which secret bile into canalculi, from which it flows into bile duct. As the bile flows through the ducts, it is modified by the addition of water bicarbonate rich solution from ductal epithelial cells. The gall bladder stores the bile produced and it concentrates it during fasting stage through reabsorption of water.

Regulation of Bile release

Let us now highlight on the mechanism of release of Bile into the small intestine… Are you ready? Okay let’s go…. It’s release is depends on the activity of the sphincter of oddi (hepatopancreatic sphincter). During inter digestive period, the sphincter is contracted/ closed, hence preventing Bile from flowing out into the duodenum through the ducts. During digestive period, fatty acids in the lumen of the duodenum stimulates endocrine cells to secrete the hormonecholecystokinin(CCK). CCK then stimulates the contraction of the smooth muscles of the gall bladder and the relaxation of the sphincter of oddi. Also, acidic chyme stimulates endocrine cells to release the hormone secretin , which stimulates the duct cells to release bicarbonate into the bile. The bicarbonate increases the volume of the bile. Hope you understood how it works…. Then take long breath… Wow, let’s continue!!!

 Hormones and their actions in bile release

Enterohepatic circulation

 

You may have pondered on the question, can bile be recycled?, Yes, but not all the components and amount is recycled.

Bile salts and some components of bilirubin can be recycled. The process of recycling bile acids is known as enterohepatic circulation. Hope you are following? Okay, let’s continue…

How is it possible?. specific transporters located at the terminal ileum move the bile from the lumen of the digestive tract into the intestinal capillaries. It’s then transported through the hepatic portal vein back to the liver where hepatocytes reabsorb the bile acids and increase its secretion into the canalculi. So this is how it’s been recycled!!!! About 95% is recycled while 5% is lost to our faeces.

Roles of bile acids in fat digestion and absorption

Remember the functions of bile we mentioned earlier about digestion and absorption of fat. Bile acids are derived from cholesterol synthesized in the hepatocytes and in conjugation Amino acids( glycine and taurine) to yield it’s active compound secreted into the canalculi- gives the absorption role.

In it’s digestion role, it performs two major actions via

A) emulsification of lipid aggregates

B) solublization and transport of lipids in an aqueous environment.

Hope you understood and enjoyed the tutor?,if yes, share your experience..

Also share to educate others!!!!!!

 

 

 

 

 

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