Bile | Bile salts|Formation | storage | Functions | Physiology

Bile

                                                        Bile 

This article discusses different aspects of bile and bile salts. Here, learn about the bile, site of synthesis, functions, and more… 

About' totalphysiology.com.'

This article is part of my mission to provide trustworthy recent health information to support the general public, patients, and professionals worldwide.

Here you will find human physiology, anatomy, and health topics.

 

Keywords: Bile salts|Formation | Storage | Functions| Enterohepatic circulation | Choleretic substances | Cholic acid | Cholagogues | Taurocholic acid  

   Table of contents

1.	Introduction
2.	Composition
3.	Secretion
4.	Mechanism of secretion
5.	Regulation of secretion
6.	Functions

Introduction: Bile is a physiological fluid that is dark green to yellowish-brown in color and produced by the liver.

In humans, bile is produced continuously by the liver and drained by bile canaliculi to the right and left hepatic ducts. The right and left hepatic ducts join to form the common hepatic duct. The cystic duct from the gall bladder joins the common hepatic duct and forms the common bile duct. 

The pancreatic duct merges with the common bile duct before it opens into the second part of the duodenum through the hepatopancreatic sphincter –also known as the sphincter of Oddi. Before opening, there is a dilatation in the duct known as the ampulla of Vater.

The tone of the sphincter of Oddi is high during inter digestive period. Therefore bile comes into the gall bladder. In the gall bladder, hepatic bile is stored and concentrated. 

Typically, bile is concentrated five times in the gall bladder by water absorption and electrolytes, but organic molecules are retained. Oddi's sphincter relaxes when food enters the mouth, and the gall bladder's contraction occurs, causing the discharge of bile into the duodenum under the influence of nervous and humoral controls.

Composition of bile:

Secretion 500-1000ml/day

Color dark green to golden yellow-transparent.

It is alkaline, 7.8 to 8.7 pH, and isotonic with plasma.

Water 97%

Bile salt 0.7%

Bile pigment 0.2%

Fat, fatty acids, and lecithin cholesterol are less than 0.1% each.

Cations  Na⁺        180-220 mEq/L  Anions   Cl^-  60-70 mEq/L

                K⁺        6-8 mEq/L                          HCO₃^- 60-70 mEq/L

                Ca⁺⁺     2.5-5 mEq/L

Bile is secreted in two stages:

Stage one: The hepatocytes secrete an initial secretion rich in bile salts, cholesterol, and other organic components.

Stage two: The initial secretion will flow towards the bile ducts. During this flowing, water and the sodium bicarbonate ion is added.  

Bile acids are steroid acids synthesized from cholesterol. Diverse Bile acids are synthesized in the liver.

Primary bile acids are those synthesized by the liver.

Secondary bile acids result from bacterial actions in the colon.

The two main primary bile acids are

cholic acid and chenodeoxycholic acid.

Secondary bile acids are:

Deoxycholic acid from cholic acid and lithocholic acid from chenodeoxycholic acid.

Conjugation of these acids occurs in the liver. Conjugation means 'join together.

So, for example, the conjugation of cholic acid with taurine forms taurocholic acid, and when it conjugates with glycine, it forms glychocholic acid.

Likewise, the conjugation of chenodeoxycholic acid with taurine forms taurochenodeoxycholic acid, and conjugation with glycine forms glucochenodeoxycholic acid.

The acids form sodium and potassium salts in the alkaline bile. They are roughly equal in concentration.

Secondary bile acids  are deoxycholic acid and (from cholic acid)

lithocholic acid  (from chenodeoxycholic acid)   also forms bile salts.

Bile salts are amphipathic molecules with hydrophobic and hydrophilic regions. The conjugated bile salts occupy the lipid/water interface and form micelles above the right concentration. 

The conjugated bile salts prevent passive reabsorption in the small intestine. As a result, bile acids/ salts in the small intestine are high enough to form micelles and solubilize lipids.

Critical micellar concentration refers to both an intrinsic property of the bile acid and the amount of bile acid necessary to function in micelles' spontaneous and dynamic formation. 

Bile acid-containing micelles aid lipases in digesting lipids and bring them near the intestinal brush border membrane, which results in fat absorption.

Bile salts do not contribute to the osmotic pressure of the bile. Therefore, the osmotic pressure of bile is identical to plasma., 290 m osm/L.

The average rate of bile salts synthesis is 0.2-0.4 gm/day. Therefore, the total pool of circulating bile salts is about 4-6 gm. This is almost limited.

Enterohepatic circulation: Bile salts enter the duodenum, of which 90-95% are reabsorbed actively from the terminal ileum in the portal vein and return to the liver. The rest, 5-10%, are converted to deoxycholic acid and lithocholic acid salts by gut flora. 

The lithocholic acid form is relatively insoluble and is mainly excreted in stools, but deoxycholate is absorbed and excreted in the urine.

As an ordinary meal needs 6-8 gm of bile salts to digest and absorb fats, the total bile acid pool is 4-6 gm. So it must circulate twice during the digestion of each meal.

Bile pigments are formed from haem of hemoglobin after RBC destruction. Bile pigments are bilirubin, and biliverdin. 

1gm hemoglobin produces 40 mg of bilirubin. 

They are excretory products and perform no digestive functions.

Regulation of bile secretion:

Bile acids are potentially toxic to cells as surfactants or detergents, so their concentrations are tightly regulated. First, activation of FXR in the liver inhibits the synthesis of bile acids and is one feedback control mechanism when bile acid levels are too high. 

Secondly, FXR activation by bile acids during absorption in the intestine increases transcription and synthesis of FGF19, which then inhibits bile acid synthesis in the liver.    

1. Nervous control: Stimulation of the vagus causes contraction of the Gall bladder and relaxation of the sphincter of Oddi. This is mediated by acetylcholine.

2. Humoral control: Secretin and CCK-PZ cause an increase in bile flow by contraction of the gall bladder. The acid in the duodenum stimulates the secretion of Secretin. Products of fat and protein digestion stimulate CCK-PZ secretion. Gastrin, Secretin, and bile salts stimulate bile secretion.

Choleretic substances increase the biliary secretion of bile salts and bile acids from the liver.

Cholagogues cause contraction of the gall bladder and increase the bile release.

Functions of bile :

1. Helps digestion and absorption of fats and fat-soluble vitamins-ADEK due to Bile salts. Dietary Bile acids facilitate the digestion of dietary fats and oils. They serve as micelle–forming surfactants, encapsulating nutrients and reducing their absorption. These micelles are suspended in the chyme before processing. Bile salts cause FXR activation with triglyceride metabolism, glucose metabolism, and liver growth alterations.

2. Neutralization of acidic chyme present in the duodenum.

3. Provides an alkaline medium for optimal functions of enzymes and hormones.

4. Excretion –bile removes many metals, copper, zinc, some drugs, and some hormones. It also excretes bilirubin.

5. Prevents precipitation of cholesterol. Free cholesterol is virtually insoluble in aqueous solutions, but it is made soluble by bile acids and lipids like lecithin in bile acids and lipids.  

6. Bile acids also have hormonal actions throughout the body, particularly the 'farnesoid x receptor' and GPBAR1' G protein-coupled bile acid receptor/TGR5'.

7. They bind less specifically to some other receptors. However, they have been reported to regulate the activity of certain enzymes and ion channels and the synthesis of various substances, including endogenous fatty acid ethanolamides.

8. Bile salts destroy many microbes present in food.

Bile acid sequestrants bind bile acids in the gut, preventing their reabsorption. So more endogenous cholesterol is shunted into the production of bile acids, thereby lowering cholesterol levels. The sequestered bile acids are then excreted in the feces.

Tests for bile acids are helpful in the diagnosis of many conditions, including types of cholestasis.

The ratio of bile acid to cholesterol saturation in bile and precipitation to produce gallstones is essential.

Excess concentrations of bile acids in the colon cause chronic diarrhea. It is found in Crohn's disease or when the ileum is abnormal.

Bile acids have some importance in the development of colorectal cancer.

Increased secretion of bile acids causes an increase in bile flow.

---------------------------------------------------------------------------------------

Like to meet again? Sign up to get an email when I publish.

Question? Email me bkp337390@gmail.com

 Follow me on Instagram @ bijaykprasad

                                                @bkpdphysiology

  Follow us on Twitter@ at bijaykrishnapr3

                                       @BijayPr60250287

 

And don’t forget to follow me on learn and fly.co.in

I am more enthusiastic, and you can get new insights from my articles later.

Thank you.

Learn More :

1. About  us

2. Contact us

3. Disclaimer

4. Privacy Policy

5. DMCA

6. About Author andAdmin.

Please submit any comments about this article. The team will work hard to evaluate the statement and make appropriate corrections.

Help to improve the content.

Question: Hi! Got any questions? I can help you.

Thank you very much for reading. I admit and appreciate that you spent some time with us. If you enjoyed reading, do me a small favour. Would you leave a review or a comment? Your comments will encourage other folks to read. 

Your name and email

Disclaimer: All possible measures have been taken to ensure the accuracy and reliability of the information; however, 'totalphysiology.com' does not take any liability for the same using any information provided by the website solely to the viewers. 'The information is provided as an educational service and public awareness. It is not medical advice. 

In case of any medical health issue, we advise you to seek the advice of a qualified doctor and follow his instructions.

Internal link:

https://totalphysology20.blogspot.com/2021/02/glands-we must know https://totalphysology20.blogspot.com/2021/03/small intestine. We must know

https://totalphysology20.blogspot.com/2021/04/large  intestine. We must know

 https://totalphysology20.blogspot.com/2021/05/gut brain axis. We must  know

External link:

https://en.m.wikipedia.org>wiki

https://www.sciencedirect.com>topics

https://www.ncbi.nim.nih.gov

https://www.ncbi.nim.nih.gov>books

https://www.healthline.com>nutrition

https://www.britannica .com>science

Please follow me on email, Twitter, and Facebook.

Pl. like, follow, and subscribe.

#english# cholagogues# choleretic #cholic acid # chenodeoxycholicacid# entero hepatic circulation#Bile salts #Formation # storage #Functions |