Bile acid

Bile acid . Derivative compound the cholesterol , consisting of 24 atoms of carbon dihydric or trihydric, is characterized by the C 17 branched aliphatic chain of 5 carbon atoms, with which acquires a basic structure of phenanthrene pentanoperhidro ring with a terminal carboxyl group.

Summary

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  • 1 Structure
  • 2 Types of bile acids
  • 3 Composition
  • 4 Functions
  • 5 Pharmacology
  • 6 Biological importance of bile acids
  • 7 Sources

Structure

Bile acids are natural substances produced by the liver and stored in the gallbladder to help digest fats . Its structure is that of a cyclopentanophenanthrene, are also related to vitamin D . They are formed from glycocolic and taurocolic acid . These in turn are formed from cholic acid as an amino acid and glycine with taurine . Liver cells dump glyco and taurocholic acids into bile in the form of sodium salts.

The pigments are:

The bilirubin after breakdown given by biliverdina. Vesicular bile contains 5% solids; the hepatic 2%. The total amount of bile secreted is about 1.0 – 1.5 mL in 24 hours, of which 80-90% is reabsorbed.

Types of bile acids

  • Cholic acid (hydroxylated in position 3-7 and 12α).
  • Lithocolic acid (hydroxylated in position 3α and 24α).
  • Deoxycholic acid (hydroxylated in position 3α and 12α).
  • Ursodeoxycholic acid (hydroxylated in position 3-7 and 24α).
  • 3-α 7-β-hydroxycholanic acid.

Therefore they are steroids , a class of unsaponifiable lipids . Furthermore, these acids are structural derivatives of cholic acid. The difference in these acids lies in the incorporation into the steroidal ring of one, two or three hydroxyl groups, one of which may be oxidized to ketone .

Composition

It is composed of bile salts, pigments, mucin, lecithin, cholesterol, inorganic and organic salts, water, etc. The bile salts are sodium glycine and taurocholate, chemically related to steroid hormones and Adrenal Corticosteroids.

They make up the bile, in which it is found forming salts that act as detergents in the small intestine, by decreasing the surface tension of the fats, causing their emulsion, which will subsequently degrade by the action of lipases. They are necessary for the absorption of fat-soluble vitamins. They have a smooth cathartic action, improve bile drainage and prevent the presence of infections, since bile is an excellent breeding ground.

Features

They are necessary for the absorption of fat-soluble vitamins such as A, D, K and E. This perhaps explains why a great deficiency of vitamin D has been found in Cuba despite sun and milk . It also increases the absorption power of iron . It is said to have a stimulating power for intestinal peristalsis. On the other hand, some doubt that it is true that it slows down the first portion of the small intestine (duodenum where digestion takes place) and speeds up the peristalsis of the thickness (colon), etc.

Its main function is to act as choleretic, also having a cholagogue action. In the states of biliary deficiencies they act as substitute therapy by supplying the deficient bile salts and at the same time they stimulate the production of the bile flow.

The bile salts inhibit cholinesterase, which hydrolyzes acetylcholine which is the substance that allows the transmission of the vagus, thus increases the power of the parasympathetic and contractions of the intestine. Where there is biliary deficiency, there is, commonly, constipation, although this could be due to putrefactions and colitis .

It also acts as a light bacteriostatic agent, inhibiting the excessive growth of the colibacil. This action has been questioned when observing that the bile ducts become infected despite being full of bile, but there is no doubt that they have antiputrefactive action.

This action could be in part due to bacteriostatic action or that by helping to complete digestion of fats, they no longer cover the proteins as before, in that they accumulated on them, favoring this accumulation and the development of putrefactive bacteria. Another function of the bile is to neutralize the chymo-acid that comes from the stomach, although in this sense its action is inferior to that of the pancreatic juice.

A derivative of cholic acid, dehydrocolic acid, has so far been shown to be the most powerful choleretic in terms of the volume of bile secreted, although this increases in liquid and not in proportion to solids. Dehydrocolic acid, therefore, is only a hydrocholeretic but is less toxic than bile salts. Very frequently they appear conjugated to the amino acids glycine and taurine. Thus, cholic acid will form taurocholic and glycolic acids.

Although it seems paradoxical, the bile salts are not the salts of the bile acids, but the sodium or potassium salts of the taurocolic or glycolic acids.

Pharmacology

Bile acids are natural substances produced by the liver and stored in the gallbladder to help digest fats. The new material appears to be stronger and more durable, and has the potential to reduce pain and emergency doctor visits due to cracks in the amalgam, “wrote the scientists, led by Julian Zhu of the Department of Chemistry at Shanxi University, China .

The liver reabsorbs and re-excretes bile salts, thus forming a cycle necessary for the absorption of fats. The main function of bile salts is to act as choleretic, also having a cholagogue action. they act as substitute therapy by supplying deficient bile salts and at the same time stimulate the production of bile flow.

The bile salts when penetrating the intestine help the digestion of fat and fat soluble vitamins and after they are absorbed they act as choleretic. It is indicated in all cases of biliary insufficiency accompanied or not by cholecystitis, cholangitis or cholelithiasis, which are non-obstructive, since they increase bile flow, make bile more fluid and finally act as a mild intestinal antiseptic.

Biological importance of bile acids

Bile acids are synthesized exclusively in the hepatocyte from cholesterol, producing the two primary acids, cholic acid (tri-hydroxylated) and deoxycholic (di-hydroxylated).

Fundamentally two mechanisms regulate its synthesis:

1.- The synthesis of cholesterol.

2.- The activity of the enzyme 7a hydroxylase.

The main functions of bile acids are:

  • Fat absorption and digestion.
  • Induction to the secretion of liquids by the small intestine.

These primary acids are conjugated in the hepatocyte through a peptide bond with the amino acids glycine and taurine, and then they are secreted as bile in the intestine. It is in the duodenum and jejunum that they develop their function in the digestion and absorption of lipids.

The absorption of bile acids begins in the ileum to the proximal part of the colon . This is the place where the process of 7a dehydroxylation of the primary bile acids, colic and chenodeoxycholic occurs, to give rise to the secondary acids deoxycholic and lithocolic respectively.

These reabsorbed acids play a regulatory role in the synthesis of new bile acids by influencing cholesterol and bile acid synthesis enzymes, hydroxymethylgluconyl CoA (HMG CoA) and 7a hydroxylase.

The liver is the only organ responsible for all the metabolism, synthesis, conjugation, transport and excretion of bile acids. Fundamentally, liver uptake is the main indicator of the integrity of the enterohepatic circulation. Any liver damage compromises one or more steps of the delicate regulation mechanism of the bile acids, always causing an increase in their serum levels.

Under normal conditions there are daily rhythmic variations of these levels that are directly related to food intake.

It has a regulatory function. Cholesterol is a precursor to compounds of great biological importance, such as sex or adrenal hormones and vitamin D, which is involved in the regulation of calcium metabolism .

 

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