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Renin Angiotensin Mechanism.

Biological Significance of Cholesterol and conversion of cholesterol to bile acids, steroid hormone and vitamin D.

 

Definition:

  • It is a sterol, a type of lipid. 

  • Cholesterol is biosynthesized by all animal cells and is an essential structural component of animal cell membranes.

Biological significance of cholesterol

  • An integral part of the cell membranes.

  • The production of bile acids and steroid hormones.

  • Needed for Vit D Synthesis.

  • The chief cause of Atherosclerosis.

  • All steroid hormones, such as androgens, estrogens, progestogens, glucocorticoids, mineralocorticoids, and calcium D, are derivations of cholesterol.

Conversion of cholesterol to bile acids:

  • Bile acids are created through cholesterol, which are necessary for solubilizing fat. 

  • Bile acids are formed by oxidizing the side chain of cholesterol molecules. 

  • In addition to hydroxylation of the rings and links to other polar compounds, other alterations are used to make these compounds more polar. 

  • Common bile acids are 

    • deoxycholic acid, 

    • cholic acid, 

    • chenodeoxycholic acid, 

    • glycocholic acid, and 

    • taurocholic acid. 

  • Synthesis of bile acids reduces the level of cholesterol in the body and enhances the liver's ability to absorb LDL particles. 

  • The recycling of bile acids helps in restoring the cholesterol levels.

Significance of Bile Acids:

  1. The bile acid digestion and absorption of lipids by emulsifying them..

  2. Production of bile acid is the most important catabolic pathway of cholesterol. Continuous conversion of cholesterol into bile acids prevents the overproduction of cholesterol in the body

  3. Excretion of bile salts serves as a major pathway for the removal of steroid nucleus from the body.

Conversion of Cholesterol to Steroid Hormones:

  • The important steroidal hormones in the body are,

    • Estrogen

    • Progesterone.

    • Testosterone.

    • Mineralocorticoids.

    • Glucocorticoids. 

  • Branching from cholesterol, one can form steroid hormones. 

  • The branch molecule for all of these is the cholesterol metabolite (and progestogen) known as pregnenolone. 

  • The progestogens are precursors of all of the other sex hormones and steroidalhormones.

  • Progesterone is first synthesized from cholesterol. 

  • Additional hormones produced by progesterone include the glucocorticoids, androgens, and mineralocorticoids. 

  • Estrogens are created by further transformation of androgens.

Conversion of Cholesterol to Vitamin D:

  • The epidermal layer of human skin synthesizes vitamin D when exposed to UV radiation. 

  • In the presence of sunlight, a form of vitamin D3 called cholecalciferol is synthesized from cholesterol in the skin. 

  • The liver converts cholecalciferol to calcidiol, which is then converted to calcitriol (the active chemical form of the vitamin D) in the kidneys.

Commonly Asked Questions:

  1. Explain conversion of Cholesterol to Bile acids.

  2. Give significance to Cholesterol in the human body.

  3. Explain conversion of Cholesterol to Steroid Hormones.

  4. Explain conversion of Cholesterol to Vitamin D.
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