Important products derived from cholesterol
In the body cholesterol is converted into several other types of biologically important steroids, viz. bile acids, bile salts and Vitamin D.
Bile acids are of two types namely primary and secondary bile acids. Primary bile acids include cholic acid and chenodeoxy cholic acid and secondary bile acids include deoxycholic acid and lithocholic acid.
Bile acids are C24 steroids, detergent like compounds that are responsible for the emulsification and absorption of lipids in the intestine.
Cholic acid is conjugated in the liver with either glycine or taurine through peptide linkages forming the bile salts glycocholic acid and taurocholic acid respectively. They combine with sodium and potassium present in the bile and form water soluble alkaline bile salts, namely sodium glycocholate and sodium taurocholate respectively.
· Bile salts are the digestion promoting constituents of bile.
· They lower surface tension and thus can emulsify fats.
· They also activate lipases.
Vitamin D is produced by irradiation of 7-dehydrocholesterol in the skin and in the kidney.
Vitamin D is a derivative of cholesterol and the precursor of para thyroid hormone which regulates calcium and phosphate metabolism in vertebrates.
Phospholipids are so designated because they contain phosphoric acid. They are present in all cells, plants as well as animals. They are present both in cytoplasm as well as in the cell membranes and serve important functions in both cell activity and cell permeability. Phospholipids are made up of fatty acids, nitrogenous base, phosphoric acid and glycerol or other alcohol. Phospholipids can be classified based on the alcohol moiety of the phospholipid as follows.
Glycerol is the alcohol moiety in this group. This include lecithins, cephalins, phosphatidyl serine, plasmalogens and diphosphatidyl glycerols.
In this the cyclic hexahydric alcohol “inositol” replaces the nitrogenous base.
In this group of substances, glycerol is replaced by a complex amino alcohol “Sphingosine”. These are clinically important phospholipids in human.