The below mentioned article provides a paragraph on sterols.
Sterols or steroids are not true fats. Steroids are derivatives of phenanthrene and have the parent nucleus (perhydrocyclopentanophenanthrene) with 17 carbon atoms consisting in 3 hexagon and one pentagon rings. When the natural steroids have a methyl group at C-13 and generally at C-10 and possess one or more alcoholic groups, then these secondary alcohols are sterols. Steroids are found free or in ester forms as cholesterides and can be extracted by organic solvents along with fat.
Sterols cannot be hydrolysed by NaOH. Hence, they are not saponifiable. Otherwise, their physical and chemical properties are very similar to those of fats. With fatty acids they form waxes. The various members of this group can be separated by fractional distillation.
Sterols are widely distributed in both animal and vegetable kingdoms. In the plants they exist chiefly as phytosterols. In the animals they are present in all cells, both in the cell membrane as well as in the cytoplasm. They always remain along with phospholipids. They are found both as free sterols as well as sterides. They are very rich in certain tissues, e.g., the nervous tissue, suprarenal cortex, gonads, etc.
Sterols can be synthesised in the body from non-sterol sources. It has been definitely proved in the case of cholesterol. The body can destroy sterols to some extent but the power is very limited. Large quantities are excreted through sebum of the skin secreted by the sebaceous glands. It is also excreted as coprosterol of the faeces, and as sex hormones and traces of cholesterol in the urine.
A number of sterol compounds, synthesised in the body, are found to have immense physiological importance in the body. Many of them have been artificially synthesized.
Important members of this class are enumerated below:
i. Female Sex Hormones:
a. Oestrogen Groups:
Oestrone, oestradiol (the natural hormones) and the various synthetic oestrogens.
b. Corpus Luteum Hormones:
The naturally occurring progesterone and similar synthetic products.
ii. Male Sex Hormones:
Testosterone and the synthetic products.
iii. Active Principles of Adrenal Cortex:
Corticosterone and the similar products isolated from the gland.
iv. Cholesterol and Other Related Compounds:
Such as dihydrocholesterol, etc.
v. Cholic Acid of Bile:
Cholic acid of bile is a sterol compound.
vi. The Vitamin D Group:
The vitamin D group and the related ergosterol also belong to this class.
Digitalis, which is of immense pharmacological importance, is also a sterol compound. Sterols are essential for life. Moreover, it is interesting to note that sterols are intimately related to cell division. All rapidly growing tumours are very rich is sterols, specially cholesterol. The most effective cancer-producing substance is a synthetic sterol compound (methyl cholanthrene).