Steroid

One of a group of polycyclic compounds closely related biochemically to terpenes. They include cholesterol, numerous hormones, precursors of certain vitamins, bile acids, alcohols (sterols), and certain natural drugs and poisons (such as the digitalis derivatives). Steroids have as a common nucleus a fused, reduced, 17-carbonatom ring system, cyclopentanoperhydrophenanthrene.
Most steroids also have two methyl groups and an aliphatic side chain attached to the nucleus. The length of the side chain varies and generally contains 8, 9, or 10 carbon atoms in the sterols, 5 carbon atoms in the bile acids, 2 in the adrenal cortical steroids, and none in the estrogens and androgens. Steroids are classed as lipids because of their solubility in organic solvents and insolubility in water. Most of the naturally occurring steroids have been synthesized and many new steroids unknown in nature have been synthesized for use in medicine, such as the fluorosteroids (dexamethasone).

steroid: Any of a group of lipids derivedfrom saturated compoundcalled cyclopentanoperhydrophenanthrene,which has a nucleus of fourrings (see formula). Some of the mostimportant steroid derivatives are thesteroid alcohols, or sterols. Othersteroids include the bile acids, whichaid digestion of fats in the intestine;the sex hormones (androgens and oestrogens);and the corticosteroid hormones,produced by the adrenalcortex. Vitamin D is also based onthe steroid structure.

Any member of a group of biochemical compounds having a complex basic ring structure. Examples are corticosteroid hormones (produced by the adrenal gland), sex hormones (progesterone, androgens, and estrogens), bile acids, and sterols (such as cholesterol).