Fused compound in the context of "Camphor"

A steroid is an organic compound with four fused rings (designated A, B, C, and D) arranged in a specific molecular configuration.

Steroids have two principal biological functions: as important components of cell membranes that alter membrane fluidity; and as signaling molecules. Examples include the lipid cholesterol, sex hormones estradiol and testosterone, anabolic steroids, and the anti-inflammatory corticosteroid drug dexamethasone. Hundreds of steroids are found in fungi, plants, and animals. All steroids are manufactured in cells from a sterol: cholesterol (animals), lanosterol (opisthokonts), or cycloartenol (plants). All three of these molecules are produced via cyclization of the triterpene squalene.

Gonane (cyclopentanoperhydrophenanthrene) is a chemical compound with formula C
₁₇H
₂₈, whose structure consists of four hydrocarbon rings fused together: three cyclohexane units and one cyclopentane. It can also be viewed as the result of fusing a cyclopentane molecule with a fully hydrogenated molecule of phenanthrene, hence the more descriptive name "perhydrocyclopenta[a]phenanthrene". The non-systematic version of the above name is "cyclopentanoperhydrophenanthrene".

It has no double bonds, that is, it is completely saturated and is considered the main structure of steroids, often referred to as the steroid nucleus. There are many forms of gonane, but only a few occur naturally in living organisms. Some common forms include 5α-gonane and 5β-gonane. Estrane, androstane, and pregnane are derivatives of gonane with additional methyl or ethyl groups attached to certain carbon positions. The term gonane is also used to describe a group of progestins that are similar to levonorgestrel but have a slightly different structure than other hormones like estranes.