Steroids are lipids based in an angular combination of four carbon
rings, three of them made of six carbons and one ring made of five carbons in
the extremity. The union of each ring to the adjacent ring is made by the
sharing of two adjacent carbons belonging to both rings.
Bile salts, cholesterol, the sexual hormones estrogen,
progesterone and testosterone, the corticosteroids and the pro-vitamin D are
examples of steroids.