information:classification
Intact ring system

Steroids can be classified based on their chemical composition. One example of how MeSH performs this classification is available at the Wikipedia MeSH catalog. Examples of this classification include:

In biology, it is common to name the above steroid classes by the number of carbon atoms present when referring to hormones: C -steroids for the estranes (mostly estrogens), C -steroids for the androstanes (mostly androgens), and C -steroids for the pregnanes (mostly corticosteroids). The classification " 17-ketosteroid " is also important in medicine.

The gonane (steroid nucleus) is the parent 17-carbon tetracyclic hydrocarbon molecule with no alkyl sidechains.