Editing Steroid (section)

==== Intact ring system ====
Steroids can be classified based on their chemical composition.<ref name="Zorea-2014">{{cite book|title=Steroids (Health and Medical Issues Today)| vauthors = Zorea A |publisher=Greenwood Press|year=2014|isbn=978-1-4408-0299-7|location=Westport, CT|pages=10–12}}</ref> One example of how [[Medical Subject Headings|MeSH]] performs this classification is available at the Wikipedia MeSH catalog. Examples of this classification include:
[[Image:Cholecalciferol.svg|thumb|alt=Chemical diagram|class=skin-invert-image|[[Cholecalciferol]] (vitamin D{{ssub|3}}), an example of a 9,10-[[secosteroid]]]]
[[Image:Cyclopamine.svg|thumb|alt=Chemical diagram|class=skin-invert-image|[[Cyclopamine]], an example of a complex C-nor-D-homosteroid]]
{| class="wikitable"
|-
! align="center" | Class
! align="center" | Example
! align="center" | Number of carbon atoms
|-
| align="center" | [[Cholestane]]s
| align="center" | Cholesterol
| align="center" | 27
|-
| align="center" | [[Cholane]]s
| align="center" | Cholic acid
| align="center" | 24
|-
| align="center" | [[Pregnane]]s
| align="center" | Progesterone
| align="center" | 21
|-
| align="center" | [[Androstane]]s
| align="center" | Testosterone
| align="center" | 19
|-
| align="center" | [[Estrane]]s
| align="center" | Estradiol
| align="center" | 18
|-
|}
In biology, it is common to name the above steroid classes by the number of carbon atoms present when referring to hormones: C<sub>18</sub>-steroids for the estranes (mostly estrogens), C<sub>19</sub>-steroids for the androstanes (mostly androgens), and C<sub>21</sub>-steroids for the pregnanes (mostly corticosteroids).<ref name="rgd.mcw.edu-C19">{{cite web |title=C19-steroid hormone biosynthetic pathway – Ontology Browser – Rat Genome Database |url=https://rgd.mcw.edu/rgdweb/ontology/view.html?acc_id=PW:0000770 |website=rgd.mcw.edu |access-date=11 April 2022 |archive-date=12 May 2023 |archive-url=https://web.archive.org/web/20230512220253/https://rgd.mcw.edu/rgdweb/ontology/view.html?acc_id=PW:0000770 |url-status=live }}</ref> 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.<ref name="pmid10715364">{{cite journal | vauthors = Edgren RA, Stanczyk FZ | title = Nomenclature of the gonane progestins | journal = Contraception | volume = 60 | issue = 6 | pages = 313 | date = Dec 1999 | pmid = 10715364 | doi = 10.1016/S0010-7824(99)00101-8 }}</ref>