300px|thumb|right|Exemple d'esquelèt molecular d'un esteroïde.
Los '''esteroïdes''' son derivats del nuclèu de ciclopentanoperidrofenantren e se compausan en mai de carbòni, idrogèn, oxigèn e azòt, se compausan tanben de 4 anèls fusionats de carbòni que possedisson divèrs grops foncionals e qu'an de parts idrofilas e idrofòbas. En çò dels mamifèrs coma l'èsser uman, complisson d'importantas foncions: 
*Regulairitz: qualques uns regulan los nivèls de sal e la secrecion de bila
*Estructurala: lo colesteròl es un esteroïde que forma l'estructura de las membranas de las cellulas amassa amb los fosfolipids. En mai, a partir del colesteròl se sintetizan los autres esteroïdes.
*Ormonal: las ormonas esteroïdas son: 
**los corticoïdes: glucocorticoïdes e mineralocorticoïdes. Existisson de multiples medicaments amb activitat corticoïda, coma la prednisona. 
**las ormonas sexualas masculinas: son los androgèns coma la testosterona e los sieus derivats, los anabolizants androgenics esteroïdes; aquestes darrièrs son apelats simplament esteroïdes. 
**las ormonas sexualas femeninas. 
**la vitamina D e los sieus derivats.

Las ormonas esteroïdas an en comun que: 
*Se sintetizan a partir del colesteròl. 
*Son d'nuclèu cellular, en activant de gèns o modulant la transcripcion genetica.
1000px|thumb|center|Esteroïdogenèsi

*

thumb|right|250px|Steroid skeleton of [[lanosterol. The total number of carbons (30) reflects its triterpenoid origin.]]
A '''steroid''' is a terpenoid lipid characterized by a carbon skeleton with four fused rings, generally arranged in a 6-6-6-5 fashion.

Steroids vary by the fungi. All steroids are made in cells either from the sterol lanosterol (animals and fungi) or the sterol cycloartenol (plants). Both sterols are derived from the cyclization of the triterpene squalene.<ref>[http://www.chem.qmul.ac.uk/iubmb/enzyme/reaction/terp/lanost.html Lanosterol biosynthesis<!-- Bot generated title -->]</ref> 
==Origin==
thumb|right|350px|Simplified version of the steroid synthesis pathway with the intermediates [[isopentenyl pyrophosphate (IPP), dimethylallyl pyrophosphate (DMAPP), geranyl pyrophosphate (GPP) and squalene shown. Some intermediates are omitted.]]
Steroids include ''de novo'' or from peripherally derived sources. The rate limiting step of steroid synthesis is the conversion of cholesterol to pregnenolone which occurs inside the mitochondrion.<ref name=Rossier></ref>

==Classification==
===Taxonomical/Functional=== 
Some of the common categories of steroids: 
*Animal steroids
**Insect steroids
***Ecdysteroids such as ecdysterone
**Vertebrate steroids
***Steroid hormones
****sex differences or support reproduction. They include androgens, estrogens, and progestagens. 
****immune function, whereas renal excretion of electrolytes.  
****Anabolic steroids are a class of steroids that interact with androgen receptors to increase muscle and bone synthesis. There are natural and synthetic anabolic steroids. In popular language the word "steroids" usually refers to anabolic steroids. 
***Cholesterol which modulates the fluidity of cell membranes and is the principle constituent of the plaques implicated in atherosclerosis. 
*Plant steroids
**Phytosterols
**Brassinosteroids
*Fungus steroids
**Ergosterols

===Structural===
It is also possible to classify steroids based upon their chemical composition. One example of how the Wikipedia MeSH catalog.  Examples from this classification include:

{| class="wikitable" 
|-
! align="center" | Class
! align="center" | Examples
! align="center" | Number of carbon atoms
|-
| align="center" | Cholstanes
| align="center" | cholesterol
| align="center" | 27
|-
| align="center" | Cholanes
| align="center" | cholic acid
| align="center" | 22
|-
| align="center" | Pregnanes
| align="center" | progesterone
| align="center" | 21
|-
| align="center" | Androstanes
| align="center" | testosterone
| align="center" | 19
|-
| align="center" | Estranes
| align="center" | estradiol
| align="center" | 18
|-
|}

==See also==
*Batrachotoxin
*List of steroid abbreviations
*Steroid biosynthesis

==References==