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Steroid skeleton. Note how the "B" ring is broken in Vitamin D.

A secosteroid is a molecule similar to a steroid but with a "broken" ring. Etym: L. "SEC-... 'to cut'"[1] - "STERE-, 'solid,' 'three dimensional,'"[2] -OID "from Gk. -OEIDES, EIDOS 'form.'"[3]

Secosteroids are very similar in structure to steroids except that two of the B-ring carbon atoms (C9 and 10) of the typical four steroid rings are not joined, whereas in steroids they are.

In humans, a well known secosteroid is Vitamin D.


  1. ^ Ayers, Donald (1972). Bioscientific Terminology. Tucson: University of Arizona Press. pp. 142.
  2. ^ Ibid.,. pp. 129.
  3. ^ "Online Etymology Dictionary". Retrieved 10 May 2012.

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