| Cholesterol is the precursor of all of the steroid hormones
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| Figure 16.7 Structure and nomenclature of the most important human steroid hormones. Their trivial and systematic (in parentheses) names are shown. For the biosynthetic pathways, see Fig. 37.7. For numbering of the atoms in a steroid molecule, see Fig. 16.1. |
| Mammals produce many steroid hormones, some of which differ only by a double bond or by the orientation of a hydroxyl group. Consequently, it has been necessary to employ systematic nomenclature to detail exact structures. There are three broad groups of steroid hormones (Fig. 16.7). The corticosteroids have 21 carbon atoms in the basic pregnane ring structure. Loss of the remaining two carbon atoms from the cholesterol side chain produces the androstane ring structure and the group of hormones known as the androgens. Finally, loss of the angular methyl group at carbon atom
19 as part of the aromatization of the A ring results in the estrane structure found in the estrogens. The presence and position of double bonds and the position and orientation of hydroxyl or other functional groups on the basic nucleus may then be described.
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