Structure of 24-ethyl-lanostane, a hypothetical steroid with 32 carbon atoms. Its core ring system (ABCD), composed of 17 carbon atoms, is shown with IUPAC-approved ring lettering and atom numbering.
Gonane, the simplest steroid, consisting only of the common steroid nucleus
Vitamin D2 supplements
Steroid 5α and 5β stereoisomers
Cholecalciferol (vitamin D), an example of a 9,10-secosteroid
Cyclopamine, an example of a complex C-nor-D-homosteroid
Simplification of the end of the steroid synthesis pathway, where the intermediates isopentenyl pyrophosphate (PP or IPP) and dimethylallyl pyrophosphate (DMAPP) form geranyl pyrophosphate (GPP), squalene and lanosterol (the first steroid in the pathway)
Mevalonate pathway
Human steroidogenesis, with the major classes of steroid hormones, individual steroids and enzymatic pathways. Changes in molecular structure from a precursor are highlighted in white.
alt=Chemical diagram|Testosterone, the principal male sex hormone and an anabolic steroid
alt=Chemical diagram|Cholic acid, a bile acid, showing the carboxylic acid and additional hydroxyl groups often present
alt=Chemical diagram|Dexamethasone, a synthetic corticosteroid drug
alt=Chemical diagram|Lanosterol, the biosynthetic precursor to animal steroids. The number of carbons (30) indicates its triterpenoid classification.
alt=Chemical diagram|Progesterone, a steroid hormone involved in the female menstrual cycle, pregnancy, and embryogenesis
alt=Chemical diagram|Medrogestone, a synthetic drug with effects similar to progesterone
alt=Chemical diagram|β-Sitosterol, a plant or phytosterol, with a fully branched hydrocarbon side chain at C-17 and an hydroxyl group at C-3

Ergocalciferol is a secosteroid formed by a photochemical bond breaking of a steroid, specifically, by the action of ultraviolet light (UV-B or UV-C) on ergosterol, a form of provitamin D2.

- Ergocalciferol

Vitamin D forms such as ergocalciferol, cholecalciferol, and calcitriol

- Steroid
Structure of 24-ethyl-lanostane, a hypothetical steroid with 32 carbon atoms. Its core ring system (ABCD), composed of 17 carbon atoms, is shown with IUPAC-approved ring lettering and atom numbering.

1 related topic

Alpha

Cholecalciferol (D3)

Vitamin D

Group of fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, and many other biological effects.

Group of fat-soluble secosteroids responsible for increasing intestinal absorption of calcium, magnesium, and phosphate, and many other biological effects.

Cholecalciferol (D3)
Calcium regulation in the human body. The role of active vitamin D (1,25-dihydroxyvitamin D, calcitriol) is shown in orange.
Global vitamin D serum levels among adults (nmol/L).
The photochemistry of vitamin D biosynthesis in animal and fungi
Thermal isomerization of previtaminD3 to vitamin D3
In the epidermal strata of the skin, vitamin D production is greatest in the stratum basale (colored red in the illustration) and stratum spinosum (colored light brown).
Liver hydroxylation of cholecalciferol to calcifediol
Kidney hydroxylation of calcifediol to calcitriol

In humans, the most important compounds in this group are vitamin D3 (also known as cholecalciferol) and vitamin D2 (ergocalciferol).

Chemically, the various forms of vitamin D are secosteroids, that is, steroids in which one of the bonds in the steroid rings is broken.