How do steroids vary physiologically?

According to nature of chemical groups attached to the cyclohexane and cyclopentane. Hormones (estrogen, progesterone, testosterone and other adrenal hormones) involved in cell-cell communication (vital roles) Vitamins (D) indespensible for normal growth and bone developement, it is produced from a precursor (cholesterol) under the effect of UV sun light. Structural roles: cholesterol cell membrane structure, OH of first cyclohexane gives it hydrophilic head responsible for amphipathy in cholesterol that forms 50% of cell membrane og animal cells. Fluidity: OH group ensures fluidity Bidirectional regulation: cholesterol stabilizes melting point at high temperatures, and prevents hardening the cell at lower temperatures.