Chemically hormones are of three types: steroids, peptides or amino derived hormones. Steroids are composed of fused hydrocarbon rings and a long hydrocarbon side chain, i.e they are derivatives of cholesterol. Cholesterol is found in animals only. It exists either free or as cholesterol ester with a fatty acid. Cholesterol is also the precursor of hormones such as progesterone, testosterone, estradiol and cortisol.