Hormones are members of a class of signaling molecules in multicellular organisms, that are transported throughout the organism’s biological networks to distant organs to regulate physiology and behavior. Hormones are instrumental in correctly developing animals, plants, and fungi. This loose definition of hormone means that many different biologically active molecules can be defined as hormones. Among the substances that can be considered hormones, are eicosanoids (e.g. prostaglandins and thromboxanes), steroids (e.g. estrogen and brassinosteroid), amino acid derivatives (e.g. epinephrine and auxin), protein/peptides (e.g. insulin and CLE peptides), gases (e.g. ethylene and nitric oxide), and even vitamins such as D3.