Substances such as carbon dioxide are called parahormones to distinguish them from true hormones, which are specialized secretions.The hormones of vertebratesHormones of the pituitary glandThe pituitary gland, or hypophysis (Figure 2: Elements in a generalized mammalian pituitary gland.Encyclop??dia Britannica, Inc.), which dominates the vertebrate endocrine system, is formed of two distinct compo