The new definition of hormone covers a number of new molecules in addition to the hormones secreted by the organised endocrine glands.
Several non-endocrine tissues secrete hormones called growth factors.
The pituitary gland secretes releasing and inhibiting hormones which regulate other endocrine glands.
All hormones produce their effects on target tissues by binding to intracellular hormone receptors.
The receptors of lipid-soluble hormones are intracellular while those of water soluble hormones are present on the plasma membrane.