[Evolution of endocrine glands and neuroendocrine systems: the "humoral code"]

Origin of complex neuroendocrine systems in evolution seems to be based on the signalling functions of molecules produced by separate groups of cells and glands, and each of these molecules "is coding" some distinct conditions of internal milieu and environment for the cell and the whole organism. Use of such "coding" molecules for the integration of the separate glands in the neuroendocrine systems permits to guaranty supply of vital substances to the organism regardless of external and internal disrupting circumstances, and to retain ability to alter the levels of the hormones produced by these systems in accordance with changes in internal milieu and environment.