[The functional significance of the multiunit construction of the hypothalamo-hypophyseal neuroendocrine systems]

The significance of multi-unit structure of the hypothalamic neuroendocrine systems is discussed. The hypothalamopituitary-adrenocortical (HPA) axis is considered as the object of appreciation of the functional role of the three-unit structure of the neuroendocrine systems. This construction of HPA axis (hypothalamus, pituitary, and adrenal glands) determines the following functional properties: 1) sequential switching of the units provides an enhancement of the preceding stage signal. The hormone concentrations gradually increase from the central unit to the peripheral one. Relatively high concentration, provided by the terminal unit, determines the action on the target organs. On the whole, the gain index for the chemical signal from the hypothalamus to the adrenal glands is 10(5); 2) under certain conditions the multi-unit system allows intervention into every unit, thus opening additional possibilities for controlling the system as a whole owing to appearance of new control loops; 3) the hormones produced in each of the units are not only used for controlling the next unit but also affect other functions.