[The prenatal mechanisms of gas homeostasis]

This article discusses the physiological mechanisms of blood gas homeostasis in the prenatal period. Support of gas homeostasis is one of the most important systems providing for normal growth and development of an embryo. In the first period, the gas homeostasis of an embryo is provided by mother's organism. However, later this function is transferred to fetus. The satisfactory results depend, above all, on the adaptive changes in blood circulation. Simultaneously, the second chain of the functional systems is developing. After birth it is generally used in the form of the respiratory and general movements in response to breathing motivation. It can also appear in the prenatal period in case of deviation of the internal environment parameters to the extent when the adaptive changes in blood circulation are inadequate to compensate for gas deficit. In a fetus the breathing motivation is in most cases expressed in patterns or successive series of movements. Movement patterns have no direct adaptive role, because the result of the actions is evaluated and directed not by reverse afferentation accompanying the movement, but by its possible result modified by the humoral system. Formation of the second part of functional system supporting gas homeostasis, is significantly impacted by the situation and the starting stimulus. This is clear from the fetus response to contact with air. In this situation the adaptive behavior provides the successful birth of an organism. Under the impact of breathing motivation, the fetus demonstrates the ability to afferent synthesis of inner irritation with autostimulus, which comes from external environment (perception of gravitation, locomotion of swimming and walking, negative reaction to water, defensive reaction, etc.). Nasal contact with air produces the breathing movements typical for a newborn. The paper discusses the steps of maturation of the components of the functional system supporting gas homeostasis, the central elements of the process, the role of respiration movements after gas exchange is maintained by lungs, the role of the lung gas exchange in displays of the functional system in question, and other regularities of systemogenesis.