Physiological aspects of adaptation of main human body systems during and after spaceflights.

Publisher Summary This chapter reviews the available medical observations, and discusses the possible mechanisms of adaptation of physiological systems to microgravity and their readaptation to earth's gravity after flight. An important mechanism of adaptation to changing environments is the formation of a functional system. The existence of a functional system or the formation of a new one is not sufficient for effective adaptation. Stable adaptation is achieved only when structural alterations develop in the cells and organs of the system, increasing its power to the level required by the environment. This is achieved by the formation of a structural track, which is the basis for long-term specific adaptation. The chapter also discusses immediate and long-term adaptation. Immediate adaptation includes activation and hyperfunction of existing functional systems or relatively rapid emergence of new and closely interrelated functional systems. Long-term adaptation is based on the formation of a systemic structural track that selectively increases the capacity of structures responsible for the control, ion transport, and energy supply in all organs and cells that constitute a single functional system responsible for adaptation.