Abstract
The origin of the most space deconditioning arises from lack of gravity in the environment. Because the gravity is transparent and not escapable as long as all animals stay on the ground, we usually do not recognize the gravity itself, only feel as weight. Many of the fundamental physiological systems such as equilibrium control, motor function, cardiovascular system with autonomic reflexes as well as the brain functions including sensation and recognition strongly depend on the gravitational factors. The most of the acute space deconditioning is initiated immediately after the gravitational unloading affecting both gravity dependent and co-working gravity independent functions. The subsequent chronic changes are the adaptive responses to compensate the mismatches between the gravity dependent and independent feedbacks. Major issues of the space deconditioning are the chronic changes induced by the compensative responses, such as bone demineralization, reduction of muscle innervation and changes in autonomic nerve responses, and even higher-order brain functions which may undergo a self-reprogrammed state. The present paper summarizes the role of gravity in the major issues of the space deconditioning including some recent findings from the long-term space flights and ground based simulation of weightlessness. [Jpn J Physiol 54 Suppl:S45 (2004)]
