Mechanisms of development of morphological changes in mammals aboard biological satellites

After orbital space flights lasting 19.5--22.5 days, disturbances are observed in mineral metabolism in rats, which are morphologically manifested as osteoporosis of the spongy sections of long hollow skeletal bones, periosteocytic osteolysis of them, atrophy and dystrophy of skeletal muscles, and inhibition of erythroid growth of bone marrow, which occurred and developed in weightlessness as a result of deprivation of motor activity due to removal (or reduction) of static load from the musculoskeletal system. Development of stress reaction, which is apparently intensified at certain stages of flight (lift off and touchdown) and during transition from weightlessness to conditions of gravitational force on earth, leads to corresponding changes in the structure and cellular composition of lymphoid organs, and to changes in the hypothalamic-hypophyseal neurosecretory system, adrenal glands, and other organs. Changes in the receptor apparatus of the vestibular system are associated with local circulatory changes occurring during weightlessness and G forces, while retinal injuries are associated with the effect of heavy charged particles of cosmic radiation. All changes are reversible and disappear completely or to a substantial degree a month after completion of the flight.