Physiological changes during spaceflight.

Before human beings first explored space, many dire predictions from the scientific community suggested that weightlessness was not compatible with life. Although these prophesies have been proven false, many physiological alterations do occur in microgravity conditions. Other systems are altered as well, but the cardiovascular, musculoskeletal, and immune systems undergo adaptations that may pose problems for the space traveler, especially on returning to gravity.