space medicine: Weightlessness


Of all the medically significant conditions experienced in space flight, weightlessness has the most drastic effects; moreover, it will be impossible to eliminate this aspect of space travel unless large space stations can be constructed that produce artificial gravity, as by rotating. Because life evolved under the constant influence of gravity, the effects of weightlessness even on the cellular level have been a concern. It was at first feared that a human being in space might lose all coordination and become completely incapacitated. While the human body does appear to adjust fairly quickly in a state of weightlessness, associated problems do occur, often causing difficulties only upon return to earth. Problems include space adaptation syndrome (nausea, motion sickness, and sensory disorientation during the first few days), weakened immune defenses, loss of bone mass, loss of muscle mass (including loss of heart muscle), a reduction in the amount of blood in the body (which may lead to low blood pressure for a time upon return to earth), and space anemia, which results as the number of red cells decreases. Many astronauts also have vision problems upon their return due to the effects of weightlessness. Space-station astronauts undergo strenuous exercise routines to maintain bone and large muscle mass, but deterioration is only slowed and rehabilition is still required after the return to earth to restore bones and muscles to their preflight conditions.

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