Life sciences space missions. Overview.

It has been known for many years that weightlessness induces changes in numerous physiological systems: the cardiovascular system declines in both aerobic capacity and orthostatic tolerance; there is a reduction in fluid and electrolyte balance, hematocrit, and certain immune parameters; bone and muscle mass and strength are reduced; various neurological responses include space motion sickness and posture and gate alterations. These responses are caused by the hypokinesia of weightlessness, the cephalic fluid shift, the unloading of the vestibular system, stress, and the altered temporal environment.