[Biology and space medicine. New prospects for internal medicine]

Most of the functional problems astronauts may suffer during and after long-term space missions are mainly associated with the reduction of the gravity force which causes a central fluid shift and a redistribution of the blood flow. Blood volume centralization induces a rapid increase in diuresis with elimination of consistent amounts of water and electrolytes which leads to a reduction of cardiac output, body fluid and to a hypodynamic state of the cardiovascular system. The effects of micro-gravity on skeletal and muscular systems are quite severe causing rapid bone demineralization, especially in the spine and lower extremities, and hypotrophy of the muscular masses. Micro-g also appears to determine cellular and molecular modifications with inhibition of the immune system, hematopoiesis and resistance to infections. Orthostatic intolerance, with feeling sick, instability and sometimes syncope, is characteristically observed after the return to earth due to a remarkable fluid shift in the lower part of the body and an acute reduction in blood flow to the brain. Physical exercise may play an important role among the countermeasures proposed to reduce most of the cardiovascular and musculo-skeletal effects of micro-g. Furthermore, micro-g offers many interesting prospects for the development of new technologies for the synthesis of biologically active substances for pharmacological use. Further severe limiting factors, for more prolonged manned space missions, are the so called "human factors" including psycho-emotional and social behaviour, especially regarding the future of astronauts after their return to earth.