Microgravity
Microgravity is a new experience for the human body and all the mechanisms that have evolved to cope with the constant tug of Earth's gravity (called "1-g") no longer function in the same way in space. But, as long as a spacecraft contains a carefully controlled atmosphere to enable normal breathing, adequate temperature regulation, and adequate shielding to guard against the dangerous radiation levels in space, the human being can survive under microgravity conditions.Imagine that you are on your first ride on the Space Shuttle. After launch, huge thrusters provide enough power to carry the spacecraft quickly through the clouds and out of Earth's atmosphere. Welcome to weightlessness! Your feet rise from the floor and you are ready to turn somersaults in the cabin, walk along the walls and "ceiling," and balance bulky objects, even other crewmembers, on the tip of a finger. You have become an instant acrobat. In weightlessness, there is no "up" or "down" as we usually sense it. You don't even know the orientation or your body at first because it has no weight for you to feel and sense "where it is." In space, your body becomes confused by the sudden change in what it has learned to expect. It will now begin to tell you so.
Upon entry to weightlessness, nearly all astronauts are troubled to some extent by a condition called space motion sickness which is similar to car or sea sickness. Because the brain on Earth has learned how to process signals about the position of different parts of the body in relation to the world around it, this sudden input of confusing signals causes many astronauts to feel sick. Also the body no longer experiences the downward pull of gravity to distribute the blood and other body fluids to the lower part of the body, especially the legs. In fact, the blood and fluids make what is called a headward shift, which means that these fluids are redistributed to the upper part of the body and away from the lower extremities. While in space, the astronauts even look different: 1) they have a puffy face because they have more fluid in the upper body, 2) they have legs that are much smaller in girth (and are called "bird-legs") because they have less fluid in the lower body; and 3) the spine straightens, lengthening the body about one inch.
Another interesting consequence of leaving the gravity-field of Earth is that the astronauts no longer need the full strength of the skeletal and muscular systems for support of their "upright" posture. When these systems are not used, they deteriorate or "decondition" somewhat. The bones lose calcium and become weaker and muscles atrophy (become weaker and partially waste away). For short space flights (of a week or so), these changes are small and pose no real problem, but for longer space flights, they are potential causes of concern. Therefore, it is necessary to exercise in space in order to maintain a certain amount of tone and strength so that the astronauts will be strong and healthy when they return to Earth.
+ Humans in Space: Environmental Challenges (Back) + Hangman
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