The biggest difference is weightlessness.
When astronauts are in a state of weightlessness, objects will float in the air, liquid droplets will be absolutely spherical, and air bubbles will not float in liquids. Astronauts stand and sleep and lie down to sleep as comfortable, walking must be careful, a little careless, will be "on the sky, down to the ground". Food should be made into chunks or toothpaste-like paste, so as to avoid the crumbs of food "floating" in the air into the eyes of the astronauts, nostrils .......
Equilibrium is one of the most common states of motion for objects. However, the balance of forces and weightlessness are two entirely different things. For example, a person standing on the ground, sitting in a chair, lying in bed, flying at equal speed in an airplane, etc., are in a state of equilibrium of forces, but are not weightless. This is because in all these cases there are mutual forces between the internal parts of the human body.
The real weightlessness should make all parts of the human body, especially the internal organs, internal organs between the mutual force disappear. The otoliths in the human vestibular organs, due to weightlessness, are no longer in contact with the surrounding nerve cells to transmit signals to the central nervous system, thus losing their orienting function. Therefore, once the vestibular organs do not work, the normal interaction between the body's internal organs disappears, it will cause space pilots to produce dizziness and nausea, vomiting and other symptoms .
Over the past three decades of space flights, scientists from Soviet Russia and the United States have collected some preliminary data. These data show that weightlessness on the endocrine, red and white blood cell production, the inner ear balance organs and osteoporosis, have a certain degree of impact, but the most obvious physiological weightlessness, no more than the space loss of water and some of the symptoms caused by it, such as space anemia, endocrine lowering, muscle atrophy in the legs and so on.
Weighlessness can also lead to a loss of calcium in the bones, which is very similar to osteoporosis in older people.
Expanded Information
The adverse effects of weightlessness are significant. In addition to causing astronauts to lose bone mass, weightlessness also leads to muscle laxity, decreased immunity and aging. Lead to a variety of space motion sickness, the last 20 years of human spaceflight history, space motion sickness frequently occur.
The human immune system owes its function to a variety of immune cells in the body, the most important of which are B and T lymphocytes, which secrete antibodies, prevent pathogenic bacteria from invading, and label them, and T lymphocytes, which kill them.
But in space, these two types of cells are not as diligent. For example, T-lymphocytes don't proliferate well in space, their numbers are much lower than on Earth, and the migration and signaling of their connections within the body is not normal. Thus, the ability to defend against foreign pathogenic bacteria is greatly reduced.
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