NEAR-ZERO GRAVITY (MICROGRAVITY) IN SPACE
The human body is an extraordinary but also a complex machine. Like other living organisms, the human body has evolved by adapting to earth’s gravitational field and the biological structure and mechanisms of the body have developed to suit normal earth gravity.
MICRO GRAVITY: The micro gravity environment in space can affect the body in three major ways.
First –there are changes in the blood system.
Second –there is a shift in body fluids towards head.
Third –there is a reduction in weight bearing forces on the body.
Because of these effects, various systems of the body can be affected by space flight. These would include the neurovestibular, cardiovascular, renal/fluid system, musculoskeletal and blood.
INFLUENCE ON BALANCE AND THE SENSE OF ORIENTATION
As stated, the first system to adapt to spaceflight is neurovestibular.This is composed of brain and vestibular apparatus.
In space, balance and orientation are disturbed. The body lacks its normal point of reference.
Function of vestibular apparatus:-on earth
The otolith organs (utricle &saccule) detect change in position of head and help in maintenance of equilibrium under static condition.
*otolith organs also detect linear acceleration of the head and help in maintenance of equilibrium during such movements.
*semicircular canals detect angular acceleration and helps in maintaining the equilibrium during dynamic phase. They also have a predictive function.
*when a person is in dynamic phase ,they predict ahead of time that the person is likely to fall off balance and help nervous system to do adjustments to prevent a fall.
(Vestibular apparatus: - the semicircular canals and the utricle and saccule collectively form the vestibular apparatus and are located in the inner ear.; they play a major role in maintaining posture and equilibrium.)
Mechanism: vestibular apparatus is used to sense movement of head. It is filled with fluid and in the fluid are calcium crystals. When motion occurs, these crystals move and bump into sensory hair cells in the vestibular apparatus, which send signal to the brain. The brain then interprets this signal to determine the direction of movement.
Since there is no gravity in space, the calcium crystals do not move in a manner similar to that on earth.
Even after the astronaut leaves earth, the brain continues to believe that its point of reference is terrestrial ones. Since this information is chaotic, astronaut has trouble adapting to this new microgravity environment and disoriented. Because the sensors in the ear and muscular apparatus cannot orient themselves in zero gravity environment. The only useful information reaching the astronauts brain is through the eyes.
In space, astronauts must take some time to lose the disoriented feelings associated with weightlessness; because of lack of gravity, the otolith organs no longer play the same role; they can sense linear acceleration, but cannot establish a vertical reference signals to the brain. Adaptation to this new environment involves learning to use nonvestibular signals that are visual, proprioceptive and tactile.
INFLUENCE ON BLOOD CIRCULATION:
One of the most visible effects of a space mission is no doubt the puffy-face, bird-leg look that astronauts get. On earth, heart is programmed to distribute blood evenly throughout the body. The heart must do more work to supply the upper body, because the force of gravity naturally draws blood downward. The lower limb does not have this problem, as the blood coming to them is gravity assisted.
In space, bodily fluids no longer flow back down naturally by gravity. The heart is still programmed the way it was on earth.so, under the pressure of the heart and the veins and an artery the blood rushes to the person’s torso, head, and results in puffy face. The veins of the neck and face stand out more than usual, the eyes become red &swollen, and legs are thinner because instead of dropping effortlessly down to the lower limbs, the blood has to be pumped there by the heart. Because of these physiological changes, astronauts suffer from space sickness.
INFLUENCE ON BONE AND MUSCLE:
In space, the musculoskeletal system continuously deteriorates. Leg muscles in particular, which are underused, become flabby and loose, tone and mass. Muscular atrophy occurs. The bones, too become weaker bcz of a loss of minerals (Ca, K, Na)
Did you know that your body gets taller in space?
Because the spine is no longer compressed by gravity, the vertebra separates slightly from one another and the body lengthens.
PHSIOLOGICAL EFFECTS OF SPACE FLIGHT:
Space sickness, disorientation, migration of organic fluids to the upper body, bone deterioration, muscular atrophy, lenghthening of spine, backache etc.
