Shifts in Body Fluids
In a weightless environment, the fluids in the human body begin to shift towards the upper body. The face becomes swollen and the chest becomes congested, similar to symptoms of the common cold. Since there is an increase of fluids in the upper body, the lower half of the body shrinks. This creates the “puffy face, bird leg” syndrome.
The liquids in a person add up to about 60 percent of the total weight in the human body. Although it seems that there is not much liquid in your body, they are located inside the cells as intracellular fluids, in the veins and arteries as part of blood plasma, and between the cells and blood vessels as interstitial fluid. The heart has to pump harder to get the blood to the upper portion of the body due to the opposing force of gravity. Likewise, getting the fluids to your legs would be easier because gravity helps it flow downwards. When gravity is removed, the adaptations from the heart make excess fluid go to the head, causing an unbalanced system and disrupting homeostasis, or the state in which the body is physically stable in its environment.
The body reacts to these fluid shifts by changing hormonal and mechanical mechanisms. One reaction is to get rid of some of the fluids. This is why astronauts do not feel thirsty when arriving in space. Part of homeostasis deals with the balance of fluid and electrolyte levels. The kidney filtration rate increases by up to 20 percent during the first week in space.
-- Our bodies filter a larger amount of fluid in a weightless environment.
On Earth, there is more blood in the lower part of the lungs. This makes it harder for the oxygen to be absorbed in the blood and the waste to be expelled, which means that the heart pumps harder to get the blood out. However, the lack of gravity causes the blood to spread out in the lungs which makes it easier on the heart. This means that the muscle mass of the heart shrinks because it can do the same job with less work. Because the heart does less work and does not have to pump as much, the blood pressure in the veins decreases, which was surprising to scientists.
Many variables are changed from the lack of weight, and its full effects are still unknown. One system’s changes may affect another system in the body.
Written By: Alvin