An Astronaut's Body
So recently my chemistry was told to write a chemistry essay on a topic that we chose from a list given to us by our teachers. I chose the title 'Chemistry on the ISS'...
The essay I handed into my teachers, while not exactly what was asked for, was very fun to write!
So without further adieu, I present my chemistry essay: 'An Astronaut's Body'.
Feel free to ask me anything in the comments!
(Loosely based on the essay title: Chemistry on the ISS)
Introduction:
The idea of traveling through the stars exploring strange new worlds, seeking out new life and new civilizations is one which has long captured the imagination of humans. The reality of what happens to an astronaut's body when they enter orbit is different to what one may think. Homosapiens have evolved on the Earth and thus our bodies are adapted to work under the gravity of Earth. Our bones hold up our body weight which created by the Earth's gravitational force. Our hearts function in a way which allows blood to flow against gravity to our brains and up from the legs to our hearts, as do other organs in the body which require fluids to go against the direction of gravity. We are used to a twenty four hour day, with one sunrise and one sunset, however astronauts experience multiple sunrises and sunsets every day. In this essay I will explore some of the affects of space on an astronaut's body, how they affect productivity on the ISS and how astronauts attempt to combat these changes.
Affects of space on the bones of the Human body:
On the ISS, astronauts cannot walk around the space station and instead float. This means that the bones of the body that normally support the body, especially those in the legs, are no longer being used as much. The reduction in weight effects the bone composition of an astronaut's body.
Bones are made up from crystals of mineral bound to protein. This structure can absorb impact without shattering. The mineral in bones is a combination of calcium and phosphate called hydroxyapatite. A structure made up purely of hydroxyapatite would be too brittle and would break easily under pressure, not idea for bones which hold up the entire body even though they make up only 12% of the body mass in females and 15% in males. A structure made up entirely of protein would be too flexible and soft, not suitable to support the body properly. A combination of the two creates a hard structure which can absorb shock without breaking.
If there is an insufficient amount of calcium in the body, calcium will be removed from the bones and circulated around the body as it has uses in blood clotting, nerve function and hormones secretion to name a few. A depletion of calcium in the bones weakens them.
Bones are constantly reshaping themselves in response to the stress placed on them. If you go for a run every day them the bones in your legs will respond to the stress of running. They are restructured by two types of cells; osteoblasts which build new bone tissue and osteoclasts which destroy old bone tissue. In healthy bones, the rate at which osteoblasts build bone and osteoclasts destroy bone is the same, therefore the net bone mass remains the same (see Figure 1). However when you go into space and no longer place any stress on your legs, the bones of your legs respond. Osteoblast cell production is reduced while osteoclast production remains the same, which results in a net loss of bone mass.
The bones most affected by decrease in osteoblast production when in space are the femur, fibula, tibia, pelvis and the lower vertebrae (see Figure 2). This break down in bone density is called disuse osteoporosis.
When the osteoclasts destroy bone tissue the products are reabsorbed back into the blood stream. One of the main products is calcium. This calcium leaves the blood stream in the kidneys, along with other waste products from the body including urea, and can form kidney stones. Kidney stones are made up from balls of mineral crystals found in urine. They travel through the urinary tract and leave the body when urination occurs.
Kidney stones cause sharp pain the lower abdomen, nausea, fever and pain during urination. They can pass out of the body naturally without pain or if they become stuck in the urinary tract ultrasound therapy can be used to break down the crystal structure. When calcium leaves the bones they become more brittle as a decrease in calcium leads to a decrease bone density.
At the moment, it is hard to treat kidney stones while on the ISS and if astronauts' bones become brittle the chances of fracturing a bone increases which could jeopardise a space mission. Disuse osteoporosis begins within the first few days of space flight, the most severe loss in bone density occurs from the second to fifth month of living in space. Extended periods of time spent on the ISS have led to bone mass loss of as much as 20%.
Research is being done into supplement pills which would help decrease the probability of developing a kidney stone while on the ISS and astronauts ensure that they exercise regularly and eat a diet rich in vitamin D to help combat disuse osteoporosis. Astronauts, once they return to Earth, do rebuild their bone mass as they place stress on their lower vertebrae and leg bones but it is a slow process.
Affect of space on fluids in the Human body:
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Figure 3: Diagram of the superficial lymph nodes in the female human body |
The human body contains many fluids which are required for the body to function correctly, the two discussed in this essay are blood and lymph fluid. Blood contains white and red blood cells, platelets and blood plasma, the entirety of the body requires blood in order to function as red blood cells contain haemoglobin which carries oxygen. Oxygen is vital for aerobic respiration. Lymph fluid is a vital part of the immune system, containing white blood cells as well as collecting toxins from the body. These toxins, produced by cells, are filtered out of the lymph fluid in the lymph nodes. Lymph nodes are found in several parts of the body including the neck and armpits. Unlike blood which flows in a continuous loop through the body, lymph fluid flows in one direction: to the neck. Here it is filtered by the superclavicular lymph nodes and the cervical lymph nodes, where all waste products are removed from the lymph fluid. The remaining lymph fluid flows into the subclavian veins in either side of the neck.
When on Earth, under the affects of gravity, the body has to work in order for blood to reach the brain and to return to the heart from the limbs. While the heart does not directly help lymph fluid move through the body, the natural movement of muscles aids the lymph fluid. However in space, the affects of gravity are not felt. The body works as strenuously as it did on Earth in order to circulate blood and lymph fluid around the body but gravity is not there to fight against the movement of the fluids. This causes fluid to leaves the legs and be redistributed in the upper parts of the body.
This causes astronauts' faces to appear 'puffy' as fluid which is not normally in the neck and head has been redistributed to those areas, lymph fluid in particular plays a part in this as it naturally flows towards the neck. This extra fluid in the head can cause congestion of the sinuses. When fluids are redistributed from the rest of the body to the neck and head the size of astronauts legs can be affected. Astronauts legs have a smaller circumference in space than they do on Earth, partially because of muscle break down as they do not have to use their legs to move around but also, because fluids which were circulating in the legs have relocated to the upper body.
Once astronauts return to Earth and are once again under the influence of gravity the fluids in the body will return to where they were. There is no way to prevent fluids from moving position in the body while in space unless an artificial gravity were to be introduced on the ISS, at which point bodily fluids would circulate naturally.
Affects of space on Sleep and Performance of an Astronaut:
Sleep patterns in space have been shown to be, in general, shorter, less restful and more interrupted than sleeping patterns on Earth. Sleep loss leads to fatigue which can affect the work productivity of an astronaut, as astronauts spend much of their time each day carrying out experiments. Astronauts also experience circadian desyncronisation. A circadian cycle is a naturally recurring 24 hour cycle which occurs with or without light fluctuations, such as sunrises and sunsets.
Studies on sleep deprivation have shown that there is a a definite correlation between sleep deprivation and response times. In a study where subjects were allowed different numbers of hours in bed and then took part in a test where their reaction times were measured it was shown that those who had only 3 hours in bed per day (modeled as total sleep deprivation) performed with severe impairments to their reaction time while those who spent 9 hours in bed per day (modeled as an average night of sleep) did not have affected reaction times.
On the ISS, where a study showed that 21 astronauts averaged 6.09 hours of sleep over 4,200 nights, when looking at Figure 5 one can estimate that with 6 hours of time in bed an astronaut's reaction time would be entering 'Impairment' (see the red cross on Figure 5). This is after 7 days with 6 hours of time in bed each day. After 3 months on this many hours of sleep one can extrapolate that an astronaut's reaction time, and therefore their performance, will have decreased. At the moment, most missions to the ISS last six months however one year missions are beginning as of March 2015, sleep deprivation will increasingly become a issue for astronauts as the length of missions increases.
Desynchronisation from circadian rhythm also affects an astronaut's performance. Circadian rhythm is the 24 hour cycle which the human body is used to following. The body temperature changes as the circadian cycle occurs, it is at its highest during the circadian peak, which is when humans are most alert, and is at its lowest during the circadian minimum, which is when the body wants to sleep. Astronauts desynchronise from circadian rhythm while on the ISS due to lighting conditions, scheduling constraints as well as other aspects of the space environment. Lighting has a large affect on circadian rhythm, the ISS orbits the Earth every 1.5 hours, resulting in 16 sunrises and sunsets everyday. This means that the natural light the ISS is exposed to regularly changes, affecting when an astronaut's body is most awake and most asleep.
Slam shifting, where the wake/sleep schedule of an astronaut is altered, is also a cause of circadian desynchronisation. Slam shifting occurs on the ISS before and after critical tasks, as well as docking and undocking of crafts. Slam shifting can result in loss of sleep and fatigue for astronauts. In 2,043 days of ISS operations Slam Shifts occurred 266 days, the shifts causing the astronauts to have to work when the their circadian rhythms were not at their peak. After the critical missions when astronauts attempted to sleep their circadian rhythm may have been at its peak, resulting the the astronaut suffering from more sleep deprivation.
If astronauts suffered from this for one day, or even one week, it would be more relatable. However, at the moment, astronauts can suffer from sleep deprivation for six months at a time. This affects their well being both physically and psychologically. Astronauts Kelly Corniness and Scott Kelly, intending to stay 365 days on the ISS, may suffer from sleep deprivation for the entire year, and if they do it will greatly affect their performance.
Astronauts regularly take sleep-inducing drugs to order to sleep, sometimes even taking two doses in one night in order to sleep. These drugs impair the ability to perform many tasks the day after use and yet sleep-inducing drug usage was reported on more than half of the nights before extravehicular activities, such as space walks, were undertaken. This places astronauts lives in danger, as space walks are very dangerous and an astronaut could easily be killed if they were not concentrating due to sleep deprivation or if they were still under the influence of such drugs. Therefore, sleep-inducing drugs is a very dangerous solution to the problem of sleep deprivation and is not the correct method for solving lack of sleep.
Conclusion:
In conclusion, while space travel is presented in most media as romantic, the human body can be deeply affected by space. Sleep deprivation, continuous congestion of the sinuses and loss of net bone mass being a few of the many problems which astronauts face when they enter orbit. The human body has evolved to function at its peak on Earth, where there is a constant gravity and constant light fluctuations, not in space. If we wish to advance space travel it is vital that solutions to these problems are found, or long space missions may not be possible due to astronauts bodies not being able to survive a mission of two or more years.