Essay

The Effects of Microgravity on Biological Processes

The future of space travel includes long duration missions in microgravity, and this drastically different environment can be detrimental to the health of both the humans onboard and any plants grown as a part of food production. Experiments studying biological processes in space may hold clues to possible solutions that could lessen the impact of microgravity during longer space flights.

In past spaceflights, astronauts have lost approximately 1% of their bone mass per month due to disuse atrophy. In a process called remodeling, bones are constantly broken down and rebuilt through osteoblasts and osteoclasts. In microgravity, this process is thrown off balance, resulting in localized bone mass loss. Disuse atrophy is very similar to osteoporosis, and growth hormones, sex hormones, and exercise have proven to slow down osteoporosis on Earth (NASA). A rigorous exercise plan on Earth followed by resistance training while in microgravity could slow the effects of disuse atrophy. In recent studies at Columbia University, researchers discovered that when serotonin production is slowed, bone loss is also slowed. A therapy that was developed was not only able to stop osteoporosis in the rodents it was tested in, but also able to reverse the process (Columbia University, 2010). Before long duration spaceflights are planned, the consequences on the human body must be taken into account. Research and development to create a medicine help maintain healthy bones must be funded. Such studies create remedies for astronauts in microgravity and also lead to spin-off medicines for osteoporosis patients on Earth. The impact of microgravity on the skeletal system could lead to dire consequences for long space flights as normal body functions slowly shut down.

Certain muscles in the human body are called antigravity muscles. These muscles, for example the calf, back, and neck muscles, help support the body against the force of gravity. In a flight lasting only 5-7 days, astronauts can lose up to 20% of their muscle mass (Canadian Space Agency). Reduced protein synthesis leads to atrophy, and contractile proteins are lost. Furthermore, actin thin filaments and myosin thick filaments become disproportional in muscles (Fitts, 2000). Hours of exercise every day to counteract this process would be time consuming for an astronaut’s busy schedule, and possible strategies to help build muscle have been tested. One procedure is the Percutaneous Electrical Muscle Stimulator (PEMS), which sends pulses into muscles, causing them to contract (ESA, 2000). The PEMS can accompany exercise aboard the spacecraft to keep astronauts’ muscular systems strong. Traditional exercise should not be forgotten, however, and daily workouts with resistance elastic bands and stationary bikes or rowing machines would also be used.

Plants are influenced by gravity, so when in microgravity, their growth patterns are strongly affected. Through gravitropism, plants situate their roots and shoots based on signals from statoliths. Falling starch grains within cells trigger the growth of roots (in positive gravitropism) and coleoptiles (in negative gravitropism).  In microgravity, plants have been observed to have unregulated growth, such as having roots and shoots that grow in the same direction. The flow of auxin within plants, which determines growth, is irregular in space. Amyloplasts gather in the roots because of gravity, causing them to grow downwards, but this phenomenon does not occur in space. The result is that plants that rely heavily on gravitropism grow in various directions. The gravitropic tendencies of plants means that in microgravity they are not as efficient. Healthy, reliable plants must be able to be grown in microgravity if mankind wishes to embark on long duration trips in space. Plants are also heliotropic, which means they grow towards light, and heliotropism and gravitropism together signal the plant where it should grow. Some plants rely more heavily on heliotropism than others, and these species/strains could be utilized in space to take advantage of plants that are least affected by the microgravitational environment.

In 2006, the space shuttle Atlantis carried salmonella bacteria into space as part of an experiment designed by Arizona State University biologist Cheryl Nickerson. Salmonellosis is the second most common food borne illness, with 30,000 confirmed cases every year in the U.S., and the most common cause of enteric disease (Salmonella, 2011). The salmonella was returned to Earth and immediately used to infect mice before it could become accustomed to Earth's gravity again. The mice became sicker faster and were affected more severely than when infected with normal salmonella, showing that the bacteria became more dangerous after being in microgravity (National Public Radio, 2007).

Previous studies have indicated that some bacteria grow faster and become more resistant to antibiotics in space. The salmonella cells were studied and changes were found in 167 genes and 73 proteins. Some salmonella even formed biofilms, a slime layer that could account for causing worse diseases and a higher resistance to antibiotics. (Stemp-Morlock, 2007). Microgravity affects how fluid reacts with cell membranes, or fluid shear. Low shear environments, such as in space and in the intestinal tract, allow bacteria to thrive. In space, astronauts' immune systems weaken, because osteopontin is affected, which is important in bone remodeling and is also found in the spleen and thymus (MSNBC, 2007). These organs create white blood cells, which battle infections. Osterpontin is an important factor in cell attachment and wound healing. Therefore, astronauts are at an increased risk of falling sick because bacteria can be altered and the body is less capable of countering illnesses.

Space travel has led to many questions and answers about biology, such as the profound role that gravity plays in biological functions. In an environment where the gravity is about one millionth the gravity on Earth, many aspects of the cycles of animals, plants, and bacteria as influenced. As these effects are discovered and counteracted, fundamental aspects of life science are discovered. A thorough understanding of the field is imperative, as the future of long duration flights depends on healthy astronauts and thriving food sources. The study of biological processes in space is vital to mission success just as the safety and design of the craft is crucial. Both aspects can determine a flight’s achievements or failures. One of the biggest challenges for scientists is countering the negative effects that microgravity has on life science.

Works Cited

Mosher, Dave. "Weightlessness might weaken immune system." msnbc.com. 4 September 2007.

Web. 9 May 2011.

Salmonella. 2005-2011. About Salmonella. Web. 9 May 2011.

"Bacteria Grown in Space Become More Deadly." National Public Radio. 24 September 2007.   Web. 9 May 2011.

"Gravitropism." Plant Physiology. Web. 4 May 2011.

"About Arabidopsis." Tair. Web. 3 May 2011.

Reddy, Anireddy. "Plant Growth in Microgravity." Colorado State University. 2003. Web. 8

May 2011.

"Weak in the Knees-A Quest for the Cure." NASA. Web. 8 May 2011.

"Space Medicine." Canadian Space Agency. Web. 3 May 2011.

"Researchers cure Osteoporosis in Mice" Columbia University. 8 February 2010. Web. 4 May

2011.

"Percutaneous Electric Muscle Stimulator." ESA. 12 April 2000. Web. 4 May 2011.

"The Labratories." Texas Aerospace Scholars. Web. 10 May 2011.

Fitts, Robert. "Microgravity and skeletal muscle." Journal of Applied Physiology. 2000. Web. 10

May 2011.

Stemp-Morlock, Graeme. "Lethal Bacteria Turn Deadlier After Space Travel." National

Geographic. 24 September 2007. Web. 10 May 2011.