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The force of gravity doesn’t just keep us anchored to the ground; it influences how our bodies work on the smallest of scales. Now with the prospect of longer space missions, researchers are working to figure out what a lack of gravity means for our physiology – and how to make up for it.
Scientists observed that returning astronauts had grown taller and had substantially reduced bone and muscle mass.
Most experiments in this field are actually conducted on Earth, though, using simulated microgravity. By spinning objects – such as cells – in a centrifuge at fast speeds, you can create these reduced gravity conditions.
Along with the force of gravity, our cells are also subjected to additional forces, including tension and shear stresses, as conditions change within our bodies.
Our cells need ways to sense these forces. One of the widely accepted mechanisms is through what are called mechano-sensitive ion channels. These channels are pores on the cell membrane that let particular charged molecules pass in or out of the cell depending on the forces they detect.
An example of this kind of mechano-receptor is the PIEZO ion channel, found in almost all cells. They coordinate touch and pain sensation, depending on their locations in the body. For instance, a pinch on the arm would activate a PIEZO ion channel in a sensory neuron, telling it to open the gates. In microseconds, ions such as calcium would enter the cell, passing on the information that the arm got pinched. The series of events culminates in withdrawal of the arm. This kind of force-sensing can be crucial, so cells can quickly react to environmental conditions.
Without gravity, the forces acting on mechano-sensitive ion channels are imbalanced, causing abnormal movements of ions. Ions regulate many cellular activities; if they’re not going where they should when they should, the work of the cells goes haywire. Protein synthesis and cellular metabolism are disrupted
Brain: Since the 1980s, scientists have observed that the absence of gravity leads to enhanced blood retention in the upper body, and so increased pressure in the brain. Recent research suggests this heightened pressure reduces the release of neurotransmitters, key molecules that brain cells use to communicate. This finding has motivated studies into common cognitive problems, such as learning difficulties, in returning astronauts.
Bone and muscle: The weightlessness of space can cause more than a 1 percent bone loss per month, even in astronauts who undergo stringent exercise regimes. In the absence of gravity, scientists have found that the type of cells in charge of bone formation are suppressed. At the same time the type of cells responsible for degrading bone are activated. Together it adds up to accelerated bone loss. Researchers have also identified some of the key molecules that control these processes.
Immunity: Spacecraft are subject to rigorous sterilization to prevent transfer of foreign organisms. Nevertheless, during the Apollo 13 mission, an opportunistic pathogen infected astronaut Fred Haise. This bacteria, Pseudomonas aeruginosa, usually infects only immune-compromised individuals. This episode triggered more curiosity about how the immune system adapts to space. By comparing astronauts’ blood samples before and after their space missions, researchers discovered that the lack of gravity weakens the functions of T-cells. These specialized immune cells are responsible for fighting a range of diseases, from the common cold to deadly sepsis.
The current best method to overcome the absence of gravity is to increase load on the cells in another way – via exercise. Astronauts typically spend at least two hours each day running and weight-lifting to maintain healthy blood volume and reduce bone and muscle loss. Unfortunately, rigorous exercises can only slow down the deterioration of the astronauts’ health, not prevent it completely.
Supplements are another method researchers are investigating.
NASA is also evaluating whether adding probiotics to space food to boost the digestive and immune systems of astronauts may help stave off the negative effects of microgravity.
http://www.biosciencetechnology.com/...%%26type%3dcta
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