Weightlessness Effect of spaceflight on the human body




1 weightlessness

1.1 motion sickness
1.2 bone , muscle deterioration
1.3 fluid redistribution
1.4 disruption of senses

1.4.1 vision
1.4.2 taste


1.5 additional physiological effects





weightlessness

astronauts on iss in weightless conditions. michael foale can seen exercising in foreground.


following advent of space stations can inhabited long periods of time, exposure weightlessness has been demonstrated have deleterious effects on human health. humans well-adapted physical conditions @ surface of earth, , in response weightlessness, various physiological systems begin change, , in cases, atrophy. though these changes temporary, have long-term impact on human health.


short-term exposure microgravity causes space adaptation syndrome, self-limiting nausea caused derangement of vestibular system. long-term exposure causes multiple health problems, 1 of significant being loss of bone , muscle mass. on time these deconditioning effects can impair astronauts performance, increase risk of injury, reduce aerobic capacity, , slow down cardiovascular system. human body consists of fluids, gravity tends force them lower half of body, , our bodies have many systems balance situation. when released pull of gravity, these systems continue work, causing general redistribution of fluids upper half of body. cause of round-faced puffiness seen in astronauts. redistributing fluids around body causes balance disorders, distorted vision, , loss of taste , smell.


a 2006 space shuttle experiment found salmonella typhimurium, bacterium can cause food poisoning, became more virulent when cultivated in space. on april 29, 2013, scientists in rensselaer polytechnic institute, funded nasa, reported that, during spaceflight on international space station, microbes seem adapt space environment in ways not observed on earth , in ways can lead increases in growth , virulence . more recently, in 2017, bacteria found more resistant antibiotics , thrive in near-weightlessness of space. microorganisms have been observed survive vacuum of outer space.


motion sickness


bruce mccandless floating free in orbit space suit , manned maneuvering unit.


the common problem experienced humans in initial hours of weightlessness known space adaptation syndrome or sas, commonly referred space sickness. related motion sickness, , arises vestibular system adapts weightlessness. symptoms of sas include nausea , vomiting, vertigo, headaches, lethargy, , overall malaise. first case of sas reported cosmonaut gherman titov in 1961. since then, 45% of people have flown in space have suffered condition. duration of space sickness varies, has lasted more 72 hours, after body adjusts new environment.


on earth, our bodies react automatically gravity, maintaining both posture , locomotion in downward pulling world. in microgravity environments, these constant signals absent: otolith organs in inner ear sensitive linear acceleration , no longer perceive downwards bias; muscles no longer required contract maintain posture, , pressure receptors in feet , ankles no longer signal direction of down . these changes can result in visual-orientation illusions astronaut feels has flipped 180 degrees. on half of astronauts experience symptoms of motion sickness first 3 days of travel due conflict between body expects , body perceives. on time brain adapts , although these illusions can still occur, astronauts begin see down feet are. people returning earth after extended weightless periods have readjust force of gravity , may have problems standing up, focusing gaze, walking , turning. initial problem, recover these abilities quickly.


nasa jokingly measures sas using garn scale , named united states senator jake garn, sickness during sts-51-d worst on record. accordingly, 1 garn equivalent severe possible case of space sickness. studying how changes can affect balance in human body—involving senses, brain, inner ear, , blood pressure—nasa hopes develop treatments can used on earth , in space correct balance disorders. until then, astronauts rely on medication, such midodrine , dimenhydrinate anti-nausea patches, required (such when space suits worn, because vomiting space suit fatal).


bone , muscle deterioration


aboard international space station, astronaut frank de winne attached colbert bungee cords


a major effect of long-term weightlessness involves loss of bone , muscle mass. without effects of gravity, skeletal muscle no longer required maintain posture , muscle groups used in moving around in weightless environment differ required in terrestrial locomotion. in weightless environment, astronauts put no weight on muscles or leg muscles used standing up. muscles start weaken , smaller. consequently, muscles atrophy rapidly, , without regular exercise astronauts can lose 20% of muscle mass in 5 11 days types of muscle fibre prominent in muscles change. slow twitch endurance fibres used maintain posture replaced fast twitch rapidly contracting fibres insufficient heavy labour. advances in research on exercise, hormone supplements , medication may maintain muscle , body mass.


bone metabolism changes. normally, bone laid down in direction of mechanical stress. however, in microgravity environment there little mechanical stress. results in loss of bone tissue approximately 1.5% per month lower vertebrae, hip , femur. due microgravity , decreased load on bones, there rapid increase in bone loss, 3% cortical bone loss per decade 1% every month body exposed microgravity, otherwise healthy adult. rapid change in bone density dramatic, making bones frail , resulting in symptoms resemble of osteoporosis. on earth, bones being shed , regenerated through well-balanced system involves signaling of osteoblasts , osteoclasts. these systems coupled, whenever bone broken down, newly formed layers take place—neither should happen without other, in healthy adult. in space, however, there increase in osteoclast activity due microgravity. problem, because osteoclasts break down bones minerals reabsorbed body. osteoblasts not consecutively active osteoclasts, causing bone diminished no recovery. increase in osteoclasts activity has been seen particularly in pelvic region, because region carries biggest load gravity present. study demonstrated in healthy mice, osteoclasts appearance increased 197%, accompanied down-regulation of osteoblasts , growth factors known formation of new bone, after sixteen days of exposure microgravity. elevated blood calcium levels lost bone result in dangerous calcification of soft tissues , potential kidney stone formation. still unknown whether bone recovers completely. unlike people osteoporosis, astronauts regain bone density. after 3–4 month trip space, takes 2–3 years regain lost bone density. new techniques being developed astronauts recover faster. research on diet, exercise , medication may hold potential aid process of growing new bone.


to prevent of these adverse physiological effects, iss equipped 2 treadmills (including colbert), , ared (advanced resistive exercise device), enable various weight-lifting exercises add muscle nothing bone density, , stationary bicycle; each astronaut spends @ least 2 hours per day exercising on equipment. astronauts use bungee cords strap treadmill. astronauts subject long periods of weightlessness wear pants elastic bands attached between waistband , cuffs compress leg bones , reduce osteopenia.


currently, nasa using advanced computational tools understand how best counteract bone , muscle atrophy experienced astronauts in microgravity environments prolonged periods of time. human research program s human health countermeasures element chartered digital astronaut project investigate targeted questions exercise countermeasure regimes. nasa focusing on integrating model of advanced resistive exercise device (ared) on board international space station opensim musculoskeletal models of humans exercising device. goal of work use inverse dynamics estimate joint torques , muscle forces resulting using ared, , more accurately prescribe exercise regimens astronauts. these joint torques , muscle forces used in conjunction more fundamental computational simulations of bone remodeling , muscle adaptation in order more model end effects of such countermeasures, , determine whether proposed exercise regime sufficient sustain astronaut musculoskeletal health.


fluid redistribution

the effects of microgravity on fluid distribution around body (greatly exaggerated).



astronaut clayton anderson observes water bubble floats in front of him on discovery. water cohesion plays bigger role in microgravity on earth


the second effect of weightlessness takes place in human fluids. body made of 60% water, of intra-vascular , inter-cellular. within few moments of entering microgravity environment, fluid re-distributed upper body resulting in bulging neck veins, puffy face , sinus , nasal congestion can last throughout duration of trip , symptoms of common cold. in space autonomic reactions of body maintain blood pressure not required , fluid distributed more around whole body. results in decrease in plasma volume of around 20%. these fluid shifts initiate cascade of adaptive systemic effects can dangerous upon return earth. orthostatic intolerance results in astronauts returning earth after extended space missions being unable stand unassisted more 10 minutes @ time without fainting. due in part changes in autonomic regulation of blood pressure , loss of plasma volume. although effect becomes worse longer time spent in space, yet individuals have returned normal within @ few weeks of landing.


in space, astronauts lose fluid volume—including 22% of blood volume. because has less blood pump, heart atrophy. weakened heart results in low blood pressure , can produce problem orthostatic tolerance , or body s ability send enough oxygen brain without astronaut s fainting or becoming dizzy. under effects of earth s gravity, blood , other body fluids pulled towards lower body. when gravity taken away or reduced during space exploration, blood tends collect in upper body instead, resulting in facial edema , other unwelcome side effects. upon return earth, blood begins pool in lower extremities again, resulting in orthostatic hypotension.


disruption of senses
vision

in 2013 nasa published study found changes eyes , eyesight of monkeys spaceflights longer 6 months. noted changes included flattening of eyeball , changes retina. space traveler s eye-sight can become blurry after time in space. effect known cosmic ray visual phenomena



...[a] nasa survey of 300 male , female astronauts, 23 percent of short-flight , 49 percent of long-flight astronauts said had experienced problems both near , distance vision during missions. again, people vision problems persisted years afterward.





intracranial pressure


because weightlessness increases amount of fluid in upper part of body, astronauts experience increased intracranial pressure. appears increase pressure on backs of eyeballs, affecting shape , crushing optic nerve. effect noticed in 2012 in study using mri scans of astronauts had returned earth following @ least 1 month in space. such eyesight problems major concern future deep space flight missions, including manned mission planet mars.


if indeed elevated intracranial pressure cause, artificial gravity might present 1 solution, many human health risks in space. however, such artificial gravitational systems have yet proven. more, sophisticated artificial gravity, state of relative microgravity may remain, risks of remain unknown.


taste

one effect of weightlessness on humans astronauts report change in sense of taste when in space. astronauts find food bland, others find favorite foods no longer taste (one enjoyed coffee disliked taste on mission stopped drinking after returning earth); astronauts enjoy eating foods not eat, , experience no change whatsoever. multiple tests have not identified cause, , several theories have been suggested, including food degradation, , psychological changes such boredom. astronauts choose strong-tasting food combat loss of taste.


additional physiological effects

after 2 months, calluses on bottoms of feet molt , fall off lack of use, leaving soft new skin. tops of feet become, contrast, raw , painfully sensitive. tears cannot shed while crying, stick ball. in microgravity odors permeate environment, , nasa found in test smell of cream sherry triggered gag reflex. various other physical discomforts such , abdominal pain common because of readjustment gravity, in space there no gravity , these muscles freely stretch. these may part of asthenization syndrome reported cosmonauts living in space on extended period of time, regarded anecdotal astronauts. fatigue, listlessness, , psychosomatic worries part of syndrome. data inconclusive; however, syndrome appear exist manifestation of internal , external stress crews in space must face.


astronauts may not able return earth or receive medical supplies, equipment or personnel if medical emergency occurs. astronauts may have rely long periods on limited existing resources , medical advice ground.








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