Boness In Space Essay, Research Paper

Boness in SpaceHypogravitational Osteoporosis: A reappraisal of literature.By Lambert Titus Parker. May 19 1987. ( GEnie Spaceport ) Osteoporosis: a status characterized by an absolute lessening in theamount of bone nowadays to a degree below which it is capable of maintainingthe structural unity of the skeleton. To province the obvious, Human existences have evolved under Earth & # 8217 ; s gravitation & # 8221 ; 1G & # 8221 ; . Our musculoskeleton system have developed to assist us voyage inthis gravitative field, endowed with ability to accommodate as needed undervarious emphasis, strains and available energy demand. The systemconsists of Bone a extremely specialised and dynamic back uping tissue whichprovides the craniates its stiff substructure. It consists of specializedconnective tissue cells called osteocytes and a matrix dwelling oforganic fibres held together by an organic cement which gives bone itstenacity, snap and its resiliency. It besides has an inorganic componentlocated in the cement between the fibres dwelling of Ca phosphate [ 85 % ] ; Calcium carbonate [ 10 % ] ; others [ 5 % ] which give it the hardnessand rigidness. Other than supplying the stiff substructure, it protectsvital variety meats like the encephalon ] , serves as a complex lever system, acts as astorage country for Ca which is critical for human metamorphosis, houses thebone marrow within its mid pit and to exceed it all it is capable of changingits architecture and mass in response to outside and interior emphasis. Itis this dynamic remodeling of bone which is of primary involvement in microgravity. To experience the impact of this dynamicity it should be noted that a boneremodeling unit [ a conjugate phenomena of bone resorption and bone formation ] is initiated and another finished about every 10 seconds in a healthyadult. This dynamic system responds to mechanical emphasis or deficiency of itby increasing the bone mass/density or diminishing it as per the demandon the system. -eg ; a individual covering with increased mechanical stresswill respond with increased mass / denseness of the bone and a individual wholeads a sedentary life will hold decreased mass/density of bone but the rightamount to back up his construction against the mechanical emphasiss she/sheexists in. Hormones besides play a major function as seen in postmenopausalfemales osteoporosis ( deficiency of estrogens ) in which the rate of bone reformationis normally normal with the rate of bone re-absorption increased. In Skeletal system whose mass represent a dynamic homeostasis in 1g weight-bearing, when placed in microgravity for any drawn-out period of clip requiringpractically no weight bearing, the regulative system of bone/calciumreacts by diminishing its mass. After all, why carry all that excess massand usage all that energy to keep what is non needed? Logically thegreatest loss -demineralization- occurs in the weight bearing castanetss ofthe leg [ Os Calcis ] and spinal column. Bone loss has been estimated by calcium-balancestudies and elimination surveies. An increased urinary elimination of Ca, hydroxyproline & A ; P has been noted in the first 8 to 10 daysof microgravity suggestive of increased bone re-absorption. Rapid increaseof urinary Ca has been noted after takeoff with a tableland reachedby twenty-four hours 30. In contrast, there was a steady addition off average faecal calciumthroughout the stay in microgravity and was non reduced until twenty-four hours 20 ofreturn to 1 G while urinary Ca content normally returned to preflightlevel by twenty-four hours 10 of return to 1G.There is besides important grounds derived chiefly from rodent surveies thatseem to propose reduced bone formation as a factor in hypogravitationalosteoporosis. Boy Frame, M.D a member of NASA & # 8217 ; s LifeScience Advisory Committee [ LSAC ] postulated that & # 8220 ; the initial diseased event after the astronautsenter nothing gravitation occurs in the bone itself, and that alterations in mineralhomeostasis and the calcitropic endocrines are secondary to this. It appearsthat zero gravitation in some ways stimulate bone re-absorption, perchance throughaltered bioelectrical Fieldss or altered distribution of tenseness and pressureon bone cells themselves. It is possible that gravitative and muscularstrains on the skeletal system cause clash between bone crystalswhich creates bioelectrical Fieldss. This bioelectrical consequence in someway may excite bone cells and impact bone remodeling. & # 8221 ; In the early

missions, X-ray densitometry was used to mensurate the weight-bearing bonespre & A ; Po

st flight. In the later Apollo, Skylab and Spacelab missions Photonabsorptiometry (a more sensitive indicator of bone mineral content) wasutilized. The results of these studies indicated that bone mass [mineralcontent] was in the range of 3.2% to 8% on flight longer than two weeksand varying directly with the length of the stay in microgravity. Theaccuracy of these measurements have been questioned since the marginof error for these measurements is 3 to 7% a range being close to theestimated bone loss.Whatever the mechanism of Hypogravitational Osteoporosis, it is one ofthe more serious biomedical hazard of prolonged stay in microgravity. Many forms of weight loading exercises have been tried by the astronauts& cosmonauts to reduce the space related osteoporosis. Although isometricexercises have not been effective, use of Bungee space suit have shownsome results. However use of Bungee space suit [made in such a way thateverybody motion is resisted by springs and elastic bands inducing stressand strain on muscles and skeletal system] for 6 to 8 hrs a day necessaryto achieve the desired effect are cumbersome and require significant workload andreduces efficiency thereby impractical for long term use other than provinga theoretical principle in preventing hypogravitational osteoporosis. Skylab experience has shown us that in spite of space related osteoporosishumans can function in microgravity for six to nine months and returnto earth’s gravity. However since adults may rebuild only two-third ofthe skeletal mass lost, even 0.3 % of calcium loss per month though smallin relation to the total skeletal mass becomes significant when Mars missionof 18 months is contemplated. Since adults may rebuild only two-thirdsof the skeletal mass lost in microgravity, even short durations can causeadditive effects. This problem becomes even greater in females who arealready prone to hormonal osteoporosis on Earth.So far several studies are under way with no significant results. Muchstudy has yet to be done and multiple experiments were scheduled on theSpacelab Life Science [SLS] shuttle missions prior to the Challengertragedy. Members of LSAC had recommended that bone biopsies need to beperformed for essential studies of bone histomorphometric changes tounderstand hypogravitational osteoporosis. In the past, astronauts withthe Right Stuff had been resistant and distrustful of medical experimentsbut with scientific personnel with life science training we should beable to obtain valid hard data. [It is of interest that in the SLS mission,two of the mission specialists were to have been physicians, one physiologistand one veterinarian.]After all is said, the problem is easily resolved by creation of artificialgravity in rotating structures. However if the structure is not largeenough the problem of Coriolis effect must be faced. To put the problemof space related osteoporosis in perspective we should review our definitionof Osteoporosis: a condition characterized by an absolute decrease in theamount of bone present to a level below which it is capable of maintaining thestructural integrity of the skeleton. In microgravity where locomotionconsists mostly of swimming actions with stress being exerted on upperextremities than lower limbs resulting in reduction of weight bearingbones of lower extremities and spine which are NOT needed for maintainingthe structural integrity of the skeleton. So in microgravity the skeletalsystem adapts in a marvelous manner and problem arises only when thismicrogravity adapted person need to return to higher gravitational field. So the problem is really a problem of re-adaptation to Earth’s gravity. To the groups wanting to justify space related research: Medical expensedue to osteoporosis in elderly women is close to 4 billion dollars ayear and significant work in this field alone could justify all space lifescience work. It is the opinion of many the problem of osteoporosis on earthand hypogravity will be solved or contained, and once large rotatingstructures are built the problem will become academic. For completenesssake: Dr. Graveline, at the School of Aerospace Medicine, raised a litterof mice on a animal centrifuge simulating 2G and compared them with alitter mates raised in 1G. “They were Herculean in their build, and unusuallystrong….” reported Dr.Graveline. Also X-ray studies showed the 2G miceto have a skeletal density to be far greater than their 1G litter mates.