169 lines
11 KiB
Plaintext
169 lines
11 KiB
Plaintext
ÜÜÜÜÜÜÜÜÜÜÜÜÜ ÜÜÜ ÜÜÜÜ
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ÜÛÛÛÛÛÛÛÛßÛßßßßßÛÛÜ ÜÜßßßßÜÜÜÜ ÜÛÜ ÜÛÛÛÛÛÛÛÛÜÜÜÜÜÛßß ßÛÛ
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ßÛÛÛÛÛÛÛÛÛÛÛÛÛÛÜ ßÛÛ ÜÛÛÛÜÛÛÜÜÜ ßÛÛÛÛÜ ßÛÛÛÛÛÛÛÜÛÛÜÜÜÛÛÝ Ûß
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ßßßÛÛÛÛÛÛÛÛÛÛÜ ÞÝ ÛÛÛÛÛÛÛÛÛÛÛßßÛÜÞÛÛÛ ÛÛÛÛÛÜ ßßÛÛÛÞß
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Mo.iMP ÜÛÛÜ ßÛÛÛÛÛÛÛÝÛ ÞÛÛÛÛÛÛÛÛÛ ÞÛÛÛÛ ÞÛÛÛÛÛÝ ßÛß
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ÜÛÛÛÛÛÛÛ ÛÛÛÛÛÛÛÛÝ ÞÛÛÛÛÛÛÛÛÝ ÛÛÛ ÛÛÛÛÛÛ
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ÜÛÛÛÛÛÛÛÝ ÞÛÛÛÛÛÛÛÛ ÞÛÛÛÛÛÛÛÛ ß ÞÛÛÛÛÛÛÜ ÜÛ
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ÜÛÛÛÛÛÛÛÝ ÛÛÛÛÛÛÛÛ ÛÛÛÛÛÛÛÛÝ ÞÞÛÛÛÛÛÛÛÛÛß
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ÜÛßÛÛÛÛÛÛ ÜÜ ÛÛÛÛÛÛÛÛÝ ÛÛÞÛÛÛÛÛÝ ÞÛÛÛÛÛÛßß
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ÜÛßÛÛÛÛÛÛÜÛÛÛÛÜÞÛÛÛÛÛÛÛÛ ÞÛ ßÛÛÛÛÛ Ü ÛÝÛÛÛÛÛ Ü
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ÜÛ ÞÛÛÛÛÛÛÛÛÛÛß ÛÛÛÛÛÛÛÛÛ ßÛÜ ßÛÛÛÜÜ ÜÜÛÛÛß ÞÛ ÞÛÛÛÝ ÜÜÛÛ
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ÛÛ ÛÛÛÛÛÛÛÛß ÛÛÛÛÛÛÛÛÛÛÜ ßÛÜ ßßÛÛÛÛÛÛÛÛÛß ÜÜÜß ÛÛÛÛÜÜÜÜÜÜÜÛÛÛÛÛß
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ßÛÜ ÜÛÛÛß ßÛÛÛÛÛÛÛÛÛÛÜ ßßÜÜ ßßÜÛÛßß ßÛÛÜ ßßßÛßÛÛÛÛÛÛÛßß
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ßßßßß ßßÛÛß ßßßßß ßßßßßßßßßßßßß
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ARRoGANT CoURiERS WiTH ESSaYS
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Grade Level: Type of Work Subject/Topic is on:
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[ ]6-8 [ ]Class Notes [General Info on what ]
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[ ]9-10 [ ]Cliff Notes [happens to your bones ]
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[ ]11-12 [ ]Essay/Report [in space. ]
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[x]College [x]Misc [ ]
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Dizzed: 10/94 # of Words: School: ? State: ?
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ÄÄÄÄÄÄÄÄÄ>ÄÄÄÄÄÄÄÄÄ>ÄÄÄÄÄÄÄÄÄ>Chop Here>ÄÄÄÄÄÄÄÄÄ>ÄÄÄÄÄÄÄÄÄ>ÄÄÄÄÄÄÄÄÄ>ÄÄÄÄÄÄÄÄÄ
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File BONES-SP.TXT has 1433 words, and 9417 bytes.
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==============================================================================
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Your Bones in Space ASTRONOMY AND SPACE SCIENCE
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SIG
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------------------------------------------------------------------------------
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Hypogravitational Osteoporosis: A review of literature.
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By Lambert Titus Parker. May 19 1987. (GEnie Spaceport)
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Osteoporosis: a condition characterized by an absolute decrease in the
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amount of bone present to a level below which it is capable of maintaining
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the structural integrity of the skeleton.
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To state the obvious, Human beings have evolved under Earth's gravity
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"1G". Our musculoskeleton system have developed to help us navigate in this
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gravitational field, endowed with ability to adapt as needed under various
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stress, strains and available energy requirement. The system consists of
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Bone a highly specialized and dynamic supporting tissue which provides the
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vertebrates its rigid infrastructure. It consists of specialized connective
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tissue cells called osteocytes and a matrix consisting of organic fibers
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held together by an organic cement which gives bone its tenacity,
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elasticity and its resilience. It also has an inorganic component located
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in the cement between the fibers consisting of calcium phosphate [85%];
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Calcium carbonate [10%] ; others [5%] which give it the hardness and
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rigidity. Other than providing the rigid infrastructure, it protects vital
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organs like the brain], serves as a complex lever system, acts as a storage
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area for calcium which is vital for human metabolism, houses the bone
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marrow within its mid cavity and to top it all it is capable of changing
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its architecture and mass in response to outside and inner stress. It is
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this dynamic remodeling of bone which is of primary interest in
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microgravity. To feel the impact of this dynamicity it should be noted that
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a bone remodeling unit [a coupled phenomena of bone reabsorption and bone
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formation] is initiated and another finished about every ten seconds in a
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healthy adult. This dynamic system responds to mechanical stress or lack of
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it by increasing the bone mass/density or decreasing it as per the demand
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on the system. -eg; a person dealing with increased mechanical stress will
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respond with increased mass / density of the bone and a person who leads a
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sedentary life will have decreased mass/density of bone but the right
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amount to support his structure against the mechanical stresses she/she
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exists in. Hormones also play a major role as seen in postmenopausal
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females osteoporosis (lack of estrogens) in which the rate of bone
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reformation is usually normal with the rate of bone re-absorption
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increased.
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In Skeletal system whose mass represent a dynamic homeostasis in 1g
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weight- bearing,when placed in microgravity for any extended period of time
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requiring practically no weight bearing, the regulatory system of
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bone/calcium reacts by decreasing its mass. After all, why carry all that
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extra mass and use all that energy to maintain what is not needed?
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Logically the greatest loss -demineralization- occurs in the weight bearing
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bones of the leg [Os Calcis] and spine. Bone loss has been estimated by
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calcium-balance studies and excretion studies. An increased urinary
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excretion of calcium , hydroxyproline & phosphorus has been noted in the
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first 8 to 10 days of microgravity suggestive of increased bone
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re-absorption. Rapid increase of urinary calcium has been noted after
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takeoff with a plateau reached by day 30. In contrast, there was a steady
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increase off mean fecal calcium throughout the stay in microgravity and was
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not reduced until day 20 of return to 1 G while urinary calcium content
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usually returned to preflight level by day 10 of return to 1G.
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There is also significant evidence derived primarily from rodent
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studies that seem to suggest decreased bone formation as a factor in
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hypogravitational osteoporosis. Boy Frame,M.D a member of NASA's
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LifeScience Advisory Committee [LSAC] postulated that "the initial
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pathologic event after the astronauts enter zero gravity occurs in the bone
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itself, and that changes in mineral homeostasis and the calcitropic
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hormones are secondary to this. It appears that zero gravity in some ways
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stimulate bone re-absorption, possibly through altered bioelectrical fields
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or altered distribution of tension and pressure on bone cells themselves.
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It is possible that gravitational and muscular strains on the skeletal
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system cause friction between bone crystals which creates bioelectrical
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fields. This bioelectrical effect in some way may stimulate bone cells and
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affect bone remodeling." In the early missions, X-ray densitometry was
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used to measure the weight-bearing bones pre & post flight. In the later
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Apollo, Skylab and Spacelab missions Photon absorptiometry (a more
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sensitive indicator of bone mineral content) was utilized. The results of
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these studies indicated that bone mass [mineral content] was in the range
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of 3.2% to 8% on flight longer than two weeks and varying directly with the
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length of the stay in microgravity. The accuracy of these measurements
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have been questioned since the margin of error for these measurements is 3
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to 7% a range being close to the estimated bone loss.
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Whatever the mechanism of Hypogravitational Osteoporosis, it is one of
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the more serious biomedical hazard of prolonged stay in microgravity. Many
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forms of weight loading exercises have been tried by the astronauts &
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cosmonauts to reduce the space related osteoporosis. Although isometric
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exercises have not been effective, use of Bungee space suit have shown some
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results. However use of Bungee space suit [made in such a way that
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everybody motion is resisted by springs and elastic bands inducing stress
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and strain on muscles and skeletal system] for 6 to 8 hrs a day necessary
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to achieve the desired effect are cumbersome and require significant
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workload and reduces efficiency thereby impractical for long term use other
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than proving a theoretical principle in preventing hypogravitational
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osteoporosis.
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Skylab experience has shown us that in spite of space related
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osteoporosis humans can function in microgravity for six to nine months and
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return to earth's gravity. However since adults may rebuild only two-third
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of the skeletal mass lost, even 0.3 % of calcium loss per month though
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small in relation to the total skeletal mass becomes significant when Mars
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mission of 18 months is contemplated. Since adults may rebuild only
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two-thirds of the skeletal mass lost in microgravity, even short durations
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can cause additive effects. This problem becomes even greater in females
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who are already prone to hormonal osteoporosis on Earth.
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So far several studies are under way with no significant results. Much
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study has yet to be done and multiple experiments were scheduled on the
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Spacelab Life Science [SLS] shuttle missions prior to the Challenger
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tragedy. Members of LSAC had recommended that bone biopsies need to be
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performed for essential studies of bone histomorphometric changes to
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understand hypogravitational osteoporosis. In the past, astronauts with
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the Right Stuff had been resistant and distrustful of medical experiments
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but with scientific personnel with life science training we should be able
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to obtain valid hard data. [It is of interest that in the SLS mission, two
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of the mission specialists were to have been physicians, one physiologist
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and one veterinarian.]
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After all is said, the problem is easily resolved by creation of
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artificial gravity in rotating structures. However if the structure is not
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large enough the problem of Coriolis effect must be faced. To put the
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problem of space related osteoporosis in perspective we should review our
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definition of Osteoporosis: a condition characterized by an absolute
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decrease in the amount of bone present to a level below which it is capable
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of maintaining the structural integrity of the skeleton. In microgravity
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where locomotion consists mostly of swimming actions with stress being
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exerted on upper extremities than lower limbs resulting in reduction of
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weight bearing bones of lower extremities and spine which are NOT needed
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for maintaining the structural integrity of the skeleton. So in
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microgravity the skeletal system adapts in a marvelous manner and problem
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arises only when this microgravity adapted person need to return to higher
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gravitational field. So the problem is really a problem of re-adaptation to
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Earth's gravity.
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To the groups wanting to justify space related research: Medical
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expense due to osteoporosis in elderly women is close to 4 billion dollars
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a year and significant work in this field alone could justify all space
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life science work. It is the opinion of many the problem of osteoporosis
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on earth and hypogravity will be solved or contained, and once large
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rotating structures are built the problem will become academic. For
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completeness sake: Dr. Graveline, at the School of Aerospace Medicine,
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raised a litter of mice on a animal centrifuge simulating 2G and compared
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them with a litter mates raised in 1G. "They were Herculean in their build,
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and unusually strong...." reported Dr.Graveline. Also X-ray studies showed
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the 2G mice to have a skeletal density to be far greater than their 1G
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litter mates.
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