Bones In Space Essay Research Paper Your

Bones In Space Essay, Research Paper

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Your Bones in Space ASTRONOMY AND SPACE SCIENCE

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Hypogravitational Osteoporosis: A review of literature.

By Lambert Titus Parker. May 19 1987.

Osteoporosis: a condition characterized by an absolute decrease in the

amount of bone present to a level below which it is capable of maintaining

the structural integrity of the skeleton.

To state the obvious, Human beings have evolved under Earth’s gravity

“1G”. Our musculoskeleton system have developed to help us navigate in

this gravitational field, endowed with ability to adapt as needed under

various stress, strains and available energy requirement. The system

consists of Bone a highly specialized and dynamic supporting tissue which

provides the vertebrates its rigid infrastructure. It consists of specialized

connective tissue cells called osteocytes and a matrix consisting of

organic fibers held together by an organic cement which gives bone its

tenacity, elasticity and its resilience. It also has an inorganic component

located in the cement between the fibers consisting of calcium phosphate

[85%]; Calcium carbonate [10%] ; others [5%] which give it the hardness

and rigidity. Other than providing the rigid infrastructure, it protects

vital organs like the brain], serves as a complex lever system, acts as a

storage area for calcium which is vital for human metabolism, houses the

bone marrow within its mid cavity and to top it all it is capable of changing

its architecture and mass in response to outside and inner stress. It

is this dynamic remodeling of bone which is of primary interest in microgravity.

To feel the impact of this dynamicity it should be noted that a bone

remodeling unit [a coupled phenomena of bone reabsorption and bone formation]

is initiated and another finished about every ten seconds in a healthy

adult. This dynamic system responds to mechanical stress or lack of it

by increasing the bone mass/density or decreasing it as per the demand

on the system. -eg; a person dealing with increased mechanical stress

will respond with increased mass / density of the bone and a person who

leads a sedentary life will have decreased mass/density of bone but the right

amount to support his structure against the mechanical stresses she/she

exists in. Hormones also play a major role as seen in postmenopausal

females osteoporosis (lack of estrogens) in which the rate of bone reformation

is usually 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 extended period of time requiring

practically no weight bearing, the regulatory system of bone/calcium

reacts by decreasing its mass. After all, why carry all that extra mass

and use all that energy to maintain what is not needed. Logically the

greatest loss -demineralization- occurs in the weight bearing bones of

the leg [Os Calcis] and spine. Bone loss has been estimated by calcium-balance

studies and excretion studies. An increased urinary excretion of calcium

, hydroxyproline & phosphorus has been noted in the first 8 to 10 days

of microgravity suggestive of increased bone re-absorption. Rapid increase

of urinary calcium has been noted after takeoff with a plateau reached

by day 30. In contrast, there was a steady increase off mean fecal calcium

throughout the stay in microgravity and was not reduced until day 20 of

return to 1 G while urinary calcium content usually returned to preflight

level by day 10 of return to 1G.

There is also significant evidence derived primarily from rodent studies that

seem to suggest decreased bone formation as a factor in hypogravitational

osteoporosis. Boy Frame,M.D a member of NASA’s LifeScience Advisory Committee

[LSAC] postulated that “the initial pathologic event after the astronauts

enter zero gravity occurs in the bone itself, and that changes in mineral

homeostasis and the calcitropic hormones are secondary to this. It appears

that zero gravity in some ways stimulate bone re-absorption, possibly through

altered bioelectrical fields or altered distribution of tension and pressure

on bone cells themselves. It is possible that gravitational and muscular

strains on the skeletal system cause friction between bone crystals

which creates bioelectrical fields. This bioelectrical effect in some

way may stimulate bone cells and affect bone remodeling.” In the early

missions, X-ray densitometry was used to measure the weight-bearing bones

pre & post flight. In the later Apollo, Skylab and Spacelab missions Photon

absorptiometry (a more sensitive indicator of bone mineral content) was

utilized. The results of these studies indicated that bo

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