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At least 1,711 records · Page 95Linked to original sources
PubMed1994

[Mineral metabolism in man under altered gravitation].

The book contains data about the functions and the metabolism of mineralized tissues, and the results of investigations of bone tissue and calcium metabolism during manned space missions and ground-based simulations. Consideration is given to the bone strength characteristics under experimental hypo- and hypergravity. The role of hormonal and physical/chemical factors in the mechanisms of iron control alterations in man during space missions of various lengths is analyzed. Evaluated is the efficiency of different countermeasures opposing the shifts in electrolyte exchange and bone mineral losses in these conditions. A concept is proposed for hypogravity-induced changes in the mineral metabolism and bone tissue status. The book is addressed to biologists, physiologists, biochemists, specialists in space biology and aerospace medicine.

Aerospace Medicine↗
PubMedDate not supplied

[The characteristics of eye regeneration in newts after complete retinal detachment induced by a change in the effect of gravitation in an experiment using a clinostat].

Morphological changes and proliferative activity of the neural retina cells after the neural retina detachment were studied in the newts subjected to microgravity in a clinostat. According to theoretical calculations, simulated microgravity could vary from 3.21 x 10(-2) to 8.05 x 10(-3) g. These conditions had a positive effect on morphological and functional restoration of the neural retina according to various criteria. Specifically, the increased number of Mullerian glial cells, increased relative volume of the plexiform layers, decreased mortality of the detached neural retina cells and increased redifferentiation of the retinal pigment epithelium and reattachment of the neural retina were observed. These changes were mainly found in the dorsal and central areas of the neural retina.

Animals↗
PubMed1997

[Skeletal muscle reaction in man to a decrease in gravitation].

Functional characteristics the triceps surae muscle were studied in sex subjects exposed for 7 days to decreased unweighting induced by "dry" immersion (DI). After DI, the maximal voluntary contraction was a significant reduced by 33.8%, and the electrically evoked tetanic contraction (Po), and the twitch tension (Pt) was not significantly changed (8.2 and 9.9%, respectively). The force deficiency increased by 44.1% (P < 0.01). The twitch time-to-peak did not change, and to half-relaxation decreased by 5.3%. The Pt:Po ratio was decreased by 8.7% (P < 0.01) after "dry" immersion. The muscle surface action potential increased by 18.8% (P < 0.01), and a decrease of the amplitude and the area by 14.6% (P < 0.05), and 2.8% (P < 0.01), respectively. A comparison of the electrical and mechanical alterations recorded in the muscle suggests that due to decreased functional demands there may be an alteration not only in peripheral processes associated with the contraction, but also in the central (motor) command to the acting apparatus. We suppose that among peripheral sites, intracellular processes of contraction play the major in the contractile impairment recorded during "dry" immersion.

Action Potentials↗
PubMed1999

A plant's response to gravity as a wave phenomenon.

In 1988 I discovered low velocity longitudinal waves plants. These waves are called W-waves because they were first found by probing freshly cut live wood. The initial velocity for these waves was found to be close to 1 m/s. These waves don't appear to be explicitly electromagnetic but in live materials they shift charge because charge is free to move. These waves usually appear as standing waves so that with multiple probes or probing one can often find evidence for a standing wave in plant materials with charge located in periodically spaced piles. It appears likely that standing waves are largely responsible the placement of structures such as branches or leaves. The standing waves also appear to have an important influence on determining the size and shape of cells and shorter wavelengths are hypothesized to be important in determining cell structure. It is the authors opinion that W-waves are just a macroscopic extension of quantum waves (which determine the structure of matter) with a continuous connection with the microscopic. Th waves are also found outside of plants traveling with much larger velocities (v), however. W-waves appear to have many unique frequencies (f). These frequencies can be measured electronically, by beating with weak electromagnetic signals, and directly with a low frequency, spectrum analyzer. One can also measure plant internodal spacings (i) and use these measurements to calculate the same characteristic plant frequencies using a previously measured wave velocity. A frequency for a particular spacing is given by f=v/2i. Characteristic plant frequencies repeat from plant to plant. For this paper the most important result is that W-waves seem to be influenced tremendously by the gravitational field. The velocity of these waves within a plant may be different depending on whether they are traveling along the gravitational field or perpendicular to it or anywhere in between. Also it appears that the frequencies of the waves are shifted to lower waves when traveling along the gravitational field as compared to traveling perpendicular to the gravitational field. Both effects may complete the picture. Gravity has a very large influence on frequencies appearing to reduce frequencies to lower values by as much as a factor of one third (or even a smaller fraction) in live plant material. This results in cell lengths and internodal spacings being up to three (or even more) times longer parallel to the gravitational field compared to perpendicular to the gravitational field. Cell lengths and internodal spacings take on immediate values between vertical and horizontal. If the gravitational field is missing or nearly so as with microgravity, the cell is missing the gravity references that determine its shape, for example. It appears that plant parts grow at discrete angles to the gravitational field. All these features constitute overwhelming proof that plants are wave operated with the characteristics of the waves involved very much influenced by the gravitational field.

Biophysical Phenomena↗
PubMed1997

Gravity constraints in infant motor development.

The effect of gravity in determining if and when during infancy movements eventuate and the rate at which they develop is unknown. In accordance with intersegmental relationships (Hof, 1992), a muscle moment during infancy would have to develop more rapidly than the gravitational moment before movement could occur. In this investigation, the effect of growth through the influence of gravity on the joint moments in the axial region when infants were in a prone or supine posture was examined. A mathematical model that considers the body to be composed of transverse elliptical cylinders, 1 cm deep and of known density, was used in estimating the mass of the 16 segments of the body. The gravitational moments about 3 joints within the axial region (C7-T1, T12-L1, and the hip) were determined by summation, using the radii from the joint transverse axis to the center of mass of the segments. Infants (N = 27) aged between 9 and 36 weeks at the beginning of the study were tested monthly 6 times, and the effect of growth on the gravitational moments was represented by first-order polynomials. Age x Joint analysis of variance (ANOVA) of the mean slopes of the regressions for the gravitational moments revealed significant main effects for age and joint. The means increased monotonically with the number of segments and decreased as infants aged. The mean slopes of the neck and trunk joints were significantly smaller than that of the hip joint. With increasing age, the gravitational slope was significantly smaller. The changes in the gravitational moments during infancy are seen as likely control parameters effecting phase shifts in motor patterns during development.

Aging↗
PubMed2000

[The cell as a gravity-dependent biomechanic system].

In the period of 1995-1997 experimental and theoretical studies with various biomechanic objects, i.e. individual cells and cell associations, were performed under changed gravity (0.00001-5 g). Experimental investigations were conducted using clinostats and centrifuges to model effects of hypo- and hypergravity, and aboard space vehicles in real microgravity. Cell cultures in vitro including fibroblasts and osteoblasts on a solid glass or plastic substrate served as objects of the studies. Changes in value and direction of the gravity vector were found to modify the morphophysiological characteristics of cells: structural organization (spatial rearrangement of the intracell component, changes in forms, sizes and quantity of cells) and functional activity (alterations in energy expenditure and intensity of intracellular metabolism). The data suggest that there should be mechanisms of gravitational sensitivity in living systems on the cellular level. As was stated, sensitivity of unicellular free-living organisms to gravity is mostly defined by the motor activity determined by the level of general metabolism. Morphological characteristics (form, size and mass) are of secondary importance. Theoretical analysis resulted in correction of one of the principle postulates of gravitational biology stating a direct link between size (mass) and gravitational sensitivity of organism. Described were consistent patterns of growth, development, and behavior of unicellular cultures in gravitational fields. Strengthening of the force of gravity (hypergravity) leads to eventual deceleration of cell growth and diminution of biomass gain. On the other hand, the spaceflight environment (microgravity) stimulates growth mechanisms. In our opinion, behind these gravitational effects are altered levels of energy spent by cells to overcome the force of gravity. Opposite trends were observed in experiments with cell cultures in vitro. During space microgravity, fibroblast cultures on the solid substrate decreased the growth rate, and inhibited cell division and migration within the substrate. Compared to the Earth's gravity, under elevated gravity these parameters were noticeably higher. It was demonstrated that the main cause of the unfavorable effects of space microgravity on the cellular level is decay in the adherence of cells to the substrate. Explored were also the most probable mechanisms of the effects of changed gravity on the cell as a biomechanic structure. Specialized and non-specialized graviceptors of various types of cells were crypt-analyzed and classified. In future, investigations should be angled for elucidation of the role of intracellular components in perception and implementation of the gravitational stimulus, and description of quantitative characteristics of energy exchange and metabolism in cells as a function of gravity force and direction.

Biomechanical Phenomena↗