College of Chemistry and Chemical Engineering, Shaanxi University of Science and Technology, Xi'an, 710021, Shaanxi, China.
Farquhar Lab, Research School of Biology, Australian National University, Acton, ACT, 2601, Australia.
J Comp Physiol B. 2020 Jan;190(1):1-16. doi: 10.1007/s00360-019-01255-3. Epub 2020 Jan 3.
To maintain calcium homeostasis during physical inactivity, precise coordination is necessary between different organs of the body. There are a number of factors which alter an organism's calcium balance, such as growth, aging, physical inactivity and acquired or inherited disorders which ultimately lead to bone loss. In non-hibernating mammals, physical inactivity causes bone loss which may not be completely recoverable during the lifespan of an individual despite a resumption of activity. Extreme physical inactivity and nutritional deprivation are two other important factors that lead to bone loss in non-hibernating mammals. The mechanism of bone loss is still poorly understood, however, there is some evidence which shows that during hibernation, smaller mammals (ground squirrels, bats, and hamsters) undergo bone loss. While on the other hand, hibernating bears do not show any sign of bone loss and retain their bone structure and strength. This may be due to differences in their hibernation patterns, as smaller mammals may excrete calcium throughout the hibernation period, which ultimately leads to bone loss, whereas bears seem to have a more developed and advanced mechanism to prevent calcium loss and maintain their bone structure. In this review, we summarize calcium homeostasis and its adaptive mechanisms with reference to bone loss in hibernating as compared to non-hibernating mammals. We also review the effect of microgravity and simulated microgravity on bone physiology and subsequent adaptation.
为了在身体不活动期间维持钙稳态，身体的不同器官之间需要精确的协调。有许多因素会改变生物体的钙平衡，例如生长、衰老、身体不活动以及获得性或遗传性疾病，这些最终都会导致骨质流失。在非冬眠哺乳动物中，身体不活动会导致骨质流失，尽管个体恢复了活动，但这种骨质流失在其一生中可能无法完全恢复。极度的身体不活动和营养缺乏是导致非冬眠哺乳动物骨质流失的另外两个重要因素。骨质流失的机制仍不清楚，但是有一些证据表明，在冬眠期间，较小的哺乳动物（地松鼠、蝙蝠和仓鼠）会经历骨质流失。另一方面，冬眠的熊没有任何骨质流失的迹象，并且保持着它们的骨骼结构和强度。这可能是由于它们的冬眠模式不同，较小的哺乳动物可能会在整个冬眠期间排泄钙，最终导致骨质流失，而熊似乎有一种更发达和先进的机制来防止钙流失并维持其骨骼结构。在这篇综述中，我们总结了钙稳态及其适应机制，以及与冬眠和非冬眠哺乳动物的骨质流失有关的内容。我们还回顾了微重力和模拟微重力对骨骼生理学及其后续适应的影响。
