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It has been known since ancient times that certain plants regularly open
their leaves in daytime and close them at night. It was assumed which this 62. ______
periodic change was triggered by the alternating sunlight and darkness. Such
leaves stick to their daily routine even when keeping in constant darkness. 63. ______
What is circadian rhythm? Many biological processes follow a 24-hours 64. ______
schedule. These cycles are called circadian rhythms. These innate rhythms are
governed by sophisticated chemical mechanisms can be described as biological 65. ______
clocks. Such rhythms are important for humans too! We sleep through most
of the hours of darkness and are awaken through most of the hours of 66. ______
daylight. Body temperature increases during the day and decreases during the
night. The secretion of various hormones that controls life's processes rises 67. ______
and falls to a circadian rhythm.
How does this relate to health? Circadian rhythms are important for
desirable functioning of the processes vital to health. This is most effectively
illustrated and the normal circadian rhythms are disrupted by lack of sleep or 68. ______
by crossing time miles. It may take days or even hours for all the bodies 69. ______
circadian rhythms to read just appropriately. The turmoil (混乱) that results
from the readjustment process when time zones are crossed experienced as the 70. ______
phenomenon of jet lag. This is also experienced by people who do shift work.
Understanding circadian rhythms may be irrelevant to the understanding and 71. ______
treatment of disease. Therapy can be more effective and toxic effects reduced
when drugs are administered at carefully selected times of the day.