|
Chronobiology is a field of biology that examines periodic (cyclic) phenomena in living organisms and their adaptation to solar- and lunar-related rhythms. These cycles are known as biological rhythms. Chronobiology comes from the ancient Greek χρόνος (''chrónos'', meaning "time"), and biology, which pertains to the study, or science, of life. The related terms ''chronomics'' and ''chronome'' have been used in some cases to describe either the molecular mechanisms involved in chronobiological phenomena or the more quantitative aspects of chronobiology, particularly where comparison of cycles between organisms is required. Chronobiological studies include but are not limited to comparative anatomy, physiology, genetics, molecular biology and behavior of organisms within biological rhythms mechanics.〔 Other aspects include development, reproduction, ecology and evolution. ==Description== The variations of the timing and duration of biological activity in living organisms occur for many essential biological processes. These occur (a) in animals (eating, sleeping, mating, hibernating, migration, cellular regeneration, etc.), (b) in plants (leaf movements, photosynthetic reactions, etc.), and in microbial organisms such as fungi and protozoa. They have even been found in bacteria, especially among the cyanobacteria (aka blue-green algae, see bacterial circadian rhythms). The most important rhythm in chronobiology is the circadian rhythm, a roughly 24-hour cycle shown by physiological processes in all these organisms. The term ''circadian'' comes from the Latin ''circa'', meaning "around" and ''dies'', "day", meaning "approximately a day." It is regulated by circadian clocks. The circadian rhythm can further be broken down into routine cycles during the 24-hour day:〔Nelson RJ. 2005. An Introduction to Behavioral Endocrinology. Sinauer Associates, Inc.: Massachusetts. Pg587.〕 * Diurnal, which describes organisms active during daytime * Nocturnal, which describes organisms active in the night * Crepuscular, which describes animals primarily active during the dawn and dusk hours (ex: white-tailed deer, some bats) While circadian rhythms are defined as endogenously regulated, other biological cycles may be regulated by exogenous signals. In some cases, multi-trophic systems may exhibit rhythms driven by the circadian clock of one of the members (which may also be influenced or reset by external factors). The endogenous plant cycles may regulate the activity of the bacterium by controlling availability of plant-produced photosynthate. Many other important cycles are also studied, including: * Infradian rhythms, which are cycles longer than a day, such as the annual migration or reproduction cycles found in certain animals or the human menstrual cycle. * Ultradian rhythms, which are cycles shorter than 24 hours, such as the 90-minute REM cycle, the 4-hour nasal cycle, or the 3-hour cycle of growth hormone production. * Tidal rhythms, commonly observed in marine life, which follow the roughly 12.4-hour transition from high to low tide and back. * Lunar rhythms, which follow the lunar month (29.5 days). They are relevant e.g. for marine life, as the level of the tides is modulated across the lunar cycle. * Gene oscillations – some genes are expressed more during certain hours of the day than during other hours. Within each cycle, the time period during which the process is more active is called the ''acrophase''.〔Refinetti, Roberto (2006). ''Circadian Physiology''. CRC Press/Taylor & Francis Group. ISBN 0-8493-2233-2. (Lay summary )〕 When the process is less active, the cycle is in its ''bathyphase'' or ''trough'' phase. The particular moment of highest activity is the ''peak'' or ''maximum''; the lowest point is the ''nadir''. How high (or low) the process gets is measured by the ''amplitude''. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Chronobiology」の詳細全文を読む スポンサード リンク
|