| Abstrakt: |
Organisms populating the Earth are under the steady influence of daily and seasonal changes resulting from the planet's rotation and orbit around the sun. This periodic pattern is most prominently manifested by the light-dark cycle and has led to the establishment of endogenous circadian timing systems that synchronize biological functions to the environment. This is the basis of predictive homeostasis (Moore-Ede 1986), evolving as an adaptation to anticipate predictable changes in the environment, such as light and darkness, temperature, food availability or predator activity. Therefore, the circadian clock is one of the most indispensable biological functions for living organisms that acts like a multifunctional timer to adjust the homeostatic system, including sleep and wakefulness, hormonal secretions and various other bodily functions, to the 24-h cycle (Buijs, van Eden, Goncharuk, and Kalsbeek 2003; Collins and Blau 2006; Hastings, Reddy, and Maywood 2003). In mammals, the circadian system is composed of many individual, tissue-specific cellular clocks. To generate coherent physiological and behavioral responses, the phases of this multitude of cellular clocks are orchestrated by a master circadian pacemaker residing in the suprachiasmatic nuclei (SCN) of the hypothalamus. [ABSTRACT FROM AUTHOR] |
