Physiology of the circadian timing system: predictive versus reactive homeostasis. Am J Physiol 250:R735-R752

The American journal of physiology (Impact Factor: 3.28). 06/1986; 250(5 Pt 2):R737-52.
Source: PubMed


Since Cannon first formulated the concept of homeostasis 60 years ago, attention has been focused on the corrective responses initiated after the steady state of the organism is perturbed. In this lecture it is argued that the concept of homeostasis should be extended to include the precisely timed mechanisms of the circadian (and circannual) timing system which enables organisms to predict when environmental challenges are most likely to occur. A mature understanding of homeostasis should encompass both "reactive" responses to changes in physiological variables which have already occurred and the "predictive" responses initiated in anticipation of predictably timed challenges. Such predictive responses have particular value because they enable physiological mechanisms to be utilized immediately, even if they involve a delay of several hours, by activating them at a suitable time in advance of a probable challenge. However, conflicts may often occur between predictions and reality. Examples from sleep-wake behavior, thermoregulation, blood volume homeostasis, and the regulation of potassium balance show that predictive responses often compromise the effectiveness of reactive homeostatic mechanisms even to the point of risking the survival of the organism. It must be concluded that the day-night cycle of the natural environment has played a fundamental role in shaping the evolutionary development of homeostatic mechanisms because of the dominating predictability of diurnal changes in illumination, temperature, food availability, and predator activity.

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Available from: Martin Moore-Ede, Jun 10, 2015
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    • "Circadian organization is important to enable an organism to maintain equilibrium in response to the daily changes in the external environmental and prepare accordingly [8]. In mammals, a number of circadian patterns (~24-h) have been described, including the timing of endocrine hormone secretion (e.g. "
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    • "Multiple dynamic equilibrium adjustment and regulation mechanisms try to maintain a stable internal condition in endotherms via a process known as " homeostasis " . While homeostasis is typically considered a " reactive " response in order to re-establish a point of equilibrium following a provocation at any time of the day, the chronobiologic view holds that homeostasis also includes a periodic process with varying setpoints in anticipation of predictably timed challenges at different times of the day in a process called " predictive " homeostasis [1]. Thus, in the healthy organism, homeostasis, i.e. the body's ability to regulate stability in its inner environment in response to changing conditions in the outside environment, is paradoxically accomplished by the rhythmic recurrence of biological processes and rhythms in different frequency ranges that co-exist. "
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    • "Most simple, uniform ''constant'' cause and effect relationships, that is, ''reactive homeostasis,'' are oversimplified cases or artifacts of experimental paradigms constructed specifically to force the living system to behave and appear constant. The complexity and cycle stage dependency of cause and effect relationships, that is, ''predictive homeostasis'' (Moore-Ede, 1986), in no way diminishes the reality, importance, or relevance of these relationships. It is, nonetheless, important to freely admit that, although solar activity may have the same temporal pattern as these human time structures, a causal connection may not exist. "
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