![]() ![]() Then, we explore the known daily and circadian variations in urinary functions. In this review, we briefly introduce circadian systems in mammals and their physiological significances, keeping urological researchers in mind. Yet, the precise mechanism or mechanisms underlying these variations remain largely unexplored. Like many other physiological processes, fluid intake, urine production, and urine storage display distinct daily and circadian variations as discussed below. Thus, it has become increasingly evident that circadian clocks play crucial roles in the orchestration of life according to time of day, and most physiological functions are tightly locked to an organism's activity and rest phases to ensure optimal performance. Moreover, disturbances to the circadian rhythm and knockouts of clock genes lead to various oxidative stress-related pathologies, including mental illnesses, cancer, obesity, type II diabetes, cardiovascular diseases, and aging. In support of this notion, the phases of DNA replication, DNA repair, and the cell cycle are found appropriately positioned in a given day-night cycle to minimize the damage. Gehring and Rosbash once hypothesized that the origin of circadian clocks in early metazoans might be a coupling of blue light receptors to molecular oscillators to avoid excess oxidative stress induced by light. The advent of endogenous circadian clocks seems to be a recent innovation in the history of life, because the core molecules that derive oscillatory functions within the cell have multiple origins among different forms of life. ![]() ![]() Indeed, almost every life form on Earth displays distinct daily or circadian variations in biochemistry, physiology, pathology, and behavior. Organisms that can predict, and prepare themselves in advance for, these environmental changes have selective advantages over those who cannot accommodate themselves until the changes of environment have taken place. One of the most predictable environmental changes on this rotating planet is undoubtedly the alternations of day and night, which accompany daily variations in environmental illumination, ambient temperature, humidity, and food and predator availability. ![]()
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