Preface

The evolution of life on Earth has a unique anticipatory quiddity that is intended to prepare and coordinate most living organisms to the daily environmental changes driven by the rotation of the planet. The constant transition from light to dark imposes sleep-wake patterns, but in addition to that, there are fluctuations in nutrient availability that impose supplementary pressure on the circadian cycle.

Most of the cells in complex organisms contain molecular clocks that control the activity of important signalling pathways. The synchronisation of these clocks to the circadian environment assures a physiologic pattern of the structure and functioning of all cells and tissues. Many physiological processes within the human organism are influenced by this circadian entrainment system in which the suprachiasmatic nucleus located in the brain acts as a master pacemaker that synchronises subsidiary clocks in peripheral cells. These biological clocks are assembled around gene expression, release modulation of signalling molecular triggers, and interlocking endocrine regulatory patterns, all in perfect coordination with rhythmical physiological and behavioural outputs.

Starting from an initial emphasis on sleep-wake cycles, feeding behaviour, and metabolism, continuing with the confirmation that circadian oscillations play a critical role in foremost physiological mechanisms, we are now witnessing a revolutionary step in chronobiology, namely, the establishment of new research realms that consider all exploratory approaches for the optimal pharmacological management of circadian oscillators and apply circadian principles to drug delivery strategies for therapeutic benefits. The book addresses these topics from the perspective of the implications of circadian rhythm in determining daily human activities, the chronobiologic echoes felt at the metabolic and endocrine levels, and in modulating pathologies outbursts and rationalising pharmacotherapy principles in a coherent individualised circadian pattern. The subject is of overwhelming importance, both for its unique applicability in everyday human life as well as for its extraordinary physio-pathological premises of being widely used to modulate environmental, nutritional, and pharmacological factors to improve quality of life and therapeutic results in perfect accordance with the unique biological rhythm of each individual. This book is a useful resource for healthcare professionals both clinically and academically interested in and impacted by research on circadian rhythms.

**Cristina Manuela Drăgoi, Alina Crenguța Nicolae and Ion-Bogdan Dumitrescu** Faculty of Pharmacy, Department of Biochemistry, "Carol Davila" University of Medicine and Pharmacy, Bucharest, Romania

**1**

**Chapter 1**

Introductory Chapter: Untangling

the Essential Links among the

of the Human Body, and the

*Cristina Manuela Drăgoi, Ion-Bogdan Dumitrescu* 

Pathological Interferences

**2. Circadian, infradian, and ultradian rhythms**

• obtaining energy (nutrients);

• protection from predators;

• regeneration or growth processes;

for future needs;

• reproduction.

*and Alina Crenguța Nicolae*

**1. Introduction**

changes [1, 2].

Nutritional, Behavioural, and

Circadian Rhythm, Homeostasis

The vast majority of living entities are subject to unavoidable and predictable conditions of 24-hour changes in their environment, having the ability to adjust to the day-night cycle. To manage these daily changes in periods of light and darkness, almost every living organism has developed an internal system of synchronisation or circadian clock. This tremendous discovery dates back to the beginning of the eighteenth century when Jean-Jacques d'Ortous de Mairan performed the first chronobiology experiment on *Mimosa pudica,* a plant that visibly responds to circadian

Each living organism carries out its activity for approximately 24 hours by:

• optimising energy consumption by using it for daily activities and storing the rest
