Human Circadian Rhythms - Article Example

Background Circadian rhythmi is an important determinant in the pathophysiology, diagnosis, and treatment of clinical disease. Due to the difficulties in conducting the necessary experimental work, it remains unknown whether ~24-h changes in pathophysiology or symptoms of many diseases are causally linked to endogenous circadian rhythms or to other diurnal factors that change across the day. Until the physiology is accurately known, appropriate treatment cannot be designed. This article encompasses an overview of clinical disorders that are caused or affected by circadian or diurnal rhythms. Introduction The circadian cycle includes 24 hrs of the day. A person usually sleeps approximately 8 hrs and is awake for 16 hrs. Throughout the wakeful hours, mental and physical functions are most active and growth increases but during sleep, voluntary muscle activities fade away and metabolic rate, respiration, heart rate, body temperature, and blood pressure are reduced. The actions of the digestive system rise during the resting period, the activity of the urinary system decreases. It is evident that hormones secreted by the body, such as the stimulant epinephrine (adrenaline), are released to its maximum just two hours before awakening to prepare the body for activity (Encyclopedia Britannica). Hypothalamus is the chief control centre especially the Suprachiasmatic nucleus (SCN), part of the hypothalamus; it receives signals about light and dark from the retina of the eye. Cyclical fluctuations of melatonin are essential for maintaining a normal circadian rhythm. Induction of sleep is generated when melatonin binds to receptors in the SCN (Encyclopedia Britannica). An understanding for the biological rhythms is fundamental part towards the perception of all aspects of life including death (Edery, 2000). Physiologic diurnal variation in cardiovascular system, heart rate and cardiac output plays an imperative role in finding the epidemiology of fatal cardiovascular events in the early hours of morning (Dunlap, 1999). It is manifested that diurnal variations are attributed to environmental stimuli or any kind of increase in sympathetic activity (Dunlap, 1999). It is evident that many features of cardiovascular physiology and pathophysiology involve alterations in the expression of genes regulating metabolic and contractile function of the heart and vasculature (Edery, 2000). In order to maintain homogeneous conditions of the body, all the biological processes must be maintained within physiologic boundaries. Failure to achieve a specific level of homeostasis results in pathogenesis (Edery, 2000, Stoleru, 2007). Various studies have shown that This can be understood as, normally our circadian rhythms are synchronized to one another by the internal biological clock, and entrained (daily reset) to the 24 hour day/night cycle by external time signals, encompassing the activities around us. Method The study is performed considering parameters like body temperature, blood pressure, heart rate, reaction time, grip strength to understand the cycle and rhythm of circadian circle. The data is collected over the period of 34 hrs. All these parameters have shown some kind of variations. A regular monitoring was performed taking these parameters in consideration and are recorded and are shown in the table in the appendix. Results: A useful analogy is that of an assembly where initially the different sections are playing in harmony under the one conductor. When the body temperature is high the blood pressure and the heart rate is also high. At 8:00 the when the day begins for office hours the body temperature is high and hence the pulse is also high the metabolic rate is high during this hour. This is followed by the evening hours at 18 hrs. No definite co-relation can be established between the body temperature, blood pressure, heart rate, reaction time and grip strength. It is observed that there is a rise in the morning hours at 8:00 and then a drop is seen in the values at around14:00 hrs. Conclusion A circadian rhythm is a 24 hrs cycle in the biological processes encompassing biochemical, physiological or behavioral process of living beings. Circadian rhythms are endogenously generated and can be entrained by external signals called Zeitgebers. The primary one is daylight. These rhythms allocate organisms to anticipate and prepare for precise and regular environmental changes (Encyclopedia Britannica). The circadian clock mechanism plays an imperative role in human health and well-being because all physiological and behavioral functions in humans occur on a rhythmic basis; this causes diurnal rhythms in human performance and capabilities (Vitaterna, Takahashi, Turek). It presents the selective advantage of anticipation, facilitating the cell to recognize the time of day. During this process, circadian clocks enable cellular responses to environmental stimuli in a rapid as well as temporary manner. Specific environmental factors exhibit highly conventional circadian rhythms (e.g. light/dark cycles), others are somewhat less predictable (e.g. feeding/fasting cycles) (Young, 2007). In addition, specific environmental factors displaying circadian rhythms may require opposing cellular responses. For example, increased physical actions upon awakening would trigger catabolic processes, whilst feeding upon awakening would require commencement of anabolic processes. A high degree of smoothness must remain intrinsic within this coordination; explicitly, circadian clocks can manipulate cellular processes without committing the cell to a specific cellular function (Young, 2007). It is imperative that circadian clocks are sensitive to environmental signals and to any alterations in the light/dark cycle. In the present study a high value of temperature in the morning is attributed to the high metabolic rate and a level of anxiety to start the day. There is a decline in the values as seen in the graph (Appendix). The decline is due to the relaxation after the lunch hours. It is therefore concluded that circadian rhythms do follow a pattern and body reacts accordingly in a rhythmic manner. The graph does not show much variation in the body temperature but show a drop in the blood pressure, heart rate and also in the grip strength at the 14:00 hrs. With the help of the graph (Appendix) we can conclude that the circadian rhythm do control the blood pressure and heart rate and thus directly affects the cardiovascular system. It is one of the biggest reasons why majority of heart related problems and even deaths do take place in the morning hours as circadian rhythm do show some impact on the cardiovascular system in the morning hours as can be concluded from the present study. Appendix Table 1. Time Body temperature Blood pressure Heart rate Reaction time Grip strength 08.00 39.6 137.6 92 6.5 30.6 Kg 10.00 37.3 141.3 85 5.8 31.3 Kg 12.00 37.1 137.7 86 4.5 33 Kg 14.00 37.2 134.3 83 5 36 Kg 16.00 37.5 140 83 4.8 40 Kg 18.00 37.9 137 81 4.6 37 Kg 20.00 37.65 131.5 72 5.8 35 Kg 22.00 37.2 132.8 83 6.1 35 Kg 00.00 37.4 132.3 76 6.5 33 Kg 2.00 37.4 138 83 9 21 Kg 4.00 37.4 136 73 8 25 Kg 6.00 37.25 127 73 7.4 26 Kg 8.00 37 133 72 7.6 26 Kg 10.00 37.4 133 51 6.5 28kg 12.00 38.2 143 58 6.5 32kg 14.00 38.5 116 53 5 34kg 16.00 37.5 127 58 4.5 40kg 18.00 36.7 134 58 5 41kg The graph shows the variation in the values of blood pressure, heart rate and the grip strength but do not show any marked variation in the body temperature, indicating that circadian rhythms do play an imperative role in controlling the heart rate and blood pressure but do not show much control over the body temperature. References: 1. Edery I. Circadian rhythms in a nutshell. Physiol Genomics (2000) 3:59–74. 2. Encyclopedia Britannica http://www.britannica.com/EBchecked/topic/118220/circadian-rhythm 3. Dunlap JC. Molecular basis of circadian clocks. Cell (1999) 96:271–290. 4. Stoleru D, Nawathean P, Fernandez MP, Menet JS, Ceriani MF, Rosbash M. The Drosophila circadian network is a seasonal timer. Cell (2007) 129:207–219. 5. Vitaterna, M., H., Takahashi, J., S., Turek, F., W. Overview of circadian rhythm http://pubs.niaaa.nih.gov/publications/arh25-2/85-93.htm 6. Young ME, Bray MS. Potential role for peripheral circadian clock dyssynchrony in the pathogenesis of cardiovascular dysfunction. Sleep Med (2007) 8:656–667. Read More