Circadian rhythm: physiological basis to clinical application
Bhatt, Janardan (2002) Circadian rhythm: physiological basis to clinical application. Journal of Applied Basic Medical Sciences, 4 (4). pp. 74-76. ISSN ISSN 0972-4729
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The supra-chiasmatic nucleus receive information of, light via visual pathway from retina. SCN send in turn signal to pineal gland (situated in the brain) and secrete hormone called Melatonin. Melatonin in synthesized from 5-Hydroxy tryptamine (serotonin) in the presence of enzyme. N- Acetyl Transferase. In the presence of Sunlight, there is decreased secretion while in the night, in the absence of light, Pineal Gland secret melatonin in physiological need. In the night time, as the person sleeps, the plasma concentration of melatonin progressively increase usually up to 4 A.M. Then plasma concentration of melatonin starts falling and reaching basal level at 6.8 A.M. This basal level of plasma melatonin will maintain throughout the day and again in the night time/sleep around 10 P.M., plasma concentration of melatonin again progressively rises. This is called phasic secretion of melatonin. This phasis secretion of melatonin is dependa upon the photoperiod i.e. duration of exposure of sunlight throughout the day. There is also a seasonal variation of melatonin secretion. In summer, as the photoperiod is increased, the melatonin secretion is decreased. This leads to increase secretion of Pituitary gland and Hypothalamic hormones, and increase the physical activity / performance, mood - level etc. This is typically observed in birds. With the onset of summer and prolongation of photoperiod various behaviours i.e. nesting, laying eggs, parenting etc. are observed.
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