\[ **BT: [[life#coordination of vital processes|coordination of vital processes]]** ] --- # circadian rhythms Circadian rhythms have been widely observed in animals, plants, fungi, and cyanobacteria; there is evidence that they evolved independently among these organisms.[^1] In [[mammals]], many physiological processes and behaviours are rhythmic. The most obvious daily process is the sleep/wake cycle, but there are also ‘clear changes in the blood concentration of several hormones and specific metabolites throughout the day’.[^2] --- ## how they work Dark/light rhythms are controlled by ‘an endogenous molecular clock within the suprachiasmatic nucleus’ (within the forebrain of mammals); molecular clockwork is made of a core group of clock genes: *Per, Cry, Clock*, and *Bmal1*.[^3] In humans, > ‘Light during the day is the main synchronizer for our circadian rhythms and controls the timing of our neuroendocrine system. For example, the hormone [[hormones#melatonin|melatonin]] is secreted only during the night and seems to be a humoral entraining signal for peripheral organs to show proper circadian rhythms.’[^4] --- ## circadian rhythms and reproduction [[Reproductive tissues contain functional molecular clock machinery.]][^5] [[Disruption of circadian rhythms causes reproductive problems in rodents.]][^6] [[Experiments in rodents with clock gene deletion resulted in (depending on which gene was affected) implantation problems, foetal reabsorption, morphological abnormalities, and ovulation problems.]][^7] [[People working ‘chronic shift-work schedules’ experience menstrual cycle issues and ‘a high risk of preterm delivery’. They are also more likely to suffer from endometriosis, increased miscarriage risk, and low infant birth weight.]][^8] ### labour/birth [[Rats give birth during the daytime, i.e. during their time for rest and sleep.]][^9] ### nursing/chestfeeding [[Rats nurse more during the day time (i.e. their sleep and rest time).]][^10] > ‘During the transition from pregnancy to lactation, there is an upregulation of the positive limb of the core clockwork as well as of clock regulatory genes in specific metabolic pathways of the rat’s mammary gland, liver, and adipose tissues to support the increased nutritional demands of lactation.’[^11] --- ## factors affecting biological periodicities [[People working ‘chronic shift-work schedules’ experience menstrual cycle issues and ‘a high risk of preterm delivery’. They are also more likely to suffer from endometriosis, increased miscarriage risk, and low infant birth weight.]][^8] ### amplification and superimposition of individual rhythms in communities [^1]: ‘Circadian rhythm’, Wikipedia, last edited 1 July 2024, 03:06 (UTC), <https://en.wikipedia.org/wiki/Circadian_rhythm>. [^2]: Mario Caba et al., ‘[[Caba et al., ‘Circadian Rhythms and Clock Genes in Reproduction’, 2018|Circadian Rhythms and Clock Genes in Reproduction: Insights from Behavior and the Female Rabbit’s Brain]]’, *Frontiers in Endocrinology*, vol. 9, no. 106 (2018), p. 2, <https://doi.org/10.3389/fendo.2018.00106>. [^3]: Mario Caba et al., ‘[[Caba et al., ‘Circadian Rhythms and Clock Genes in Reproduction’, 2018|Circadian Rhythms and Clock Genes in Reproduction: Insights from Behavior and the Female Rabbit’s Brain]]’, *Frontiers in Endocrinology*, vol. 9, 106 (March 2018), p. 2. <https://doi.org/10.3389/fendo.2018.00106>. [^4]: Mario Caba et al., ‘[[Caba et al., ‘Circadian Rhythms and Clock Genes in Reproduction’, 2018|Circadian Rhythms and Clock Genes in Reproduction: Insights from Behavior and the Female Rabbit’s Brain]]’, *Frontiers in Endocrinology*, vol. 9, 106 (March 2018), p. 4, <https://doi.org/10.3389/fendo.2018.00106>. [^5]: Mario Caba et al., ‘[[Caba et al., ‘Circadian Rhythms and Clock Genes in Reproduction’, 2018|Circadian Rhythms and Clock Genes in Reproduction: Insights from Behavior and the Female Rabbit’s Brain]]’, *Frontiers in Endocrinology*, vol. 9, no. 106 (2018), p. 1, <https://doi.org/10.3389/fendo.2018.00106>. [^6]: Mario Caba et al., ‘[[Caba et al., ‘Circadian Rhythms and Clock Genes in Reproduction’, 2018|Circadian Rhythms and Clock Genes in Reproduction: Insights from Behavior and the Female Rabbit’s Brain]]’, *Frontiers in Endocrinology*, vol. 9, no. 106 (2018), p. 1, <https://doi.org/10.3389/fendo.2018.00106>. [^7]: Mario Caba et al., ‘[[Caba et al., ‘Circadian Rhythms and Clock Genes in Reproduction’, 2018|Circadian Rhythms and Clock Genes in Reproduction: Insights from Behavior and the Female Rabbit’s Brain]]’, *Frontiers in Endocrinology*, vol. 9, no. 106 (2018), p. 2, <https://doi.org/10.3389/fendo.2018.00106>. [^8]: Mario Caba et al., ‘[[Caba et al., ‘Circadian Rhythms and Clock Genes in Reproduction’, 2018|Circadian Rhythms and Clock Genes in Reproduction: Insights from Behavior and the Female Rabbit’s Brain]]’, *Frontiers in Endocrinology*, vol. 9, no. 106 (2018), p. 1, <https://doi.org/10.3389/fendo.2018.00106>; Mario Caba et al., ‘[[Caba et al., ‘Circadian Rhythms and Clock Genes in Reproduction’, 2018|Circadian Rhythms and Clock Genes in Reproduction: Insights from Behavior and the Female Rabbit’s Brain]]’, *Frontiers in Endocrinology*, vol. 9, no. 106 (2018), p. 4, <https://doi.org/10.3389/fendo.2018.00106>. [^9]: Mario Caba et al., ‘[[Caba et al., ‘Circadian Rhythms and Clock Genes in Reproduction’, 2018|Circadian Rhythms and Clock Genes in Reproduction: Insights from Behavior and the Female Rabbit’s Brain]]’, *Frontiers in Endocrinology*, vol. 9, no. 106 (2018), p. 3, <https://doi.org/10.3389/fendo.2018.00106>. [^10]: Mario Caba et al., ‘[[Caba et al., ‘Circadian Rhythms and Clock Genes in Reproduction’, 2018|Circadian Rhythms and Clock Genes in Reproduction: Insights from Behavior and the Female Rabbit’s Brain]]’, *Frontiers in Endocrinology*, vol. 9, no. 106 (2018), p. 3, <https://doi.org/10.3389/fendo.2018.00106>. [^11]: Mario Caba et al., ‘[[Caba et al., ‘Circadian Rhythms and Clock Genes in Reproduction’, 2018|Circadian Rhythms and Clock Genes in Reproduction: Insights from Behavior and the Female Rabbit’s Brain]]’, *Frontiers in Endocrinology*, vol. 9, 106 (March 2018), p. 3, <https://doi.org/10.3389/fendo.2018.00106>.