Cortisol is a steroid hormone released in greatest quantities when we wake up in the morning and during times of stress. In times of stress, it’s production is controlled by the hypothalamus, pituitary and adrenal glands through the HPA axis. Cortisol increases bodily functions considered essential to the fight or flight response such as heart rate, blood pressure, blood glucose, respiration and muscle tension; and reduces those considered detrimental to the fight or flight response such as the digestive, reproductive and growth processes. In the short-term, this can be essential to survival, but if high levels of cortisol are produced long-term this can have a harmful effect on many bodily functions such as the digestive and immune systems.(2017). Hormone Health Network. What is Cortisol? [online] Available at: http://www.hormone.org/hormones-and-health/hormones/cortisol [accessed 20 Oct. 2017]. (2017). You and Your Hormones from the Society for Endocrinology. Cortisol. [online] Available at: http://www.yourhormones.info/hormones/cortisol/ [Accessed 16 Oct. 2018]. Mayo Clinic. (2016). Chronic stress puts your health at risk. [online] Available at: https://www.mayoclinic.org/healthy-lifestyle/stress-management/in-depth/stress/art-20046037 [Accessed 19 Nov. 2018].