SALIVARY CORTISOL
            
             An increased amount of cortisol is released in response to a stressor which lasts longer than a few minutes this is released through a system called the hypothalomic-pituatry-adrenal axis (HPA axis). HPA axis is the combined system of corticopin-releasing hormone (CRH) adrenocorticotropohic hormone (ACTH) and cortisol release. Cortisol release is controlled by the paraventricular nucleus (PVN) which is positioned in the hypothalamus it is here that CRH is released when the person is put under stress this in turn causes the release of ACTH by acting on the pituitary gland this ACTH then causes the adrenal cortex to release cortisol. Cortisol is usually released in approximately fifteen minute bursts this occurs as CRH and ACTH are only released in pulses not a prolonged release over time this results in the level of cortisol dips between these pulses. Cortisol itself has roughly a half life of 100 minutes in blood. A prolonged burst of ACTH can cause the adrenal cortex to increase in size so that it can cope with the extra production of cortisol where as the opposite occurs if there is a decrease in the long term production of ACTH. The level of cortisol in the body is kept at safe levels by a process of negative and positive feedback throughout the brain. A certain amount of cortisol is always found in the bloodstream. Much like other things cortisol also has a circadian rhythm controlled by the suprachiasmatic nucleus the body's internal clock. Cortisol peaks are found in the morning at approximately eight to ten o'clock with the lowest amounts of cortisol being found in the evening before bedtime. This is due to the suprachiasmatic nucleus sending messages to the paraventricular nucleus approximately every hour causing CRH to be released resulting in the release of cortisol as described earlier. Abnormal circadian rhythms have been found in people with illnesses such as chronic fatigue syndrome, irritabl...