The bodys reponse to stress: The Hypothalamic-Pituitary Adrenal Axis (HPA) • The response is controlled by the hypothalamus and pituitary gland. • Hypothalamus is a small structure at the base of the brain • Pituitary gland ‘master gland’ as it releases many hormones into the bloodstream 1)The HPA Axis is activated when higher brain centres evaluate a situation as stressful 2) instructs the hypothalamus to release the CRH hormone to stimulate the release of ACTH from the pituitary gland 3)The ACTH travels to the adrenal glandsand triggers the release of the hormone cortisol– a vital part of the stress response – mobilising energy reserves –increasing heart rate & blood flow
The Hypothalamic Pituitary Adrenal (HPA) Axis Stressor in the environment Higher Brain Centres (Cerebral Cortex & Limbic system) evaluate the stressor • Causes higher heart rate & blood pressure • To get blood and • glucose/fatty acids the muscles • To prepare the body for • fight or flight • If there is a lot of cortisol it suppresses the immune system Hypothalamus CRH Hormone Pituitary gland ACTH hormone in bloodstream The steroid hormone cortisol is released into bloodstream Adrenal glands http://www.youtube.com/watch?v=V08dW http://www.youtube.com/watch?v=RyP8L3qTW9Q&feature=related z5XNBA
The General Adaptation Syndrome (GAS) (Selye, 1956) 1st phase – the alarmphase, the presence of a stressful event is registered – could be a threat from an outside or physical stressor – such as an injury or illness affecting the body - the hypothalamic-pituitary adrenal (HPA) Axis prepare the body for energy expenditure (fight or flight) – ‘Take note: nowadays many of the stressors are psychological’ 2nd phase is resistance– the body’s stress response is fully activated and coping with the stressor, so from the outside things appear to be back under control 3rd phase of exhaustion if the stressor is long lasting and chronic. Hormone levels are depleted or too high for too long, and stress related conditions such as high blood pressure, cardiovascular disorders and suppression of the immune system
The three phases of the General Adaptation Syndrome (GAS) (Selye, 1956) Phase 1: Alarm Stress response system activated (HPA Axis activated) Phase 2: Resistance Body copes with stress Phase 3: Exhaustion Stress related illness may develop Evaluation points?