May8th2008 - What is Stress? Defining stress is harder than...

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1 Neuroendocrinology of Stress What is Stress? • Defining stress is harder than it sounds – A state of threatened homeostasis – The thing responsible for the imbalance. aka stressor – The body’s response to the imbalance. aka stress-response Threat to Homeostasis • Lava from a volcano is about 700° C • Body temperature is 37 C° • Standing to close to lava for too long will disrupt homeostasis Other Sources of Stress • Predators • Food deprivation • Social stress Biological Responses to Stress • Hormones released from the hypothalamus trigger a cascade of hormonal responses Hypothalamic Response • The paraventricular nucleus of the hypothalamus releases C orticotropin R elasing H ormone (CRH) • In mammals CRH travels to the pituitary gland via the portal blood vessels
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2 Pituitary Response • CRH travels to the posterior pituitary • CRH stimulates the release of A dreno c ortico t ropic h ormone into general circulation Adrenal response • ACTH stimulates the adrenal cortex to release glucocorticoids – Humans, most domestic animals: cortisol – Most rodents: corticosterone Negative Feedback • Indoor temperatures are regulated by negative feedback loops • Many physiological systems are regulated in a similar way + - Hypothalamus stressors CRH Anterior Pituitary ACTH Adrenal Cortex GC S p i n a l C o r d + + - - Sympathetic Nervous System Response • Nerve endings release norepinephrine – Increase heart rate, respiration, blood pressure • Adrenal medulla releases epinephrine – Increase blood glucose levels Hypothalamus stressors NE NE Medulla EPI
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3 Goal of “Stress Hormones”: To make as much energy available for immediate use as possible The stress response is non-specific short-term adaptive long-term maladaptive Acute vs. Chronic Stress • Hypothesized that short term (acute) activation of HPA axis is relatively benign • Long term (chronic)
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May8th2008 - What is Stress? Defining stress is harder than...

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