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  • Stress is the body's response to a physical pressure  such as illness or injury; or a psychological  

  • pressure such as fear or anxiety. In the short-term, the stress  

  • response is adaptive. It helps the body  fight, cope with, or flee the stressor.  

  • Chronic stress, however, is maladaptive, and may  become detrimental to the body's normal functions

  • Stress response is mediated mainly by  the sympathetic nervous system and the  

  • endocrine system. It occurs in 3 stages of  the so calledGeneral Adaptation Syndrome”. 

  • Stage 1 - Alarm reaction: Upon perceiving the stressor,  

  • the body produces a fast, “fight or  flightresponse via the activation of  

  • the sympathetic nervous system, the SNS. SNS activation results in an immediate  

  • release of the neurotransmitter norepinephrine  from sympathetic nerves; and shortly after,  

  • the secretion of epinephrine and norepinephrineas hormones, from the adrenal medulla

  • These substances increase cardiac  output, accelerate respiratory rate,  

  • release glucose from stored glycogen, and direct  blood flow to the heart and skeletal muscles.  

  • They also dilate pupils, enhance alertness  and cognition, and reduce pain sensation.  

  • At the same time, SNS activation  also inhibits body processes that  

  • are less important in emergenciessuch as digestion and urination

  • Stage 2 - Resistance or Adaptation. This stage is due mainly to the  

  • slow response - the activation of the  hypothalamus-pituitary-adrenal (HPA) axis

  • In response to stressors, the hypothalamus  produces corticotropin-releasing hormone (CRH).  

  • CRH promotes the secretion of adrenocorticotropic  hormone, ACTH, from the anterior pituitary.  

  • ACTH then stimulates the production  of cortisol by the adrenal cortex

  • Cortisol, known as the stress hormonehelps the body stay on high alert to deal  

  • with long-term stress. Cortisol overall  effect is to increase energy supply

  • - In the liver, it promotes  catabolism of glycogen to glucose

  • - In the muscles, it acts to reduce  glucose uptake and consumption,  

  • and increase degradation of muscle proteins into amino acids, which can then be used  

  • to synthesize glucose, fats, or generate energy. - In adipose tissue, cortisol promotes  

  • lipid breakdown for additional energy. - In the pancreas, it acts to decrease  

  • insulin and increase glucagon secretion, which  together leads to increased blood glucose

  • In addition, cortisol maintains higher blood  pressure by increasing the sensitivity of  

  • vascular smooth muscle to vasoconstrictors  and inhibiting the release of vasodilators

  • At the same time, cortisol also reduces  inflammation and suppresses the immune system

  • Stage 3 - Exhaustion: Stress response is meant to restore the body's  

  • homeostasis, but a chronic or repeated stressor  will eventually exhaust the body's resources,  

  • causing a progressive wasting of muscles. The  HPA axis may become dysregulated. A sustained  

  • elevation of blood pressure and heart rate  may lead to cardiovascular diseases. Prolonged  

  • inhibition of digestive and urinary functions  may cause gastrointestinal and renal disorders.  

  • Chronic stress also weakens the immune systemmaking the body more susceptible to infections.

Stress is the body's response to a physical pressure  such as illness or injury; or a psychological  

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