During fight-or-flight nonessential body functions such as digestion, urinary, and reproductive activities are inhibited.
2) The Resistance Reaction
This stage is primarily initiated by the hypothalamus releasing hormones and is a longer-lasting response. Hormones involved are: Corticotropin-releasing hormone (CRH), growth hormone releasing hormone (GHRH), and Thyrotropin-releasing hormone (TRH). CRH stimulates the anterior pituitary to secrete ACTH which in turn stimulates the adrenal cortex to increase release of cortisol. Cortisol stimulates gluconeogenesis by liver cells, breakdown of triglycerides into fatty acids (lipolysis), and catabolism of proteins into amino acids to produce ATP or to repair damaged cells. Cortisol also reduces inflammation. GHRH causes the anterior pituitary to secrete eGH and acting via insulin-like growth factors (IGFs), eGH stimulates lipolysis and glycogenolysis (the breakdown of glycogen to glucose in the liver). TRH stimulates the anterior pituitary to secrete thyroid stimulating hormone (TSH) which promotes secretion of thyroid hormones. These hormones stimulate the increased use of glucose for ATP production. The resistance stage is what continues even after the stressor has been removed. This is why your heart continues to pound long after the stressor is removed. If the resistance reaction fails to combat the stressor, we move into the Exhaustion stage.
3) Exhaustion
When body resources are depleted and they cannot sustain the resistance stage, exhaustion sets in. Prolonged exposure to high levels of cortisol and other hormones involved in the resistance stage cause wasting of muscle, suppression of the immune system, ulceration of the GI tract, and failure of the pancreatic beta cells. Pathological changes may occur.
Stress and Disease
The exact mechanisms are not known. However, there are identified stress-related disorders: gastritis, ulcerative colitis, IBS, hypertension, asthma, RA, migraines, anxiety, depression.
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