Answer
The body's general response to threat or stress has been called the general adaptation syndrome of Hans Selye (GAS). There are three stages in the GAS: the fight or flight response (fof), the resistance reaction, and the exhaustion stage.
The reactions of the fof are triggered by neural signals from the hypothalamus(amygdala-hypoth). These stimuli travel by way of sympathetic nerves of the autonomic nervous system (ANS), and serve to mobilize the body for activity. Some of the factors in the mobilization process are increases in the amount of glucose and of oxygen made available to brain, heart and skeletal muscles; these are the organs are most important in a physical emergency. Other factors are the increase in blood volume, and in blood pressure mediated through the renin-angiotensin-aldosterone system.
Work Step by Step
If a stress is prolonged and unremitting, the resistance reaction enables the body to keep resisting This stage of the stress reaction is initiated by hypothalamic releasing hormones. The important ones are coticotropin releasing hormone (CRH), thyrotropin releasing hormone (TRH), and growth hormone releasing hormone (GHRH). CRH stimulates the secretion of ACTH which increases the secretion of cortisol from the adrenal cortex; TRH promotes secretion of thyroid stimulating hormone which increases secretion of thyroid hormones; GHRH acts on the anterior pituitary to increase the secretion of human growth hormone (HGH). These hormones serve to increase the levels of gluconeogenesis and lipolysis. The increased levels of glucose available make possible synthesis of increased levels of ATP which is necessary to support the body's continued resistance to the enduring stress. Cortisol also has the effect of suppressing inflammation.
Exhaustion
If the body cannot sustain the resistance to the unabating stress, its resources become depleted, and exhaustion supervenes. Some of the signs (SS) of this stage may be muscle wasting,-- caused by the high levels of cortisol;--, immune suppression, digestive tract ulceration, and failure of the beta pancreatic cells-- with diabetes.
