In chronic stress, particularly when a person lives with long-standing uncertainty about safety or shelter or other risky situations, there is a chronic over-stimulation of the fight/flight response and the sympathetic nervous system.
The most prominent hormonal effect is on adrenaline and cortisol from the adrenal glands. These hormones can raise the blood sugar levels and cause chronic overstimulation of the insulin-producing beta cells of the pancreas.
We can measure hormone levels in the blood fairly easily, and we can measure cortisol in the saliva, as well. In research studies we can measure brain activity using functional MRI scanning with hyperactivity of the subconsious parts of the brain involved in flight/flight. In animal experiments they can monitor sympathetic nervous system activity and tone. This is not practical for individual patients however.
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