Pioneering stress researcher Hans Selye, M.D., a Canadian physiologist, noted a consistent pattern of response to stress and termed these the general adaptation syndrome (GAS), commonly referred to as the “fight-or-flight” response.
The GAS occurs in three stages:
- Alarm reaction
- Stage of resistance
- Stage of exhaustion.
Initially, the body’s biochemistry tends to react to stress in an orderly fashion. Stimulation of the sympathetic nervous system (part of the autonomic nervous system) activates the secretion of hormones from the endocrine glands and constricts both the blood vessels and the involuntary muscles of the body.
When the endocrine glands (pancreas, thyroid, thymus, pituitary; sex glands, and particularly the adrenals) are stimulated, heart rate, glucose metabolism, and oxygen consumption increase.
The parasympathetic nervous system is also stimulated, which begins a process of relaxation. The pituitary gland responds by releasing a variety of hormones throughout the body, which influence the defensive and adaptive mechanisms.
Endorphins, the body’s own natural painkillers, are also released.
Dr. Selye points out, however, that eventually chronic stress depletes the body’s resources and its ability to adapt.
If stress continues and remains unattended for a long period, coping functions will be compromised and illness will result.’