We usually think of stress as an event or a life situation that causes irritation, anxiety and restlessness to us. In our daily conversations “stress” is almost equivalent to anxiety and pressure. “I have a lot of stress” means “I am under a lot of pressure.” But more technically, “stress” is a nonspecific reaction of our bodies to a wide array of different stimuli. These stimuli are called “stressors.” Different stressors cause a non-specific reaction in the body called stress. By non-specific, it is meant that the changes are almost the same in response to different types of stressors.
Let’s take a closer look at the stress response: When we perceive a stimulus as a “stressor,” the “stress response” kicks off in the body. The “stress response” is composed of three levels:
1. The first level of response is the neural phase. It usually takes a couple of seconds and involves both the autonomic and neuromuscular nervous systems. In the autonomic part, It is often the sympathetic system that is activated. The nerve endings produce epinephrine and the end result is an arousal state with manifestations like increased heart and respiratory rates. Another part of this fast response is the activation of the nerves going to the muscles with the effect of muscular contraction.
2. The second phase is the neuroendocrine phase or the famous “fight or flight” reaction. It involves the stimulation of the inner part of the adrenal gland by the sympathetic system leading to the secretion of epinephrine ( and also norepinephrine to a lesser extent). The impact of these hormones are identical to the sympathetic nervous system but lasts longer. Increased blood pressure, increased heart rate and cardiac output, increased stimulation of skeletal muscles, increase plasma free fatty acids, triglycerides, cholesterol are the widespread consequences of this phase, to name only a few.
3. The third step of the stress response is the endocrine phase which causes the most chronic forms of the stress response. It is composed of:
- Increased secretion of pituitary ACTH followed by cortisol from the adrenal cortex
- Increased secretion of Growth hormone from the pituitary gland
- Increased secretion of thyroid hormones
This collection of complex neural and endocrine phenomena is what we call “stress response.” As mentioned above this response is non-specific. Many stimuli can cause this response. Anything that evokes this response is a “stressor.” The function of this response is to provide an arousal state so that we can react to threats quickly and efficiently. Increased heart rate, increased breathing to increase the oxygen level, muscle contraction, liberating glucose and lipids, all provide a condition of a quick response to a threat. Everything that is not momentarily needed, like digestion, sexual arousal, repair of tissues, is slowed down to the benefit of the more urgently needed activities.
In times of immediate physical danger, this response is hugely beneficial. Even with short-term challenges like ending a project or passing an exam some degrees of stress promote performance. The problem starts when the amount of stress gets higher than the optimal level, or the stress response is prolonged too much and gets chronic. This is when an adaptive process turns into a maladaptive and adverse one. In later posts, I will talk more about the stressors and the diseases related to stress.
