Stress has a bad reputation, but the stress response can save one’s life. Say you step out into the street only to hear the shrill air-horn and diesel grumble of a speeding bus. The stress response has you covered, fixing your attention, quickening your heart rate, and preparing your muscles to launch you into a leap back onto the sidewalk. One’s body features a stress response to drive one to respond to any — real or imagined — threat to one’s well-being. 

Stress only becomes a problem when the stress response doesn’t get flipped off, as can happen in a modern life of work deadlines, family commitments, and social obligations. Stress isn’t bad, but it can be costly.

Knowing how the stress response works will help you understand why it’s beneficial, what causes the feelings you experience, and how practices like breath exercises and meditation can help counter it when it’s out of control. 

Here is a brief description of what happens in the body when the stress response is triggered, which usually begins with sensory information that the body takes in that could be threat — be it that blaring horn or a workplace memo. 

1. Amygdala talks to hypothalamus:

Receiving this sensory input, the brain sends an inquiry to the amygdala. If the amygdala finds the information worrisome, it sends an urgent message to the hypothalamus.

2. The hypothalamus coordinates a response:

The hypothalamus is sometimes called the body’s command center. It sends signals to various parts of the body to urge actions. The hypothalamus triggers messages to be sent by both of the body’s major communications systems — the nervous system and the endocrine system (i.e. hormones sent through the blood.) If the nervous system is analogous to the telephone — rapid communication between two points — the endocrine system is more like email — slower but broader communications.

3. Stress hormones (e.g. adrenaline and cortisol) are released:

Among the signals sent by the hypothalamus are messages to glands to release hormones. For example, the adrenal glands at the kidneys release adrenaline (a.k.a. epinephrine.) 

4. Heart rate and blood pressure rise:

That adrenaline signals the heart to beat more frequently. This means that more blood will be in any given section of a blood vessel — hence higher blood pressure. This is why you might feel your pulse pounding when you jump out of the way of that moving vehicle.  The faster heart rate is needed to send more oxygen and glucose carrying blood to the muscles to prepare them to work as well as to the brain to maintain attention. 

5. Respiration gets harder and faster:

This is related to item # 4. The respiration rate increases so that one can move more oxygen to the muscles and brain in preparation for fighting, fleeing, and maintaining attentiveness. 

6. Glucose is released:

Besides oxygen, the muscles and brain need another fuel to do their work. This is where the massive release of glucose stores comes into play. Glucose is a sugar molecule that your body and brain use for energy. 

As an aside, you may have heard that stress contributes to obesity through the excess of a hormone called cortisol. While discussion of that process is outside the scope of this article, this is the process from which that problem derives.

7. Digestive disruption: 

If you’ve ever gone for a walk after eating a big meal, you may have found yourself sluggish. When the body is sending a lot of blood to the gut for digestion, that’s blood that’s not available to the muscles and the brain. For this reason, digestive processes are put on hold during stress response. This is great for a brief bout of stress, but if one remains stressed for an extended time, the disruption of digestion can become harmful. 

8. Hyperarousal: 

It’s easy to think that the brain’s portion of energy consumption must be minimal. Unlike leg muscles, which are very dynamic, the brain just sits inside the skull. However, the brain uses about twenty percent of the body’s energy. Maintaining awareness is costly in terms of energy, so the brain tends to want to shift into low gear. (Note: this is part of why meditation is so difficult, because the body doesn’t want to maintain attention in a low stimulation environment, so it keeps telling the energy- costly system of vigilance to shut down.) 

As we mentioned, the stress response is an effective way to spur the body into action in order to avoid harm. We don’t want to eliminate stress. However, if stress becomes continuous, the body and mind can not keep up with the demands it makes. That’s where practices like yoga nidra and pranayama can be used to shift over into rest and digest mode.