For many Americans, stress levels are on the rise.
The term “stress” was first coined in the 1930s by Hans Selye, and we’ve been talking about it ever since — perhaps no more so than this past year.
You likely know what stress feels like, but what is actually happening in your body during this experience?
Consider this your crash course on the body’s stress response.
How your body responds to acute stress
“Stress in general is proadaptive, it’s supposed to help you,” says Abigail Schindler, an assistant professor at the University of Washington School of Medicine’s Department of Psychiatry and Behavioral Sciences.
Schindler explains that your body’s response to acute stress, or short-term stress, enables you to handle difficult or dangerous situations. Once the threat has passed, your body returns to a state of balance, called homeostasis.
Various factors, like genetics, personal history and environment, can cause you to perceive a situation as threatening or stressful. Once identified, a stressor activates multiple systems in your body.
The sympathetic nervous system: your fight or flight response
One of the main systems activated by stress is your autonomic nervous system, which helps regulate involuntary body functions like heart and respiratory rate, blood pressure and digestion.
This system has two branches: the sympathetic nervous system, which prepares you to deal with a stressor, and the parasympathetic nervous system, which calms you down after the threat has passed.
“The amygdala, which has a big role in emotional responses, is the first brain region to process a threat or stressor,” says Michele Bedard-Gilligan, a psychologist who sees patients at UW Medical Center – Roosevelt.
Your amygdala communicates this threat to your hypothalamus, the part of your brain in charge of bodily functions and hormones, which in turn activates your sympathetic nervous system, aka your fight or flight response.
In a matter of seconds, your sympathetic nervous system releases adrenaline throughout your body. It’s this rush of hormones that causes your heart to beat faster and push blood into your muscles and your breathing to increase so you can take in more oxygen. With the increase in blood and oxygen, your muscles tense and your senses sharpen.
“Adrenaline decreases all your bodily functions not critical to fighting or fleeing,” Schindler notes. “The attention gets shifted to things like your heart rate, which prepare you to fight or flee.”
The HPA axis: your second wind
When the initial boost from your sympathetic nervous system subsides, your hypothalamus triggers a second system in your stress response: the hypothalamic-pituitary-adrenal (HPA) axis.
“The HPA axis is similar to the sympathetic nervous system. It starts with your brain releasing hormones into your circulatory system,” Schindler says.
In this case, cortisol is the hormone released into your body. The additional hormones keep your sympathetic nervous system engaged and your body on high alert.
“These systems are working together. A lot of signaling molecules in the sympathetic nervous system are interacting with the HPA axis. So, it’s a concert of signaling that is going on, all working toward the same goal, just in different ways,” Schindler says.
As the cortisol floods your system, your metabolism slows down and your immune function increases, helping to protect you from infection and heal any injuries. Cortisol, combined with adrenaline, releases stored fat and sugar in your body to give you a burst of energy.
The parasympathetic nervous system: your rest and digest response
Once the threat has passed, your parasympathetic nervous system, sometimes called the rest and digest response, kicks in. This is the second branch of your autonomic nervous system, and it functions as a mirror to the sympathetic branch.
“Where the sympathetic system is preparing you for a threat, the parasympathetic is calming you down,” Schindler says.
This occurs in part through a negative feedback system. When your body releases cortisol, it also initiates a feedback loop that prevents you from continuing to release additional cortisol. Without the additional stress hormones, your parasympathetic system is able to calm your body down when the threat subsides, allowing your heart rate to slow and returning your body to its baseline state.
How your body responds to chronic stress
When you experience chronic stress, your body initiates the sympathetic nervous system and HPA axis, but because the stress doesn’t go away, your body isn’t able to calm down. Instead, you continue to release adrenaline and cortisol, overstimulating your body.
“Most people can only handle so much stress before their feedback mechanisms and signaling molecules start to break down,” Schindler says.
Because your stress response involves so many systems, chronic stress can cause a whole host of problems.
Your muscles remain tensed, which can cause migraines and tension headaches, along with pain in your shoulders and neck. Your heart rate and blood pressure stay high, which may increase your risk of hypertension, heart attack and stroke. Your prolonged stress response can also exacerbate preexisting conditions and disrupt your gut microbiome.
Additional effects of prolonged stress can include weight gain, irritable bowel syndrome, fatigue and metabolic disorders like diabetes, immune disorders and depression, to name a few, Bedard-Gilligan notes.
Part of the reason so many people struggle with chronic stress is because the scenarios that stress us out have changed over time. While the stress response worked well for prehistoric humans running from or fighting off a predator, it is less helpful for current psychological stressors like relationship problems or financial insecurity.
“Many of the systems we are talking about are older, primitive systems,” Schindler says.
While the research is ongoing, scientists are beginning to look at the ways we respond to these new kinds of stress. Along with the typical flight or fight response, researchers have identified two additional responses: fawn, when you try to pacify a person or situation, and freeze, which can include feeling mentally frozen or physically unable to move.
Signs of stress
“Stress can show up in ways we don’t necessarily recognize,” Schindler says.
Just as muscle tension, headaches and an upset stomach can all signal you’re stressed, so too can problems relaxing, sleeping or concentrating. Schindler also notes that worrying or ruminating before you sleep or having anxiety-filled dreams can be also indicators of stress.
While stress can help us in moments of danger, it’s important to find ways to cope with prolonged stress. If you’re experiencing ongoing or intense stress, it can help to work on relaxation techniques, practice deep breathing or try restorative yoga. You can also talk with a friend or seek support from a mental health expert.
With some support and a coping mechanism or two, you can help move through the stress response and allow your body to finally relax.