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What is the stress response in the body? How can your stress response both help and harm your body?
According to biologist Robert Sapolsky, if you feel exhausted and constantly stressed, then the stress response in your body may be working overtime. In Why Zebras Don’t Get Ulcers, he argues that people today are more stressed than ever before, and it’s causing major physical and mental harm.
Read on to learn about the stress response in the body and how chronic stress affects it, according to Sapolsky.
How Your Body’s Stress Response Works
In Why Zebras Don’t Get Ulcers, biologist and neuroscientist Robert Sapolsky argues that people today are more stressed than ever before, and it’s causing major physical and mental harm. Fortunately, there are steps you can take to reduce stress in your life and curb the damage caused by chronic stress. To better understand how stress affects you, let’s take a look at how the stress response in the body works and how chronic stress affects its functioning.
Sapolsky points out that when you identify a stressor, your brain has two main ways of activating the stress response in your body. The first is through the release of neurotransmitters by the autonomic nervous system. The second is through the release of hormones. When you’re chronically stressed and these systems are activated too often, it can disrupt the body’s functions and potentially cause harm.
Autonomic Nervous System
According to Sapolsky, the autonomic nervous system controls involuntary processes (like the stress response in the body), and it consists of two key parts: the sympathetic and parasympathetic nervous systems. These two systems work in tandem to respond to and then recover from stress.
The sympathetic nervous system turns on during times of stress (fight or flight) and helps your body respond almost immediately during a perceived emergency. It does this by releasing neurotransmitters through the nerve endings all over your body. The two key neurotransmitters the sympathetic nerve endings release are the closely related epinephrine (more commonly known as adrenaline) and norepinephrine. Both of these neurotransmitters make your body immediately react to a stressor.
When you encounter a stressor, the sympathetic nervous system activates and epinephrine quickly reaches your organs and causes physiological changes in your body—your heart rate increases and blood flow is diverted to your muscles from other parts of the body. These physiological changes are meant to help you deal with the current stressor.
The parasympathetic nervous system is best understood as working in opposition to the sympathetic nervous system. It promotes calm, vegetative activities, like growth, energy storage, and digestion. After a stressful event, the parasympathetic nervous system slows your heart rate and returns blood flow back to the rest of your body.
In a healthy person, there’s a balance between the sympathetic and parasympathetic systems—you get stressed, so the sympathetic activates. The stressful event ends, so the parasympathetic kicks into gear. When you’re consistently stressed, however, you’re constantly turning on your sympathetic nervous system and turning off your parasympathetic one. This can, among other things, cause harm to your cardiovascular and metabolic systems, lower your immune response, and affect your brain functioning, leading to many health problems (some of which we’ll cover in depth later in the guide).
(Shortform note: To better understand the functioning of the autonomic nervous system and how it relates to stress, you can look at the simple act of breathing. In The Body Keeps the Score, Bessel van der Kolk explores the process of breathing and its effect on the heart. Inhaling activates the sympathetic nervous system, while exhaling activates the parasympathetic. Measuring heart-rate variability (HRV), the variation in time between heartbeats, can provide insight into the health and balance of your autonomic nervous system. If you have a low HRV, your heart rate and breathing are out of sync, and you’re more likely to have a hyperactive stress response in and suffer from stress-related diseases like heart disease and cancer.)
Hormonal Release
The second way your body reacts to stress is through the release of hormones. Similar to its effect on the autonomic nervous system, the constant activation of the stress response in the body caused by chronic stress disrupts the balance of the hormonal system, causing health issues.
When a chemical messenger like epinephrine is transmitted through nerve endings, it acts as a neurotransmitter. When it’s released into the bloodstream by the adrenal gland, it acts as a hormone. There are many different hormones responsible for a wide variety of bodily functions. Some of these hormones are released during stress, and some are blocked. In a chronically stressed person, there’s often too much of certain hormones in the bloodstream and not enough of others. Additionally, because hormones are released into the bloodstream, their effects last longer than the effects of neurotransmitters.
(Shortform note: Because hormones are released into the bloodstream, the scientific community has long believed that the stress-regulating effects of hormones aren’t seen as quickly as the effects of neurotransmitters. A 2016 study, however, found evidence that hormones might also play a role in the immediate response to stress. The research found that the pituitary gland, also known as the “master gland” of the brain, becomes immediately active when encountering a distressing situation, and the hormones released have an immediate effect on one’s subsequent behavior.)
On top of epinephrine and norepinephrine, Sapolsky points to one other type of hormone that’s vital to the stress response in the body: glucocorticoids. Glucocorticoids affect multiple body systems and have several different functions related to the stress response. Glucocorticoids help activate the body’s stress response, they help with the recovery from the stress response, and they also work as anticipatory hormones, helping your body prepare for the next stressor. An overactive stress response can cause elevated levels of glucocorticoids, leading to issues related to all the different functions and bodily systems affected by glucocorticoids.
| Cortisol: The Stress Hormone Perhaps the most important glucocorticoid is cortisol, also known as the “stress hormone.” Though Sapolsky mentions cortisol, he writes about glucocorticoids more broadly and doesn’t single out cortisol as the most significant stress hormone, even though it’s generally thought of as such in scientific literature. Cortisol is released after epinephrine so that you continue to stay alert after a stressful event. Cortisol also activates the release of glucose from your liver to provide energy during stress. Cortisol also has a wide variety of functions on top of regulating the body’s stress response, which may explain why chronic stress can contribute to so many different diseases and ailments. Cortisol helps regulate metabolism, blood pressure, blood sugar, the sleep cycle, and the immune system. High cortisol levels can result in weight gain, hypertension, high blood sugar, and many other symptoms. |
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Here's what you'll find in our full Why Zebras Don't Get Ulcers summary:
- The physical and mental harm chronic stress does to your body
- The steps you can take to reduce stress in your life
- Why you should make your life more predictable
