We live in a world riddled with stress. It seems as though everyone is stressed all the time, about everything. Job interviews, family, and even evening traffic all induce this same, negative feeling. But what is stress actually? Are there different kinds? And most importantly, what does this mean for our experience and response to it?
In order to cover all these aspects let’s imagine a stressful situation: you are on a hike in the woods with your brother when he suddenly falls down and injure his leg.
So your walking along during your hike and everything is going well. Your heart is beating faster because you’re getting your steps in. Your body is using up all the energy from the muffin you ate at breakfast so that you can walk successfully up the mountain. Your body is in allostasis in order to maintain homeostasis.
Lets break down the meanings and differences between allostasis and homeostasis. Homeostasis is the condition in which your body is functioning well, doing all of it’s necessary jobs, and is balanced. Allostasis is the process by which your body makes adjustments in response to changes or stressful events in order to get back to homeostasis.
Think about it this way, your car is in homeostasis when its the summer time and your just casually cruising around around town. Now imagine, its the dead of winter and your going to take it on a cross country road trip. You need to do a bunch of additional things so that the car can manage the stressors of driving hundreds of miles in bad conditions. So, being the responsible car owner you are, you put on snow tires, get the oil changed, and change the windshield wipers. The car is now adjusted to proceed working properly (maintaining homeostasis) given its new and stressful situation.
Ok back to the hiking scenario. Now you are on a tricky part of the climb and your brother falls down, scrapes his leg, and isn’t getting up. Your brother is undergoing acute stress. This is the type of stress that is short-term and is usually brought on by a certain event. In this case, falling and getting injured is the stressful event.
First, your brothers body will kick into high gear and release an array of hormones of that fall under two different categories: catecholamines and glucocorticoids. Hormones are chemical messengers that essentially make other stuff happen throughout the body. Catecholamines are hormones involved with the sympathetic nervous system which is well known for eliciting the “fight or flight” response. Hormones such as epinephrine and norepinephrine (you may know them as “adrenaline” ) fall under the class of catecholamines. Glucocorticoids on the other hand are released via the HPA axis which is very involved in stress responses. It includes the hypothalamus which is a structure within the brain that is responsible for keeping the entire body in homeostasis which is that state of balance.
It is worth going into more detail about the function of the HPA axis because of its prominent role in regulating stress. It has three main parts:
1. Hypothalamus
2. Pituitary Gland
3. Adrenal Gland
The hypothalamus is the “switch board” and dictates which hormones get sent to the body when. It sends messengers and relays information to both the pituitary and adrenal gland telling them which hormones they should release. The hypothalamus also helps with important functions such as sleep, thirst, appetite, and body temperature. In general, the HPA axis dictates whether your body is in a “fight or flight” or “rest and digest,” as seen and described on an experiential level in the figure below. When your under stressful conditions, the HPA generally activates the “fight or flight” response.
These two classes of hormones work together to elicit responses that deal with the injury (the stressor) so that your body can stay in this balanced state as much as possible. These responses include increasing heart rate, the rate at which your body mobilizes energy, and your breathing rate which is all necessary when you’re injured. They also assist in directing immune cells to parts of the body that need protection, in your theoretical brothers case, the scrape on the knee. In this way, stress is good because it is helping your body create the appropriate response to the situation which in turn protects your body.
Additionally, catecholamines and glucocorticoids facilitate the making of memories while experiencing stressful events. This function is crucial for encoding certain situations as dangerous and avoiding them in the future.
To test this concept ask yourself if you remember where exactly you were on the morning of September 11th in 2001? You probably do. Now how about the morning of September 10th? There’s the difference.
Ok so fast forward a few weeks after the fall. You are shuffling your brother around to doctors appointments, struggling to pay the high medical bills, and your trying to keep up with work. You’ve been increasingly stressed ever since the accident. You realize that studying is becoming harder and your not doing as well on your tests in school.
This leads us to the second type of stress called chronic stress which occurs over a long period of time. In response to chronic stress the body releases an increased magnitude of glucocorticoids which can have damaging effects on different brain structures.
Research done with rats shows that chronic stress leads to increased magnitude of glucocorticoids being released over extended periods of time. (McEwen, 2000) Glucocorticoids can be damaging to the hippocampus, which is largely responsible for declarative memory. Examples of declarative memory include remembering facts such as dates and definitions. Additionally, chronic stress has been found to inhibit neurogenesis, which is the creation of new neurons. These two consequences of ongoing stress combined could be the reason for struggles in the classroom.
So now we’ve covered the two types of stress, acute and chronic, as well as the two main classes of hormones associated with stress including glucocorticoids and catecholamines. Hopefully this helps our understanding of what is happening with our brain and body next time we have too much work to do, take a tumble, or are just really stressed!
References
Mcewen, B. S. (2000). The neurobiology of stress: from serendipity to clinical relevance11Published on the World Wide Web on 22 November 2000. Brain Research, 886(1-2), 172–189. doi: 10.1016/s0006-8993(00)02950-4
On Psychology and Neuroscience 