In this video I describe homeostasis, which refers to maintenance of an optimal state, and allostasis, which clarifies that an optimal state is actually a range of possible states depending on context. Next I discuss Hans Selye’s theory of General Adaptation Syndrome, which he derived from his work studying the effects of chronic stressors on rats. He found that many different chronic stressors all resulted in swollen adrenal glands, a smaller thymus, and peptic ulcers. He proposed a 3 stage process for coping with stressors: Alarm, Resistance, and Exhaustion. While not all of his conclusions have been validated today, Selye’s work began investigation into the negative effects of chronic stress.
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Video Transcript
Hi, I’m Michael Corayer and this is Psych Exam Review. In this video we’re going to look at homeostasis allostasis and the work of Hans Selye and his idea of General Adaptation Syndrome. So we’ll start with homeostasis; this comes from the Greek for “similar” and “stand” and it refers to the idea that the body wants to maintain some optimal state. Now we actually saw a bit of this in the unit on motivation because we talked about drive reduction theory. The idea of drive reduction theory was that we have some optimal state and if we depart from that state then this activates drives that will motivate the behaviors that will return us to the optimal state. This is very similar to the idea of homeostasis; that we have some optimal state that we want to maintain and if we depart from that that activates processes that will return us to the optimal state.
But when it comes to the stress response we might wonder how it could be that the stress response works for different situations. So different things are stressful and they activate the stress response, but how is this able to return us to the optimal state? We might think of something like cold exposure, we might say being exposed to cold is stressful, it’s going to evoke a stress response and part of what that stress response might be doing is helping maintain our body temperature at the right level, in this case warming our body. And yet we might recognize that being exposed to excessive heat is also stressful, and that means it evokes a stress response and part of what the stress response is doing in this situation is cooling our body. So how can it be that the stress response works for these opposite situations? We might also wonder about the idea of an optimal state; what exactly does that mean if we think about something like blood pressure? Is there really an optimal blood pressure for all situations at all times?
This brings us to the idea of allostasis; this is a variation on the idea of homeostasis. This is the idea, and it comes from the Greek for “variable stand“, it’s the idea that the idea of optimal covers a wide range of possibilities. There’s not one single optimal state for something like blood pressure. It’s going to depend on context and it’s going to depend on the situation. And so if you are laying on the couch watching Netflix then the optimal blood pressure for that activity is going to be very different than the optimal blood pressure if you’re running a marathon. And so the idea of allostasis is that we’re actually constantly adjusting; we’re constantly changing things like our blood pressure to cope with the demands that we’re placing on it. In fact, just standing up from the couch actually places demands on you to change your blood pressure in order to cope with this situation.
Now we’re going to turn to the work of Hans Selye, who is a Hungarian endocrinologist who spent most of his career in Canada. Here’s a picture of Selye here and Selye was studying the effects of an ovarian extract on rats. So what he did was repeatedly inject the rats with this extract and what he found was the rats who were given these repeated injections had swollen adrenal glands, a shrunken thymus, and they developed peptic ulcers, which are small holes in the lining of the stomach. So it might seem that this extract causes these symptoms, but when Selye looked at rats who were given saline injections he found these same effects; swollen adrenal glands, a shrunken thymus, and peptic ulcers. So what he realized was that it wasn’t the extract that was causing these symptoms; it was actually the stress of receiving these painful injections. And so this chronic stressor was responsible for these symptoms and so what Selye did was he exposed rats to a number of other chronic stressors and what he found was the same results. They also developed swollen adrenal glands, a shrunken thymus, and peptic ulcers. So he exposed them to things like cold, he exposed them to heat, exposed them to trauma, exposed them to infection, and they all had these same symptoms with this chronic exposure, the exposure to these stressors.
Based on this work Selye proposed General Adaptation Syndrome. He thought there was a general explanation for what was going on; that this applied to any chronic stressor. He proposed a three-stage response to stressors. The first stage is alarm and this is where the organism has to mobilize resources in order to confront whatever the threat is. And then if the threat continues, if the stressor is still there over and over again, then the organism will enter the next stage which is resistance. This is where it tries to adapt to this high level of arousal from repeatedly confronting the stressor. And in order to do this it’s going to have to draw on additional resources that it might not normally use. So it begins drawing on fat and muscle in order to have the energy to repeatedly confront the stressor and in order to conserve resources it will shut down other processes like digestion, reproduction, and growth. And then if the stressor continues beyond this point he thought eventually the organism will reach the stage of exhaustion. This is where the ability to resist completely collapses; the organism can no longer confront the threat or the stressor and the stressor now damages organs and causes aging and potentially death.
A silly mnemonic that you can use to remember this General Adaptation Syndrome is “people with GAS ARE stressed”. Remembering that the GAS there stands for General Adaptation Syndrome and the ARE represents Alarm, Resistance, and Exhaustion. Now it turns out that Selye wasn’t quite correct in some of his ideas from General Adaptation Syndrome. One thing is that he thought the stress response was identical for all stressors and that turns out not to be the case and we’ll see in some future videos the idea that the response to stressors can’t vary a bit.
Another area where Selye wasn’t quite accurate is with the idea of exhaustion. So he thought that eventually your resistance cannot be maintained and so you become exhausted and then the stressor damages you. But it turns out it’s actually the stress response itself that seems to be causing the damage. It’s not that you can’t confront the stressor, it’s that repeatedly activating your stress response actually wears you down, and we’ll see exactly how that works in the next videos. And this brings us back to the idea of glucocorticoids that I mentioned in a previous video. This is one of the main pathways for how this damage to the body occurs from the stress response, is via these glucocorticoids and their effects on the body and particularly their effects on the immune system. And that’s what we’ll look at in the next video. I hope you found this helpful, if so, please like the video and subscribe to the channel for more. Thanks for watching!
