This video, we're going to be going over stress physiology, and we're going to begin by just reviewing some things that we learned way back in chapter three, about the brain and the body. So if you feel comfortable with how you remember all that physiology and kind of brain and body systems, go ahead and skip the next few minutes but if you do want a refresher stick around. Alright, so we're going to begin by just talking about the nervous system. As I'm sure you guys remember, we have the autonomic nervous system which is a branch of the peripheral nervous system. And our autonomic nervous system essentially innervates our organs, vessels, and glands, and there are two divisions of our autonomic nervous system.
So we have our parasympathetic division and our sympathetic division. Now that parasympathetic division is irrelevant to us today, forget about it for now, and the sympathetic division is the part that becomes activated when we are stressed. So that sympathetic division is basically going to mobilize resources to prepare us for fight or flight. So that's that body system that kind of gets that increased heart rate. It dilates the bronchioles so you can take in more oxygen.
It's going to decrease blood flow to the gut because we're not prioritizing digestion. We're going to have increased blood flow to muscles to kind of get us ready for activity. So our sympathetic nervous system is going to play a pretty big role in today's lesson. Now, as you may recall, an important part of the brain in relation to our sympathetic nervous system is the hypothalamus. So the hypothalamus is that little structure located right below our thalamus.
And as you may recall, it's really important for survival functions, and in particular, it does activate the fight or flight response when we are under stress or in danger so that is also going to play a really big role today. Now, one more thing to remember before we get into today's lesson are hormones. So, as you may recall, hormones are chemicals that essentially travel outside of the nervous system. So, for example, in the bloodstream. And they basically are a different way that the brain can regulate the body. And hormones are released by glands.
And there are two glands that are relevant to our lesson today. So the first is the pituitary gland, which is located in the brain. And this is sometimes called the master gland because it kind of like controls all the other glands. The other one that's relevant to us today are the adrenal glands. So these are located right on top of the kidneys, and the adrenal glands release stress hormones.
So adrenaline and cortisol. And both of those are going to be very important for today's lesson. Now one thing that we did not go over, back in chapter three, is that the adrenal glands actually have two parts to them. So they have a medulla and a cortex. Now you don't have to be able to, like, label this anatomy or anything, but just be aware that they do have these two parts.
So the medulla is essentially in the middle of the adrenal band, so medulla middle. Those m's go together. And then the cortex is essentially the outside, so it's the outer layer just like how the cortex of the brain is the outer layer of the brain. Alright. So that is all of our recall information, and now we're going to get into today's lesson.
So our body essentially has two responses to stress, and they differ slightly in their mechanisms and in their timeline. So the first one that we're going to go over is sympathetic activation, and this is basically serving as our immediate reaction to stress. So basically, this one starts like we kind of talked about with our hypothalamus. So it starts up in the brain, the hypothalamus realizes that we're in danger, and then the hypothalamus essentially signals to our sympathetic nervous system. And then the sympathetic nervous system is basically going to communicate with the adrenal medulla, which is going to release adrenaline. So adrenaline gives us that kind of immediate spike of energy, kind of mobilizes the body to prepare us for fight or flight.
So this would happen like if you were walking down a hiking trail and there was a rattlesnake right in front of you. Right? You'd you'd have that immediate jolt of adrenaline, so that is this system kind of taking over and the effect that it's going to have on your body again is this very immediate fast reaction on organs and blood flow, the same response that we've talked about already where we're going to have increased heart rate, increased respiration, more oxygen coming in, more blood flow to the muscles, etc. So that is our sympathetic activation. Now sometimes stressors aren't always these really fast immediate things, right?
Sometimes you have finals looming over you that are going to happen in two weeks, and for a situation like that, we have to kind of maintain a stress response for a bit longer. Adrenaline is not going to be quite as useful. So in situations where we have more kind of prolonged stress, we're going to have activation of our HPA axis. So this is going to allow us to have a more sustained reaction to stress. So this one also begins with our hypothalamus.
They're all going to start with our hypothalamus basically recognizing some kind of stressor, but now in this case, our hypothalamus is going to communicate with our pituitary gland, so it's going to basically say hey pituitary gland, master gland, you gotta mobilize your guys, you know, get them going we're having a stress response and so the pituitary gland then communicates to the adrenal cortex that it needs to release cortisol. So we have the release of our other stress hormone. This one is actually nice and easy to remember because cortex and cortisol actually sound quite similar. So the cortex releases cortisol, the medulla releases adrenaline, And so the effect here is going to be somewhat similar to our sympathetic activity but kind of lower in magnitude. So it's going to do things like increase glucose availability, It's going to kind of suppress digestion a little bit. It's going to suppress immune function.
We'll talk about that in a video, coming up a little bit later. So we're going to see some kind of just more kind of prolonged and sustained effects on the body. And one nice way to remember, this kind of sequence of events is that each of the letters in HPA axis basically stands for the body parts that are involved. So we have h for hypothalamus, p for pituitary, and then a for adrenal. Alright, so just to kind of sum everything up and put all of that together to kind of compare and contrast what's happening here, we have our sympathetic activation.
This is our immediate reaction to stress. These always begin with our hypothalamus, but now the hypothalamus is communicating with our sympathetic nervous system, and we're going to have the release of adrenaline in this case to kind of give us that immediate effect on the body. In cases of more sustained or prolonged chronic stress, we're gonna have activation of that HPA axis. Again, we always start with our hypothalamus. In this case, the pituitary is involved, and we're going to be releasing the hormone cortisol which will provide us with that prolonged stress response over time.
Alright, so those are the two physiological responses that our body has to stress and I will see you guys in the next one. Bye bye.
