Control and Regulation

00:00 So in this case, we're going to have a variable that's regulated. That regulated variable, something will affect it. So let's say there is an external stressor out there and that's going to cause a change in your regulated variable. What you need to do? How do you know that variable is too high? You need to have various sensors in the body to pick that up. Just like we had baroreceptors when pressure was elevated. So you have a sensor and you may have multiple sensors that all are going to gather the data that is generated by this regulated variable. Now that you have the sensors garnering that data, it needs to send it somewhere because the sensor itself cannot determine what to do. So it sends the data to an integrated system or sometimes also a coordinating system and that is going to coordinate our response to that change that happened to our regulated variable and that signal is then sent to effectors and these effectors are going to be able to then change or cause an alteration in our regulated variable. So we have this four-kind of prong system where we have a regulated variable, sensors, an integrator and coordinating center and effectors all trying to do the various aspects of making sure our regulated variable is coordinated or regulated within a various range. Okay, let's go back to our heart example to try to tease this out further and so we can denote where our regulated variables are, where our sensors are, where our integrator and coordinating system are and what our effectors are going to be. So we will take a look at that in the next diagram. So our sensors in our system for controlling arterial blood pressure are going to be baroreceptors. Now there are a number of different baroreceptors located in the blood or just outside of the blood in the blood vessel system and those are in the carotid sinuses, they are here in your neck, your aortic arch which is just above the left ventricle or where the blood is pushed out. Those will allow us to give us insight into what blood pressure is but notice that you don't have baroreceptors everywhere, you just have them located in key spots. So why would this be key? Well in terms of the aortic arch, it's going to be right after you squeezed out the blood into the systemic circulation. So you want to know what is the pressure in which the heart is pushing out blood. The other key component to this is to know that the blood going to the brain is very important. So you'd want to have baroreceptors in the carotid sinuses to be able to pick up that blood pressure going to the brain. Those are going to be our main regulated baroreceptors. They are sent via various cranial nerves, vagus or cranial nerve X for the aortic arch and the glossopharyngeal or cranial nerve IX for the carotid sinuses. Where are they sent to? They are sent to the medulla and this is our integrating center. Remember when we integrate something, we are grabbing a hold of all the information and this is done from a specific brainstem component called the NDS or the nucleus tractus solitarus. This is our gathering area. You can think of it something like the train depot, all the information is coming back to a central location so that we know where the information is coming from but just because the information is coming back doesn't necessarily mean that we know what to do with it so we need to have some place and this is a coordinating center that is going to be able to take all these information and let us decide what to do with it. So in a blood pressure example, we have three main places or effectors that we might be able to accomplish. So we have a cardiac decelerator region and this is in the parasympathetic nervous system. We have a cardiac accelerator system in the sympathetic nervous system and a vasoconstrictor component in the sympathetic nervous system. These are the things which we can change. So what happens if you have an decrease in blood pressure? The parasympathetic nervous system is going to try to slow down the heart. So how do you slow down a decelerator? Well you're going to have to inhibit it. So you're inhibiting the decelerator.

04:51 You're also going to be giving a positive signal to the portions of the heart that have to do with heart rate and that increases your heart rate. You're going to increase your contractility.

05:07 You're going to increase the signal sent to your arterioles which are part of your blood vessels that cause vasoconstriction. You're going to increase the signal to the portions of the veins that can also venoconstrict. So in our example here, we have an increased signal to the sinoatrial node from the sympathetic nervous system, contractility, arterioles and veins. From the parasympathetic nervous system, we have a negative signal from the decelerator region which will allow us to increase the sinoatrial node depolarization rate. So what does this mean all these different aspects? It means we're going to get an increase in heart rate, an increase in contractility, an increase in vasoconstriction, increase in venoconstriction in response to the signal that was sent to us from the carotid sinuses and that was a decrease in blood pressure.

06:06 Now, there are pathophysiology examples that we can think of that will affect these regulated loops and one of the ones that I will just point out is atherosclerosis or another component that we could think of is aging because both of these can blunt baroreceptor responses because they change the vessel walls in such ways that the vessel walls are stiffer. If a vessel wall is stiffer, what happens is it doesn't distend as much or become bigger in responses to changes in blood pressure. So if blood pressure goes up, it should stretch the blood vessel.

06:45 If it stretches the blood vessel, it impacts or enacts changes in the nerve that's right around that blood vessel and therefore if you have a blood vessel and you have the nerve that's right next to it, as it distends it pushes on that nerve and will transduce the signal back to the brain. In this case if you have a stiffer vessel, less information travels through a stiff vessel and therefore you don't respond to the same extent and so you can change your person's baroreceptor responses in aging or in atherosclerosis and that impacts your ability to regulate a variable such as arterial blood pressure.