let's talk about blood pressure homeostasis and what homeostasis means is balance so how is it that our body is able to create balance for our blood pressure so this is the heart and we've got branches of the aorta coming off of it I haven't been drawing these branches every single time but this time I think it's quite helpful to see we've got here the left brachial artery going out to the left arm and we've got the left cored artery here and again I'm writing left and right from the perspective of the person whose heart this is and you've got here the right cored artery and the right braul artery so this is blood going to the right arm and we've got blood going to the right neck one interesting thing if you look at the right kateed is that it bulges right here in fact both sides do and they bulge right before they split and so that bulge is actually called the cored sinus right here cored sinus and we call it that because a sinus is any cavity and so this is the right cored sinus and this is the left cored sinus another spot I'm going to talk about in this video is the aortic Arch which is right there so these three spots the two cored sinuses and the aortic Arch are really really interesting and actually they're very important for learning about how it is that our body is able to create balance in our blood pressure so at the top I drew kind of a blowup version of the kateed sinus and at the bottom is the aortic Arch and if you look closely under a microscope you'd see nerve endings on the outer layer of of the vessel and so these nerve endings basically join up and form a nerve and these on the oh cored sinus do the same thing and they are basically going to form two large nerves that go off and they send information about what's happening in the blood vessel specifically about stretch so as blood is pulsing through this vessel right here this cred sinus or as it's pulsing through the aorta even that wall is being stretched out and as it gets stretched out these nerves they're actually called they're very special nerves they're called Barrow receptors Barrow meaning pressure and they're receptors for pressure so they're bar receptors these Barrow receptors are feeling the effects of stretch and what they do is they send a signal down the nerve that tells the brain how much stretch is happening and so if this is the brain let's say and you have here your midbrain midbrain these nerve endings are going to actually go here and tell the brain communicate information about how much stretch is happening in those vessels now we know that the more pressure is in the vessel the more it's going to stretch so follow with me in a little example so let's say we have blood pressure here and let's say I have my blood pressure of 115 over 75 and in green I'll write Action potentials per minute action potentials per minute so what happens is that as my blood pressure is 115 over 75 those nerves are feeling a certain amount of stretch whatever that amount is and they're going to send a signal not just one but they're going to send a handful so let's say they send 10 signals 10 signals I'm going to draw them out here five six let's say seven 8 nine and 10 10 in one minute and actually let's just imagine that both nerves are doing this right so they're doing 10 per minute well that's a pretty normal number let's say and this over time becomes what the brain regards as my normal set point the brain starts to assume that if 10 action potentials are fired per minute then that's pretty normal for me so it regards this as my normal set point now if my pressure goes up let's say that I'm running late to an exam or something happens that you know really worries me and my pressure goes to one 40 over 90 now I have hypertension and this is my new pressure this would be much higher than normal so my body would would register this and my nerves would start firing let's say 30 times per minute 30 times per minute so if they're firing at 30 times per minute then my body is thinking or my brain is thinking well that's higher than normal so this must be high it regards this as high and on the flip side let's say that you know I have um let's say I cut my arm and I lose a lot of blood and my blood pressure starts to fall my stretching is going to happen less than before so it's going to send less Action potentials per per minute maybe only seven per minute and again my midbrain is going to get seven little green arrows per minute seven you know Action potentials per minute and it's going to think well that's very odd you know before it was uh 10 per minute so this represents a fall in blood pressure so now you have high blood pressure in pink and a fall in blood pressure in blue so what exactly can the brain do what can the brain do to help normalize or create balance so let me write that in over here let's write response question mark response so the body has a couple of strategies and they're basically summed up in the autonomic nervous system autonomic nervous system and there's two major branches of your autonomic ner system or two parts to it let's say Parts one is called the sympathetics sympathetics almost like sympathy and the other is called par parasympathetics they're very similar words except the word parah is in front of this one and I want you to remember now that there's a formula and I'm going to write that formula down here here just to just to remind us that pressure equals flowtimes resistance and additionally I want you to remember that flow this this one right here is going to be related to stroke volume times heart rate so if I can do anything if my body can do anything to raise the stroke volume or the heart rate or the resistance then my pressure will go up and vice versa if I can drop the stroke volume or heart rate or resistance then my pressure will go down okay so what the sympathetics do is they have an effect on the heart and the The Vessel so the heart and the blood vessels and these blood vessels are all over the body not just not just the cored sinus or the aortic Arch I'm talking about all blood vessels and so the sympathetics are going to for the heart they're going to increase the heart rate and they're going to increase the stroke volume and the parasympathetics do the opposite they actually drop the heart rate and drop the stroke volume and the way that they do that the heart rate is controlled by how many um beats you get per minute obviously that's the heart rate uh and the sympathetics are going to cause the heart cells that control that to work faster and the parasympathetics will slow them down and for the stroke volume the sympathetics force the heart to contract harder and then you have more volume of blood gushing out with every beat and the parasympathetics make the heart work less forcefully so you have less blood gushing out with every beat and the sympathetics finally they actually cause Vaso constriction Vaso constriction and you guessed it the parasynthetic do the opposite so they cause Vaso dilation and Vaso constriction and Vaso dilation basically mean whether the artery stays open or closes down so for the sympathetics the arteries and arterials primarily mostly As the arterials they start to get smaller and as they get smaller that increases resistance and for the parasympathetics they will cause the arterials to get bigger to dilate and that will cause the resistance to fall so taking a quick peek at our equation that I wrote out for you on the on the right you can see that the sympathetics basically do everything that will help to increase the pressure so if you have a pressure again of 140 over 90 then what will happen is your body will see that as a high pressure and will try to get the parasympathetics to be active we'll activate all the parasympathetic nerves and if your pressure is low if it's 90 over 60 then the body is going to respond by getting all the sympathetics to react you see how that works and of course if your pressure let's say is 15 over 75 and the bar receptors are firing you know the usual 10 times per minute then there should be really overall no response so here you would really get no response because the body is thinking well everything is already balanced there's nothing for it to do so this is how the body is able to control blood pressure in a rapid way so that's the final point I want to make that the input here the beer receptors these are nerves and the autono nervous system obviously these are nerves so the information going in is the bar receptors the information going out is the autonomic nervous system and all of this is happening rapidly this is all very rapid and when I say rapid I mean on the order of kind of seconds to minutes so within seconds to minutes this response can happen so this is a fantastic fantastic example of how your body can take in information really quickly and really respond quickly to help keep your blood pressure balanced