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Current time:0:00Total duration:11:06

Video transcript

I'm going to quickly sketch out the human heart we're also going to label some vessels coming off of it so the big vessel of course is the aorta this is the giant a aortic arch and the aortic arch has a couple of key branches that go for example up to the head and neck has other branches as well they go out to the arms but these branches that are going up are the ones I'm going to focus on so out here on this right side we have the right common carotid artery and it's called the common because eventually what's going to happen is it's going to kind of bulge here and then it's going to split and it's going to split into the internal branch this is kind of going inside and the external branch over here so this would be called for example the right external carotid artery and the same thing is happening on the other side and we name it kind of the same way we say okay there's an internal branch and an external branch this would be the internal and this might be the external branch of the left common carotid artery so I think you you're getting the the idea now these are unnamed exactly the same way and these are the ones we're going to kind of focus on now previously we had talked about how in these particular locations kind of in the internal side and then this bulgy side we have what are called the carotid sinus the carotid sinus or sinuses I suppose but the carotid sinus is right there and the sinus refers to any sort of open area or open space and there's also an area over here in the aortic arch and these two areas they are the home for our baroreceptors our baroreceptors are basically little nerves that are going to detect pressure so they're going to detect stretch or pressure that is in the vessels and they're going to kind of give information back to the brain and that's going to help regulate our blood pressure now in this video we're actually going to focus on chemo receptors chemo receptors are are also important in giving us information but they're going to give us information about things like oxygen levels carbon dioxide levels pH of the blood things like that so these chemo receptors and this gets confusing they're located in a similar region but not exactly the same region I'm actually going to shade in chemoreceptors might be and then also you might get some over here so these three areas are where chemoreceptors are and they're very of course closely related to where the baroreceptors are but they're actually in slightly different locations and we call them the aortic body and the carotid body the carotid body and a auric body and the reason we call them we use a term body is that it's a body of tissue so that's why that word gets used and this is actually you can see now slightly different location and certainly a different job so let me blow up some of these regions and show you close up what this might look like so let me draw for you the carotid body on this side and on the other side will do the aortic body and I'm basically just kind of zooming in on it so you can see up close what this might look like so you can kind of visualize it so for the carotid body you might have you know the external artery the internal artery and coming off of the external artery might have little branches right little branches serving this tissue that's in the middle and these branches of course you're going to bring it some more you're going to get all the way down to the capillarity level and once you have little capillaries in here there's going to be a bunch of little cells and these cells are of course going to get the nutrition from the capillary and taking together all these cells you know if you kind of zoom out of this picture this would be a little body of cells or a body of tissue and that's why we call this the carotid body and really the same thing is going on on the aorta side so on the aorta side you've got little branches coming off the aorta of course and these branches are going to branch again and again and again and again and eventually you're going to get just lots and lots of little capillaries and these capillaries are going to serve all these little blue cells and I'm drawing here and these are the chemoreceptors that we're talking about so these blue cells together make up a body of tissue and that's where we get the the term a ordered body and carotid body now on the carotid side one interesting fact is that this body of tissue gets a lot of blood flow in fact some of the highest blood flow in the entire human body it's about two liters per minute for a hundred grams and just to kind of put that in perspective for the carotid body imagine that you have a little two-liter bottle of soda I was thinking of something that would be about two liters and soda came to mind and you can imagine pouring this soda out over something that's about 100 grams maybe a tomato that's about a hundred gram tomato and if you could do this in one minute if you could pull out this bottle in one minute imagine how wet this tomato is going to get how much perfusion in a sense this tomato is going to get that is how much perfusion your carotid body gets so really puts it in perspective how much blood flows go into that area so let's now zoom in a little bit further let's say I have a capillary and inside my Kapler I've got little red blood cell here floating around and my red blood cell course has some hemoglobin in it which is a protein and this protein has got some oxygen bound to it I'm going to draw a little blue oxygen molecules and of course there's some oxygen out here in the plasma itself as well and if we're in our carotid body or a artic body you might have these special little blue cells that I've been drawing our peripheral chemoreceptors cells and specifically they have a name these things are called Glomus cells Glomus cells I had initially Mis stated it as a Globus cell but actually it's an EM Glomus and these oxygen molecules these are oxygen molecules over here are going to diffuse down into the tissue and get into our Glomus cell it's going to look something like that and if you have a lot of oxygen in the blood of course a lot of molecules are going to diffuse in but if you don't have too much in here then not too much is going to make its way into the cell and that's actually the key point because what our cell is going to be able to do is start to detect low oxygen levels low oxygen levels in the gloma cell tells the cell that actually there are probably low levels in the blood and when the levels are low this cell is going to depolarize its membrane is going to depolarize and what it has on the other side are little vesicles that are full of neurotransmitter and so when these vesicles fact that hey there's a depolarization going on these vesicles are going to dump their neurotransmitter out and what you have waiting for them is this nice little neuron so there's nice little neuron waiting patiently for a signal and that signal is going to come in the form of a neurotransmitter so this is how the communication works there's going to be a depolarization the vessels release their neurotransmitter and that is going to send an action potential down our neuron and if the oxygen levels fall really low let's say they get dangerously low or the cell is very unhappy then you're going to get much more neurotransmitter getting dumped out and you're going to get many more action potentials so this is how the Glomus cell helps to detect oxygen and in fact it also detects carbon dioxide because remember this cell is going to be making carbon dioxide let's say this is a little molecule of co2 and that co2 is going to diffuse out and into the blood but let's say that the blood has a lot of carbon dioxide already let's say that it's loaded with carbon dioxide lots and lots of it in this situation it's going to be very difficult for carbon dioxide to to make its way from the Glomus cell all the way out into the plasma and as a result carbon dioxide starts building up the tissue starts gathering more and more co2 because it can't go anywhere and this Glomus cell is going to say hey wait a second our co2 levels are starting to rise there are high co2 levels and again that's going to make the cell unhappy and it's going to send out more neurotransmitter and it's going to of course send out more action potentials so two different reasons why you might get action potentials coming out of this Glomus cell and now I want to remind you that there's this little formula right there's this formula where carbon oxide binds with water and it forms h2 co3 and that's going to break down into bicarbonate bicarbonate and a proton so this is our formula so if co2 levels are rising like the example I just offered then the proton level must be high as well so a high proton concentration I'm going to put it in brackets to indicate concentration or another way of saying that would be a low pH so these are the things that are going to make our gloma cells send off more action potentials so if you're like me you're thinking oh wait a second this is really interesting you know our cell is depolarizing it can depolarize it also has this neurotransmitter that I mentioned our Glomus cell then right here in blue is basically sounding a little bit like it has properties of a nerve cell this is a nerve cell and the reason for that is that if you actually take a look these two cells have kind of a common ancestor cell and so in development when the the fetus is developing there is a type of tissue called the neuro ectoderm the neural ectoderm and both of these cells this nerve cell and this Glomus cell both are derived from this neural ectoderm so it makes sense that they would have a lot of common features so we know the Glomus cell is not in neuron but it's going to be talking to neurons in fact you're going to have many neurons kind of working together in this area and they're going to kind of join up both in the aortic body and the carotid body and these neurons going back to the original picture are going to meet up into a big nerve and this nerve is going to be called the vagus nerve the vagus nerve is going to be the one for our a or tech body sometimes also called cranial nerve number 10 and up here with the carotid body we have a nerve as well this is another nerve this one we call it the glosso pharyngeal nerve pharyngeal nerve so these two nerves the vagus nerve the glossopharyngeal nerve this one this glossopharyngeal nerve by the way is cranial nerve number 9 these two nerves are not part of the brain they're headed to the brain right so these two nerves are fundamentally taking information from chemoreceptors that are outside of the brain they're not located in the brain right they're peripheral and they're taking information about chemicals and taking that information to the brain that's why we call them these blue areas the carotid body in the aortic body we call them peripheral chemoreceptors