okay we're going to go ahead and get started this morning hope everybody had a good weekend got a little bit of rest so what we're going to focus on talking about today is continuing our discussion about blood vessels uh so we're moving through that material we should finish uh discussing blood vessels on Wednesday uh a few things before we get started so I know I got emails from a few of you last night about this because we have so many things due on Sunday but there was a a Blackboard outage some of you may have noticed this if you were scrambling to finish your assignments last night uh just because uh I know some of you rely on that last minute time to finish your assignments um if you weren't able to get your assignments in just uh I I've given everybody an extension so all the pre laabs all the in-class activities those are now due tonight at midnight so if you weren't able to submit your stuff on blackboard last night you have until this evening at midnight so you or for some reason you forgot now you got a little bit extra time to to finish those before uh before uh the deadline so and just uh if you did have trouble make sure you go ahead and and do that um in terms of lab this week just a reminder that we're working on uh lymphatic vessels working a little bit on blood pressure uh and also remember that a lot of the models that are out are some of the same models we had for blood vessels and so this is one of your last opportunities to really see some of these different models with respect to blood vessels remind that that's a a large portion of your lab practical and we'll talk about the lab practical in in lab this week with us myself or Dr Bennett so and hopefully hopefully the studying for that is coming along nicely and and hopefully we'll be able to get some clarity this week in terms of what to expect on that lab practical so again that's that's next week and then in terms of any other upcoming due dates again we're finishing the blood vessels on Wednesday in terms of our lecture and so that means those Dynamic study modules for blood vessels will be due on Friday questions about anything else okay so in terms of what we're talking about today we're going to talk a little bit more about blood pressure uh specifically we're going to think about how our bloody how our body regulates blood pressure in terms of both short-term and long-term regulation how blood pressure blood flow can just kind of vary depending on our physiological state so again when we think about blood pressure there's a lot of different factors that can affect what our blood pressure is at any given time within our body uh and to understand that we can even return to this equation that we talked about for looking at how we calculate blood flow so remember we calculate blood flow by looking at differences in blood pressure divided by resistance so again if if blood pressure is high that tends to lead to a higher blood flow whereas res if resistance is higher this tends to shut down blood flow uh but if we want to sort of think about how blood pressure is affected one thing we can just do is we could we can just rearrange this equation a little bit we can multiply both sides by resistance and suddenly now we're sort of orienting this equation in terms of blood pressure and so what we see when we rearrange this equation is that blood pressure is affected by both blood flow and resistance and in fact both of these things if either resistance or blood flow go up those are both going to lead to an increase in blood pressure so so in terms of how we regulate blood pressure you can see on this table or on this chart here there's just a lot of different things that can go into potentially increasing our blood pressure and by blood pressure here we're talking about just our mean arterial pressure so for example if we saw an increase in stroke volume so increaseing the amount of blood we're pumping with each heartbeat or or we increase our heart rate you know that's going to increase our cardiac output that's therefore going to increase our blood flow and so that's one way of increasing our blood pressure uh and then on on the other side we can change our resistance so for example if we uh basoc constrict our blood vessels to decrease their diameter or if our blood viscosity were to go up in some way or our blood vessels were to lengthen in some way all of those things would increase our peripheral resistance and that would also tend to increase our blood pressure so again we can see a lot of different factors that can lead to changes in blood pressure and so our body can change some of these factors whether you know in terms of maintaining homeostasis if we want to maintain a certain blood pressure sometimes we need to increase or decrease our blood pressure because it's too high or too low so in terms of regulation of blood pressure you we we can regulate blood pressure on a shortterm uh level so you know something that we regulate within the span of a few seconds a few minutes or also we can regulate blood pressure over a longer term you over the course of hour or days so we're going to we're going to talk about short-term regulation first so again if if blood pressure is too high or too low what can our body immediately do to respond and bring ourselves back into homeostasis so in terms of that short-term regulation the main things that we're altering on a on a minute to- minute basis is Alter we're altering our cardiac output and we're altering our blood vessel diameter these are all things that we can change pretty quickly so looking back at this flowchart could say put boxes around the things that our body can pretty immediately alter so we can immediately alter our stroke volume or our heart rate and we can also immediately alter the diameter of our blood vessels and and in terms of what our body is doing to alter these things we have both neural and hormonal controls that are affecting both of these processes so and we'll talk about both of these but we'll talk about the neural controls first and so when it comes to neural controls we have different receptors that are tied to our blood and our blood vessels that can lead to some of these different changes the The receptors we're going to speak the most about are what we call Barrow receptors uh we think of barometric pressure so Barrow receptors are literally pressure sensors so they're actually sensing our blood pressure and our blood vessels and then our body is responding to those changes in pressure so so let's talk about those those Barrel receptors and then just neural controls in general so when it when it comes to our neural controls again the our neuro our our neurological system is our nervous system is affecting uh the our cardiac output and our vasod dilation basoc constriction and so therefore we have sort of two main nerve centers that are that are controlling this so we have a cardiac center that's affecting our heart rate uh and and our stroke volume and therefore our cardiac output and then we have the vasom motor centers that are affecting the constriction or dilation of our blood vessels and so both the neural and cardiacs the vasom motor and cardiac centers are located in the medulla ablang of our brain stem and so with both of these we have you know both sympathetic and parasympathetic controls so in this diagram for example we're looking at the cardiac center and So within the cardiac center we have a cardio acceleratory Center and those are sympathetic neurons that are speeding up heart rate uh and then we have parasympathetic neurons that are we call our cardioinhibitory Center that are slowing things down again we we can think back to sort of the fight ORF flight response you know we are encountered with some sort of immediate threat we need to run away or put up a fight again it's it's useful under those circumstances to have sympathetic neurons that are speeding things up for us and getting us ready to to face that threat whereas parasympathetic is again the opposite slowing our heart rate down uh you slowing down a lot of other factors as well so again when it comes to our sympathetic neurons those are going to increase our heart rate parasympathetic neurons in our cardiac center are decreas in heart rate uh and then also when it comes to then our basom motor Center our sympathetic neurons are constricting our blood vessels and our parasympathetic neurons are dilating our blood vessels so again those those are the main controls but in terms of what triggers those controls we talked before about how there's these receptors we call Barrow receptors that are within our blood vessels and and so again these Barrow receptors they're pressure sensors and the way they work is they're just basically sensing how much our blood vessels are stretching out because remember that the greater our blood pressure is the more stretch we're going to induce on those blood vessels uh and so in terms of where our Barrel receptors are located we have a couple of different locations we have uh some Barrel receptors that are just right in the middle of our aortic Arch so and then we have another couple of barrel receptors that are located our kateed sinus so our kateed sinus that's in our Comm it's right where our common kateed artery is branching off into our internal and external kateed artery that's where the cored sinuses we think about all these locations whether they're the aortic Arch or the Fred sinus remember these are areas where our blood pressure is going to be relatively high and pulsatile so it's very much sensitive to what's going on in the heart so of course you want your Barrel receptors if they're going to be modulating cardiac activity you want them to be actually sensing that cardiac activity so so this location of the bar receptors is actually pretty critical uh so in terms of again how these are working they're they're looking at the stretch of these blood vessels so again if you have a high degree of stretch that indicates a high blood pressure which could be caused by a lot of different factors could be caused by high blood volume or just a high degree of flow or you know if your these particular arteries are constricted a little bit then they're indicating a high degree of resistance and so then our barel receptors are feeding back to our neural system to either well if if our blood pressure is really high they feed back to our nervous system and try to lower our blood pressure so let's talk about what this would all look like in in whole so again the idea is we want to stay in homeostasis with respect to our blood pressure at any given time we don't want it to be too high or too low so let's say we have some sort of imbalance where we have a really high blood pressure so that that high blood pressure is going to stretch out our kateed and aortic arteries and therefore you know that's going to stimulate those Barrel receptors and so those Barrel receptors then are going to send first of all just a message to our cardiac center within our brain and so again if if our blood pressure was too high we want to increase the activity of those parasympathetic neurons that are inhibiting our cardiac activity and we want to decrease the activity of those sympathetic neurons that are part of aard cardio acceleratory Center so if we do those two things and that's going to have effects on our heart rate where we again we have fewer sympathetic impulses more parasympathetic impulses and therefore our heart rate's going to decrease and our cardiac output is going to decrease again that's only half the equation we not only want to stimulate the cardiac center but we also want to stimulate that baso motor Center and so again if blood pressure is too high we want to lower it back down so our vas for with respect to our vasom motor Center one way we can lower our blood pressure is to dilate our blood vessels because if we dilate our blood vessels we now have less peripheral resistance and that will also lower blood pressure so so again we're basically seeing a situation where our blood pressure is too high that's going to stimulate our cardiac and our basom motor Center both in ways that are going to tend to decrease blood pressure both by lowering heart rate uh and by dilating our blood vessels and and we would see the reverse of this too if our Barrel receptors were not stimulated because our blood pressure was too low then in that case we would actually see our cardiac center would be stimulated in such a way to increase heart rate and our basom motor Center would be stimulated in a way to promote basil constriction to raise blood pressure back up again again there's this there's this balance that's going on here so again that's that's the neural Center and then also remember that there's some hormonal controls to blood pressure too some of this we talked about in our first chapter when we were talking about hormones so we know that there's a a series Ser of hormones that can affect things like cardiac output or Vaso constriction so for example we talked about epinephrine and norepinephrine remember that those are very much trigger with our fight ORF flight response and so if you have high levels of epinephrine or norepinephrine stimulating all these sympathetic neurons to increase our cardiac output allow for Basil constriction and therefore increase our blood pressure we also have a few other hormones some of which we talked about like anti-diuretic hormone in certain situations can also uh lead to an increase in vasil constriction and blood pressure uh same with Angiotensin which is a hormone we'll talk about in more detail later and then we also have another hormone called atrial ntic peptide or& secreted by our heart we didn't talk about this in our our first chapter but this is our one hormone that actually can lead to vasodilation and therefore decreased blood pressure so again we see a lot of different hormones most of which tend to increase blood pressure but& is one that tends to decrease blood pressure again both hormonal and and uh and neural controls can can regulate blood pressure in the short term again that short-term regulation is all about changing cardiac output changing your degree of vasod dilation or Vaso constriction but also you know when we think about those short-term regulations those are all situations where we're dealing with a certain blood volume in general but when we think about long-term regulations of blood pressure this is where we can actually change that blood bum and therefore change you know sort of what's what our cardiac system is operating on uh and so when we think about long-term regulation of blood pressure we're talking about regulating that blood volume because again if blood volume gets to be too high that's going to inherently increase blood pressure and if blood volume tends to get too low that's going to inherently decrease blood pressure so if we really want to regulate blood pressure long term we want to make sure we have that ideal blood volume and so this is where our kidneys come into play so this is something we'll talk about more later this semester here too but in terms of controlling blood pressure by the kidneys basically uh again if if we have a long-term decrease in blood pressure for instance that's an indicator that we have low blood p and so our kidneys can do a couple different things first of they can directly act on that low blood volume so for example if we have low blood volume therefore low blood pressure then what the kidneys can do is they can reduce the amount of blood that's actually filtering from those glomular capillaries into the kidneys themselves and so therefore just by having less filtration of that blood plasma into the kidneys you're keeping more blood plasma in the circulatory system so you're going to reduce the amount of urine that you're putting out and therefore for assuming we have access to adequate hydration we can build up our blood volume while decreasing the amount of urination and so you know longer long term that's going to increase our mean arterial pressure uh but at the same time you want to make sure that your kidneys are still filtering your blood you don't want to cut that off entirely and so another long-term control of the kidneys are able to exsert is this more indirect mechanism where we still are filtering blood into the kidneys still filtering blood plasma but we use this indirect mechanism called the reenan Angiotensin elone mechanism which you may recall when we talked about the objectives for this chapter I said we weren't going to talk about this very much um that's that's still true there's just a few things that we need to be aware of with with respect to this mechanism so far um mostly just has to do with sort of how this system works how these hormones are working so in the case of this indirect mechanism so again we're just going to pay attention to the things I point out with arrows we're not going to worry about any of the other stuff just yet but if we had a low mean arterial pressure what happens is our kidneys release this comp compound called Arena and then renin leads to the production of another enzyme called Angiotensin and Angiotensin you think about the name angio blood vessel tensin you know think of tension so angot tensin is is actually something that constricts blood vessels so that that's the main thing that Angiotensin does so again this this makes sense with everything we know so far if we have a low blood pressure we release renin and then Angiotensin and we constrict our blood vessels to try to get our blood pressure back up something else that happens though too is that that Angiotensin leads to the release of aldosterone an anti-diuretic hormone and and remember we've talked about both of these hormones before as being ones that increase blood volume they promote reabsorption of water in our kidneys and so both of those things then are going to lead to that release or lead to that reabsorption of water and again lead to an increase in blood volume so really when we're looking at this reenan Angiotensin aldosterone mechanism I think the main takeaway is that it leads to Vaso constriction and it also leads us to retain and increase our blood volume time right so I'd like us to just think about how pressure relates to Vaso constriction vasod dilation and heart rate think about all these factors together and and so to do this we're going to go back to an example I I gave you earlier so remember we talked about when we were talking about muscular arteries we we talked about this diving reflex where when we dive underwater and hold our breath we constrict some of those muscular arteries and therefore we cut off blood flow almost entirely to certain organs within our body uh and so when we do that we're basically restricting all the blood in our body to you know blood that's flowing between the heart lungs and brain and so what I'd like you to think about is again we we've taken a certain volume of blood and we've constricted it to a smaller space so what I'd like you to think about is what do you think is going to happen to the blood pressure in those blood vessels that are leading the heart lungs and brain in the immediate aftermath of that sort of mass basil constriction that we're seeing here uh and then I'd like to think about you know what are the most likely types of receptors that are going to then sense this change in blood pressure that occurs uh and then will this lead to a neural or a hormonal response in terms of what our you know what our body is going to do and then as a result of that previous question I'd like you to think a little bit about how potentially you might predict heart rate might change would heart rate go up go down or stay the same so think about these questions here for a minute and then we'll discuss with the group okay well let's go ahead and talk about this one and kind of again work through some of these different interplays between you know bzo constriction bzo dilation and also how heart rate all comes into this again thinking about this sort of short-term control of of blood pressure here so again if we think about if you hold your breath and dive underwater you would see this basil constriction a lot of these muscular arteries are serving a lot of your organs are going to vase open strict so as a result of that what happens to your blood pressure yeah yeah whenever we have a you know Mass baso constriction that's going to increase our blood pressure because because we have the same amount of blood but now we're confining it to a much much smaller space and so that's that's always going to lead up to a buildup of pressure whenever you decrease the volume without decreasing any of the mass or anything in there you're therefore going to see this increase in pressure so therefore we're seeing an increase in pressure Within the blood vessels uh what types of receptors are going to tend to sense that most most acutely yeah yes we we see those barel receptors loc in the aorta or in the cored sinus both of those barel receptors should be detecting that stretch in the blood vessel walls uh and so then what type of response is that going to trigger if those Barrel receptors get stretched out yeah that's going to lead to a neural response those Barrel receptors directly tied to our cardiac and vasomotor centers and so therefore we're going to see a response so speaking of that response you know our our cardiac center might change our heart rate so how would we expect heart rate to change in response to this increase in blood pressure that that we see as a result of diving we expect heart rate to go up or down yeah we'd expect heart rate to go down again blood pressure is too high the one way to bring yourself back into homeostasis is to bring your heart rate down so if blood pressure is high if you decrease heart rate that's going to tend to counteract that increase in blood pressure it'll help to bring blood pressure back down especially in this situation that the cardiac center is going to be especially important because in this diving animal or diving person vasodilating is not really an option because you still want to conserve oxygen all that sort of stuff and so you don't really want to vasod dilate but the one thing you can control is your heart rate so you can bring that down just wanted to show you some data this is again you'll see this response in people if we hold our breath and and put our heads underwat we will see a diving reflex but it's very much exaggerated in animals that do a lot of diving so for example there's a lot of studies done on seals and so here we're just looking at some data taken for seals where then seals can die for a pretty long period of time but you see when those Dives get really long let see their heart rate you know their normal resting heart rate is in the 60s but they start diving for long periods of time their heart rates can go down to like about 10 beats per minute uh and again this is all just due to the fact that they're really constricting a bunch their blood flow to a bunch of different organs leading to that increase in blood pressure so the best way to bring it back down is to de increase heart rate so so it's kind of this cool little interplay that we see questions about any of that okay all right so again we we talked about you know blood flow blood pressure and and how that's controlled on this sort of whole body sort of basis on on both short and longterm time scills but another thing I'd like to talk about here that kind of brings everything together and and clears up a few sort of head scratchers I guess is that in addition to controlling blood flow and blood pressure on this whole body level we also have this ability to locally control blood flow and blood pressure we call this intrinsic uh control of blood flow and this is through a process we call Auto regulation so so just to give you an example of of what this intrinsic control blood flow might look like so let's say we exercise uh we undergo some strenuous exercise this is going to change our blood flow to certain areas of the body so what I'm showing you here is a just a chart that's looking at basically where our blood is allocated to different parts of our body when we're at rest over here on the left versus when we're exercising on the right and you know we know that when we're at rest of course our heart rate's lower our stroke volume's not as high and so our cardiac outputs not very high and our cardiac output here we have at 5,800 milliliters per minute when we exercise of course our cardiac output goes up that's what we're seeing here as our cardiac output is increased about three times its resting rate there uh so heart rate goes up our stroke volume goes up but what's where it gets a little bit interesting is that all that increase in cardiac output doesn't go doesn't distribute itself evenly to different parts of our body we see disproportionate increases and decreases to certain parts of our body so for example at rest we have about 20% of the blood in our body at any given point is serving our skeletal muscles but when we start exercising where we're really using our skeletal muscles a lot suddenly about 70% of the blood circulating through our body is serving our skeletal muscles uh but then on the other hand blood that say serving our abdomen where a lot of our digestive organs are are located or our kidneys suddenly we see that blood flow actually decreases to those parts of the body so we're actually seeing that it's not NE you know when we exercise we generally say that blood flow and blood pressure increase but then you always have to ask yourself well to what parts of the body are we talking about because we are seeing that blood flow is increasing the skeletal muscles but it's actually decreasing to other parts of the body and some of this starts to make sense when you think about you know experiences that that some of you have probably had you know when you exercise for example if if you've eaten too recently you might get stomach cramps and a lot of that is just due to the fact that your stomach's no longer receiving as much blood flow and therefore oxygen and so suddenly your stomach's trying to operate using like Anor robic metabolism to digest things and that's not as efficient and it leads to you know cramps of those muscles that are that are in the stomach so again where it's reflecting this differential blood flow to different organs so in terms of what allows for these intrinsic controls there's there's some different lots of different stimuli that we can think about but in a lot of tissues it just has to do with sort of what's going in or what's coming out of that particular tissue so for example if there's inadequate oxygen delivery to a tissue that leads to local regulation to increase blood flow to that particular tissue you know if we think about that exercise an example if we exercise suddenly our muscles our skeletal muscles don't have enough oxygen and so we need to increase blood flow to that particular area uh also our our our skeletal muscles would be building up metabolic waste they're producing CO2 we need to get rid of those so we need to increase blood flow to that area or other metabolic waste there too um and then also sometimes we see blood intrinsic blood flow can be controlled by things like heat especially on our skin so for example if it's hot outside we tend to vasodilate little capillary beds in our skin because we want to bring heat to our body surface so we can dissipate that heat more easily whereas when it's cold outside we tend to basal constrict the arterials leading to those capillary beds because we want to hold the heat inside of us so there's lots of different things that can lead to these intrinsic controls of certain areas on these smaller sorts of scales and another thing to note which again I think will sort of clear up some some sort of head scratchers that we might have had before is that these intrinsic controls override the extrinsic or whole body uh inputs and where I think this sort of brings everything together is you know we've talked several times about epinephrine uh you know again this this hormone that triggers this fight ORF flight response and when we think about what epinephrine does we we know that it promotes an increase in heart rate and and then also basoc constriction of blood vessels but then again we think of you know the fight ORF flight response you need your skeletal muscles to be receiving plenty of oxygen so basal constriction is actually the opposite of what we would want within those skeletal muscles uh so so what that what that really means then is that although epinephrine constricts blood blood vessels on sort of this whole body level these intrinsic controls can still vasodilate some of the capillaries are leading into our skeletal muscles so although as a sort of a whole body response we see constriction of blood vessels to the areas that need more blood we can still basoda so again it allows all these different parts of the body to sort of work together to make sure that there's enough blood getting to the parts of the body that need the blood that given period another thing we can think about with respect to this this Auto regulation again the intrinsic controls that are allowing for certain areas of the body to receive more or less blood is so far we've just talked about sort of short-term needs about you what happens if you start exercising over the course of a few minutes but we also can see these intrinsic controls can meet longer term needs uh so so for example and let's say that instead of exercising just you know going from arresting to exercising get that sort of short-term response let's say we're thinking about a person who's began an exercise program for a longer period of time that you know exercise is now part of their daily routine and you know I think a lot of you have probably noticed that when you begin an exercise program you're not as good at completing your workout as you are a few weeks down the road after your body's had time to adjust and so this is where we're thinking about these long-term adjustments that your body is making so for example you know let's say you start a running program you might notice that your legs muscles and your legs get tight earlier part of that is that they're not getting enough oxygen not getting rid of metabolic waste quickly enough and so what your body does to adjust and make you better at running over the course of the next few weeks is it can actually increase the number of blood vessels that are serving those muscles that you're regularly using now and that's through a process we call angiogenesis so so just to kind of illustrate that you know if we have just a few capillaries for example that are serving a certain muscle in our body you know before ogenesis again there's just a few capillaries but your body can actually grow blood vessels in those particular areas make a more elaborate network of of blood vessels capillaries Etc that are serving that particular area so again this is a sort of long-term change that we would see in response to something like an exercise program for example with respect to your skeletal muscles and in terms of what stimulates this angiogenesis um there's a compound called vascular endothelial growth factor that stimulates blood vessel growth so so just to kind of walk you through an experiment that that showed this all showed how this works this is this is an experiment done in mice where mice were just put onto a exercise regimen cute little experiment right um they were just instructed to run on a wheel for for a certain period of time and so therefore they're becoming more active than they were before and so what the investigators found in this period so we're looking at just the days of training over which this is occurring and on the Y AIS we have the levels of vascular endothelial growth factor so we can see just even within a few days these mice are increasing their levels of vascular endothelial growth factor within their muscles and so then if when the investigators looked at what happened over the course of the study so now we're looking at the amount of capillaries per square Mill meter within the muscles and so we're looking at Day Zero when the when the mice first started their exercise period versus day 30 when they finished their exercise period you can see that the capillary density you know we started around 450 capillaries per square millimeter ended around 900 capillaries per square m so we doubled our capillaries our capillary volume in that period of time so again that's that's certainly going to make the mouse a lot better at exercising in the future if it's able to get enough blood supply to those muscles so again we see very long-term responses that allow us to Route blood get into the areas that need it so let's think about this a little bit further here so you're actually going to help me interpret some of my own research here this is some data that I collected a while back uh looking at uh water loss in some birds and so one thing that we'll see as we go forward is that capillaries you know when when they're serving a tissue they actually tend to lose water to the surrounding tissues as as blood is flowing through those capillaries so what that means is that when we're thinking about capillaries that are say in the skin of a person they contribute to the amount of water that we're losing from our body something we call cutaneous water loss and so what this graph is showing here is we're looking at cutaneous water loss measurements at different temperatures uh in birds that were measured in the summer or in the winter I captured two different groups of birds brought them into the lab and then measured them at different temperatures so I measured the winter birds at 25 30 35 and 40° Cel same for the summer birds and so we can see those cutaneous water loss values here so what I'd like you to do is is relate this to what we might what we think might be going on with the capillaries so first of all just based upon the pattern that we see for both winter and summer Birds I'd like you to think about do those do those arterials leading into the capillaries in the skin do they tend to vasodilate or basoc constrict as temperature increases and you can interpret this just by looking at cutaneous water loss and then secondly is is this state of vasod dilation or basoc constriction is that stimulated by extrinsic or intrinsic stimuli and then lastly I'd like you to think about whether the SU or winter birds probably have more capillaries In Their Skin just based upon the data that we're seeing here and therefore what chemical signal would have stimulated more capillaries in that group so think about those questions for a minute and then we'll discuss okay well let's go ahead and talk about this one again we're we're just using some of this data here for water loss as a way to sort of infer things about the number of capillaries that are in our skin and also whether those capillary beds are whe whether they're perfused with blood because of dilation of the of the arterials coming in or whether they're restricted from blood due to constriction of those arterials so again we're we're looking at a couple different groups of birds and we can see in both of these groups we're seeing that water loss is increasing as as temperature gets higher so just based upon that do we think those arterials leading into the skin leading into those capillaries in the skin do we think they're vasod dilating or basoc constricting to cause this pattern yeah yeah they're they're baso dilate remember when when when those arterials leading into a capillary baso dilate that means we're putting more blood into those capillaries and and that therefore we're increasing the amount of pressure within those capillaries which can therefore lead to more fluid leaking across those capillary walls and leading to in this case water loss uh so when we think about that baso dilation of capillaries and the routing of more blood into in this case the skin is that something that's stimulated by extrinsic or intrinsic stimuli extrinsic again is whole body intrinsic is more local so what are we seeing here yeah this I I would say is a little bit more intrinsic because it's just happening to the skin whereas other things are happening in other other parts of the body um and another thing to sort of think about here too is when we think about intrinsic controls these localized controls if we go back a few slides here so remember when it comes to these intrinsic controls our stimuli often times are you know not only things like inadequate oxygen delivery or inadequate removal of metabolic waste but especially when it comes to skin like we're talking about here the application of heat causing baso dilation of those capillary beds and so that's that's exactly what we're seeing here is where increasing the temperature that these birds are being exposed to and it's adding that heat stimulus they want to now get rid of some of that extra heat because it's hot outside and so they're baso dilating those capillaries in their skin to try to bring that heat to the surface where they can lose it so again that that's always a good clue that you're dealing with an intrinsic stimuli when you're when it's matching up directly with what we know about intrinsic stimuli whether it's heat oxygen CO2 Etc so then we can we can look at our summer and our winter birds and we see those two different sort of trajectories we definitely see that our summer birds have higher rates of water loss than our winter birds so which group do we think has more capillaries in the skin yeah sum are birds because their rates of water loss are higher that tells us that there's more blood going through the skin leading to higher rates of water loss here uh and so therefore I'd be willing to bet that if you were to say sample the skin and look at the say some different chemicals that are within the skin you might find a certain chemical signal in Greater abundance in those summer Birds uh that would lead to more capillaries In Their Skin what what's what's the name of that compound remember the name of the compound so the compound is vascular endothelial growth factor which stimulates the process of angiogenesis yeah so so definitely the summer birds have engaged in more angiogenesis and that angiogenesis was stimulated by vascular endothelial growth factors so yeah no doubt you'd probably find more vascular endothelial growth factor in those summer Birds questions about any of that all right well that is a nice logical stopping point for today and so we'll finish up talking about blood vessels on Wednesday so I will see you then or I'll see some of you in the lab this afternoon