so we're moving on to blood vessels beginning with the basic anatomy of blood vessels before we look at the specific names of many of the blood vessels in the body which is kind of part of our lab based exploration of blood vessels so blood vessels are what carry blood they begin and end at the heart and there are five major types that we'll discuss and these are kind of an order of the blood flow from the heart right so right off of the heart arteries carry the blood away from the heart and they eventually branch and branch and branch and when the branches get a certain size then we call them arterioles meaning just the diminutive form of artery the tiny arteries and then those will branch and branch and get smaller and smaller to make capillaries and it is within capillaries that you have the sight of gas exchange with tissues after that occurs the capillaries start to dump their blood into tiny tiny veins called venules which merged to form veins and then the superior vena cava inferior vena cava bring that blood back to you the heart and when you're thinking about blood vessels you can think about this little friend here these are tunics and tunics is like an old-timey coat and I'm going to show you here now you can see these three tunics if you look let's say at this artery this darker colored red region here this is a tunic then you have this second tunic here and finally this third tunic cure it veins will look different but they'll have the same three tunics they might not be as clear you just got to kind of imagine that here this innermost layer is a tunic kind of a thinner middle layer and then they also have an outer layer so we'll talk about these differences between arteries and veins but they each have these three to mix these three coats so that most internal code is called the Tunica interna or Tunica intima the intimate code or the internal code and it's just an endothelial layer endothelium is a simple squamous lining of the blood vessels it's the same as the endocardium there's no difference between them we just changed the name because we've left the heart now we're inside a blood vessel arteries do have a special structure in there called the internal elastic lamina which is a elastic layer that helps them deal with the pressure from the heart so you know when you take your pulse or something you're you're feeling for an artery because it's in arteries that they carry the pressure wave from the heart so this elastic band will help the arteries deal with that the middle layers the tunica media this means the middle coat has a lot of smooth muscle and the autonomic nervous system is going to control the contraction and relaxation of that smooth muscle and because the term vaso means vessel we call that vasoconstriction and vasodilation and in the tunica media in arteries you have another elastic lamina the external elastic lamina serving the same purpose as the internal elastic lamina the outermost coat which you can call the Tunica externa or the tunica adventitia there are a bunch of loose collagen fibers you are protecting the vessel and anchoring it down so if you were to look down at your arm and find a blood vessel that you can see if you tug on the skin you'll see that that blood vessel will move with the skin so it is anchored down to those deeper skin layers and some unique structures you'll find on some of the larger blood vessels are called vasa vasorum in because vaso means vessel vasa vasorum means the vessels of the vessels and why would a humongous vessel like an artery need its own vessels well because of what we just described there's all this tissue in there are these collagen fibers there's this muscle that's contracting and relaxing relaxing there's a bunch of work going on so anytime something's doing work it means energy to achieve that function it needs oxygen it needs nutrients it needs waste carried away so big vessels big arteries and veins will have vessels embedded in the Tunica externa to supply nutrients and take away waste here's a diagrammatic look comparing an artery to a vein so again you can look for the these three layers external media and interna you'll see those on both sides can see the three tunics are the same the same names you'll find that arteries and veins both can have those vasa vasorum we discussed they can both have smooth muscle although typically you'll see more in arteries they both have an endothelial layer so all that leaves is really just these elastic internal and external elastic membranes and a bunch of other elastic fibers inside arteries to help them deal with the pressure from the heart there are different types of arteries though starting with elastic arteries those are also called conducting arteries because they are the early arteries that are sending the blood to certain places they're very thick because they're right next to the heart so we're talking like the very early branches off of the heart and there's a lot of smooth muscle the smooth muscle in this case actually makes the elastic fibers so you're not doing a ton of contracting and relaxing of these tunica media in these elastic arteries but the smooth muscle makes these elastic fibers usually smooth muscle doesn't have that job it's up to fibroblasts which you might remember from early and discussing tissues but in this case that's why you have all that muscle in there and really when you think of elastic arteries don't think about that muscle I would say think about the elastic properties of these elastic arteries think about how they are expanding and recoiling with these pressurized waves and that modulates blood pressure and what I mean by that is like this imagine that these arteries weren't elastic they're just mostly thick muscle pretty strong they'd be almost like a rubber hose if you had a rubber hose and you went to the spigot and you cranked up the water and then you lowered it and you cranked up the water and lowered it you cranked up the water and Lord I think of that it's like the heart beat the heart's pushing water and then it's relaxing and pushing it and then relaxing the pressure would be super high and then almost often and super high and then almost off as you turn that spigot back and forth so imagine that happening inside your body with these like high pressure waves and low pressure and the high pressure and low pressure that's not good so instead what you have is these imagine a hose let's say that as you crank up the pressure the hose gets bigger and then as you lower the pressure it gets smaller if that could happen the water would always be coming out at roughly the same pressure so that's what your elastic arteries do for you modulate blood pressure by changing the diameter of the hose as the pressure comes through different than muscular arteries those really do have that tunic and media layer that smooth muscle that's intended for constrict contracting and relaxing to help distribute where the blood is going to go and eventually you get out of the arteries and into arterioles these tiny arteries that are sometimes called resistance vessels because the big thing they do for your body is they're really helping to slow the blood down the blood goes into these small small vessels it slows down and you need that blood to be really slow and it reaches the capillaries because you can't just have it whizzing through you need time in the capillaries for the oxygen and co2 to trade places for nutrients to leak out etc so these resistance vessels they're very thin they have a relatively incomplete tunics so I have here this picture of an arterial showing how there is smooth muscle here same as in this diagram they included some smooth muscle cells but as you can see up here they're incomplete they're just partially helping wrap around the arteriole a bit and they'll still contract and relax typically they're doing that in response to the sympathetic nervous system is what would make them contract because if you're in a fight or flight situation most stuff is not getting blood so if your sympathetic nervous system stimulant stimulates your arterioles then you're talking about like shut down digestion shut down reproduction etc most of the blood needs to go to the heart lungs and skeletal muscle one more note before we leave the arterial system is that without getting too much into physiology I want to make sure you understand like why we have all this muscle in what is doing here's an image of like how blood pressure can change by you putting your thumb over the end of a hose right that's all that happens during vasoconstriction is you're changing the blood pressure and sometimes in your body you want to be able to do that and we won't get into the details physiology concept but whenever you're thinking about muscle contracting and relaxing one of the things I can do for your body is help change your pressure the other thing it can do is change distribution so these little dials here are like smooth muscle if you turn this dial you will send less blood out through one port and more blood out through another and so blood pressure and blood distribution are the big things that are affected by the arterial system and of course the goal here is to get that blood down into the capillaries the smallest of the blood vessels and typically they're about the size of one red blood cell and because they have only an endothelium just that intimate internal tunic nothing else around them and because the blood is moving so slowly now thanks to the resistance vessels the arterioles now there's time for gas exchange and we should say nutrients and waste exchange as well with the interstitial fluid with the fluid out here that all the cells are basically bathed you there are different types of capillaries three types continuous fenestrated and discontinuous or often called sinusoidal source sinusoidal and the major difference between these three is how leaky they are because all the capillaries are leaky and we'll talk a lot about that when we explore the lymphatic system but some are leakier than others so we'll ask how vici are each of these why are they so leaky structurally and where are they found so functionally why are they leaking so much so let's start with these continuous capillaries continuous capillaries are the least leaky and they're the most common so if we look at this picture here of continuous you can see the endothelium here all the cells are nice and tight next to each other there are little cliffs in between the cells ain't little lines but the cells are connected pretty tightly stuff will it get out I mean oxygen and co2 will go right through the endothelium other stuffs can get out too you know like little tiny water molecules and stuff so there's plenty of leaking happening but nothing big is gonna get out with fenestrated capillaries then you have fenestrations all these little pores that you see in the endothelium those are called fenestrations why would you want some stuff to leak out or leaking to happen more quickly well how about the choroid plexus you should know the function of the choroid plexus from previous studies and this job is to make CSF what does it make it out of it makes it out of blood but you need to mmm you know you need a lot of stuff leaking out of these vessels to make a lot of CSF you'll he's also in the kidneys because the kidneys are trying to filter your blood so you need to let a lot of stuff out to be able to filter it and fenestrations are also found in some endocrine organs because endocrine organs make hormones hormone is a chemical messenger travels in the blood to a target cell so the key point there is travels in the blood it has to be able to get into the blood and it can get in there by going through these little fenestrations sinusoids are the most leaky of all the capillary types with big fenestrations these big big pores and also these big intracellular gaps so you can imagine like lots of stuff we'll leave through those gaps we'll see that in the liver which is trying to process the blood returning from your intestines so needs to get stuff out to be able to process it bone marrow in red bone marrow you're making all the cells that go into your blood how you gonna get them into the blood they have to be able to squeeze into the capillaries so these gaps are big enough for entire cells to squeeze through to get into your blood the spleen is one of the organs that chews up old red blood cells so same thing live cells need to be able to be passed out and more endocrine organs like the adrenal glands have these sinusoidal capillaries again we're trying to put hormones into the blood so lots of kinds of capillaries and the thing about capillaries says basically if you have a chunk of your body's tissues what you want to do is have capillaries that are like a checkerboard running every which way through that tissue so that all the cells get bathed in nutrients and get their waste picked up so that's pretty much what happens in these structures called capillary beds so the blood arrives through a arterial terminal arterial will enter into this capillary bed spread throughout all of these capillaries make the exchange of nutrients and gas and wastes and those capillaries will merge back together and now this blood can return through a vein yule and go back to the heart the thing about these capillary beds is usually they're closed most of the time your capillary beds are closed if they were all open at once then you die there would be no blood left in your heart or your blood vessels these capillary beds are all over the place and would take up all this blood so usually they're closed usually these structures call pre capillary sphincters are contracted and the blood is moving just through this middle channel here which is made up of two parts the meta arteriole is like a little mini arterial and then this thoroughfare channel it's like a mini van yule and together they combine to form what's called a vascular shunt this doesn't mean your tissues are not receiving any oxygen or nutrients or collecting wastes but it's not much right a little bit of oxygen and co2 and wastes are going to be exchanged with this vascular shunt but this will be closed temporarily until the tissues here start to cry out for help as the co2 levels start to increase a bit then these capillary sphincters will relax and blood can flow throughout the capillary bed supply that oxygen pick up that co2 and then the sphincters will contract again so capillary beds as we saw interwoven networks of capillaries capillaries don't operate on their own they operate in these these bends we saw how pre capillaries fingered sphincters work we saw how vascular shunts work one other thing we'll mention is arterial anastomosis arterial anastomosis are interconnected arteries that are guaranteeing a reliable blood supply let me show you on the previous slide what this would look like we see this arteriole right here and there's this blood coming to this capillary bed through this single arterial well if you had a blockage in that arteriole then this capillary bed would be toast no blood could arrive just from one little block in one little arterial so many of your capillary beds are supplied by anastomosis which means that imagine that here there was a split or a fork there's actually two arterials I'm coming from this side from the left one coming from the right and then they merge for a moment and then they send a blood into the capillary bed so now if either of these two got blocked by something there would still be a backup access for that capillary bed and it will still give blood so that's what we mean by an anastomosis guaranteeing a reliable source of blood and sometimes these look very complex like the circular structure here is called the Circle of Willis or the arterial cerebral Circle we'll talk about it later on but you can see it's that circular structure is like a roundabout it's gonna give lots of different ways to access the brain even more sure that those capillary beds can receive blood a last note on capillary beds we said that they're usually closed so like why would you want to open a capillary bed and some of these are more obvious than others one ways reason would be to modulate blood pressure so if your body just opens up a lot of capillary beds at once overall blood pressure will drop so it's one way for your body to perform homeostasis of blood pressure cellular knee is pretty important and hopefully you could come up with at least 3 or 4 or 5 reasons that you would your cells would suddenly need blood I was just scratching note seeing what I could come up with how many here's my list exercise you're gonna send blood to skeletal muscle so you need those capillary beds to open up sex if you need something to become erect then sending blood in there it's the ticket if you are using certain parts of your brain you know those functional MRI machines can monitor where well blood is going by tracking sugars or something to different parts of your brain so extra blood will be used in those capillary events at different times if you're growing a fetus inside of you then you'll need to have lots of capillaries down in the placenta or if you're digesting you need a lot of blood to not just help with picking up and transporting all of the nutrients from your food but also all the contractions of the stomach and the intestines that's muscle that will require more blood more capillary beds to open what about cell reservation if you're a little bit cold so like if you run to the mailbox on some cold morning or something the body will send blood out to your ears and nose to warm them up but if you're deathly cold even though your nose and your ears are cold and your fingertips and your toes the body will draw the blood away and keep it in the core to protect you know your brain and your heart so if you're definitely cold it's kind of performing the opposite action of being a little bit cold and if you're under some physical threat and the blood will drains out of your superficial skin that's in response to perhaps some trauma that you might receive from a fight or flight situation so you're less likely to lose blood if you close a lot of capillary beds in your skin for humans we also use capillary beds a bit for communication so depending on your skin color you might visibly flush if you're embarrassed but also don't forget some people are just kind of red you know all the time this prints so and so it seems pretty red to me okay so now we just get the blood back to the heart this will go much quicker venules are just little veins they often have incomplete tunics so maybe no Tunica externa and incomplete tunica media kind of like arterioles and the Bloods moving pretty slow still this is a good place for diabetes and that term and this image should sound familiar to you from previous class then we're into the veins veins have some special adaptations to keep that blood moving back to the heart especially because you've got to fight gravity to pull the blood back up from your legs so they have big lumens they're much larger and open compared to arteries to limit the resistance beside the vessels there are valves which we'll look at on our last slide and a few other things they rely on pulsation of nearby arteries and these pumps and these are what are gonna make a big role in helping prevent you from collapsing if you are standing still for long times one of the reasons you don't want to stand upright that long especially with these locked legs is you're not allowing these special adaptations to help the blood get back to your brain so pulsation I'm here by arteries this is what we mean if we mean that arteries and veins tend to run counter currently like this next to each other so as the arteries pulse they're kind of nudging the blood in the veins to keep it moving pretty straightforward so - with the skeletal pump we're just saying that often arteries and veins run next tune in between and around skeletal muscle so as you're moving right maybe shifting your weight from leg to leg a little bit as you're standing still at a wedding or a military lineup that contracting and relaxing of skeletal muscle will nudge the blood back to the heart and the respiratory pump you'll get into the details of this more in physiology partial pressures and things like that I tried to get the most basic image I could of this where it's just showing that you have a thoracic cavity and an abdominal cavity separated by the diaphragm as you breathe as you use your respiratory system to breathe pressure changes between the thoracic cavity and the abdominal cavity will actually draw the blood back up towards the heart that's called the respiratory so last we'll just look at this adaptation of veins called valves use our little folds of the Tunica interna kind of like the semilunar valves of the heart in their structure and you know you just want as blood gets smushed let's say we're going up because these are most common in the legs and limbs as the blood moves back up through the pulsation of an artery or a skeletal muscle pump or a respiratory pump or whatever the blood will move up and if it does try to start moving back downwards it will hit those little cusps and be prevented from continuing downward but if you have an issue with these valves like one is a little bit broken or just totally has gone away that can lead to the blood starting to pool and the blood will back up and stretch out the walls of the veins and I put these pictures here because I I always kind of thought varicose veins were kind of like this you know like little blue lines but real like severe varicose veins are much more intimidating and look like that there are lots of treatments compression stockings and so on in this image someone had laser treatments but they'll also go in there and they can take those veins right out depending on where they are in your body so lots of different treatments for these varicose veins the trouble with varicose veins is this other term here descending valvular incompetence and what that means is this person perhaps had a valve go bad up here well no big deal you have a lot of valves but all of a sudden there's all this extra weight of blood on the next valve making it more likely that that valves gonna go and now this valve has three times as much or whatever extra weight from the blood above it and down and down and down we go each valve causing the incompetence of the valve underneath it in this descending valvular incompetence this last picture here is actually not a valve at least not when you're born with this is one new ingenious thing they're doing with valve sis going in and dissecting out the inside of the vein to make a fake valve they're called mono cusps attaching this valves so it's just one little flap it's not quite like the flat valves that we normally have but it's a way to use our own body to make valves from existing tissue so you're not going in there and trying to like you know put some synthetic valve or a pink valve or something in that vessel so that's the anatomy of blood vessels and now we'll be moving on to looking at part 2 and part 3 on naming the different blood vessels in the body