Lecture 9 - Blood Vessels & Circulation

Added: 2026-05-14

[00:00:00]hi everyone here in this module we're going to be focusing on chapter 15 which looks at all the blood vessels in the body and the different circulatory paths that they take this will be the last lecture in our three-week series looking at the cardiovascular system so to this point we've looked at the heart the main pump of the cardiovascular system we've looked how blood flows through the heart then last module we took a look at blood its overall composition some of the disorders associated with it now today we're going to look at how the heart can actually transport all of that blood throughout the circulatory system and looking at the blood vessels that actually get the oxygen that we need to those tissues so to start off there are two major types of blood vessels in the body so you've probably heard of these arteries and veins so the arteries have blood flowing away from the heart at all times okay whereas in the veins blood is always flowing back towards the heart so a quick way to remember this is arteries away both start with the same first letter the arteries will always be delivering away and in systemic circulation that happens to be that they're carrying oxygenated blood right which is high in oxygen because that's what our tissues need and in systemic circulation the veins carry deoxygenated blood right because it has to go back to the heart to be sent out to the lungs and then pick up new oxygen again before being delivered around the rest of the body now the arteries are traveling away veins traveling back towards the heart there needs to be some bridge or connection um to be able to connect the arteries to the veins and that's through the capillary networks and here you can see all of these capillaries that they have here um sitting within the tissue cells this could be anywhere this could be your skin muscle tissue you name it okay any tissue cell that's going to require oxygen to be able to survive which is all of them you're going to have capillaries that are nearby those cells to be able to deliver the oxygen that's contained within the hemoglobin molecules on the red blood cells that are in this blood okay so the arteries are delivering blood away from the heart towards the capillaries then the blood cells are going to move into the capillary network okay and it's important to note these capillaries are very thin we'll talk about the structure in a few slides but the capillaries are very thin to allow for that diffusion of oxygen from the blood inside the capillary to the tissues that surround the capillary okay and then those blood cells continue along and then they move into the venous portion of circulation where they move into the vein and then that is drained all the way back to the heart to continue the circuit again okay so arteries are delivering away from the heart toward the capillaries and then the veins from the capillaries are returning blood cells back towards the heart take a look first at the outer diameter of these two vessels okay we have an artery here on the left and we have a vein on the right with this artery and vein looking at their diameter from the external appearance for the most part they look pretty similar right the vein maybe you could argue with me slightly slightly larger in diameter but let's for the purposes of this explanation let's assume that the actual diameter of these vessels from an external perspective is equal okay so the artery and the vein are the same diameter from the outside now what we're going to do now is take a look at the three layers that make upper blood vessels and you'll see they share the same names and they're made of the same tissues however they're modified differently based upon the needs of that specific vessel and now before i go into that i just wanted to jump ahead to this slide i've created a summary of all of the main information you need to be taking away from this discussion okay everything that i'm saying is all included here in these following slides on arterial and venus structure okay so let's start with the layers on the the outermost layer you have the tunica externa and then deep to the tunica externa you have the tunica media which you can see here now the tunica externa is made up of connective tissue whereas the tunica media is made up of smooth muscle tissue and then if we move into the deepest layer the tunica intima it is made up of simple squamous epithelial tissue okay and now in the blood vessels we call this simple squamous epithelial tissue the endothelium now let's take a look at some of the differences between them so tunica externa between the arteries and the veins both made of connective tissue however if you notice here the tunica externa is a lot thinner in the artery than it is in the vein once we get talking about the function of these two different vessels you'll see why that's so important that the vein has a much thicker connective tissue that surrounds the vein if we move into that middle layer the tunica media and we can see the tunica media is made up of smooth muscle but the tunica media in the artery is much thicker than the tunica media here in the vein and the reason that is is because our arteries are needing to be able to vasoconstrict and vasodilate so vasoconstrict would be decreasing the amount of space in the inner lumen and then vasodilate to open that inner lumen up the arteries need to be able to do this because this tunica media layer is contracting in sequence with your heartbeat right if i asked you right now to go find the distal part of your radius take your second and third digit from your opposite hand and just place them just on top of sort of the anterior portion of the radius there that's where your radial pulse is located now the fact that you can feel your pulse that far away from the heart is because this tunica media of all of your arteries is pulsing and contracting at the exact same time that your heart is ejecting blood from um from itself okay so the tunica media in the arteries is so important because you need to maintain that pressure a pressure at the heart needs to be the same all throughout the body now in the veins not as important right we still have a muscular layer it's to add a bit of muscle tone so that the vein just doesn't balloon out but definitely you're having more of a passive filling of your veins whereas here in the arteries there's an active contractile force that's going on to maintain high blood pressure throughout your arterial system now something else you'll notice here and i mentioned vasoconstriction dilation right so constriction making the artery smaller so the muscles contracting and then relaxing to make the artery bigger now the tunica media doing that you're going to be having a lot of change in shape right stretch and then recoil going on and so because of that outside and inside of the tunica media you can see right here almost looks like cheese right that's representing the elastic tissue that exists to allow for that stretch and recoil of the artery so the arteries are very dynamic in comparison to the veins if we go a little bit deeper you see this purplish layer here that's part of the tunica intima okay the tunica intima on both that is the basement membrane if you go back in our lecture to where we talked about epithelial tissue all of the epithelial cells to attach to something deeper they need to have a basement membrane that they are connected to that is going to attach to the other tissue deeper to them so that's what that purple layer is it's just showing you that basement membrane that these epithelial cells are connected to so now if we go right into the deepest part of the tunica intima we're now looking at the endothelium and the endothelium is made up of simple squamous epithelial cells okay and if you remember which i know you do uh the simple squamous epithelial cells those are the thinnest epithelial cells that we have in the body so why would we want that well eventually when we get into the capillaries that we were talking about we only have this layer of the tunica intima making up those blood vessels so that makes the capillaries as thin as possible to allow for oxygen to leave and for carbon dioxide to come into your bloodstream so we'll talk about that a little bit more when we get there but for now as long as you're seeing here simple squamous epithelial tissue is what makes up this endothelium now a couple of differences here looking at the tunica intima the artery you can see the lumen is much smaller okay so the inner lumen lumen is the inner space so think of a hose right the inner inner space where you would actually have in this case blood flowing through the inner lumen of the artery is much smaller than that of the vein and that's because we want to maintain a higher pressure to be able to actually effectively deliver the blood to the tissue it needs to get to now in contrast the veins you're going to be passively having blood filling these structures so the lumen is a lot larger in the vein compared to the artery now in addition to that the vein also contains one-way valves all right so in this case here the way that this valve is directed i know that blood is going to be filling and moving in this direction back towards the heart we'll talk about it a little bit later but the way that the veins actually help to move the blood back to the heart is not just by you know pouring blood into them and then they just passively feel that's part of it but every time you move and your skeletal muscle contracts it squeezes on the vein and every time it does that it propels the blood upwards back towards the heart okay so i'm talking here for an example of a vein in your leg okay um and then when it contracts it's going to propel the blood back towards the heart but then when it relaxes gravity is going to want to pull that blood back down so what these one-way valves do is they prevent any retrograde motion they prevent backflow so once the blood is moved past that one-way valve it's in this next part of the vein and it won't go any further back so the two differences there a much larger lumen in the vein and the presence of one-way valves okay so use this uh summary chart to be able to go through and work through the differences here between arteries and veins the one thing i would add the types of tissue so tunica externa connective tissue tunica media smooth muscle tissue tunica intima simple squamous epithelial known as the endothelium now we're going to take a look at how we connect these arteries and veins together in these capillary networks okay one thing i should mention here i want you to think of your arteries as a major highway in your veins as a major highway here in the arteries you're moving along the highway and now you need to go and pick something up at the grocery store so you need to go to the off-ramp okay the off-ramps are known as arterioles the arterials connect the artery into the capillary network so your off ramp is the arterial the arterial feeds into the capillaries now i want you to think of that you're in a neighborhood and this is where you're going to eventually find the grocery store you're at the grocery store you dump off your oxygen you pick up your carbon dioxide and then you continue along your way and then you need to get back on the highway so you're going to get on an on-ramp okay that on-ramp is your venual venules are the smaller veins the on-ramps they get that blood back onto the major vessels and then send that blood through the veins now you're back on the highway going back towards the heart okay so that's a good analogy a good way to think about what's going on here capillaries are microscopic and they're everywhere anytime you nick your finger and you have a little bit of blood that comes out that is a capillary that you have nicked essentially with capillaries though remember they are everywhere okay anywhere on the surface of your skin that you're looking any organs any muscle tissue capillaries are everywhere now we needed to be able to regulate how much blood is flowing into these capillary networks because not only are we giving off oxygen taking up carbon dioxide but this is the most peripheral in the body that you're going to be and so you can lose a lot of heat through delivering blood into your capillary networks we have these structures known as pre-capillary sphincters i haven't introduced you to them yet but you know the feedback mechanism specifically the negative that enable us to regulate our body temperature if you were to go outside what would happen to your hands and kind of turn a little you know purpley bluey you would be restricting the blood flow why because you want to keep the heat in your blood to the core of your body so if you're working out or something you start you're sweating your face is getting flushed your body is trying to be able to release heat so what it does is it allows more blood to flow in these capillary networks okay the way that it does this is by either contracting or relaxing these pre-capillary sphincters and that's how we regulate whether we're going to let more heat off in the capillaries and let more blood flow into them or whether we're going to keep more blood into the core of our body and prevent blood from moving into the capillaries so with these pre-capillary sphincters here let's say it's cold outside your pre-capillary sphincter is going to be contracted okay because you're going to want to prevent blood from moving into the capillaries to be given off more heat so that's why you end up with that purplish bluish tinge because you have less blood in your capillaries when you're cold now in this example here it's showing you they're relaxed well this would be a situation where you are hot or just even normal body temperature and your pre-capillary sphincters are going to be relaxed to be able to allow blood to flow into the capillary beds to deliver that oxygen and to give off the heat if you're trying to keep your body temperature cooler so you're trying to bring it down the sphincter is going to be relaxed letting more heat out if you're cold then your body is going to contract these sphincters and keep the blood into the core now some diseases that can occur here with the arterial system atherosclerosis is the deposition of fatty deposits here beneath the endothelial lining of your arteries so anytime you have high cholesterol levels you're more likely to then have damage to the endothelium which then if there's damage it allows for the deposits to start to form and any time that happens you can see here what's happening is that you end up with a reduced inner lumen so what do you think the problem is going to be there well you're restricting blood flow right anytime you restrict blood flow you're going to be inhibiting the ability for those red blood cells platelets everything to just keep flowing and moving we talked about before that if blood sits still it tends to clot so when you have atherosclerosis and you have reduced inner lumens of your arteries it restricts blood flow and can make yourself more prone to developing blood clots and if a clot is large enough to get stuck well now you're dealing with something well pretty serious especially if it happens in your brain or to arteries that are delivering blood to your heart right with a stroke or with a heart attack now if that is left unchecked for prolonged periods of time then what ends up happening is that the calcium in our blood can start to deposit and calcify that fatty tissue now we talked about what happens when our cartilaginous skeleton becomes calcified right it turns to bone so the same thing is essentially happening anytime you calcify something you're making it hard and brittle so if you're starting to do that to the walls of the arteries you're also losing that elastic ability to be able to manage and regulate blood pressure and here you're seeing a cross section normally let's say you would have had an inner lumen that would have been proportional to the whole space well here you have a plaque deposit on this which is then sort of closing in this lumen you can also see some of those calcifications taking place so severely restricting that inner lumen and preventing blood from flowing through that artery now in early stage um you can use vasodilators sorry to be able to just relax let's think of this term vaso is referring to the blood vessel itself and then dilators so you're opening up that inner lumen they help to relax that tunica medial layer to allow the vessel to increase in diameter further treatments required than an angioplasty where they actually go in and they can mechanically widen the vessel to allow for more blood flow through that can be done but also then they can ultimately um go through and implant a stent if you look at driveways they just have the ditches along the side of the road to continue that ditch along and underneath the driveway they would have a big metal sort of tunnel right to allow for the water to still continue to flow so it's the same kind of idea here they're putting in sort of like a mechanical tunnel that's gonna keep that vessel stretched open and allow for blood to flow freely through that vessel aneurysms are abnormal widening specifically like a ballooning of the arterial walls now one of the problems here not only do you have a weakened artery at this point which will make it more prone to to bursting and then ultimately hemorrhaging but you also now you do not have a smooth conduit through which blood can flow freely you're going to get blood stuck in around parts of that ballooning and then what can happen is blood can start to clot which is making you more prone to embolisms and then if they happen to your brain then ultimately strokes okay um so yeah what can happen here some complications well simply the aneurysm can rupture and now this is a one that's located in the brain but you can have an abdominal aortic aneurysm which we'll look at next and then thoracic abdominal aortic aneurysms and those happen to be the largest vessels in your body so when they burst they tend to be fatal so thrombus formation is referring to the formation of a clot and if that clot becomes mobile then it becomes an embolism now this is what i was talking about here with the abdominal aortic aneurysms so to give you a bit of back story um the major blood vessel that comes off the heart is the aorta it's delivering oxygenated blood to the rest of your body now the aorta descends down through the thoracic cavity and as it does so it's known as the thoracic aorta and then as soon as it moves past the diaphragm roughly around here once it passes through the diaphragm it officially becomes the abdominal aorta okay so because it's in the abdominal pelvic cavity it's now known as the abdominal aorta now what i want you to see here to reference yourself you're looking at an x-ray of an individual that's taken from a lateral perspective so they were standing sideways and the rays went through them um here we can see the sacrum right and then you're looking at l5 4 3 2 1. those are your vertebral bodies and then here's your t12 okay so the abdominal aorta sits just in front of that and typically you're not wanting to see much more than a shadow okay because really it's it's a vessel made of connective tissue muscle and epithelial tissue so the x-ray should not be um being absorbed like you see here with your bony tissue but what we are seeing here is quite a bit of calcification of this aorta okay so we have arterial sclerosis that's been going on as a result you have a weakening then of the vessel walls and so now we can see that there is a definite ballooning right an aneurysm has started to develop here now hopefully you can appreciate all the blood going to your lower extremities is passing through here if this bursts the internal bleeding would essentially be fatal within a very short period of time so they can at a certain point surgically repair these sometimes they can go undetected though as well because typically they present like in this case for an abdominal aortic aneurysm it can present is back pain it can easily miss it so in this case here you can see the ballooning you have these calcium deposits around the outside of the aneurysm there which is identifying that uh that ballooning because then you can see below that being less of it right so definite widening here in this region now in terms of the veins one of the most common venous disorders that can occur are varicosities okay also known as varicose veins now as we mentioned the tunica intima of your veins have those one-way valves and if they are working properly they should close and prevent any blood from flowing backwards but what can happen is over time there can be damage to the valves they can become weak and competent and essentially become leaky where they are no longer preventing blood from flowing backwards which is going to cause blood to pool now remember how the veins they have a very thin tunica media right and all that's holding them together is connective tissue so if you have a lot of blood pooling in these veins over time they can become dilated significantly and as they do then they can become if it happens to be more superficial then they can cause a lot of pain for patients but ultimately become various causticities like this now a simple way to treat them if you catch in an early stage is through compression stockings okay so compression stockings can come in different grades um not sure if any of you know anybody who uses those but um the mild grade would be sort of like a mid calf so like a high tube sock kind of height but keep in mind a lot more pressure than your socks would just be putting on a medium grade would be relatively in the mid thigh area okay so that's to compress all the way up to here and then the highest grade you can get is sort of like a full stocking that goes all the way up to sort of essentially as high as your pants would go and so what that's doing that's applying compression here to these veins and essentially doing the passive work of holding them holding them tightly together to keep less blood from just sitting in them and pooling in them okay so we're going to move forward looking at systemic circulation looking at all of the arteries and veins throughout your whole body with the exception of the arteries and veins that deliver blood to your lungs which is pulmonary the arteries and veins delivering blood to and from your heart muscle which we've already looked at the coronary arteries hepatic portal circulation we'll take a look at which is specifically how your liver receives all of the venous blood from your digestive organs to filter it and then fetal circulation which there's a few differences between an adult's circulatory system and that of a fetus so by the end of today you will know the overall branches that go into the upper lower extremities up into your your head okay so i'm going to be focusing in on uh just the primary structures that you need to know so if you have this in front of you then great as we go through this i would say highlight the terms that i'm talking about because those are the ones that would be fair game for your exam so first off here we're going to start at the heart right because we know the right side of the heart is receiving deoxygenated blood from the body so that's all coming from the vein so we're going to get to that in a couple of slides when we look at the venous system but then once it leaves the right ventricle and pumps out through the pulmonary trunk the deoxygenated blood is headed out to the lungs why to pick up oxygen so then it comes back to the left side from the left atrium left ventricle and then out through the aorta so that's where we're starting this whole story so we're looking here from the left ventricle you have oxygenated blood that's going to leave the left ventricle and pass into the aorta the aorta is the largest artery in the body and here you have the ascending aorta coming right off of the left ventricle and then it takes a turn at the top which is known as the arch of the aorta and this is an important landmark because there are three major vessels that come off the arch of the aorta and we'll talk about those in a second so from the arch then the aorta takes a turn goes behind the heart and now it is descending so this from the arch downward is known as the descending aorta but we give it two different names based on the body cavities that it's in so up here we're in the thoracic cavity so we label it as the thoracic aorta so from the arch down that's the thoracic aorta now as soon as the thoracic aorta passes through the diaphragm it becomes the abdominal aorta you see all the way down here to about your umbilicus okay so what we're going to do because i'll take you down through the lower extremities afterwards we're going to focus here on the three main trunks first and then we'll pass into the head and then the upper extremities okay so coming off of the arch of the aorta and it's important to know in sequence first you have the brachiocephalic trunk okay the brachiocephalic trunk runs off to the right hand side of the body and we'll talk about what it splits into in just a second okay so the first branch you have is a brachiocephalic trunk the second branch you have is the left common carotid and then the third branch that you have coming off is the left subclavian artery okay so in sequence brachiocephalic left common carotid and left subclavian okay so you might be noticing okay well we have the brachiocephalic going off to the right but then we have two left vessels left common carotid which it looks like is going up into the head and then the left subclavian which is going into the upper extremity well you have those two vessels over here on the right as well but because the heart sits a little bit more to the left side of the body we have this brachiocephalic trunk that heads off to the right before the common carotid and subclavian come off of it okay so that's why you have four main vessels a left and a right common carotid and a left and a right subclavian but you only have three vessels that come off of the arch the aorta that's because we have a brachiocephalic trunk that connects the arch to the right common carotid and the right subclavian okay so let's start off here with the common carotids now they're both going up into the head the common carotid right around the angle of the mandible so if you find your lower jaw and just go to the posterior aspect of it where you can feel sort of the the angle of your jaw and then just come in a little bit medially this is where you would find your carotid pulse typically okay and you're landmarking roughly right about here this is the common carotid that you're on and you're feeling that before it splits to the internal carotid and the external carotid now this is where it gets easy the internal carotid goes inside of your skull and the external carotid stays outside of your skull so think about now what tissues is each vessel going to be supplying with oxygenated blood well the external will be anything that sits outside of your skull the muscles um your skin now the internal carotid is going inside the skull so what sits inside your cranial cavity your brain okay so the internal carotid very important because it ultimately um leads in and feeds all of the cerebral vessels that are going to be supplying your brain with oxygenated blood okay and that's where we're going to stop for now common carotid is the main arterial vessel headed into your head and then it has two branches the external carotid and the internal carotid okay then you're set the internal carotid then is going inside so it's feeding the brain and the external carotid is staying outside now both right and left common carotids do the same thing so the right common caudate has an internal branch and an external branch okay so common carotids are the arterial vessels feeding your brain and your head with oxygenated blood and then we have the subclavians which you can see is named after the clavicle that is right there okay so this blood vessel on both sides runs underneath the clavicle hence why it's called subclavian and then that vessel continues all the way along into your upper extremity okay so we're going to stick here with the right but the exact same branches exist on the left so the subclavian which is under the clavicle eventually moves into the armpit which is your axillary region okay so same vessel it just called a different name based on the region that you're in so you have your right subclavian right under the clavicle and then in the axilla you have your axillary artery which continues into your arm and now it's the brachial artery and then here just past the elbow it splits and you know your forearm bone so you know the names of these you can see it over here your radial and your ulnar arteries all right so as long as you remember radius do the thumbs up so your radius is lateral ulnar's medial then there you go you know how to label the arteries in the forearm so from subclavian subclavian axillary brachial and splits into radial and ulnar okay so now we're going to move here through the descending aorta to get us down to the lower extremity so the descending aorta when it's in thoracic cavity is known as the thoracic aorta passes through the diaphragm becomes the abdominal aorta so right at your umbilicus the abdominal aorta splits and it becomes the common iliac left and right the common iliac then splits into the internal and external iliacs okay so it's done a similar thing to what you saw with the carotids so you have a common on left and right and then that splits into internal and external now the internal supplies this local region the inguinal region with oxygenated blood whereas the external iliac is the vessel that continues all the way down the rest of your lower extremity so it's the same vessel we're just going to be talking about different names based on the region that you're in okay so past this bifurcation it becomes the external iliac artery and then once you're in the femoral region it's now known as the femoral artery the artery then courses behind the knee where it's called the popliteal artery and then it sends a branch anteriorly where it's called the anterior tibial you can see there's also part of that artery that stays posterior and that's the posterior tibial so a lot of these arteries when you're looking at the upper and lower extremities they are named just based on the regions or the bones that they are associated with so because you've already learned that that should make this part a little bit easier for you so remember if you're looking at an artery blood is always going to be flowing away from the heart now as we mentioned the tunica media maintains pressure and also contracts and with the same rhythm that your heart is contracting at so this is what maintains our pulses so this is a way that we can peripherally you know someplace distal to the heart we can calculate somebody's heart rate so some of these pulse points here you can palpate on yourself if you just go up to your temple you have the superficial temporal arterial pulse down around your lower jaw you can feel the facial arterial pulse now a carotid arterial pulse this is the one that you would feel right underneath the ankle of the mandible and that's usually a pretty strong pulse and easy to find the brachial pulse which typically you'll locate this down around the cubital fossa if you're looking in anatomical position at yourself the anterior part of your elbow that's the cubital fossa so right in there just medial to the biceps tendon you can usually find the brachial pulse and that's important when you're taking somebody's blood pressure with a cuff and a stethoscope and then furthermore the brachial artery splits into the radial and ulnar now you can find the ulnar pulse it's a little harder but the radial artery you can find just by placing your second and third digits just at the distal anterior portion of the radius okay so sort of right in around here within the groin or even a little bit more inferior here you can feel the femoral pulse behind the knee the popliteal pulse is relatively prevalent but these are two very common pulse points that you will probably use if you're checking heart rate manually it's likely that the patients are going to be hooked up and you're going to be seeing their pulses and heart rates through those methods but it is a way that manually you can assess the patient say they're lying in bed and you can go down to their lower extremity here right around their ankle and find these two pulses so the posterior tibial where i want you to go is with your second and third digits again here from your one hand find your medial malleolus so that's that inner ankle bump okay find that and then i want you to go posterior off of that back and you should be between your achilles tendon and the medial malleolus so now moving your fingers around just slightly you should be able to locate a pulse there that one's usually the most easiest you can kind of if you're with a patient you just kind of wrap your hands around the ankle that way and feel the pulse back there now you can also check the dorsalis pedis which is on the dorsum of the foot right when you're laying down it's the part of the foot that's facing upwards and you can usually feel the pulse there as well so now with the venous system we're no longer looking at the left side of the heart right because we're talking about deoxygenated blood and if they're in the veins you know that the blood is going to be flowing back towards the heart right so in any of these vessels we're ultimately coming in a retrograde fashion in a way compared to the arteries okay so arteries were always from the heart away now we're looking at blood draining back towards the heart the two major blood vessels and we talked about these before when we looked at the heart are the superior vena cava and the inferior vena cava and what i want you to do right now is i want you to take your arms in anatomical position here and i want you to lift your arms up okay so that they're in line with your shoulders in this position any structures that are located above the heart are all going to be draining in through the superior vena cava and in that same position any structures located below the heart are all going to be draining back through the inferior vena cava okay so it's important to be in that position just so you can easily reference okay so upper extremities are coming into the through the top through the superior vena cava and then your head and your neck are all draining in through the superior vena cava as well now the right and left sides of your body are connected by the left and the right brachiocephalic veins so in the arterial system you only had a right brachiocephalic here you have left and the right so it's a mirror image in the venous system okay and then let's look here at the head and the the neck region so you have external and internal vessels but instead here they're known as the jugulars okay so the jugular veins are draining the head and your brain with deoxygenated blood to get that back to the heart okay so the external jugular is draining the outside of your skull and the internal jugular is draining the inside of your skull right which would be your brain both of those structures uh then draining down into the brachiocephalic which connects into the superior vena cava i'm going to be talking about the rest of the structures going in this direction towards the hands but remember blood is always flowing back towards the heart okay so the brachiocephalic vein is connected to the subclavian vein which then connects directly to the axillary so similar and then the axillary connects directly to the brachial but instead here you have two main brachial veins whereas we only had one brachial artery from the brachial veins it looks like it gets really complicated but just follow with me here you have a branch that goes to the ulnar vein and a branch that continues to the radial vein okay so that looks pretty similar right in terms of naming you've got subclavian axillary brachial ulnar radial okay so it looks a lot like what we just saw in the arterial system now the additions that we have here if you go back into that superman position where your arms are going to be up in the horizontal you can see this major vessel that runs down the entire lateral surface of the arm is known as the cephalic well when your arms are up in this position here cephalic is closest to the head okay so the lateral vessel is known as cephalic whereas this other lateral medial vein that runs along the entire medial surface this is known as the basilic and so the way you can remember this is in that position again okay with your arms up here the basilic is going to be running under the base of your arm in that position okay so that's a way that can help you remember which is which so cephalic is running on the lateral portion down the arm and forearm and the base silica is running down the medial portion of the arm and forearm so now let's take a look at all structures below the heart so they're all going to drain back through the inferior vena cava now the inferior vena cava in this case though runs all the way down to your umbilicus okay so the only vessel here through the thoracic and abdominal in terms of main venous structures is the inferior vena cava there's no divisions okay so at the umbilicus again you have another split and it splits into the common iliac left and right so then the common iliac splits into the internal iliac and external iliac the external continues as the femoral popliteal and then anterior posterior tibial there's also a fibular that runs along the fibula okay so a lot of similarities there's to the arterial system again the only other exception is along the entire medial aspect of the leg both lower and thigh you have a new vein known as the great saphenous vein this is the one that is most prone to creating varicosities okay so if you're going to have a varicose vein the most likely culprit is going to be this great saphenous along the medial aspect so remember blood in to say the great sappiness is going to drain all the way up medially and then empty into the external iliac common inferior vena cava back to the right atrium and you can use this to sort of trace the blood flow from anywhere but the most important for you to understand at this point is to be able to label the structures you're able to take blood from your patients there's three major blood vessels that you'll be looking at two of them we've already talked about so running along the medial aspect is the basilic okay running along the lateral is the cephalic the other one that's most commonly accessed is the median cubital that sort of connects base silicon it runs right across if you look at your anterior portion of your elbow in that cubital fossa you can actually visualize the medium vein typically with pulmonary circulation we're looking at the blood that is going to be flowing towards the lungs and then back to the heart from the lungs now why are we sending blood to the lungs in the first place well that's because we've just received all of that deoxygenated blood through the superior and the inferior vena cava in this right atrium the right atrium contracts and sends the blood through the tricuspid valve into the right ventricle the right ventricle contracts and sends the blood up through the pulmonary valve into the pulmonary trunk and that leads directly into the left and the right pulmonary arteries okay so you'll notice something to this point your arteries have been colored red which implies oxygenated blood but here we have pulmonary arteries are blue let's think about this blood is flowing away from the heart to get to the lungs why are we going to the lungs to pick up oxygen so this is the exception okay in the pulmonary circulatory system pulmonary arteries contain deoxygenated blood whereas the pulmonary veins contain oxygenated blood so the pulmonary artery's blood is flowing away so that's still true but in this case it's the blood flowing away from the heart towards the lungs picking up oxygen and coming back towards the heart through the pulmonary veins ending up emptying into the left atrium left atrium contracts moves blood through the mitral valve also known as the bicuspid into the left ventricle the left ventricle contracts sends that blood up through the aortic semilunar and from there it's sent to the aorta and now you know exactly where it's headed now another circuit part of our circulatory system is hepatic portal circulation so hepatic portal circulation we are looking at a single vein known as the hepatic portal vein and hepatic refers to liver and then it's literally a portal through which all of the venous blood that's being drained from all of your digestive organs is going to be fed through the hepatochordal vein and then it empties into the liver what's the main function of the liver it's going to take in all the nutrients you're absorbing it's going to take everything essentially from your digestive system it's going to put it in the liver and the liver's job is going to be to filter it to organize things to store anything that you're in excess of we can convert fats to glucose vice versa glucose to fat also the liver can detoxify that blood right from any medications you know acetaminophen's one that can have an impact on the liver if you take too much in a short period of time that's because all of this is ultimately getting absorbed and then sent back through the liver and it's the liver's job to filter it all once the liver has done its job then it sends all of that blood through the hepatic veins which then empty into the inferior vena cava and where's the inferior vena cava going back up towards the right atrium right where it's going to empty that blood back into the right atrium and it enters back into circulation that way so the hepatic portal circulation is essentially looking at this one vessel the hepatic portal vein that's taking all of the venous blood from your digestive organs and it's draining it into the liver so that the liver can filter it now as i mentioned before fetal circulation has a few structures that are unique to the fetus and that's because of the conditions in which they are developing in first i want you to think okay well what's different from a fetus than us in terms of our respiratory system they're not breathing okay so they don't need to have blood going out to the lungs and back to pick up oxygen because where are they getting their oxygen from the mother right from the placenta so just to make sure everybody's on the same page here we're looking here at the umbilicus of the fetus here you have the umbilical cord which is connected to the placenta okay this is on the fetal side and then here would be the maternal okay so the placenta really acts as a huge filter right oxygen is able to get into the fetus that way and then carbon dioxide that's used up is able to go back uh to the mother and then she can breathe that out herself okay so that's how the baby receives oxygenated blood straight through the placenta so another thing that the um fetus body is not doing is filtering blood right that's also done by the placenta so we have a couple of bypasses set up so that the fetus does not have blood passing through the liver and also so that it doesn't have to go out through the pulmonary circuit so let's take a look at those the two bypasses that we have to bypass the pulmonary circuit they are the ductus arteriosus which you can see right here and foramen ovale the foramen ovale is like a channel or a hole between your right and your left atria okay so let's start here if you have blood in the right side of the heart and us it's deoxygenated it then is sent out through the pulmonary arteries to pick up oxygen and comes back and sent throughout the body now when you're looking at a fetus the fetus does not pick up its oxygen from the lungs so instead of having the blood to have to travel through the pulmonary artery back through the pulmonary veins and through the left side out through the aorta there's this bypass in fetal circulatory system the ductus arteriosus which is connecting this pulmonary trunk or the pulmonary arteries directly to the aorta okay so this just speeds up and makes it the process more efficient in delivering that blood back into the placental side to pick up more oxygen okay so that's the ductus arteriosus then the foraminal valley think about it for us the right side of the heart is deoxygenated the left side of the heart is oxygenated if we had a past passageway through here we'd be mixing our deoxygenated with oxygenated blood and our heart would have to work a lot more to get more blood out because we wouldn't be delivering enough oxygen to the tissues now with a fetus again because they're not receiving oxygen from their lungs they're receiving it from the placenta we have the foramen ovale that acts as a bypass here from the right to the left side of the heart so instead from the right atrium the blood would pass through the left and then out through the aorta okay so those two the ductus arteriosus and the foramen ovale are two bypasses in fetal circulation that allow for the blood to move through and bypass the pulmonary circuit now the last bypass we're going to talk about is this structure here known as the ductus venosus so instead of the blood being sent back through the liver through the hepatic portal circulation the fetus's liver is not fully developed and it's not filtering anything anyway because everything that it receives is from the mother and is filtered there so instead of having the blood flow through the liver we have the ductus vinosus which allows us to bypass that liver and then send the blood through the rest of the circulatory pathway okay so here through the inferior vena cava back into the right atrium and throat circulation so those three main bypasses are there because the placenta is doing our job that both the liver and the lungs don't need to do in the fetus now what can happen with the foramen ovale remember that opening between right and left atrium it can stay open after the baby is born now typically that first breath when they start crying when they're born that first breath bringing air pressure into those lungs is enough to actually seal off a lot of these openings but what can happen is that they can remain open in some cases and it's known as a patent foraminal valley so if it's severe enough you're going to be seeing low oxygen levels right in that infant and if it was a big enough opening then they could um surgically repair it now if it you know wasn't causing any any big problems then it may be something that they find later on in life but it depends really on how big the opening is in determining whether or not they need to surgically intervene or not now all of our vessels contain some form of pressure right it's the the force that's being exerted from the fluid which is our blood to the the walls of the vessel that it's in now let me take a look here in the aorta which comes right off the left ventricle the major arteries and even smaller arteries you notice here how you relatively for the most part based into large arteries you have blood pressure being maintained relatively consistently that is because of the tunica media maintaining uh that pressure throughout most of our arterial system where you really see a drop-off here is in these off-ramps right whenever the blood needs to travel into the tissues it passes through the arteriole which then goes into the capillary and this is where you see a huge drop in blood pressure finally the venous system is relatively low in blood pressure and when you have blood emptying back into the right atrium through the inferior and superior vena cava that blood is just essentially pulling into those chambers now blood pressure you know ideal measurement 120 over 80 that's looking at systolic pressure over diastolic so i want to define those terms for you systole is a state of heart contraction right we talked about that two lectures ago and diastole is when the heart is relaxed okay so systolic pressure is the pressure that you're measuring when the heart is in a contracted state and the diastolic pressure is the pressure that still exists when the heart is relaxed okay so that's why the systolic is always higher than diastolic because you're always going to have a higher pressure when the heart is contracting versus when it's relaxing now some of the factors that can influence blood pressure directly are the actual strength of contraction so that um your stroke volume which we looked at right your stroke volume is the amount of blood ejected by the heart in one contraction well if you have a stronger contraction you're going to be able to force more blood out of the heart now if you increase your heart rate you're also going to be increasing your blood pressure we're going to take a look at that relationship a little bit later and how our body maintains that blood volume is looking specifically at the water content there so if you're retaining more water whether it's a hormonal influence or whether you have you know high salt intake whatever the cause may be if you're retaining more water in your blood that's going to lead to higher blood pressure looking at the ability for a fluid to flow so if you think of something like honey if you were to pour that out and then versus pouring out water honey would be much more viscous so it has a higher viscosity whereas water has a much lower viscosity so in this case here the more blood cells you have so if you have a higher hematocrit like in somebody with polycythemia their blood would be much more viscous so it would be slower to flow which is going to cause a bit of backup and that's going to increase pressure as well okay so all of those factors cause direct increases or decreases on blood pressure depending on what's happening with them now peripheral resistance is is another one so if you increase resistance which you can see here by vasoconstricting you're going to be increasing the pressure whereas if you decrease resistance by vasodilating right opening up that vessel you're going to be decreasing pressure so that tunica media is able to vasoconstrict or vasodilate depending on your body's current blood pressure and the needs that you have to be able to effectively deliver that blood to your tissues now one of the ways neurologically through which we can help to regulate our blood pressure is by changing our heart rate so we have these structures known as baroreceptors that are located in the the aorta and the carotid arteries now do you remember that's where the highest pressure is going to be in the body so it's a good place to have pressure receptors now think barometer right that's how we measure pressure outside so a baroreceptor is measuring pressure specifically blood pressure within the heart um so we have these barrel receptors they're going to detect changes in blood pressure if your blood pressure goes up there are going to be signals sent back to your brain stem specifically the medulla which are then going to cause your heart rate to slow down slightly through the parasympathetic system so if your blood pressure is going up slightly parasympathetic system is going to cause heart rate to slow down which will ultimately cause your blood pressure to come down vice versa if your blood pressure has dropped then those baroreceptors can send a signal that can stimulate the sympathetic nervous system and this causes your heart rate to speed up so if your blood pressure is increasing we can lower our heart rate and if our blood pressure is decreasing we can increase our heart rate okay so the heart as you know receives both the parasympathetic and sympathetic depending on what the needs are okay so parasympathetic would be to rest and digest right so slow it down whereas sympathetic would be to accelerate or speed up the heart rate okay so it's a reciprocal relationship your blood pressure is going up we're going to decrease our heart rate vice versa blood pressure's going down you're going to increase your heart rate now also slower but more sustained mechanisms are hormonal feedback mechanisms now we're going to talk about these when we look at the urinary system next semester so we won't go into them too much right now but the rast system is a cascade of different hormones that are all involved in ultimately increasing your blood pressure so if your blood pressure is dropping your body has the ability to secrete angiotensinogen which is an active form and then it activates into angiotensin which angiotensin then works on the blood vessels to cause them to vasoconstrict right so if you reduce the lumen you're increasing resistance you're going to increase your pressure and part of that feedback is that that signals then the adrenal gland to secrete aldosterone another hormone which then causes us to increase the amount of fluid that we're retaining so think about that if you retain more fluid your blood volume goes up so your blood pressure would go up okay and then lastly the antidiuretic hormone is one released from our pituitary gland and that can also cause us to retain more water and increase blood volume okay so all of these feedback mechanisms here if you just want like a quick sort of what what are they all doing they're all going to be helping to increase blood pressure in the event that you have uh lower or a drop in blood pressure now blood pressure over 140 over 90 is classified as hypertensive primary essential hypertension is idiopathic which means unknown origin okay or just no single cause causing it secondary hypertension is due to some other disease one of the most common ones is kidney disease right if your kidneys aren't able to effectively manage your water balance then you would be retaining more um if they can't get rid of enough of the you know sodium that's in your blood you're going to keep more water in where that would cause you to increase blood volume and then would increase your blood pressure you