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06.06 Blood Vessels

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  1. General structure
    1. Tunica externa (adventitia)
      1. External layer
      2. WFCT
    2. Tunica media
      1. Middle layer
      2. Smooth muscle
    3. Tunica interna (intima)
      1. Internal layer
      2. Endothelium
        1. Simple squamous epithelium

Nursing Points


  1. Types
    1. Arteries
      1. Carry oxygenated blood away from heart to body
      2. Under high pressure → not compressible
      3. Elastic arteries
        1. Larger arteries
        2. Closer to the heart → higher pressure
        3. Examples
          1. Aorta, brachiocephalic artery, common carotid arteries, subclavian arteries, common iliac arteries
      4. Muscular arteries
        1. Smaller, farther away, but still palpable pulsation/pressure
        2. Examples
          1. Internal and external carotid arteries, axillary arteries, brachial arteries, radial and ulnar arteries, internal and external iliac arteries, femoral and deep femoral arteries
    2. Arterioles
      1. Smaller arteries
      2. Diameter reduced
        1. Mostly the tunica media is reduced
          1. Smooth muscle reduced to rings instead of continuous
    3. Capillaries
      1. Connect arterioles to venules
      2. Single cell layer thick
        1. Endothelium only
    4. Venules
      1. Same size as arterioles
      2. Less smooth muscle
    5. Veins
      1. Same size as arteries
      2. Veins are compressible due to far less smooth muscle present
  2. Functions
    1. Arteries
      1. Carry blood away from heart
      2. Most carry oxygenated blood
        1. Except pulmonary artery (de-ox)
      3. Elastic arteries
        1. Initiate and conduct the pulse wave
          1. Left Ventricle contracts → pressure increases in aorta
          2. Left Ventricle relaxes → pressure decreases in aorta
        2. Originates in aorta
        3. Pulse = HR
      4. Muscular arteries
        1. Conduct blood through body regions
    2. Arterioles
      1. Major controller of BP
        1. Vasomotor tone
          1. Constant diameter
          2. Constant pressure
        2. Vasodilation
          1. Diameter increases
          2. Pressure decreases
        3. Vasoconstriction
          1. Diameter decreases
          2. Pressure increases
    3. Capillaries
      1. Exchange vessels between blood and tissue fluid
        1. Nutrients
        2. Wastes
        3. Gases (oxygen and carbon dioxide)
    4. Venules and veins
      1. Participate in returning blood to heart
    5. Largest veins (arms and legs)
      1. Contain internal valves
        1. BP in veins is lower than arteries
        2. Valves prevent backflow in venous system
      2. Muscular pump
        1. Skeletal muscle contractions in arms and legs
        2. To keep blood in the veins moving to heart
        3. Under relatively low pressure

Betts, J.G., et al. (2017). _Anatomy and physiology_. Houston, TX: OpenStax, Rice University. Retrieved from

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Video Transcript

We’re gonna talk about blood vessels, really the structure and function of blood vessels, and I’m actually really excited about this lesson because once you understand this, it’s gonna help you greatly in your future career. So let’s talk the general structure first of all. Blood vessels are made up of three different layers. If we look here, this is kind of the cross-section of a blood vessel. You can see the three layers. You have the tunica externa, tunica media, and tunica intima or tunica interna. So you get the tunica externa, external, the outer layer and it’s really made of white fibrous connective tissue or WFCT. The tunica media is our middle layer, and it’s smooth muscle. Now keep that in mind, we’re gonna talk about kind of the differences in some of our blood vessels with this tunica media and this smooth muscle a little bit later on. Then our internal layer is the tunica interna or intima. Internal, interna, and that’s simple squamous epithelium. So I want to draw you a quick picture to help this make sense before we roll on. If you think about having your heart right here in the middle, coming out of your heart you have arteries. Those arteries turn into arterials, which then turn into capillaries. Those capillaries then turn into venules, those venules turn into veins, and then blood is brought back to the heart. So coming out of the heart is artery, that turns into arterial, that turns into venule, that turns into vein. And that cycle keeps the blood moving throughout the body. Now we’re going to go into each type of blood vessel really quick to help you understand a little bit more about how they work. Arteries are large blood vessels that carry blood away from the heart. They’re elastic, with our larger arteries being closer to the heart. Things like our aorta, our common carotid arteries, subclavian arteries, common iliac arteries, again are going to be much closer to the heart. Then we have these, you know, muscular arteries that are further away from the heart, but pulsation is still palpable. If you think about your axillary arteries, your brachial arteries, your radial and ulnar arteries, these are the ones that we’re feeling these pulses on as we assess a patient. Then your arterials. Your arterials are really much smaller arteries, they have a reduced diameter, and they have this smaller tunica media, which is our muscular layer. So that’s really where our arterials are and what they’re made of. Then, if we look at our capillaries. Your capillaries connect your arterials to your venules and they’re very simple single-layer endothelium cells. And we’re going to talk about why that’s important here in just a minute. But remember that your capillary is really the connection between your arterial and your venule. Now let’s talk about the veins and the venules. Your venules are the same size as arterials, but they contain less smooth muscle. Your veins are really the same size as your arteries, but they’re much more compressible and their job is to carry deoxygenated blood back to the heart. All right. That’s a quick overview. Now let’s talk about the functions of these different vessels. Again, your arteries, their main function is to carry oxygenated blood away from the heart, with the exception being pulmonary arteries. These are elastic and they initiate and conduct the pulse wave. So think about it like this: in your left ventricle when it contracts, you’re then going to see an increased aortic pressure. During ventricular relaxation you’re going to see a decreased aortic pressure. And you really think about the pulse being this heart rate. As you feel this pulse, it’s really a heart rate, and that’s that contraction, that increased pressure, happening in these arteries. They’re very muscular and they carry blood all throughout the body. Then your arterials. Your arterials are really the main major factor, the main controller of blood pressure. With vasodilation, what you’re going to see is an increased diameter and a decrease in pressure. With vasoconstriction, you’re gonna see a decrease in diameter and an increase in pressure. Think about it kind of like a hose. If you have a hose and you have fluid going through it, if we double the size of that hose or double the diameter of that hose, increase that diameter, we’re gonna see pressure go down if we don’t have an increase in volume. If we cut the size of that diameter in half but have the same amount of liquid going through, the same amount of fluid going through, or decrease that diameter, that pressure’s gonna go up. So it’s really important to keep that in mind. That’s gonna come back into play so much during your career with this vasodilation and vasoconstriction and then how we try to manipulate that with fluids or with medications. All right. What is the function of capillaries? When you think capillary, I really want you to think of exchange. Okay, capillaries are exchange vessels between blood and tissue fluid. We’re exchanging things like nutrients, gases, and wastes. So that’s what’s really happening between those arterials and those venules. When we get into that middle messy layer of the capillaries, all this exchange starts to happen. Okay? Now we talk about venules and veins. Their job is to get blood back to the heart. Our largest veins actually contain these little valves. The purpose of those valves is to prevent backflow. These don’t have that strength and that power that those arteries have, so to prevent that backflow and to get all that blood pushed, you know, from our legs all the way back up to our heart, we need to make sure that blood doesn’t start going backwards. And that is the purpose of these valves. We also have what’s called a muscular pump. Surrounding these veins is skeletal muscle. Now as that skeletal muscle contracts, it’s then going to squeeze on these veins and that’s also going to further push that blood, propel that blood, back up to the heart. And then we’ve got these valves to help prevent it going backwards. So let’s review really quickly some of the key points about blood vessels. Our arteries and our arterials, their job is to take oxygenated blood away from the heart and get it to the tissues. We gotta get that oxygen over to our tissues, and that’s the job of these arteries or arterials. One way I remember that is: artery starts with A, away starts with A, so we’re carrying blood away from the heart. Then we have these capillaries. Between our arterials and our venules, we have these capillaries. Their job is to exchange fluids, gases, and wastes. That’s going to lead into our venules and our veins. Their job is to get this blood back to the heart. Hopefully our blood’s done its job, now we gotta get it back to the heart to start the whole process over again. Arteries have a lot of pressure; they’re very elastic, and arterials are the major regulator in blood pressure. Keep that in mind as you move on. It’s going to help you a ton. Veins are under much lower pressure and they require valves and skeletal muscle to help get this blood moving in the right direction and not going backwards. So we have artery to arterial to capillary to venule to vein and our heart is sitting right in the middle of all that. And we want to keep our blood moving this direction. As long as that’s happening we’re exchanging as we need to, we’re getting everything where it needs to go, and our patient’s going to be happy and healthy. You guys, I hope that helps you understand blood vessels a little bit. It’s truly a fascinating system and we get into this a lot more in future courses, but I want you guys to go out and be your best self today. Happy nursing!