Types of Capillaries (Nursing)

by Rhonda Lawes, PhD, RN

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    00:00 Let's try a question. What do you think? Does the liver have capillaries or sinusoids? Alright, I'll admit it. That's a trick question. Let me tell you why. Organs like the liver, spleen, and bone marrow they have these blood vessel structures called sinusoids instead of what you traditionally think of as capillaries. Let me explain. So, what is the difference between sinusoids and other types of capillaries? Well, you actually have 3 types of capillaries in your body.

    00:31 These are the main types. Now, remember capillaries, it's the area where veins and arteries connect. They're usually pretty fragile. Why? Right, because they're exchanging stuff in between the capillaries and the veins. So, they're pretty fragile. Now, you have 3 major types that we're going to talk about. Starting on the left you see continuous, in the middle is fenestrated, and on the end is, there you have it, sinusoids. That's why it was a little bit of a trick question because well it's not what we usually think about when we think about capillaries in the traditional manner. They're really important in those special organs. Now, I'm going to walk you through some specific differences between all these, but I wanted you to see all three of them at the same time. There're about 3 primary types of capillaries that you have in your body. Now, let's look briefly at these before we go on to the next slides. You see the kind of light blue there. That's the basement membrane. Now, you have basement membranes all throughout your body. It's a very thin layer, and it's right on top of the endothelial layer. So, each one of these 3 has basement membrane, but they look different. Continuous and fenestrated have similar basement membranes, but when you look at the sinusoid, that's radically different. Look at the endothelial layer in the continuous and the fenestrated. Well, they're definitely different, right. The continuous is complete and whole, the fenestrated has the holes all in it, and take a look at the sinusoid. Yeah, that is a big difference. So let's break these down a little more. It'll help you understand where in your body these 3 primary types of capillaries live. Now, the continuous ones are abundant in your skin, your muscles, your lungs, and even in your CNS. Now, continuous capillaries of the brain have a unique job.

    02:29 They form the blood-brain barrier. Remember the blood-brain barrier has super tight junctions with no spaces in between because it keeps the CNS protected. It keeps out things that we don't want to get into the brain. Now, that could become problematic when somebody has an infection in their brain like meningitis or encephalitis because we have a hard time getting most antibiotics over that blood-brain barrier, but that's where your continuous capillaries are located. They're located in the skin, muscles, lungs, and the central nervous system. Look at that basement membrane, it's complete and intact. Look at that endothelial layer, it's also complete and intact. Now, so look at the next 1 example. We look at the fenestrated, and we're going to compare the fenestrated to the discontinuous. Now the fenestrated contains really small pores just like little holes. So, small molecules like oxygen and carbon dioxide and nutrients and proteins and waste can be exchanged. That's awesome, right, because we need that to happen in our body so we can live. Now fenestrated is found in the intestines, the kidneys, and in organs and glands of the endocrine system. So, continuous, no holes, everything is intact. Fenestrated has little tiny holes, but that basement membrane layer is still intact. Now, we're going to look at the sinusoids which is the type of capillary in the liver. Now, these have larger pores. So look at the difference between fenestrated and discontinuous sinusoidal endothelium. You've got large pores that allow blood cells and larger proteins to pass between the vessels. Okay, so we find the discontinuous ones in the sinusoids of the liver, the spleen, and the bone marrow. So, now you got it. Now, you know what sinusoids are and how they are different than other types of capillaries and why bigger things can get through.

    04:33 Remember with the continuous, tight and tiny, that's in several areas in your body including your blood-brain barrier. Stuff is locked down pretty tight. Then you look at the fenestrated.

    04:44 Smaller molecules can fit through like some CO2 and O2. That's really important. And finally, you have the sinusoid which is what we're talking about within the liver, and that's why bigger objects can pass through.

    About the Lecture

    The lecture Types of Capillaries (Nursing) by Rhonda Lawes, PhD, RN is from the course Liver Functions and Dysfunctions (Nursing).

    Included Quiz Questions

    1. They are enclosed by tight junctions
    2. They have intercellular clefts
    3. Their basement membrane is not intact
    4. They have small pores
    1. They have a discontinuous endothelium
    2. They have an incomplete basement membrane
    3. They have a complete endothelium
    4. They have small pores
    5. They have no intercellular clefts
    1. Skin
    2. Muscles
    3. Lungs
    4. Central nervous system
    5. Bones

    Author of lecture Types of Capillaries (Nursing)

     Rhonda Lawes, PhD, RN

    Rhonda Lawes, PhD, RN

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