In today's video, you're going to get an overview of the types of connective tissue in the body and learn why those types of tissues show up in the anatomy that they do. If you're new here, welcome! My name is Patrick and on this channel we learn anatomy.
On the chance that you've already watched my histology basics video, the first minute or two of this video is going to sound familiar. Obviously, I'd recommend watching this one anyway for a refresher, but if you want to skip to the new information, you can click this time on the screen. So for the rest of you, Let's get into this lesson.
Connective tissue is one of the four types of tissue we have in our bodies. The others, muscle, nervous, and epithelial, all serve unique purposes and have pretty clear-cut roles in the body. Like muscles produce force, nervous tissue transmit signals, and epithelial tissues line organs and secrete mucus.
Connective tissue is literally everything else. Ligaments and fascia are some of the obvious types of connective tissue, but so is bone, and blood, and lymph. Like, yes, we have liquid connective tissue, that is a real thing. And in general, we can split connective tissue into three categories.
Loose proper, dense proper, and specialized. We're gonna build on this flowchart over the course of the video, and if you want it as a study guide, there's a copy linked down in the doobly-doo. So, as expected, the tissue gets its name depending on what it's built from.
And each proper connective tissue has some degree of the following three components. Ground substance, structural fibers, and living cells. Ground substance is kind of a liquidy, intermediary substance for dissolved particles to float around in.
Stuff like electrolytes or enzymes can float from a capillary through ground substance to make its way across tissues to a cell. The fibers in connective tissue give the tissue some kind of structure and mechanical properties. Again, think of them like building materials.
You could choose the dense, thick collagen fibers if you want resistance to tensile force, or thin reticular fibers which usually get laid down in a meshwork style. creating more spaces between fibers. Then there's elastin, which is stretchier and more pliable.
There's even variation within those fibers for specific purposes. Our bodies make 28 types of collagen, again, all with different purposes. Like, type 1 collagen is more appropriate for ligaments, while type 2 collagen is more common between our joints.
And while a long strand of collagen protein isn't alive, there is a living part of connective tissue, cells. The most common of which are fibroblasts, cells that live to supply the tissue around it with those structural fibers, hence fibroblasts. That's not all though, there are also wandering immune cells like the occasional macrophage that goes looking around for bad guys.
And as you could probably infer, Loose connective tissue is going to be heavier on the ground substance and lighter on the fibers, while dense connective tissue is the opposite. It has a higher density of fibers and less ground substance. We'll come back to specialized connective tissue, but for now, let's address the elephant in the room. What's the point of loose connective tissue? I mean, if the point of connective tissue is to connect, then shouldn't a material with a high fiber content and higher tensile strength just be a better option like always?
Asked an 18 year old me in front of the entire class proving that I didn't do the assigned reading when I was a freshman in college? So just like in our house metaphor, there's a time and place to use beefier materials. I want you to think the same thing about connective tissue. There's a time and place for each material. You'll use dense connective tissue proper for anatomy that needs to resist a straightforward, strong tensile force.
Best example is probably ligaments, the regular dense connective tissue that attaches bone to bone. They exist to prevent any type of excessive motion in one particular direction. Like your anterior talofibular ligament keeps you from too much ankle inversion, so a strong bundle of dense connective tissue ties down your talus to your fibula to try to restrict that motion.
And it's not just the density of fibers that gives ligaments their strength, but also their arrangement. Ligaments'fibers run in parallel directions, unlike irregular dense connective tissue, which might not have the same single direction tensile strength. but it's good at resisting multi-directional force. That's what makes it perfect for the capsule around your shoulder. The glenohumeral joint needs a large range of motion, so having a bunch of spindly, dense ligaments around it wouldn't be a great idea.
It would look like a big fishing net. But you still need to keep the ball of the humeral head in the shallow glenoid fossa, or socket. So you do need dense tissue, which is perfect, irregular for the multi-directionality, and dense for the strength.
This type of connective tissue also makes up 80% of connective tissue in our dermis, the middle layer of skin. This will be a separate video, but the skin as an organ does so many complicated and intricate tasks. It's got hair follicles and capillaries and nerves and oil glands all around it to do stuff like thermoregulation and sensation So to give it a little extra structural integrity we have irregular dense connective tissue right in the middle of the dermis But you'll notice above that is a less dense layer called the papillary layer And below that in the hypodermis is adipose tissue, which is still connective tissue again. This is a perfect A perfect demonstration of form matching function. Loose connective tissue is soft and squishy.
So it isn't as strong when it's pulled apart, but it offers more of like a mattress quality. The most dominant kind is areolar tissue, referencing all the space, the open air of loose tissue. Our bodies use this tissue in the papillary layer of the skin for exactly that reason.
We can fill all kinds of stuff in that layer. And that's what makes loose connective tissue so unique is that this shifts towards more ground substance and less structural fibers. allows more dissolved stuff, or immune cells like macrophages and mast cells.
Just like areolar tissue, reticular tissue is pretty spaced out and has predominantly reticular fibers to give it support. I know, anatomists are terrible at naming things. To make things worse, that layer of dense irregular tissue in the dermis is called the reticular layer, despite not being reticular tissue. Finally, that adipose tissue in the hypodermis is loose connective tissue.
I know it doesn't seem like it's connecting anything to anything, but when you imagine loose connective tissue more as support than connection, it becomes more clear. And I hesitated to call adipose tissue loose connective tissue because during my fact check for this script, I found sources that said fat was loose connective tissue while some said it was firmly a specialized connective tissue, in the same category as blood, lymph, cartilage, and bone, our final category in the flowchart. All of these tissue types technically count as connective tissue. And like, Cartilage, which you'd think should be dense connective tissue, is actually specialized.
But that's a good question to jump off on though. What's so special about it? Well, allow me to introduce you to chondrocytes, cells that are unique to cartilage. Like the fibroblasts and other connective tissue, chondrocytes make extracellular matrix, but they make it differently.
And when we're looking at these specialized connective tissues, it's those unique cells, like chondrocytes, that make them special. Like, our bones are mostly collagen that have been hardened with calcium. The structure of bone really isn't that special.
It's still the same stuff as in other connective tissue. But osteocytes, or mature bone cells, are unique to bone. Erythrocytes, or red blood cells, or red blood corpuscles if you want to be that guy, are unique to blood, and so on.
But all of those cells started from the same layer as an embryo, and get replenished from the same stem cells as an adult. So, Really, these seemingly unrelated tissues have a lot more in common than we first thought, and they all fall under the connective tissue umbrella. One other thing that I find fascinating is how blood, a connective tissue, is made inside of bones, another connective tissue.
I have a video that you can check out right here if you're interested in the physiology of bone, not memorizing a skeleton, but like some good physiology. Otherwise check out these playlists to keep on learning. Subscribe right here hit the bell so you get notified when I post a new video have fun be good. Thanks for watching