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  • Let's say you want to get a piercing. Under your own free will, you're choosing for

  • someone to take a needle, quickly poke a hole in your body, which you can then adorn with

  • all kinds of cool decorations. People get piercings for all kinds of cultural and aesthetic

  • reasons, but a few spots on the body get pierced more than others including different spots

  • on the ear, nose, and belly button. Here in the US, the most common visible piercing is

  • through the earlobe, but it's fairly common to see a piercing a few centimeters higher

  • on the earThis is a structure called the helix, and it's what people are talking

  • about if they want to pierce their cartilage. And while the lobe and helix are near each

  • other, they behave differently than each other. Like, there's a reason you see the larger

  • gauges in earlobes and not in cartilage piercings. That has to do with the entire nature of cartilage

  • and the role it plays in our bodies. This type of tissue is part of the bigger type

  • of connective tissue, one of our four tissue types, the others being nervous, muscle, and

  • epithelial tissues. And as we'll see, connective tissue encompasses a lot of different cell

  • types, from the cartilage in your ears and nose to the liquid blood in your veins. In

  • today's episode, we'll talk about the role of connective tissue in our body and

  • see how researchers are tackling different injuries and surgeries with their deeper understanding

  • of this particular anatomy.

  • When you think of connective tissue, you probably don't

  • think of anything exciting. It's just kinda there, holding stuff together, right? I mean,

  • it's not contractile like muscle and it doesn't send electrical signals like nervous

  • tissue, so what is it actually doing? Well, aside from making sure your body doesn't

  • fall apart, a lot. Connective tissue is probably the hardest tissue type to define in a concise

  • way because it includes so many different types of cells including the ones in bones,

  • the cushioning between your jointseven your red blood cells are considered connective

  • tissue. It can be liquid like blood and lymph, or proper connective tissue like ligaments.

  • But there are a few features that most connective tissue will have in common, so let's break

  • them down. All connective tissue is going to start with the extracellular matrix, a

  • collection of fluid and structural fibers. How those things are arranged and organized

  • then tells us more about the tissue. This matrix can have a lot of structure to it and

  • make a firm, dense tissue, or very few fibers and be looser and more cushioning. This lets

  • us sort connective tissue into two big groups. Like we have loose connective tissue that

  • make up the more pliable structures that hold organs in place. And we also have dense connective

  • tissue that makes up some of the extra thick structures in our body like tendons and ligamentsThat

  • makes sense, ligaments connect bones to bone and tendons connect bones to muscles. Between

  • those two slides for instance, you can probably guess which one is dense and which one is

  • loose based on the pictures aloneThis one is dense while this one is loose. If you got

  • it right, good job, ten Seeker bucks for you. By the way, those Seeker bucks have no monetary

  • value and can buy you absolutely nothing. As the name implies,

  • that dense connective tissue just has more fibers in it compared to the loose connective tissue.

  • But those fibers are where some of the interesting properties come in. A lot of those fibers

  • are made from collagen, a strong protein that gives structure and support to tissues. Collagen

  • is the most common protein in our body and we have twenty eight versions of it, each

  • with slightly different properties. Some of those collagen proteins are so durable that

  • they can resist breaking down for tens of millions of years. In fact, back in the early

  • 2000's, scientists found preserved collagen in a T rex fossil from almost seventy million

  • years ago. Collagen might also be the casing for your sausage or hot dogs, but honestly,

  • the sausage manufacturing process is a nebulous black box of mystery, so who knows what you're

  • actually getting. Other than those tough collagen fibers, the matrix can be built with thinner,

  • crosslinking fibers called reticular fibers, as well as elastic fibers that can give some

  • stretchiness to your tissues. That elasticity is especially useful in places like the lungs,

  • bladder, and major blood vessels like the aorta. Now, if you look back at the loose

  • connective tissue picture, you'll notice what looks like a lot of empty space. That's

  • ground substance, a gelatinous material that's mostly water with a few dissolved proteinsIt

  • acts kind of like a glue for the fibers, and gives the cells and capillaries a way to exchange

  • nutrients and chemicals. All your connective tissue will have those three things: fibers,

  • ground substance, and the actual living part, cellsLike adipose tissue, or fat, is a

  • connective tissue. It has plenty of structural fibers, but its cells, or adipocytes, store

  • lipids for energy. Still counts as a specialized connective tissue. Now, I've been spending

  • so much time at the cellular level because once we see how all those cells, fibers and

  • ground substance come together, the tissues themselves are less uniform. Like bone for

  • example. It may be more rigid than what you typically picture as connective tissue, but

  • it has structural fibers like collagen, some ground substance, and all kinds of different

  • cells like osteocytesEven our fluid connective tissue like lymph and blood have a liquid

  • matrix and cells, just like typical connective tissue. They just don't have supporting

  • fibers. We have episodes dedicated to both lymph and blood by the way, so make sure to

  • check those out if you'd like a refresher. Now, we opened the episode talking about cartilage,

  • which is only one of those connective tissue types. More specifically, it's a type of

  • supportive connective tissue. And that type of cartilage in the ear that we mentioned

  • isn't necessarily representative of the rest of the body's cartilage. Again, it

  • seems like this stuff is simple but there are so many variations that all do unique

  • thingsFor instance, you might not notice your hyaline cartilage now, but you will if

  • you develop arthritis. This is the most common type of cartilage in our body. It's thin,

  • glassy looking, and structurally weaker than the other types of cartilageYou have a

  • version of this coating the ends of certain bones called articular cartilage, creating

  • a smooth surface so your joints can bend around with less friction. When that smooth surface

  • breaks down over time, that joint is more likely to develop osteoarthritisIt might

  • seem weird that hyaline cartilage is so common, considering that the cartilage we're used

  • to seeing superficially is very different. We're more used to elastic cartilage which

  • includes tissue in the ear and tip of the nose, but you also have some around your tracheaAnd

  • you guessed it, this stuff is more elastic than the other types. No matter how much you

  • try to deform or bend your nose cartilage, it always springs back to center. When people

  • break their nose, they're breaking the nasal bone which only goes about a third of the

  • way down your whole nose. The nasal cartilage just goes along for the rideThere's also

  • a less elastic, but more supportive fibrous cartilageIf you were to dissect a human

  • spine, you'd find thick fibrous discs between each vertebrae. There is some gelatinous goop

  • within those disc too but the outer layer is fibrousAnd if you looked inside your

  • knees you'd find a curved meniscus sitting on top of the tibia. Both of these pieces

  • of cartilage provide cushioning to bony structures and have lots of collagen fibers in them.

  • Now, that meniscus can present some problems. A meniscus tear is a fairly common orthopedic

  • injuryUnfortunately, the meniscus can't repair itself very well, so doctors will usually

  • elect for surgery if the tear is bad enough. Depending on the exact location and severity

  • of the tear, surgeons might stitch it back together or just take the whole meniscus outBut

  • those surgeries can have all kinds of complications like an increased risk of arthritis or a build

  • up of thick, fibrous tissue inside the knee. In the past few years, researchers have tried

  • using stem cell injections as a new treatment optionUnfortunately, they've run into

  • some challenges with delivering the right kind of stem cells to the injured spotSo

  • back in 2017, researchers at the University of Pennsylvania came up with a creative workaround.

  • They made a microscopic scaffold — a patch of matrix without cells in it, and loaded

  • it with two special chemicals. One was an enzyme to loosen the dense matrix, and the

  • other was a growth factor that attracted stem cells to the location. They tried out their

  • treatment on cow meniscus, and it worked as expected. The enzyme and growth factor combo

  • allowed the meniscus to start its repair process. Now, they still have to test this treatment

  • in large animals before beginning human trials, but it's an interesting start.

  • Studying connective tissue is a great reminder for me that even when anatomy seems straightforward,

  • it has the ability to surprise you with its depth and complexity. Man! I love this stuff.

  • Thanks for watching this episode of Seeker Human. I'm Patrick Kelly.

Let's say you want to get a piercing. Under your own free will, you're choosing for

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