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  • Flo Hyman had always been a tall girl.

  • I mean... really tall.

  • By her 12th birthday, she was already six feet, and by 17 she’d topped out at just over 6’5’’.

  • Initially self-conscious about her stature, she learned to use it to her advantage when

  • she started playing volleyball.

  • She attended the University of Houston as the school’s first female scholarship athlete,

  • and at the age of 21, she was competing in World Championships. Nine years later she

  • made it to the 1984 Olympics and helped her team win the silver medal.

  • After the Olympics, Hyman moved to Japan where she gained fame playing professional volleyball.

  • But all of that ended in 1986 when out of nowhere, she collapsed and died during a game.

  • She was 31 years old.

  • Hyman’s initial cause of death was thought to be a heart attack, but an autopsy revealed

  • that she died from a tear in her aorta, caused by an undiagnosed condition known as Marfan Syndrome.

  • Marfan Syndrome is a genetic disorder of the connective tissue. People suffering from it

  • have a defect in their connective tissue that substantially weakens it over time.

  • And youve got connective tissue pretty much everywhere in your body, so it can cause big problems.

  • Outwardly, those with Marfan’s tend to to be especially tall and thin, like Flo Hyman,

  • with loose, flexible joints and noticeably longer limbs and fingers.

  • Those long fingers and bendy joints have actually helped some athletes and musicians do things

  • that the rest of us can’t -- famous blues guitarist Robert Johnson, piano virtuoso Sergei Rachmaninov,

  • and Italian violinist Niccolo Paganini are all believed to have had Marfan Syndrome.

  • But these abilities come at a great cost -- as people with Marfan’s get older, their weakening

  • tissue can cause serious problems in the joints, eyes, lungs, and heart.

  • The fact that a single genetic mutation can affect your bones, cartilage, tendons, blood

  • vessel walls, and more, shows that all of those structures are closely related, no matter

  • how different they may seem.

  • Weve covered the basic properties of nervous, muscle, and epithelial tissue, but we haven’t

  • gotten to the most abundant and diverse of the four tissue types -- our connective tissue.

  • This is the stuff that keeps you looking young, makes up your skeleton, and delivers oxygen

  • and nutrients throughout your body. It’s what holds you together, in more ways than one.

  • And if something goes wrong with it, youre in for some havoc.

  • And that means were gonna be talkinabout Jello today.

  • Uhwell get to that in a minute.

  • The springiness here? That’s connective tissue. So is the structure in here, and the

  • stuff inside here, and the tendons popping out here

  • Connective tissue is pretty much everywhere in your body, although how much of it shows

  • up where, varies from organ to organ. For instance, your skin is mostly connective tissue,

  • while your brain has very little, since it’s almost all nervous tissue.

  • Youve got four main classes of connective tissue -- proper, or the kind you’d find

  • in your ligaments and supporting your skin, along with cartilage, bone, and blood.

  • Whaaaa?

  • Sounds a little weird, but your bones and your blood are just types of connective tissue!

  • So, despite the name, your connective tissues do way more than just connect your muscles to your bones.

  • Your fat -- which is a type of proper connective tissue -- provides insulation and fuel storage

  • -- whether you like it or not -- but it also serves structural purposes, like holding your

  • kidneys in place, and keeping your eyeballs from popping out of your skull.

  • Your bones, tendons, and cartilage bind, support, and protect your organs and give you a skeleton

  • so that you can move with a purpose, instead of blobbing around like an amoeba.

  • And your blood transports your hormones, nutrients, and other material all over your body. There’s

  • no other substance in you that can boast this kind of diversity.

  • But if theyre so different, how do we know that anything is a connective tissue? Well,

  • all connective tissues have three factors in common that set them apart from other tissue types.

  • First, they share a common origin: They all develop from mesenchyme, a loose and fluid

  • type of embryonic tissue. Unlike the cells that go on to form, say, your epithelium,

  • which are fixed and neatly arranged in sheets, mesenchymal cells can be situated any-which-way,

  • and can move from place to place.

  • Connective tissues also have different degrees of vascularity, or blood flow. Most cartilage

  • is avascular, for example, meaning it has no blood vessels; while other types of connective

  • tissue, like the dense irregular tissue in your skin, is brimming with blood vessels.

  • Finally -- and as strange as it may sound -- all connective tissues are mostly composed

  • of nonliving material, called the extracellular matrix. While other tissue types are mainly

  • made of living cells packed together, the inert matrix between connective-tissue cells

  • is actually more important than what’s inside the cells.

  • Basically, your connective tissue, when you see it up close, looks and acts a lot like this.

  • Yeah. The most abundant and diverse tissue in your body, that makes all of your movements

  • and functions possible? Turns out it’s not that different from the dessert that Aunt

  • Frances brings to every holiday party.

  • The jello that gives this confection its structure is like that extracellular matrix in your

  • connective tissue. The actual cells are just intermittent little goodies floating around

  • inside the matrix -- like the little marshmallows.

  • And although it may not look like it in this particular edible model, the extracellular

  • matrix is mostly made of two components. The main part is the ground substance -- a watery,

  • rubbery, unstructured material that fills in the spaces between cells, and -- like the

  • gelatin in this dessert -- protects the delicate, delicious cells from their surroundings.

  • The ground substance is flexible, because it’s mostly made of big olstarch and

  • protein molecules mixed with water.

  • The anchors of this framework are proteins called proteoglycans. And from each one sprouts

  • lots and lots of long, starchy strands called glycosaminoglycans, or GAGs, radiating out

  • from those proteins like brush bristles.

  • These molecules then clump together to form big tangles that trap water, and if youve

  • ever made glue out of flour, you know that starch, protein and water can make a strong

  • and gooey glue.

  • But running throughout the ground substance is another important component: fibers, which

  • provide support and structure to the otherwise shapeless ground substance. And here, too,

  • are lots of different types.

  • Collagen is by far the strongest and most abundant type of fiber. Tough and flexible,

  • it’s essentially a strand of protein, and stress tests show that it’s actually stronger

  • than a steel fiber of the same size. It’s part of what makes your skin look young and

  • plump, which is why sometimes we inject it into our faces.

  • In addition, youve also got elastic fibers -- which are longer and thinner, and form

  • a branching framework within the matrix. Theyre made out of the protein elastin which allows

  • them to stretch and recoil like rubber bands; theyre found in places like your skin,

  • lungs, and blood vessel walls.

  • Finally, there are reticular fibers -- short, finer collagen fibers with an extra coating

  • of glycoprotein. These fibers form delicate, sponge-like networks that cradle and support

  • your organs like fuzzy nets.

  • So, there’s ground substance and fibers in all connective tissue, but let’s not

  • forget about the cells themselves.

  • With a tissue as diverse as this, naturally there are all kinds of connective tissue cells,

  • each with its unique and vital task -- from building bone to storing energy to keeping

  • you from bleeding to death every time you get a paper cut.

  • But each of these signature cell types manifests itself in two different phases: immature and

  • mature. You can recognize the immature cells by the suffix they all share in their names: -blast.

  • Blastsounds kinda destructive, but literally it meansforming” -- these

  • are the stem cells that are still in the process of dividing to replicate themselves. But each

  • kind of blast cell has a specialized function: namely, to secrete the ground substances and

  • fiber that form its unique matrix.

  • So chondroblasts, for example, are the blast cells of cartilage. When they build their

  • matrix around them, theyre making the spongy tissue that forms your nose and ears and cushions your joints.

  • Likewise, osteoblasts are the blast cells of bone tissue, and the matrix they lay down

  • is the nexus of calcium carbonate that forms your bone. Once theyre done forming their

  • matrix, these blast cells transition into a less active, mature phase. At that point,

  • they trade in -blast for the suffix -cyte. So an osteoblast in your bone becomes an osteocyte

  • -- ditto for chondroblasts becoming chondrocytes.

  • These cyte cells maintain the health of the matrix built by the blasts, but they can sometimes

  • revert back to their blast state if they need to repair or generate a new matrix.

  • So, the matrices that these cells create are pretty much what build you -- they assemble

  • your bone and your cartilage and your tendons and everything that holds the rest together.

  • Not bad for a bunch of marshmallows floating in jello.

  • BUT! There is another class of connective tissue cells that are responsible for an equally

  • important role. And that is: protecting you, from pretty much everything.

  • These are cells that carry out many of your body’s immune functions.

  • I’m talking about macrophages, the big, hungry guard cells that patrol your connective

  • tissues and eat bacteria, foreign materials, and even your own dead cells.

  • And your white blood cells, or leukocytes that scour your circulatory system fighting

  • off infection, theyre connective tissue cells, too.

  • You can see how pervasive and important connective tissue is in your body. So a condition that

  • affects this tissue, like Marfan Syndrome, can really wreak havoc.

  • One of the best ways of understanding your body’s structures, after all, is studying

  • what happens when something goes wrong with them. In the case of your connective tissue,

  • Marfan Syndrome affects those fibers we talked about, that lend structure and support to

  • the extracellular matrix.

  • Most often, it targets the elastic fibers, causing weakness in the matrix that’s the

  • root of many of the condition’s most serious symptoms.

  • About 90 percent of the people with the disease experience problems with the heart and the

  • aorta -- the biggest and most important artery in the body. When the elastic fibers around

  • the aorta weaken, they can’t provide the artery with enough support. So, over time,

  • the aorta begins to enlarge -- so much so that it can rupture.

  • This is probably what happened to Flo Hyman. She was physically exerting herself, and her

  • artery -- without the support of its connective tissue -- couldn’t take the stress, and it tore.

  • There's SO MUCH going on with your connective tissue -- so many variations within their

  • weird diversity -- that were going to spend one last lesson on them next week, exploring

  • the subtypes that come together to make you possible.

  • But you did learn a lot today! You learned that there are four types of connective tissue

  • -- proper, cartilage, bone, and blood -- and that they all develop from mesenchyme, have

  • different degrees of blood flow, and are mostly made of extracellular matrix full of ground

  • substance and fibers. We touched on different blasts, and cyte, and immune cell types, and

  • discussed how Marfan Syndrome can affect connective tissue.

  • Thanks for watching, especially to our Subbable subscribers, who make Crash Course possible

  • for themselves and also for the rest of the world. To find out how you can become a supporter,

  • just go to subbable.com.

  • This episode was written by Kathleen Yale, edited by Blake de Pastino, and our consultant,

  • is Dr. Brandon Jackson. Our director and editor is Nicholas Jenkins, the script supervisor

  • and sound designer is Michael Aranda, and the graphics team is Thought Café.

Flo Hyman had always been a tall girl.

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Tissues, Part 3 - Connective Tissues: Crash Course A&P #4

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