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 asthe school’s first female scholarship athlete, and at the age of 21, she was competing inworld championships. nine years later she made it to the 1984 olympics and helped herteam win the silver medal. after the olympics, hyman moved to japan whereshe gained fame playing professional volleyball.
but all of that ended in 1986 when out ofnowhere, she collapsed and died during a game. she was 31 years old. hyman’s initial cause of death was thoughtto be a heart attack, but an autopsy revealed that she died from a tear in her aorta, caused by anundiagnosed condition known as marfan syndrome. marfan syndrome is a genetic disorder of theconnective tissue. people suffering from it have a defect in their connective tissue thatsubstantially weakens it over time. and you’ve got connective tissue pretty mucheverywhere in your body, so it can cause big problems. outwardly, those with marfan’s tend to tobe especially tall and thin, like flo hyman, with loose, flexible joints and noticeablylonger limbs and fingers.
those long fingers and bendy joints have actuallyhelped some athletes and musicians do things that the rest of us can’t -- famous blues guitaristrobert johnson, piano virtuoso sergei rachmaninov, and italian violinist niccolo paganini areall believed to have had marfan syndrome. but these abilities come at a great cost -- as peoplewith 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 canaffect your bones, cartilage, tendons, blood vessel walls, and more, shows that all ofthose structures are closely related, no matter how different they may seem. we’ve covered the basic properties of nervous,muscle, and epithelial tissue, but we haven’t
gotten to the most abundant and diverse ofthe 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 whatholds you together, in more ways than one. and if something goes wrong with it, you’rein for some havoc. and that means we’re gonnabe talkin’ about jello today. uh…we’ll get to that in a minute. the springiness here? that’s connectivetissue. so is the structure in here, and the stuff inside here, and the tendons poppingout here connective tissue is pretty much everywherein your body, although how much of it shows
up where, varies from organ to organ. forinstance, your skin is mostly connective tissue, while your brain has very little, since it’salmost all nervous tissue. you’ve got four main classes of connectivetissue -- 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 andyour blood are just types of connective tissue! so, despite the name, your connective tissues do waymore than just connect your muscles to your bones. your fat -- which is a type of proper connectivetissue -- provides insulation and fuel storage -- whether you like it or not -- but it alsoserves structural purposes, like holding your
kidneys in place, and keeping your eyeballsfrom 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, insteadof 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 thiskind of diversity. but if they’re so different, how do we knowthat anything is a connective tissue? well, all connective tissues have three factors in commonthat set them apart from other tissue types. first, they share a common origin: they alldevelop from mesenchyme, a loose and fluid type of embryonic tissue. unlike the cellsthat 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 degreesof vascularity, or blood flow. most cartilage is avascular, for example, meaning it hasno blood vessels; while other types of connective tissue, like the dense irregular tissue inyour 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 extracellularmatrix. while other tissue types are mainly made of living cells packed together, theinert matrix between connective-tissue cells is actually more important than what’s insidethe cells.
basically, your connective tissue, when yousee it up close, looks and acts a lot like this. yeah. the most abundant and diverse tissuein your body, that makes all of your movements and functions possible? turns out it’s notthat different from the dessert that aunt frances brings to every holiday party. the jello that gives this confection its structureis like that extracellular matrix in your connective tissue. the actual cells are justintermittent little goodies floating around inside the matrix -- like the little marshmallows. and although it may not look like it in thisparticular edible model, the extracellular matrix is mostly made of two components. themain part is the ground substance -- a watery,
rubbery, unstructured material that fillsin the spaces between cells, and -- like the gelatin in this dessert -- protects the delicate,delicious cells from their surroundings. the ground substance is flexible, becauseit’s mostly made of big ol’ starch and protein molecules mixed with water. the anchors of this framework are proteinscalled proteoglycans. and from each one sprouts lots and lots of long, starchy strands calledglycosaminoglycans, or gags, radiating out from those proteins like brush bristles. these molecules then clump together to formbig tangles that trap water, and if you’ve ever made glue out of flour, you know thatstarch, protein and water can make a strong
and gooey glue. but running throughout the ground substanceis another important component: fibers, which provide support and structure to the otherwiseshapeless ground substance. and here, too, are lots of different types. collagen is by far the strongest and mostabundant type of fiber. tough and flexible, it’s essentially a strand of protein, andstress tests show that it’s actually stronger than a steel fiber of the same size. it’spart of what makes your skin look young and plump, which is why sometimes we inject itinto our faces. in addition, you’ve also got elastic fibers-- which are longer and thinner, and form
a branching framework within the matrix. they’remade out of the protein elastin which allows them to stretch and recoil like rubber bands;they’re 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 fibersin all connective tissue, but let’s not forget about the cells themselves. with a tissue as diverse as this, naturallythere are all kinds of connective tissue cells,
each with its unique and vital task -- frombuilding bone to storing energy to keeping you from bleeding to death every time youget a paper cut. but each of these signature cell types manifestsitself in two different phases: immature and mature. you can recognize the immature cells bythe suffix they all share in their names: -blast. “blast†sounds kinda destructive, butliterally it means “forming†-- these are the stem cells that are still in the processof 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 blastcells of cartilage. when they build their
matrix around them, they’re making the spongy tissuethat forms your nose and ears and cushions your joints. likewise, osteoblasts are the blast cellsof bone tissue, and the matrix they lay down is the nexus of calcium carbonate that formsyour bone. once they’re done forming their matrix, these blast cells transition intoa 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 thematrix built by the blasts, but they can sometimes revert back to their blast state if they needto repair or generate a new matrix. so, the matrices that these cells create arepretty much what build you -- they assemble
your bone and your cartilage and your tendonsand everything that holds the rest together. not bad for a bunch of marshmallows floatingin jello. but! there is another class of connectivetissue 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 yourbody’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 leukocytesthat scour your circulatory system fighting off infection, they’re connective tissuecells, too.
you can see how pervasive and important connectivetissue 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 yourbody’s structures, after all, is studying what happens when something goes wrong withthem. in the case of your connective tissue, marfan syndrome affects those fibers we talkedabout, 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 serioussymptoms. about 90 percent of the people with the diseaseexperience problems with the heart and the
aorta -- the biggest and most important arteryin the body. when the elastic fibers around the aorta weaken, they can’t provide theartery with enough support. so, over time, the aorta begins to enlarge -- so much sothat it can rupture. this is probably what happened to flo hyman.she was physically exerting herself, and her artery -- without the support of its connectivetissue -- couldn’t take the stress, and it tore. there's so much going on with your connectivetissue -- so many variations within their weird diversity -- that we’re going to spendone last lesson on them next week, exploring the subtypes that come together to make youpossible. but you did learn a lot today! you learnedthat there are four types of connective tissue
-- proper, cartilage, bone, and blood -- andthat they all develop from mesenchyme, have different degrees of blood flow, and are mostlymade of extracellular matrix full of ground substance and fibers. we touched on differentblasts, and cyte, and immune cell types, and discussed how marfan syndrome can affect connectivetissue. thanks for watching, especially to our subbablesubscribers, who make crash course possible for themselves and also for the rest of theworld. 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 editoris nicholas jenkins, the script supervisor
and sound designer is michael aranda, andthe graphics team is thought cafã©.
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