Technically, we’re all simply meat. Yeah, you would say that what makes us human is our feelings, or ideas, or reminiscences, however bodily, we’re not all that completely different from this. We’re used to pondering of meat because the muscle tissue that individuals cook dinner and eat — however the reality is, you would eat that stuff uncooked. A hen breast or a steak or a pork chop is tender sufficient that it doesn’t want cooking. What does want cooking is the entire connective tissue that’s in and across the muscle, and will get in the best way of our meal. So one of many fundamental causes people started to roast, and boil, and bake meat within the first place, was to interrupt down these connective tissues that we are able to’t chew, so we might get the meat. Now, you would possibly’ve observed that connective tissues form of seem to be a seize bag of supplies that don’t actually slot in different teams. Our muscle, nervous, and epithelial tissue sorts are extra uniform, extra clearly grouped collectively. Typically, our connective tissues simply seem to be the leftovers you throw within the stew pot. However appearances are deceiving, and our incapacity as a species to tolerate these tissues in our meals is only one reminder that irrespective of how completely different tendon, bone, or a hunk of fats might seem, they’re certainly very intently associated. All of them spring from the identical embryonic cells, and their buildings are dominated, not by cells, however by an extracellular matrix filled with fibers. And it’s these fibers which have given people essentially the most hassle in our meat-eating historical past. It wasn’t till we discovered how you can cook dinner the stuff the that we had been capable of denature, or change the pure construction of, these protein fibers in order that they grew to become gentle and pliable. Take a hen for instance. You couldn’t simply pull the pores and skin off a residing hen — like ethically you couldn’t try this but additionally you in all probability couldn’t. Its residing pores and skin is anchored by connective tissue that’s filled with collagen fibers. However should you roast that hen, and break aside that collagen, abruptly the pores and skin simply peels proper off with no effort in any respect. So connective tissues, as evidenced by this mess right here, are good reminders of how generally issues are extra related than they seem. They’re additionally scrumptious . . . should you’re into that. So we all know what our connective tissues have in frequent, and we all know that we’ve bought 4 differing kinds — however what do they seem like, what do they do, and the place are they discovered — each in your butcher store, and in your physique? Maybe your most numerous kind is your basic connective tissue correct. It is available in each unfastened and dense subclasses, primarily based on what number of fibers it has in its floor substance. Pull on the again of your hand. See that fleshy tent there? That’s one instance of unfastened connective tissue. There’s a number of floor substance in right here, and the elastin fibers assist it snap again into place, whereas the collagen helps anchor it so you’ll be able to’t, like, snag your pores and skin on a zipper and watch it simply fly off. However strive pulling in your Achilles’ tendon, or these wing tendons right here, and there isn’t a number of give. That’s as a result of a tendon is an instance of dense connective tissue, with much more collagen. You would chew and chew and chew on a collagen-dense tendon and by no means get wherever. That’s why butchers trim off most dense connective tissue earlier than promoting cuts of meat. So unfastened connective tissues have fewer fibers, and extra cells and extra floor substance. Areolar tissue is the most typical unfastened connective tissue you’ve gotten, discovered ALL over your physique, slightly below your epithelial tissue, and wrapped round your organs. It’s bought a unfastened and random association of fibers, with only a few fibroblast cells that make these fibers. Should you take a look at it underneath a microscope you’ll see that its most apparent characteristic is that it appears to be like prefer it has a number of open house in it. This makes areolar tissue makes it nice at holding the watery, salty floor substance that surrounding tissues draw from. Your adipose tissue, in the meantime, is your fats tissue, the unfastened connective tissue that’s in right here. Reasonably than being principally floor substance, this one is usually cells — adipocytes — which retailer lipids for later use, insulate the physique in opposition to warmth loss, and develop pot bellies and love handles. The typical individual’s weight is about 18 % adipose tissue, and it’s these fats shops that maintain us alive when meals is scarce. With no fats shops, you’d die inside a number of days of your final sandwich. Reticular tissue is like areolar tissue, however with a woven mess of reticular fibers — moderately than collagen and elastin fibers — therefore the identify. This tissue supplies the gentle inside framework, or stroma, of the spleen, lymph nodes, and bone marrow, and it helps a number of creating blood cells. Simply as your areolar tissue is a form of sponge for watery floor substance, your reticular tissue is what holds your blood in place in a lot of your organs. Actually, all of those unfastened connective tissue correct sorts share an ethereal dispersal of fibers … which is why they’re simpler to eat after cooking — and why you’ll be able to pull cooked hen pores and skin aside. Then again, you’ll be able to’t simply rip a tendon or ligament in two, and even chew it, as a result of it’s product of that dense common tissue, filled with tight bundles of collagen fibers all operating parallel. You may see how neat and clean a slide pattern appears to be like underneath a scope, the fibers being these white, versatile buildings. They supply nice resistance to pressure when that pressure is exerted in a single route. That’s why you discover this tissue in your tendons, which join muscle to bone or different muscle, and your ligaments, which bind bones collectively wherever you’ve bought a joint. However what if these collagen fibers aren’t all stacked recurrently in rows? Then it varieties dense irregular tissue, whose fibers are thicker and organized erratically — it’s discovered wherever pressure could be exerted in a number of completely different instructions, like the leathery dermis underlying your pores and skin. And eventually, your physique has locations that require extra elasticity than rigidity, like say, round your joints. That’s the place you’ll discover dense elastic tissue — for instance, connecting your vertebrae in order that your backbone can curve and twist. A few of our largest artery partitions are product of this stretchy elastic tissue, too, which supplies each help and adaptability. From fats to tendons, connective tissue correct is essentially the most numerous group on this tissue household. However for the previous couple of minutes you’ve additionally been watching a distinct kind of connective tissue bob up and down as I discuss — cartilage Cartilage doesn’t have any blood or nerves, and it stands up in opposition to each pressure and compression fairly effectively — it’s that whitish gristle you see on the finish of pork ribs or hen wings in your grocer’s freezer — and it’s one other factor that you simply’re not going to have a lot luck chewing. Hyaline cartilage is your most typical kind — it’s form of glassy trying and supplies pliable help. It connects your ribs to your sternum and retains the tip of your nostril all perky. Its floor substance is wealthy with these sticky, starchy proteoglycans, and though it has collagen fibers, if you take a look at it underneath a scope, you’ll be able to’t actually see them — as a substitute the tissue appears to be like glassy, therefore the identify “hyal” which means glassy, or clear. Elastic cartilage is similar to hyaline, however with extra elastic fibers which are simpler to see, and it’s present in locations the place power and stretchability are wanted. Like, it’s why I can pull on my ear with out it ripping off. And simply as your physique wants agency components and stretchy components, it additionally wants shock absorbers. That’s the place your fibrocartilage is available in. It’s dominated by thick fibers of collagen and is sweet at withstanding a number of stress, so it makes up the discs between your vertebrae, and your knee joints the place it retains your bones from grinding collectively. And talking of bones! Though you may not consider one thing so exhausting and sturdy as residing tissue, bones positively are. The phrase “bone” can check with a complete organ — like your femur or scapula — or simply bone tissue. And that bone, or osseous tissue, is simply calcified connective tissue, excellent for supporting and defending your physique’s varied buildings. Spongy bone tissue is often discovered within the heads of lengthy bones and within the inside layer of flat bones just like the sternum. This spongy tissue is powerful, however porous, even to the bare eye, and it makes use of this further room to make and retailer bone marrow. Compact bone tissue then again is kind of dense, with no seen areas. It varieties the exterior layer of your bones and shops calcium for bone cells to make use of to make extra tissue. Now, if bone doesn’t conjure up your conventional picture of a tissue, blood in all probability doesn’t both — I imply, it doesn’t appear to attach issues, or lend help, and but, blood is our fourth kind of connective tissue. And when you concentrate on it, it clearly does join distant components of your physique and supplies some rigidity to different components. Similar to different connective tissues, blood develops from mesenchyme and is made up of cells surrounded by an extracellular nonliving matrix: On this case, the bottom substance is your blood plasma, which has protein fibers floating round in it. Your blood’s fundamental job, after all, is delivering items — it transports cells, and vitamins, and hormones, and wastes, and all types of different stuff, conserving all of the components of your physique related within the course of. Most of your blood cells are erythrocytes, or your well-known pink blood cells that zoom round, carrying oxygen and carbon dioxide by way of your physique. You’ve additionally bought bigger, infection-fighting white blood cells, or leukocytes within the combine, and your platelets, the small cell fragments wanted for blood clotting so {that a} paper reduce doesn’t bleed you dry. Not like different connective tissues, it doesn’t actually have what you’ll name fibers, however as a substitute has a bunch of protein dissolved within the plasma, and people protein molecules will type fiber-like buildings when your blood must clot. So. You’re taking your 4 main varieties of tissues, and the entire subtypes of every that’s taken us weeks to discover, and you’ll in all probability see how they’ll come collectively in lots of, many combos to type your whole physique’s organs. And identical to that chaotic cafeteria full of middle-schoolers — we’d be hopeless messes with out our hierarchy of group, our inside and outer boundaries, and the power of our methods to speak with one another. THAT is what our tissues do for us, and we wouldn’t exist with out them. In the present day we wrapped up our four-episode sequence on tissues, with a survey of the sub-groups of unfastened and dense connective tissue, together with areolar, adipose, reticular, tendons, ligaments, dense irregular, and dense elastic tissue. We additionally talked concerning the three cartilage sorts, spongy and compact bone connective tissue, and the way and why our blood can also be a connective tissue kind. Due to all of you for watching, particularly to our Subbable subscribers, who make Crash Course doable to themselves and in addition to the remainder of the world. To search out out how one can change into a supporter, you can go to Subbable.com. And don’t overlook to go to Youtube.com/CrashCourse and subscribe. This episode was written by Kathleen Yale, the script was edited by Blake de Pastino, and our guide is Dr. Brandon Jackson. It was directed by Nicholas Jenkins & Michael Aranda and our graphics group is Thought Cafe.