Understanding the Skeletal System

Okay, our next organ system is the skeletal system. By now in lab, we've started looking at bones, which is a major achievement for A&P 1. And so this is a huge organ system. Chapter 7 is a very big chapter. In your book, there are lots of great pictures of all the bones. you've looked at in lab. But one of the first things you need to know is, of course, the human total. So you have 206 bones in the body. Also, I think it's kind of good to, as we're starting to learn our vocab, because remember, learning anatomy is kind of like learning a foreign language. language. So the more of these roots of words that you know, the better off you'll be in the long run. So for skeletal, we'll have some new ones and some old ones. Osteo means bone. Sido or site means cell. Genic, like genesis, means to build. Chondro means cartilage. Peri means around, like a perimeter fence. Indo, inside. Heme, hemato, blood. Clast, to break. Enter, between. Poi means means to produce, that's probably the hardest one. Blast in Latin means bud, but I would just go with build. So if you just think build for blast. So we always start every organ system with kind of what's the point, what does it do? Well, the skeletal system is pretty obvious. It includes your bones and structures that connect bones. So if you look at this picture, we have tendons, which goes muscle to bone. So I always remember the Achilles tendon on my ankle goes from my heel bone to my calf muscle, so my foot can go up and down. And ligaments are bone to bone, and all of the various cartilages that are inside. But there are six functions of bones. The first three you would probably get. The second three, I'd have to be in an all-white room for a very long time to have just come up with it on my own. But the first three are pretty obvious. Support. I mean, when you think about your skeletal system, that's pretty much what it does. It forms a framework. It's kind of like scaffolding when they do construction. It supports the body and it cradles your soft organs like your pelvic bone. The pelvic bones kind of protect all of your lower gastrointestinal, urinary and reproductive organs. Bones in your legs, of course, support your overall body. The atlas supports the skull. Remember, that was the definition of that in lab. So the point is it gives us kind of an internal scaffolding. Protection. When you look at a skeleton... you see the rib cage and you see the skull. So in lab, we've done the parts of the skull and it looks like a football helmet. And the rib cage itself protects vital organs like your heart and your lungs. So when you look at a skeleton, you can kind of guess where the important, even if you had, no knowledge whatsoever. You could kind of guess where the important stuff is because it's protected by bone. And then of course movement. Now it really goes to the muscles but if the muscles didn't have the bones to attach to we would all be a pool of mushy goo on the floor. three functions that you may not think of. Inorganic salt storage. Your skeleton is kind of like a bank account, and so it's a good place to store especially calcium and phosphorus. Part of your homeostasis, there's that word again, is maintaining that supply of calcium. There has to be a certain percentage of calcium in your blood at all times for your muscles to work and for your nerves to fire. So if you get real excited about some dilly bars at Dairy Queen, which is a good day, and you have too much calcium, well you might as well store it in your savings account. count, you might as well put it in your bones. If you have a day where you haven't had anything to eat, that's a sad day, your body can pull that calcium and phosphorus from your bones to put it into the blood. So it becomes this reservoir. I never thought of the skeleton that way. In fact, when I was a kid, I used to eat a lot of food. I used to eat a lot When I first saw the skeleton, I just assumed it was just this dead thing inside our body that kind of held us up. But it's very metabolically active and very much alive. So it's not like we put calcium in our skeleton and we're done. We can actually pull it back out. hematopoiesis heme means blood poi means to make so this literally means to make blood so all of your blood cell formation whether we're talking about those erythrocytes the red blood cells to carry oxygen and carbon dioxide or the leukocytes which carry kind of these infection fighters is what they are, so it's kind of our immune system. The platelets for blood clotting, all of these are formed inside our bone marrow, which is technically a part of the skeletal system, specifically in the red marrow. which we'll be getting into the difference, but red marrow I'm sure they named because of blood. Whereas the last one here, energy storage, we don't often think of this one, but yellow marrow, fat in the adult medullary cavity, basically in your bone marrow, you have some yellow marrow. Anytime we see yellow, we just saw yellow in our last unit, anytime we see yellow really just usually means fat. And so we can store energy by also having this fatty yellow marrow in our bones, it kind of cushions them a little bit. And so we see this in our... our spongy bone, which will make more sense in a few minutes. So a bone, remember, is a connective So it fits the definition of a tissue, a bunch of cells working together. Bone is very vascularized, so it heals very, very fast. But it's made of two phases. So we call it biphasic, because it's two phases. We have the organic phase, which we had that term before. and the inorganic phase. So the organic phase is the bone cells, so they're alive, plus collagen, which collagen is those big protein ropes. So we kind of get the flexibility but also mostly strength from this. Remember, when you pull on collagen, it would be like pulling on a rope. There's not a lot of give to it. The whole purpose is for it to be strong. But it has a little bit of flexibility. The bone cells maintain structure. They don't really support. They just make the structure, but that's not what's actually giving your bone. bones any kind of strength. So this is over one third of your bone mass. So it allows for a little bit of give. When you bump your leg or hip into like a desk or something, you don't want your bones to shatter. We want our bones to be strong, yes, but we don't want them to be fragile. So like for a wedding gift, we got this really, really pretty crystal base, which I mean, I'm not a crystal base kind of person, so I'm like, what the hell am I going to do with this? But it was nice. But it's expensive, I'm sure, and it's really heavy crystal. Like I could hurt somebody with this thing. But if I don't, I'm going dropped it, it would probably shatter into a bazillion pieces. So it's really, really strong, but it's fragile. We don't want our bones to be fragile because think about what we expect them to do. So we want them to be strong, but we want to have a little bit of give. That crystal vase doesn't have any give to it. Whereas if you, you know, kind of crack your knee on a desk, this organic phase gives your bones just a little bit of flexibility to where they can take that hit and not shatter. But we need this. strength. So this is the second phase which is two-thirds so this is the majority of your bones. It makes your bones very rigid and strong which is what you think of when you think of skeletal tissue. So this is the inorganic phase and inorganic starts with I and so does ionic. So remember inorganic molecules are held together by ionic bonds. So these are things that would dissolve in water. So these are our salts, primarily calcium phosphate again, kind of comes into play. So bone tissue is like protein ropes that have kind of sprinkled crystallized calcium on top of them. So we get the best of both worlds like Miley Cyrus. We get strength, but we get a little bit of flexibility. So you could do a little experiment with bone. You could take two chicken bones and you could put one in a solution that has a bunch of enzymes to digest proteins, like meat tenderizer. If you cook and you use meat tenderizer, you sprinkle meat tenderizer on the meat. And what it actually does is it kind of starts the digestion before you, which is kind of gross. It starts starts taking those big proteins and starts breaking them down into their amino acids, like taking little kid scissors to it. So it makes the meat more palatable. When you chew on it, it's easier to chew. So you could do this same thing. You could take this bone and put it in a bowl full of meat tenderizer and water and let it sit. What it will do is digest the proteins away. So all you're left with is the inorganic solids. So after a while, if you take that bone out, it'll still look like a bone because 66% of it is still. there, if you tap that bone on the side of a desk, it would shatter into a bazillion pieces because you've taken out that flexibility. The second experiment we could do is put a chicken bone in an acid that would dissolve the calcium and phosphorus, that would dissolve the ionic solids. So the only thing that you would have left would be the squishy collagen, the organic part. So after a while you could take that bone out of the acid, rinse it off, you could actually tie it in a knot. So you could see how either one of these would not be good. We don't want our bones to be so loose. loosey-goosey that they can't even support us, but we don't want our bones to be so fragile that, you know, they break so easily. So we need both. There is actually a condition called osteogenic imperfecta, where children are born with really, really brittle bones. It's usually diagnosed at birth because, sadly, like their collarbones will break during birth, and they'll usually shatter other bones, like skull bones and things during that process. You can see how awful it would be, painful it would be to have 20-something fractures before you're even one years old. old and most of the time those children don't survive beyond that. There are two types of bones, compact bone and spongy bone. Now in lab when we did tissues we looked at compact bone, how it looked like tree rings and barnacles under the microscope. Compact bone is exactly what it says, it's compact, it's dense. So this is the outer layer of all bones. So in lab when you were looking at bones, which I realize a lot of ours are fake, they kind of have this slick outer coating, that's compact bone. So if you look at at this picture over on the right, the outer edge there is thicker. That's the compact bone. The benefit to compact bone is it's stronger, especially along the axis of the bone, the shaft in the middle of the bone. If you look at your femur, which is what the This picture is of, because you have that huge ball socket there. Your femur could support 40 times of your body weight. 40 times! So if you look, a 150-pound person, which I am not, can support 3 tons. 6,000 pounds your femur can hold. But just from that direction. So it's very... very strong from top to bottom. So think about if you took like empty beer cans, like four beer cans and you stacked them on top of each other. And you put your hand on the top and the bottom and push. That'd be very strong. You could carry those four empty cans around. as long as you're pushing on the ends. But as soon as somebody comes up to you and karate chops it, those cans are going to go flying. So the femur is like that. It can handle your body weight from up and down, which if you think about it, as an animal, that's the only thing it should have to do. So we could climb trees and run around in loincloths and be chased by saber-toothed tigers. But our bones were never designed for riding in cars, for roller coasters, for skydiving, and all the other crazy things we do because we're human. So our body is designed pretty well. but it's easy to break the femur in a car accident because it doesn't take a side hit very well. The ends of the bone have what's called spongy bone. You don't need to know cancellous bone. Spongy bone is fine. If you look at the picture up above, it looks like a sponge. The difference is when you hear spongy bone, you tend to think of a sponge being squishy. This bone is not squishy. lab, make sure that you touch some spongy bone because we have some real bones in there. And you, I always think spongy bone is kind of a pain because if I'm carrying the bones and you can see spongy bone, the sponge will like, the spongy bone will like snag your clothes. It actually hurts. It's very sharp. this picture looks it looks like it's got all these little teeth it kind of does but if you look at the picture down below by having kind of the Holy Holies it that's the spongy bone at the end of the joints there it creates these little crevices for your bone marrow to sit in so these branches are called trabeculae and you don't really need that term right now but we will see that term in amp2 because it just kind of means branching the benefit to spongy bone there's a couple one it's usually in our joints like it is in this picture picture because it's equally strong from all angles. So if you think about your joints, if you bend your elbow right now, the shaft of your humerus, your upper arm bone, doesn't really take a lot of abuse. It's the ends of the humerus and the ends of the radius and the ulna that take all the abuse in that joint. So wouldn't it make sense that you would want bone that could kind of take a hit from all angles? Because think about the things you do to your elbow joint. You kind of turn it in all directions. Also, compact bone is really heavy. Spongy bone is a lot lighter. lighter. Your skeletal system is already 18% of your body weight. So you're dragging a lot of weight around. Well, imagine if this was all compact bone. Half of our body weight would be skeleton. We'd be exhausted just dragging our sag carcass around. And the other benefit to this is it can be made really quickly. Compact bone takes a lot of time. Spongy bone can be laid down really fast. In fact, if you break a bone, you almost instantly start growing spongy bone back. So the trabeculae, again, is this little branches. I like this picture better because you can really see the difference between compact bone and spongy bone. So there's a thin layer of compact bone all over the bone. But then it's thicker, of course, along the shaft where it's designed to take a pretty big hit. The trabeculae are lined with endosteum. Endosteum is a really thin connective tissue. Think of it like tissue paper. Medulla is very squishy. Or, sorry, marrow in the medullary cavities. Marrow is very, very squishy. See? And so we don't want something so fragile like jello bumping and grinding against hard bone all day. So to line the little scary teeth of that spongy bone, you kind of have this equivalent of tissue paper, just like when you wrap a present. So endosteum is just a connective tissue. Endo means inside. Osteo means bone, just to protect the marrow. So red marrow, again, to make blood. Yellow marrow is going to be fat. So this picture here is showing compact bone around the outside. Spongy bone. bone in the middle and you can immediately see the difference. If you look at the bottom picture there, that's a skull bone where you have a spongy bone in the middle like the meat in a sandwich and you have the compact bone like the bread on the outside. Okay, so bone membranes. When you're looking at bone, we forget sometimes that it used to be alive because we just kind of look at the dead remnants left over upstairs. We don't really see these tissues because we don't look at living bones. But you have periosteum, which if you look at the bottom picture there, is kind of showing, especially on the right, it's kind of showing it being stripped off like a jacket off of a person. And then you have the compact bone underneath. See the little tree rings that look like the barnacles that we saw in lab. So peri, of course. means around, osteo means bone. This is a double layer protective membrane. Just like your coat, you have the outer part that the world sees, and then you have the inner lining that's touching your body. So the outer layer is made of dense, irregular connective tissue. So it's really, really tough, and it's made of lots of collagen, kind of going in no particular direction whatsoever. The inner layer has osteoblasts and osteoclasts. Blast means to build, clast means to build. to destroy. Like if you clash with something, you're tearing it down. Osteo means bone. So you have these cells that are bone builders and these cells that are bone destroyers, which we'll see them here in a second. We also have a richly supplied blood and nerve. and lymphatic vessels going in there. So if you look, that big blood vessel in the bottom picture is actually going through that periosteum. The bone has to be fed. Bone is very bloody. There's going to be lots of nerve tissue. If you've ever broke a bone, it hurts like hell. And lymphatic vessels, which for now, we don't really do the lymph system until next semester. For now, lymphatic is kind of for your immunity. So you want to keep the bone healthy. Then there's endosteum, which is labeled at the top there. And so you can see that's the lining right before the yellow. bone marrow on the bottom kind of right picture there so you have that big yellow bone marrow in the middle you have the bone and then you have endosteum because remember we don't want ooey squishy bone marrow bumping and grinding against that bone so we've got that nice layer of connective tissue the endosteum but this also has osteoblasts and osteoclasts which means you can build and destroy bone from the outside and from the inside just like when you remodel a house you can work on the roof and the siding or you can paint the walls on the inside side. When we look at a bone from this angle, we can still see the periosteum like a jacket. We can also see the endosteum. Periosteum serves as an insertion point for your tendons and your ligaments. So this is kind of an important concept. A tendon and a ligament, remember, are the really thick, dense collagen fibers running in all direction that we saw in our tissue unit. But tendons and ligaments take a lot of abuse because they're the ones constantly being used. So we don't want them to tear and we don't want them to rip off. We don't want them to be attached to the... the bone like a tack or a nail is attached to a wall. Think about if you took a rubber band and nailed it to the wall. Well, as soon as you stretched it, it would just tear right around that nail. So it would kind of be similar if our tendons and ligaments were like tacked onto our bones like that. And they're not. Tendons and ligaments just kind of merge with the periosteum. So it's kind of like your clothes where you have seams. Usually where you have seams is where you get issues like tearing and things like that. We don't have a seam without a seam. with our tendons and ligaments. They just kind of merge directly into that periosteum. So this is just a structurally smart thing. So it's all this collagen. It's just thicker around our tendons and ligaments. The endosteum, again, is that connective tissue to protect the bone marrow and to line those trabeculae because they're pretty scary. On this picture, we also have two new terms, which are kind of bad. Epiphyses or the epiphysis of the epiphysis. are the ends of the bone. I've always remembered this because E for epiphysis and E for end. And then the diaphysis is the middle or the shaft. So as we just saw, the epiphysis would have lots of spongy bone. The diaphysis would have lots of impact bone. But besides the bone, there's lots of cartilage associated with your skeleton. As our bones grow, as you go from a zygote, which is a fertilized egg after our parents had the naughty sex, ew, and our body starts to grow and we're kind of the size of a big jelly bean, It's not like we start with bone. So very early on in embryonic development, there's no osseous tissue, there's no bone tissue. What we do lay down is kind of these precursors to bone, which are basically cartilaginous molds. So think of it like a jello mold. If you pour Jell-O into a Jell-O mold, you get a shape. If you pour Jell-O onto a kitchen counter, you get a big mess. So when the bone goes to attach, when the bone goes to form, it kind of has to have something to lay down on, which is the cartilage. So embryonic skeleton is initially the hyaline cartilage that we saw in the microscope that then gets replaced by bone. Some of it remains. So if you look on an adult rib cage, we have that costal cartilage where it still is there. It's also on a lot of... of our epiphyses on a lot of the ends of our bones, which we call the articulation ends of bones. If you articulate, you come together. So where you come together, you can have a lot of friction. So we have these cartilage kind of coverings on the end of our bones to reduce bump and grind. If you've ever eaten chicken, you see that when you eat chicken and you're pulling the meat off, that the ends of the bones kind of have this weird jello cartilage stuff. So places we have cartilage still are costal cartilage like shown in this picture. There's the C-shaped rings in our windpipe made of cartilage, which if you're skinny and you lean back, which... I am not, and rub your windpipe. You can feel them. When they do a tracheotomy, which is where they cut a hole in the trachea so someone can breathe, if there's an obstruction, they have to go in between those two rings. But we want these big rings to keep our windpipe open. If you've ever had a kid, like, clothesline you or something, it hurts. But we don't want our windpipe to collapse ever. The external nose, most of our nose is cartilage, and the long bones of our embryo. endocardionic skeleton. So when you still have growth, the epiphyseal plate is open. We call that your growth plate if you've ever heard of those, but we'll be seeing them again. We also have some elastic cartilage still in our body, especially in our ear and in our epiglottis. which we mentioned before. And fibrocartilage is important to our skeletal system, especially between those two vertebrae and our knees. So remember, our cartilage and fibrocartilage is full of collagen, which is really, really, really tough. So the meniscus of our knees and the vertebral disc, they can take quite a beating. But they do. We put a lot on our body. And then the symphysis pubis, where our two pubic bones come together. Determining bone age. Now in lab unfortunately we've kind of gotten a lot more fake bones because they just hold up. It's like before students would drop real bones, and they would just break. They would always break. So we start switching to the fake bones because they're anatomically correct, and they don't break at all. as easily. But we do still have a few real bones up there. So if you don't mind touching the real bones, you can try this next time you're in lab. You probably can't get an exact approximation of age until you're like specializing in this. Like forensic anthropologists, if you've ever watched the show Bones or any of those kind of CSI shows, they always find a skeleton and they're like, they look at the skeleton for two seconds and they say, oh, there's a 14 year old Asian female. She smoked, she liked pop music and she wore red. And it's like, it's just a skeleton. And so obviously they can't get all of that information from a glance, but they can tell a lot from Bones. People that specialize in this can get the age down to usually one or two years, which is pretty impressive, but characteristics they look for. How shaggy is the bone? Older bones have little projections on them, because as we get older, we just don't lay bone down in such a uniform manner, so we kind of get weird, abnormal deposits. Young bones tend to be really smooth. Also, as we get older, we've used our body, and when you use your body and you use your muscles, the skeleton grows back a lot stronger. And so if you kind of feel around on your body, like around your wrist, you have all these bumps. Any time you have a bump is usually where a muscle has been pulled. pulling on it. So the skeleton builds in response. So the more lumpy, bumpy you are, the more you've been using your muscles. And so younger people just haven't had the time to do that. Growth plates. Epiphyseal plates, which, I mean, we just call them growth plates, is where you still have cartilage that's being converted into bone. So as our bones are growing, on the ends we have these big, thick rings of cartilage. And so, like on the femur, on both ends you have rings of cartilage that are going cartilage bone, so the bone is lengthening. Well, once we reach a certain age, those cartilage rings fuse into bone, and then we're done growing in height. But there's different ages for different bones when we expect these to fuse. So then we have this little scar line called the epiphyseal line. So if they find a bone and it still has growth plates open, then Depending on the bone, they can make an assessment on age. Some of your growth plates don't completely fuse until you're like 25, but some fuse when you're like 10. So people know this, people have charts and tables and graphs and everything else about this. So when they find a bone, they can make a pretty good estimate. So bone size, in general, bigger bones, bigger people, of course. I mean, if you found infant bones or, you know, five-year-old bones, those are going to look a lot different than a, you know, 20-year-old person. But size, though, isn't great. You'd really have to use a lot of other factors because, because when we had some real bones in lab, we used to have this one tibia that was just huge. Like the person must have been so tall. And then we had one that was really tiny and always messed people up. Bone density, the degree of ossification, how hard is the bone. Again, as we get older, we get women, one in five women gets osteoporosis. You're just not as good at depositing minerals. And so if the bone looks pretty fragile, it's probably an older person. So they use all kinds of factors. Bone structure itself. We classify bones based on shape. And the good thing is they don't use too many nerdy words. So they start with long bones. If you've ever watched a cartoon dog carry around a cartoon bone like the one I tried to draw here, that's basically a long bone. You've got a shaft, you have two knobby ends. And see, I tried to draw the periosteum on there. So your femur, your tibia, which is your lower shin bone, your humerus, which is your upper arm bone, your metacarpals and metatarsals, and your feet and your toes. These all have this classic look. They're long with two ends. Short bones. Again, they didn't get fancy. Those carpals in the wrist. Some lovers try positions they can't handle. The scaphoid lunate. See, I need to do this fast. Scaphoid lunate trapezium. Some lovers try positions. They haven't done this in a while. Scaphoid lunate triquetter. See, I'm bad at this today. So the point is, we did these in lab. Um... So now I can't let it go. Scaphoid, lunate, triquetral, or triquetrum, pisiform. Trapezium, trapezoid, gaptate, hammock. See, you always have to say it fast. So if we haven't learned the wrist bones yet in lab, don't stress about it. We'll be getting there. But we call them the carpals in general. And as we see in this little x-ray, they're really tiny, short little cube-like bones. Same thing with the ankle bones. We have the cuboid and the cuneiform and the navicular and then metatarsals and everything else. So those were all kind of... even though they're a little bit bigger than the wrist, they're still short. They don't really have much shape to them. Flat bones are flat. They're thin, they're usually curved, and they look like sandwiches, where you've got spongy bones in the middle, which would be the meat. You have the compact bone on the outside, which would be the bread. You have lots of trabiculae covered with endoosteum to protect the medullary cavity, which would have the bone marrow. And you've got the red bone marrow, which is hematopoietic. Heme means blood, poi means to make, and so this is making all of your red blood cells and platelets. Or you may have some yellow marrow in there, which is basically fat to store energy. energy. So these flat bones kind of encase most of your soft tissues. So most of your cranium, most of your skull bones, the breast bone, which would be the sternum, your ribs, your scapula, which is your shoulder blade, and your clavicle, which is your shoulder your collarbone would all be flat bones. And so this picture just kind of shows the spongy bone in the middle, which remember, it's not soft and squishy. It's just spongy. So we got the holes for the marrow to fit in and the compact bone. So it looks like a sandwich. We have irregular bones. Irregular bones are the crazy looking bones. They're not long, they're not short, they're not flat, they're strange. Those vertebrae that we've seen in lab, they look like little spaceships. They're crazy. Nothing crazier looking than a spinal cord. Auditory ossicles, these are your bones. your ear bones. These are the smallest bones in the body. And in lab, we only have that one representative mounted in that kind of wood block. They're so small and they're so weird shaped. And the hip bones, the dreaded coxal bones. Oh, so much we have to know. on those bones and they're so weird looking. Also your facial bones like the maxilla and the mandible are irregular bones. They just look odd. Sesamoid bones is probably the hardest word out of all these. At least long, short, irregular is not too bad. Sesamoid are bones that develop within a tendon. The only example is the patella. So your kneecap develops within the tendons in those, in those, around those knee bones. So sesamoid is kind of a weird world. word weird word and sutural bones they're also called wormium bones which i actually can remember wormium more than suture but we had sutures in lab those little lines on your skull but sometimes when those sutures come together when the skull fuses see how in this picture the sutures have kind of trapped little islands of bone so these wormium bones become their own little island of bone so 206 is quote-unquote human bone total but some people have a few more But not everybody has these, so they don't name them individually because it's kind of a random thing. It's just when the suture spews, sometimes they trap little islands of bones. So we call these wormium bones or suture bones. Okay, the parts of a long bone. Some of these we've discussed already. The diaphysis, remember, is the shaft, and so that's the compact bone. Because if you look at a bone like this as the humerus, it's really strong from end to end. It doesn't take a good side hit. So when people break a humerus, it's usually a side hit because that bone's not... designed for that. So the diaphysis is the shaft with compact bone and the medullary cavity for bone marrow. And then the knobby ends there are the epiphyses. So in this picture, we've got yellow marrow, basically fat. The epiphyses are the ends. So lots and lots of spongy bone, which they've blown up there on the right. So we can see the little crevices there, the little spaces. That gives us space for blood to work its way in there and also more kind of for the marrow to have a place to be. Lots of hyaline cartilage on the ends of these bones because of the bump and grind at the joints when we're moving. And the epiphyseal line, if you look at that picture, the epiphyseal line is that faint line that goes across, kind of separating the epiphyses from the diaphyses. Those were your growth plates. So in a bone that's still growing in length, that would be a little line of cartilage. But in an adult bone, it's just kind of a scar. You can actually see these on x-ray. Now, I didn't want to go into rad tech, and I'm not an expert. an expert by any means on breaks. Frankly, if you showed me this x-ray, I'd be like, oh, look at that fracture. And they'd be like, no, that's the growth plate. So we call this the epiphyseal line or the growth line. And it's just there between the ends and the shaft. So it's where that growth plate used to be, the epiphyseal plate. But you can call it growth plate. And it used to be a disc of hyaline cartilage that was being converted into bone, making the bones longer and longer and longer till we reach adulthood. And then we're done growing.

In your book, there are lots of great pictures of all the bones. you've looked at in lab. But one of the first things you need to know is, of course, the human total.

So you have 206 bones in the body. Also, I think it's kind of good to, as we're starting to learn our vocab, because remember, learning anatomy is kind of like learning a foreign language. language.

So the more of these roots of words that you know, the better off you'll be in the long run. So for skeletal, we'll have some new ones and some old ones. Osteo means bone.

Sido or site means cell. Genic, like genesis, means to build. Chondro means cartilage. Peri means around, like a perimeter fence. Indo, inside.

Heme, hemato, blood. Clast, to break. Enter, between. Poi means means to produce, that's probably the hardest one. Blast in Latin means bud, but I would just go with build.

So if you just think build for blast. So we always start every organ system with kind of what's the point, what does it do? Well, the skeletal system is pretty obvious. It includes your bones and structures that connect bones. So if you look at this picture, we have tendons, which goes muscle to bone.

So I always remember the Achilles tendon on my ankle goes from my heel bone to my calf muscle, so my foot can go up and down. And ligaments are bone to bone, and all of the various cartilages that are inside. But there are six functions of bones. The first three you would probably get.

The second three, I'd have to be in an all-white room for a very long time to have just come up with it on my own. But the first three are pretty obvious. Support.

I mean, when you think about your skeletal system, that's pretty much what it does. It forms a framework. It's kind of like scaffolding when they do construction.

It supports the body and it cradles your soft organs like your pelvic bone. The pelvic bones kind of protect all of your lower gastrointestinal, urinary and reproductive organs. Bones in your legs, of course, support your overall body. The atlas supports the skull.

Remember, that was the definition of that in lab. So the point is it gives us kind of an internal scaffolding. Protection.

When you look at a skeleton... you see the rib cage and you see the skull. So in lab, we've done the parts of the skull and it looks like a football helmet.

And the rib cage itself protects vital organs like your heart and your lungs. So when you look at a skeleton, you can kind of guess where the important, even if you had, no knowledge whatsoever. You could kind of guess where the important stuff is because it's protected by bone.

And then of course movement. Now it really goes to the muscles but if the muscles didn't have the bones to attach to we would all be a pool of mushy goo on the floor. three functions that you may not think of. Inorganic salt storage. Your skeleton is kind of like a bank account, and so it's a good place to store especially calcium and phosphorus.

Part of your homeostasis, there's that word again, is maintaining that supply of calcium. There has to be a certain percentage of calcium in your blood at all times for your muscles to work and for your nerves to fire. So if you get real excited about some dilly bars at Dairy Queen, which is a good day, and you have too much calcium, well you might as well store it in your savings account. count, you might as well put it in your bones. If you have a day where you haven't had anything to eat, that's a sad day, your body can pull that calcium and phosphorus from your bones to put it into the blood.

So it becomes this reservoir. I never thought of the skeleton that way. In fact, when I was a kid, I used to eat a lot of food. I used to eat a lot When I first saw the skeleton, I just assumed it was just this dead thing inside our body that kind of held us up.

But it's very metabolically active and very much alive. So it's not like we put calcium in our skeleton and we're done. We can actually pull it back out. hematopoiesis heme means blood poi means to make so this literally means to make blood so all of your blood cell formation whether we're talking about those erythrocytes the red blood cells to carry oxygen and carbon dioxide or the leukocytes which carry kind of these infection fighters is what they are, so it's kind of our immune system.

The platelets for blood clotting, all of these are formed inside our bone marrow, which is technically a part of the skeletal system, specifically in the red marrow. which we'll be getting into the difference, but red marrow I'm sure they named because of blood. Whereas the last one here, energy storage, we don't often think of this one, but yellow marrow, fat in the adult medullary cavity, basically in your bone marrow, you have some yellow marrow. Anytime we see yellow, we just saw yellow in our last unit, anytime we see yellow really just usually means fat. And so we can store energy by also having this fatty yellow marrow in our bones, it kind of cushions them a little bit.

And so we see this in our... our spongy bone, which will make more sense in a few minutes. So a bone, remember, is a connective So it fits the definition of a tissue, a bunch of cells working together.

Bone is very vascularized, so it heals very, very fast. But it's made of two phases. So we call it biphasic, because it's two phases. We have the organic phase, which we had that term before. and the inorganic phase.

So the organic phase is the bone cells, so they're alive, plus collagen, which collagen is those big protein ropes. So we kind of get the flexibility but also mostly strength from this. Remember, when you pull on collagen, it would be like pulling on a rope. There's not a lot of give to it. The whole purpose is for it to be strong.

But it has a little bit of flexibility. The bone cells maintain structure. They don't really support. They just make the structure, but that's not what's actually giving your bone. bones any kind of strength.

So this is over one third of your bone mass. So it allows for a little bit of give. When you bump your leg or hip into like a desk or something, you don't want your bones to shatter.

We want our bones to be strong, yes, but we don't want them to be fragile. So like for a wedding gift, we got this really, really pretty crystal base, which I mean, I'm not a crystal base kind of person, so I'm like, what the hell am I going to do with this? But it was nice.

But it's expensive, I'm sure, and it's really heavy crystal. Like I could hurt somebody with this thing. But if I don't, I'm going dropped it, it would probably shatter into a bazillion pieces.

So it's really, really strong, but it's fragile. We don't want our bones to be fragile because think about what we expect them to do. So we want them to be strong, but we want to have a little bit of give. That crystal vase doesn't have any give to it.

Whereas if you, you know, kind of crack your knee on a desk, this organic phase gives your bones just a little bit of flexibility to where they can take that hit and not shatter. But we need this. strength. So this is the second phase which is two-thirds so this is the majority of your bones. It makes your bones very rigid and strong which is what you think of when you think of skeletal tissue.

So this is the inorganic phase and inorganic starts with I and so does ionic. So remember inorganic molecules are held together by ionic bonds. So these are things that would dissolve in water.

So these are our salts, primarily calcium phosphate again, kind of comes into play. So bone tissue is like protein ropes that have kind of sprinkled crystallized calcium on top of them. So we get the best of both worlds like Miley Cyrus. We get strength, but we get a little bit of flexibility. So you could do a little experiment with bone.

You could take two chicken bones and you could put one in a solution that has a bunch of enzymes to digest proteins, like meat tenderizer. If you cook and you use meat tenderizer, you sprinkle meat tenderizer on the meat. And what it actually does is it kind of starts the digestion before you, which is kind of gross.

It starts starts taking those big proteins and starts breaking them down into their amino acids, like taking little kid scissors to it. So it makes the meat more palatable. When you chew on it, it's easier to chew. So you could do this same thing. You could take this bone and put it in a bowl full of meat tenderizer and water and let it sit.

What it will do is digest the proteins away. So all you're left with is the inorganic solids. So after a while, if you take that bone out, it'll still look like a bone because 66% of it is still. there, if you tap that bone on the side of a desk, it would shatter into a bazillion pieces because you've taken out that flexibility.

The second experiment we could do is put a chicken bone in an acid that would dissolve the calcium and phosphorus, that would dissolve the ionic solids. So the only thing that you would have left would be the squishy collagen, the organic part. So after a while you could take that bone out of the acid, rinse it off, you could actually tie it in a knot.

So you could see how either one of these would not be good. We don't want our bones to be so loose. loosey-goosey that they can't even support us, but we don't want our bones to be so fragile that, you know, they break so easily.

So we need both. There is actually a condition called osteogenic imperfecta, where children are born with really, really brittle bones. It's usually diagnosed at birth because, sadly, like their collarbones will break during birth, and they'll usually shatter other bones, like skull bones and things during that process.

You can see how awful it would be, painful it would be to have 20-something fractures before you're even one years old. old and most of the time those children don't survive beyond that. There are two types of bones, compact bone and spongy bone. Now in lab when we did tissues we looked at compact bone, how it looked like tree rings and barnacles under the microscope. Compact bone is exactly what it says, it's compact, it's dense.

So this is the outer layer of all bones. So in lab when you were looking at bones, which I realize a lot of ours are fake, they kind of have this slick outer coating, that's compact bone. So if you look at at this picture over on the right, the outer edge there is thicker. That's the compact bone. The benefit to compact bone is it's stronger, especially along the axis of the bone, the shaft in the middle of the bone.

If you look at your femur, which is what the This picture is of, because you have that huge ball socket there. Your femur could support 40 times of your body weight. 40 times!

So if you look, a 150-pound person, which I am not, can support 3 tons. 6,000 pounds your femur can hold. But just from that direction. So it's very...

very strong from top to bottom. So think about if you took like empty beer cans, like four beer cans and you stacked them on top of each other. And you put your hand on the top and the bottom and push.

That'd be very strong. You could carry those four empty cans around. as long as you're pushing on the ends. But as soon as somebody comes up to you and karate chops it, those cans are going to go flying. So the femur is like that.

It can handle your body weight from up and down, which if you think about it, as an animal, that's the only thing it should have to do. So we could climb trees and run around in loincloths and be chased by saber-toothed tigers. But our bones were never designed for riding in cars, for roller coasters, for skydiving, and all the other crazy things we do because we're human. So our body is designed pretty well. but it's easy to break the femur in a car accident because it doesn't take a side hit very well.

The ends of the bone have what's called spongy bone. You don't need to know cancellous bone. Spongy bone is fine. If you look at the picture up above, it looks like a sponge. The difference is when you hear spongy bone, you tend to think of a sponge being squishy.

This bone is not squishy. lab, make sure that you touch some spongy bone because we have some real bones in there. And you, I always think spongy bone is kind of a pain because if I'm carrying the bones and you can see spongy bone, the sponge will like, the spongy bone will like snag your clothes.

It actually hurts. It's very sharp. this picture looks it looks like it's got all these little teeth it kind of does but if you look at the picture down below by having kind of the Holy Holies it that's the spongy bone at the end of the joints there it creates these little crevices for your bone marrow to sit in so these branches are called trabeculae and you don't really need that term right now but we will see that term in amp2 because it just kind of means branching the benefit to spongy bone there's a couple one it's usually in our joints like it is in this picture picture because it's equally strong from all angles.

So if you think about your joints, if you bend your elbow right now, the shaft of your humerus, your upper arm bone, doesn't really take a lot of abuse. It's the ends of the humerus and the ends of the radius and the ulna that take all the abuse in that joint. So wouldn't it make sense that you would want bone that could kind of take a hit from all angles?

Because think about the things you do to your elbow joint. You kind of turn it in all directions. Also, compact bone is really heavy.

Spongy bone is a lot lighter. lighter. Your skeletal system is already 18% of your body weight.

So you're dragging a lot of weight around. Well, imagine if this was all compact bone. Half of our body weight would be skeleton. We'd be exhausted just dragging our sag carcass around. And the other benefit to this is it can be made really quickly.

Compact bone takes a lot of time. Spongy bone can be laid down really fast. In fact, if you break a bone, you almost instantly start growing spongy bone back. So the trabeculae, again, is this little branches. I like this picture better because you can really see the difference between compact bone and spongy bone.

So there's a thin layer of compact bone all over the bone. But then it's thicker, of course, along the shaft where it's designed to take a pretty big hit. The trabeculae are lined with endosteum. Endosteum is a really thin connective tissue.

Think of it like tissue paper. Medulla is very squishy. Or, sorry, marrow in the medullary cavities.

Marrow is very, very squishy. See? And so we don't want something so fragile like jello bumping and grinding against hard bone all day. So to line the little scary teeth of that spongy bone, you kind of have this equivalent of tissue paper, just like when you wrap a present. So endosteum is just a connective tissue.

Endo means inside. Osteo means bone, just to protect the marrow. So red marrow, again, to make blood.

Yellow marrow is going to be fat. So this picture here is showing compact bone around the outside. Spongy bone. bone in the middle and you can immediately see the difference.

If you look at the bottom picture there, that's a skull bone where you have a spongy bone in the middle like the meat in a sandwich and you have the compact bone like the bread on the outside. Okay, so bone membranes. When you're looking at bone, we forget sometimes that it used to be alive because we just kind of look at the dead remnants left over upstairs.

We don't really see these tissues because we don't look at living bones. But you have periosteum, which if you look at the bottom picture there, is kind of showing, especially on the right, it's kind of showing it being stripped off like a jacket off of a person. And then you have the compact bone underneath.

See the little tree rings that look like the barnacles that we saw in lab. So peri, of course. means around, osteo means bone. This is a double layer protective membrane.

Just like your coat, you have the outer part that the world sees, and then you have the inner lining that's touching your body. So the outer layer is made of dense, irregular connective tissue. So it's really, really tough, and it's made of lots of collagen, kind of going in no particular direction whatsoever. The inner layer has osteoblasts and osteoclasts.

Blast means to build, clast means to build. to destroy. Like if you clash with something, you're tearing it down.

Osteo means bone. So you have these cells that are bone builders and these cells that are bone destroyers, which we'll see them here in a second. We also have a richly supplied blood and nerve.

and lymphatic vessels going in there. So if you look, that big blood vessel in the bottom picture is actually going through that periosteum. The bone has to be fed.

Bone is very bloody. There's going to be lots of nerve tissue. If you've ever broke a bone, it hurts like hell.

And lymphatic vessels, which for now, we don't really do the lymph system until next semester. For now, lymphatic is kind of for your immunity. So you want to keep the bone healthy. Then there's endosteum, which is labeled at the top there. And so you can see that's the lining right before the yellow.

bone marrow on the bottom kind of right picture there so you have that big yellow bone marrow in the middle you have the bone and then you have endosteum because remember we don't want ooey squishy bone marrow bumping and grinding against that bone so we've got that nice layer of connective tissue the endosteum but this also has osteoblasts and osteoclasts which means you can build and destroy bone from the outside and from the inside just like when you remodel a house you can work on the roof and the siding or you can paint the walls on the inside side. When we look at a bone from this angle, we can still see the periosteum like a jacket. We can also see the endosteum.

Periosteum serves as an insertion point for your tendons and your ligaments. So this is kind of an important concept. A tendon and a ligament, remember, are the really thick, dense collagen fibers running in all direction that we saw in our tissue unit.

But tendons and ligaments take a lot of abuse because they're the ones constantly being used. So we don't want them to tear and we don't want them to rip off. We don't want them to be attached to the...

the bone like a tack or a nail is attached to a wall. Think about if you took a rubber band and nailed it to the wall. Well, as soon as you stretched it, it would just tear right around that nail.

So it would kind of be similar if our tendons and ligaments were like tacked onto our bones like that. And they're not. Tendons and ligaments just kind of merge with the periosteum. So it's kind of like your clothes where you have seams.

Usually where you have seams is where you get issues like tearing and things like that. We don't have a seam without a seam. with our tendons and ligaments. They just kind of merge directly into that periosteum. So this is just a structurally smart thing.

So it's all this collagen. It's just thicker around our tendons and ligaments. The endosteum, again, is that connective tissue to protect the bone marrow and to line those trabeculae because they're pretty scary.

On this picture, we also have two new terms, which are kind of bad. Epiphyses or the epiphysis of the epiphysis. are the ends of the bone.

I've always remembered this because E for epiphysis and E for end. And then the diaphysis is the middle or the shaft. So as we just saw, the epiphysis would have lots of spongy bone.

The diaphysis would have lots of impact bone. But besides the bone, there's lots of cartilage associated with your skeleton. As our bones grow, as you go from a zygote, which is a fertilized egg after our parents had the naughty sex, ew, and our body starts to grow and we're kind of the size of a big jelly bean, It's not like we start with bone.

So very early on in embryonic development, there's no osseous tissue, there's no bone tissue. What we do lay down is kind of these precursors to bone, which are basically cartilaginous molds. So think of it like a jello mold.

If you pour Jell-O into a Jell-O mold, you get a shape. If you pour Jell-O onto a kitchen counter, you get a big mess. So when the bone goes to attach, when the bone goes to form, it kind of has to have something to lay down on, which is the cartilage. So embryonic skeleton is initially the hyaline cartilage that we saw in the microscope that then gets replaced by bone. Some of it remains.

So if you look on an adult rib cage, we have that costal cartilage where it still is there. It's also on a lot of... of our epiphyses on a lot of the ends of our bones, which we call the articulation ends of bones. If you articulate, you come together.

So where you come together, you can have a lot of friction. So we have these cartilage kind of coverings on the end of our bones to reduce bump and grind. If you've ever eaten chicken, you see that when you eat chicken and you're pulling the meat off, that the ends of the bones kind of have this weird jello cartilage stuff. So places we have cartilage still are costal cartilage like shown in this picture.

There's the C-shaped rings in our windpipe made of cartilage, which if you're skinny and you lean back, which... I am not, and rub your windpipe. You can feel them. When they do a tracheotomy, which is where they cut a hole in the trachea so someone can breathe, if there's an obstruction, they have to go in between those two rings.

But we want these big rings to keep our windpipe open. If you've ever had a kid, like, clothesline you or something, it hurts. But we don't want our windpipe to collapse ever.

The external nose, most of our nose is cartilage, and the long bones of our embryo. endocardionic skeleton. So when you still have growth, the epiphyseal plate is open. We call that your growth plate if you've ever heard of those, but we'll be seeing them again. We also have some elastic cartilage still in our body, especially in our ear and in our epiglottis.

which we mentioned before. And fibrocartilage is important to our skeletal system, especially between those two vertebrae and our knees. So remember, our cartilage and fibrocartilage is full of collagen, which is really, really, really tough. So the meniscus of our knees and the vertebral disc, they can take quite a beating. But they do.

We put a lot on our body. And then the symphysis pubis, where our two pubic bones come together. Determining bone age.

Now in lab unfortunately we've kind of gotten a lot more fake bones because they just hold up. It's like before students would drop real bones, and they would just break. They would always break. So we start switching to the fake bones because they're anatomically correct, and they don't break at all. as easily.

But we do still have a few real bones up there. So if you don't mind touching the real bones, you can try this next time you're in lab. You probably can't get an exact approximation of age until you're like specializing in this.

Like forensic anthropologists, if you've ever watched the show Bones or any of those kind of CSI shows, they always find a skeleton and they're like, they look at the skeleton for two seconds and they say, oh, there's a 14 year old Asian female. She smoked, she liked pop music and she wore red. And it's like, it's just a skeleton.

And so obviously they can't get all of that information from a glance, but they can tell a lot from Bones. People that specialize in this can get the age down to usually one or two years, which is pretty impressive, but characteristics they look for. How shaggy is the bone?

Older bones have little projections on them, because as we get older, we just don't lay bone down in such a uniform manner, so we kind of get weird, abnormal deposits. Young bones tend to be really smooth. Also, as we get older, we've used our body, and when you use your body and you use your muscles, the skeleton grows back a lot stronger.

And so if you kind of feel around on your body, like around your wrist, you have all these bumps. Any time you have a bump is usually where a muscle has been pulled. pulling on it. So the skeleton builds in response. So the more lumpy, bumpy you are, the more you've been using your muscles.

And so younger people just haven't had the time to do that. Growth plates. Epiphyseal plates, which, I mean, we just call them growth plates, is where you still have cartilage that's being converted into bone. So as our bones are growing, on the ends we have these big, thick rings of cartilage. And so, like on the femur, on both ends you have rings of cartilage that are going cartilage bone, so the bone is lengthening.

Well, once we reach a certain age, those cartilage rings fuse into bone, and then we're done growing in height. But there's different ages for different bones when we expect these to fuse. So then we have this little scar line called the epiphyseal line.

So if they find a bone and it still has growth plates open, then Depending on the bone, they can make an assessment on age. Some of your growth plates don't completely fuse until you're like 25, but some fuse when you're like 10. So people know this, people have charts and tables and graphs and everything else about this. So when they find a bone, they can make a pretty good estimate. So bone size, in general, bigger bones, bigger people, of course. I mean, if you found infant bones or, you know, five-year-old bones, those are going to look a lot different than a, you know, 20-year-old person.

But size, though, isn't great. You'd really have to use a lot of other factors because, because when we had some real bones in lab, we used to have this one tibia that was just huge. Like the person must have been so tall. And then we had one that was really tiny and always messed people up.

Bone density, the degree of ossification, how hard is the bone. Again, as we get older, we get women, one in five women gets osteoporosis. You're just not as good at depositing minerals. And so if the bone looks pretty fragile, it's probably an older person.

So they use all kinds of factors. Bone structure itself. We classify bones based on shape.

And the good thing is they don't use too many nerdy words. So they start with long bones. If you've ever watched a cartoon dog carry around a cartoon bone like the one I tried to draw here, that's basically a long bone.

You've got a shaft, you have two knobby ends. And see, I tried to draw the periosteum on there. So your femur, your tibia, which is your lower shin bone, your humerus, which is your upper arm bone, your metacarpals and metatarsals, and your feet and your toes. These all have this classic look. They're long with two ends.

Short bones. Again, they didn't get fancy. Those carpals in the wrist.

Some lovers try positions they can't handle. The scaphoid lunate. See, I need to do this fast.

Scaphoid lunate trapezium. Some lovers try positions. They haven't done this in a while.

Scaphoid lunate triquetter. See, I'm bad at this today. So the point is, we did these in lab.

Um... So now I can't let it go. Scaphoid, lunate, triquetral, or triquetrum, pisiform. Trapezium, trapezoid, gaptate, hammock. See, you always have to say it fast.

So if we haven't learned the wrist bones yet in lab, don't stress about it. We'll be getting there. But we call them the carpals in general.

And as we see in this little x-ray, they're really tiny, short little cube-like bones. Same thing with the ankle bones. We have the cuboid and the cuneiform and the navicular and then metatarsals and everything else. So those were all kind of...

even though they're a little bit bigger than the wrist, they're still short. They don't really have much shape to them. Flat bones are flat. They're thin, they're usually curved, and they look like sandwiches, where you've got spongy bones in the middle, which would be the meat.

You have the compact bone on the outside, which would be the bread. You have lots of trabiculae covered with endoosteum to protect the medullary cavity, which would have the bone marrow. And you've got the red bone marrow, which is hematopoietic.

Heme means blood, poi means to make, and so this is making all of your red blood cells and platelets. Or you may have some yellow marrow in there, which is basically fat to store energy. energy. So these flat bones kind of encase most of your soft tissues.

So most of your cranium, most of your skull bones, the breast bone, which would be the sternum, your ribs, your scapula, which is your shoulder blade, and your clavicle, which is your shoulder your collarbone would all be flat bones. And so this picture just kind of shows the spongy bone in the middle, which remember, it's not soft and squishy. It's just spongy.

So we got the holes for the marrow to fit in and the compact bone. So it looks like a sandwich. We have irregular bones. Irregular bones are the crazy looking bones.

They're not long, they're not short, they're not flat, they're strange. Those vertebrae that we've seen in lab, they look like little spaceships. They're crazy.

Nothing crazier looking than a spinal cord. Auditory ossicles, these are your bones. your ear bones. These are the smallest bones in the body. And in lab, we only have that one representative mounted in that kind of wood block.

They're so small and they're so weird shaped. And the hip bones, the dreaded coxal bones. Oh, so much we have to know. on those bones and they're so weird looking. Also your facial bones like the maxilla and the mandible are irregular bones.

They just look odd. Sesamoid bones is probably the hardest word out of all these. At least long, short, irregular is not too bad. Sesamoid are bones that develop within a tendon.

The only example is the patella. So your kneecap develops within the tendons in those, in those, around those knee bones. So sesamoid is kind of a weird world. word weird word and sutural bones they're also called wormium bones which i actually can remember wormium more than suture but we had sutures in lab those little lines on your skull but sometimes when those sutures come together when the skull fuses see how in this picture the sutures have kind of trapped little islands of bone so these wormium bones become their own little island of bone so 206 is quote-unquote human bone total but some people have a few more But not everybody has these, so they don't name them individually because it's kind of a random thing.

It's just when the suture spews, sometimes they trap little islands of bones. So we call these wormium bones or suture bones. Okay, the parts of a long bone. Some of these we've discussed already. The diaphysis, remember, is the shaft, and so that's the compact bone.

Because if you look at a bone like this as the humerus, it's really strong from end to end. It doesn't take a good side hit. So when people break a humerus, it's usually a side hit because that bone's not... designed for that.

So the diaphysis is the shaft with compact bone and the medullary cavity for bone marrow. And then the knobby ends there are the epiphyses. So in this picture, we've got yellow marrow, basically fat.

The epiphyses are the ends. So lots and lots of spongy bone, which they've blown up there on the right. So we can see the little crevices there, the little spaces. That gives us space for blood to work its way in there and also more kind of for the marrow to have a place to be. Lots of hyaline cartilage on the ends of these bones because of the bump and grind at the joints when we're moving.

And the epiphyseal line, if you look at that picture, the epiphyseal line is that faint line that goes across, kind of separating the epiphyses from the diaphyses. Those were your growth plates. So in a bone that's still growing in length, that would be a little line of cartilage. But in an adult bone, it's just kind of a scar.

You can actually see these on x-ray. Now, I didn't want to go into rad tech, and I'm not an expert. an expert by any means on breaks. Frankly, if you showed me this x-ray, I'd be like, oh, look at that fracture.

And they'd be like, no, that's the growth plate. So we call this the epiphyseal line or the growth line. And it's just there between the ends and the shaft.

So it's where that growth plate used to be, the epiphyseal plate. But you can call it growth plate. And it used to be a disc of hyaline cartilage that was being converted into bone, making the bones longer and longer and longer till we reach adulthood.

And then we're done growing.

Transcript for:Understanding the Skeletal System

Transcript for:
Understanding the Skeletal System