all right so let's take a look at the anatomy of them so let's first look at long bone anatomy so uh we look at a long bone this is showing a live long bone here's a dead long bone on that side so the diaphysis is the middle portion of the long bone so that's what that's trying to show is the diaphysis all right uh this is mainly compact bone and then inside of that is what is known as a medullary cavity so the medullary cavity is a cavity within the diaphysis of a long bone and that cavity contains yellow bone marrow so yellow bone marrow contains fats and lipids all right so next is the epiphyses epiphyses is pleural epiphysis is singular all right so these are the ends of the long bone so there's one end there's the other end all right so what we see in there is there's a thin layer of compact bone around spongy bone in there all right in red bone marrow that's what you're trying to see there fills in those internal cavities here now on this one end this live bone you can see here is some articular cartilage so articular cartilage is a thin layer of hyaline cartilage that surrounds the ends of a bone so we see a thin layer down here as well all right this is where bones come into contact with each other it's going to reduce friction here between the bones so you know the you're not having actual bone against bone it's hyaline cartilage against hyaline cartilage so that's going to protect the bone look at membranes that are found in here uh one is a periosteum peri means around austin refers to bone so you can see this membrane right there this is a fibrous connective tissue covering of bone all right now so we see this on a long bone but this covers all of them so periosteum isn't just specific to long bones now the periosteum is continuous with tendons and ligaments now tendons connect muscle to bone and ligaments connect bone to bone so connective tissues there next is enostium which you can't really see but the enostium is a thin connective tissue that lines the medullary cavity so it lines that medullary cavity in there now both uh the periosteum and the endoscene contain osteoblasts and osteoclasts which we'll talk about here in a little bit all right so let's look at microscopic structure so we look at microscopic structure we see these kind of structures here so this right here all right you can see them here and here and there and there and that is called an osteon these are the structural units of compact bone and they are made of concentric circles of bone and those concentric circles of bone are called lamella so that's a bony material now the bony material bone is made of collagen and inorganic salts known as hydroxyapatite all right now hydroxyapatite is mainly made of calcium and phosphate now one of the things about this why we have these two substances so the hydroxyapatite is a hard structure right but because it's so hard it also is uh can make it brittle all right and that's why we have collagen in the bone because the collagen makes bone less brittle so let's look at this picture here this is showing a fibula one of our lower leg bones uh they did a chemical reaction which they removed the mineral so you can see it's pretty bendy here uh and they did a different chemical reaction where they removed the collagen as you can see it's very brittle there all right so we want to have both the hardness uh that the hydroxyapatite provides but also uh the collagen removing its brittleness okay so right smack in the middle of the asean is what is known as the central canal so this is a tube in the asean that contains blood vessels and nerves all right now you can't see it there but you can see blood vessels there and this makes bone a living material so if we damage the bone by having blood vessels there we can repair that material all right now you're seeing these sideways tubes and those are called perforating canals so those are two um uh so these are tubes that connect the central canals to each other all right next are lacunas so lacuna are these small cavities within the bone and each of those well go in the wrong direction each of those um uh contains an osteocyte a bone cell now you're seeing all these little lines in there and so those little lines are called cannaliculi so these are small tubes in the bone that allow the osteocytes to connect to each other and the these osteocytes connect by gap junctions all right so this guy connects to that guy through that canaliculi and there's um the bone cells are connected by those gap junctions all right let's take a look at bone growth bone development and growth so bone development growth is known as osteogenesis in both processes we're going to talk about we're going to talk about what is known as ossification an ossification is a conversion of connective tissue into bone so let's take a look at uh bone development so first here so looking at this picture here so the first type is called intermembranous ossification so intra within membrane so this is a process of of replacing mesenchymal connective tissue to form bone so here we're going to start off with mesenchyme all right so uh that's where we start uh and then ossification centers are going to appear in that fibrous connects tissue so this is what's going to happen next there's that offication center and so here these mesenchymal cells are going to specialize into osteoblasts so that's what we see there there's the osteoblasts and yellow so these are mesenchymal cells there all right and those osteoblasts develop produce deposit of bony matrix around them so this is what we see starting to be made they start making bone essentially the result of this is a spongy bone form of the bone so this is the bone it's just all spongy bone at this point all right then periosteum is going to form around the edges of that bone all right and then they're going to fill in the edges here with compact bone all right so that's how uh intermembranous ossification occurs we're going to start off with mesenchyme mesenchymal cells are going to specialize in the osteoblasts they're going to start to produce uh bone uh they're going to convert that uh so they're gonna make a spongy bone form of the bone periosteum is gonna form on the edges and then we're gonna fill in the spaces on the edges making compact bone there so this is how we make most of our bones so irregular bones are made this way flat bones are made this way um short bones are made this way sesamoid bones are made this way so the only ones that are not made this way are long bones so let's take a look at the next one that's where we get longbone development here okay so next is endochondral ossification endo means within chondro refers to cartilage so endochondral ossification this is the embryonic formation of bone by the replacement of hyaline cartilage with bone so here the first thing is we're going to start with a hyaline cartilage model of the bone which is what we see here all right and then chondrocytes in the middle of that bone are going to specialize in osteoblasts just kind of like what we saw before and so they're going to start to convert that cartilage to bone so on this picture you see this light purple is trying to show cartilage the darker purple is where we're converting that cartilage to bone and then we're seeing that bone development there okay so those isoblasts are going to convert that cartilage to bone and then they're going to work their way towards each epiphysis all right and so this is going to lead us right into the next thing which is growth of lung bones all right so here we have uh our long bone all right and so we see right here this structure right there in the middle or at the end of that and that is known as the epithelial plate commonly known as growth plates so there's a band of cartilage where bone growth occurs and it separates the epiphysis from the diaphysis so if i go to the one of these pictures here this is showing the uh hand off a child and you can see there's epsilon plate this is bone here that's the epiphysis there's the diaphysis so that this is still cartilage in that area that we can see there on that x-ray okay so let's go back to this picture here all right so in the absolute plates new chondrocytes and uh cartilage are made in the epithelial plate and they're pushed towards the diaphysis and so what this does is that pushes the epiphysis up so as new cartilage is made it's pushed down that epiphysis moves up because that's the only thing that can happen there and so what happens there is that elongates diaphysis the diaphysis is going to get longer as the epiphysis moves up all right so in the diaphysis you see in this darker purple area is a zone of calcification and that's where uh that cartilage is converted into bone or ossified all right so we have two things that work we have in the epsilon plate we're constantly making new cartilage and cartilage cells and then right below that in that zone of calcification is we're converting that cartilage to bone now both of these processes are controlled by hormones and we'll get to those hormones here in a little bit but these two processes will continue uh bone growth occurring there in the epsilon plate converting that cartilage to bone in that zone of calcification what's eventually going to happen is that zone of calcification is going to overrun that epsilon converting it to bone and when that occurs this is what you see bone growth will stop all right let's take a look at uh the growth in bone width this will move for me okay so osteoblasts uh here in the periosteum um lay down some bones so here osteoblasts and periosteum we're laying down some bone uh the bone forms grooves around the blood vessels so you can see there and then there and eventually they overtake that blood vessel and this will form an osteon right there in the middle and this gets our bone to grow uh out in with you