this content is recorded exclusively for dr young's anatomy class it is not to be uploaded or distributed to any social media sites or streaming sites and not to be used without the permission of dr young welcome to chapter six looking at bones here we're going to focus on the actual bone tissue the location of the bones we covered in lab so whenever we're looking at bones we're looking at the skeletal system bones are going to have a lot of functions that we usually don't think about first one is protection we think about bones protecting especially with skull skull protects the brain really really well other bones don't protect as much like our long bones they're very interior so muscles are wrapped around them not providing a whole lot of protection there bones are really good at storing minerals calcium phosphate magnesium calcium is going to be the big one two-thirds of our bones are made up of straight calcium blood cells are also formed in the actual bone whenever we look at red bone marrow that's where blood cells are actually made our white blood cells tend to also be made from the red bone marrow fat storage we have yellow bone marrow so quite a bit of fat is literally stored right within those bones and then of course movement our muscles are going to attach to the bones and actually pull on them and use them as leverage so we can actually get movement and then of course they provide support this one we think about quite a bit we work walk on our legs we can pick things up with our hands so they do provide a whole lot of support when we look at overall bone structure there's actually five types of bones that we can kind of make into big categories we have our long bones which are long short bones which are things like our wrist bones and our ankle bones so carpals are wrists tarsals or ankles we have a couple flat bones which include the ribs some of the bones in the skull and then the sternum we have a lot of irregular bones when we can't find a good category to place things in we're just going to throw them in irregular so all of our vertebrae here again some of our skull bones are going to fit into this vertebrae just kind of have weird shapes to them sesamoid bones we only have one sesamoid bone it's patella it gets its very own category sesamoid translates into bone or in a nut-like so patella kind of looks like a nut when you look at it so it gets its very own little category in there so here's all the different bone types with the whole skeleton kind of just blown up for you so you can see where they come from we got long bones short bones those flat bones irregular and then the sesamoid with that patella now we're going to look at the structure of our bones so we're going to focus mainly on the long bones the periosteum is basically the outside connective tissue it makes a really good place to run blood vessels and nerves through our bones get a huge blood supply they're not only maintaining weight helping with movement storing mineral minerals but they're gonna actually be making those red blood cells so they need a huge blood supply going to them we have little perforating fibers that it's going to help to anchor the periosteum to the outside of the bone if you've ever taken a chicken bone and kind of scraped the actual chicken bone and some white stuff comes off that's a periosteum of that chicken bone you can literally kind of scrape it off and we have the same thing the diathesis is going to be the main long middle portion of our bones the epiphysis is going to be either end the diaphysis is generally filled with bone marrow especially when we're looking at long bones so it could be that red bone marrow or the yellow bone marrow we're also going to have compact bone and spongy bone compact bone is really really compact the cells are really packed tight together and it's going to be really strong it resists twisting and a lot of weight or linear compression being put on it spongy bone is said to be kind of honeycomb like it kind of looks like a sponge it has little holes all throughout it this still provides really good support as far as twisting goes but it's not as compact not as strong can't take that linear compression quite as well but we tend to find this at the ends of our bones where our joints are going to be because we're going to have extra supporting structures there like our ligaments tendons and all the other connective tissue helping to make up that joint while the spongy bone does it allows our bones or entire skeletal system really to be quite a bit lighter because the lighter it is the less energy we have to use if we look on the very inside of our bones we have the endosteum this is going to be basically just that very inner epithelial lining there epiphyseal lines this is going to be an actual line that separates the epiphysis from the diaphysis so the end from that shaft or middle portion this is where we actually find cartilage while we're growing it's usually called the growth plate it's kind of the common name for it so that bone is literally going to be cartilage in there until we reach our full height and then it actually does become bone so here's just another picture of those long bones so you can see the epiphysis on either end epiphyseal lines where we're going to grow the diaphysis which is the shaft the medullary cavity runs through that diaphysis is which is where we're going to find that bone marrow don't forget the periosteum is running along the outside of the bone which is that connective tissue where blood vessels run through and then spongy bone tends to be towards the end of the epiphysis and then we have nice compact bone all the way along the outside like we looked at before blood supply is going to be really important to the bone blood supply is going to be the big difference between a lot of our cartilages that have poor blood supply and connective tissue in general bone is completely opposite has a huge blood supply going to it we have nutrient arteries running through the bone that actually run up through little nutrient for ramen a foramin is just a little hole so arteries are real are literally going to run up through the bone to supply all the cells on the bone with as much blood to get the nutrients and oxygen that needs to do its job red bone marrow remember is where red blood cells actually get made at so not only do we need the blood to maintain the bone we need that huge blood supply to make sure that red bone marrow is getting enough oxygen enough nutrients to actually make new red blood red blood cells yellow bone marrow is our second option for bone marrow so this is made of fat so this is going to be a good energy storage uh as we get older more of our bone marrow actually converts to yellow bone marrow instead of red bone marrow now we're going to look at some of the microscopic structure of the bone or some of the individual cells actually helping to build the bone up and break the bone bit down so when we're looking at bone or osseous tissue we have a big inorganic matrix this is mainly going to be calcium the organic component is mainly going to be collagen fibers now you have to have the mix of both the actual minerals especially the calcium makes the bone really strong but you still need to have a little bit of flexibility you don't want it to be really brittle so that's where the collagen fibers are going to be important so if we look at bone if you remove the collagen fibers the organic part of it super brittle and they just crumble if you remove the calcium the organic part then it becomes so soft that it just bends so you have to have that nice mix between the two now for our individual bone cells are actually going to be making up this bone we have osteoblast osteocytes and osteoclasts osteoblasts build bone so there's a b in blast they build it this is what's going to be laying down that bony matrix is going to be these osteoblasts now we also have osteogenic cells these are going to be the cells that literally turn into the osteoblasts but they're just the precursors osteocytes actually become the bone cells an osteocyte is a bone cell but what happens the osteoblast literally will trap itself as it's laying down the matrix and they become the osteocytes these little little pockets called lacunae the little kunai is what the osteoblasts trap themselves with so they literally lay down the matrix all around them and they become trapped and then they just become a bone cell osteoclast these break down bone so they use hydrogen ions enzymes these are going to be active especially when our body needs extra calcium but they're always continuously breaking down old bone and we're always building new bone about every 12 to 15 years you end up with a brand new skeleton now we talked about compact versus spongy bone before these cells are going to be acting a little bit different and arranged in a little different pattern be when we look at the difference between our compact and spongy bone looking at compact bone first compact bones are made of osteons an osteon is one functional unit of bone these are arranged in basically circles of osteocytes called lamellae these are going to form a circle-like pattern making up that compact bone here you can see in the picture through each one of these layers we're going to have a central canal running down through all of them this central canal is where your blood vessels and your nerve is actually going to run through the bone now there's also little lines on the ridges of each one of these circles the darker areas are the lacunae which have the osteocytes in them and the little lines that connect them are the caniculi the caniculi is how oxygen gets distributed nutrients from those blood vessels so these cells have surrounded themselves in the matrix so they use a little cuniculi little canals to basically share things in between each other and here's a picture of an actual osteon so you can see the darker areas are lacunae which have the osteocytes and the small lines of the caniculi blood vessels will be coming right up through that central canal and put a whole bunch of those osteons together and that's going to be making up that compact bone when we look at our spongy bone those cells aren't nearly as densely packed together remember this is kind of like a sponge spongy bone is going to be arranged in what's called trabeculae now you still have osteons but they don't make up that nice round pattern like we actually saw with our compact bone they also don't have a central canal where the blood vessel runs right up through the bone since it's a spongy bone and has little holes in it blood vessels can actually just interweave themselves in between those holes and then you can distribute the oxygen nutrients throughout that entire spongy bone without having to have that central canal but we do still find the osteoblast osteocytes and osteoclasts within both types and here's just a bigger picture blown up for you of that spongy bone so blood vessels just literally interweave themselves through the whole maze and then distribute everything out to the individual osteons throughout the trabeculae