hey everyone welcome to professor long's lectures in anatomy and physiology i'm professor bob long as you guys know from watching previous videos these videos are intended for students who are enrolled in my class i want them to learn the material the way that i present it if you're in another instructor's class then you need to learn all the details and all the stuff that they cover it may be slightly different than how i do it i hope these videos help all of you understand the material if they do please hit like and subscribe so that i can continue to get some feedback and continue to um do new videos better videos and edit them and make them much more slick and more professional but for now i'm going to time crunch to this coronavirus shutdown now if you are in my class we're doing a continuation of our bone lectures we've done the formation we've done an introduction to bone we've drawn long bones and talked about the different shapes of bones we did the bone wedge model with osteons and concentric lamellae and interstitial lamellae and all of that and then in the last video i did what's called endochondral ossification bone formation of most of your long bones of the body and how they grow within a hyaline cartilage model we're going to move on to page 43 and we're going to talk about intramembranous ossification the intramembranous means within a membrane and if you remember your skin is a membrane it's a call it's called the cutaneous membrane and it has two layers an epidermis and a dermis the dermis of your skin is where flat bones or dermal bones grow by a process called intramembranous ossification now when i first type this up it's on the top of page 43 i have some steps here and it followed our textbook but we're getting a new edition of the textbook and i don't like the way that i really typed this up it's a little confusing so we're not going to follow this exactly i'm going to rewrite some details here of what's happening and draw this out for you so you can see what's called intra membranous ossification so intra membranous ossification is formation of bone within mesenchymal or embryonic tissue in the layer of your skin called the dermis and we call the bones that form this way dermal bones or flat bones the flat bones of the skull the the um what we call the calvaria or the cranium of the skull your collar bone your clavicle the sternum your ribs all of the flat bones develop this way even parts of the scapula okay so in intramembranous ossification if you remember from early on in the semester we drew out the layers of the skin and if you think about it the top layer of our skin up here and imagine if i did this in a three-dimensional cutout like a big flat piece of skin okay well where this corner is i would still have this going back to this corner so we're trying to look at this sort of a 3d cut out and then down here would be all the hypodermis i mean the dermis okay so we have epidermis and then we have the dermis of our skin and then down here we would have hypodermis remember the epidermis has a lot of areolar connective tissue and dense irregular tissue mixed in and there's a lot of protein fibers here and within this embryonic layer this is occurring while we're in the womb within this embryonic tissue some cells are going to differentiate and the cells that differentiate are called osteoprogenitors there's some cells called osteoprogenitors we've talked about this these are cells before they're making bone will mutate essentially or develop into osteoblasts and as the gen these cells generate into osteoblasts they're going to start laying down some bone tissue along all these little fibers these protein fibers and all the different directions that they grow and if you look at the edge it looks like little pointy things sticking out and they call those little points in here spicules which means little spikes so within the dermis of our skin some mesenchymal cells called osteoprogenitors will turn into or form into osteoblasts and start to lay down some little spicules of bone and this type of tissue is called osteoid osteoid means close to bone or similar to bone or like bone but it's not completely bone yet okay and what they do is they simply in order to form these spicules they lay down calcium salts onto the protein fibers that are already there now over time that we will continue this growth and essentially what this whole thing is is a primary ossification center so there's going to be a long three-dimensional band of these little spikes or spicules that grow through this flat layer of of um the dermis now over time it will grow out and those little spikes or spicules if i were to just focus on this tissue will continue to grow out along stress lines and things and what we are forming essentially is the trabeculae of bone we've talked about what trabeculae are their plates of bone and we grow these trabeculae out forming this long plate of spongy bone over time we're going to start to remodel some of this tissue here and we'll lay down a thin plate of compact bone and it will grow sort of in three dimensions so we get a big flat piece of bone forming and in the middle there's a whole bunch of spongy bone with a little and it's trabeculae with some compact bone all around the edges now i know that doesn't exactly follow the steps in the note set and if we wanted to follow the steps in the note set within a layer of embryonic tissue some stem cells that's the first blank called osteoprogenitors differentiate into osteoblasts and begin forming calcium salts and it forms bone and even though there's a single blank there essentially we're forming an ossification center or a primary ossification center the osteoblasts start to get trapped in the matrix and become osteocytes and then the cells from this ossification center will grow out in little spicules or trabeculae and basically the next line of step three would say small struts develop near the spicules and form the ossification center as it continues to grow and those struts would be the trabeculae okay and then eventually a plate of spongy bone is formed and we remodel and form compact bone around the edges of that okay and that's what a flat bone would look like if you ever slice one of the skull bones open it's got a thin layer of compact bone and it's filled with spongy bone we don't form a marrow cavity now in the marrow cavity of long bones we have yellow marrow but in these spaces between the trabeculae of flat bones we have what's called red marrow red bone marrow and that's where a lot of blood cell production occurs so this doesn't exactly follow the steps i'm actually going to put a link to a video that talks to this and my canvas page for those of you who are enrolled in my class you can do a google search for these videos of the formation of of uh intramembranous ossification and you can find videos of it but essentially i need you to know these things intermembranous ossification is the formation of bone with one within a membrane of embryonic tissue it is the dermis of your skin and some stem cells called osteoprogenitors form form or differentiate into osteoblasts and lay down a thin layer of spicules by depositing calcium salts onto the proteins forming some osteoid and then we start to grow those little spicules out and as they grow longer they're forming trabeculae of spongy bone and then we remodel some of the tissue and put a layer of compact bone around that that's pretty much it so there's not a lot of put the steps in order but i think you should know where it occurs in the body know that it's the flat bones of our body and know that um we don't form a marrow cavity but we've cut we fill all the empty space in here with red bone marrow okay now that's rather short and sweet compared to all the steps of endochondral ossification i'm a little bit more interested in endochondral ossification than i am in tremendous okay now what we need to talk about is bone growth and length and bone growth and diameter for our long bones especially once our bones are formed they continue to grow and as they continue to grow they're going to grow in both length and diameter when we're born our bones are little tiny things the reason you're as tall as you are now is because your bones continue to grow longer and that bone growth and length is called interstitial growth i'm gonna write all this out and if they only grew longer then our bones would be really long skinny things like um like this meter stick i knew there was one in this room somewhere i saw it earlier and if i try to put a whole bunch of weight on this meter stick on the ends it's going to flex over time because it's not strong enough to withstand all the weight and it would start to flex i know you probably can't see that but if i set this here and press down on it you can see it starts to flex a little well then our bones would be all bowed especially our legs from supporting our body weight but if i made this really thick like a two by four i could stand on top of it and it wouldn't flex so our bones need to grow in diameter as well as grow in length bone growth and length is called interstitial growth bone growth in diameter is called appositional growth and we're going to write all these steps out why because i want you to learn it too i want you to or i need to have enough stuff to make a lot of test questions so i'm just kidding um so interstitial growth this is how bones grow longer now if you recall when we looked at a bone during development we have the marrow cavity we have the diaphysis we have the two epiphyses i'm not going to put the spongy bone in here but separating the diaphyses from the epiphyses is a plate of cartilage that we call the metaphysis or growth plate and the reason it's called the growth plate is because this is where the bones are going to continue to grow longer so you have to remember and then we also have some hyaline cartilage out here i'm going to leave the articular cartilage off but that is hyaline cartilage that fills our growth plate and we would have our secondary ossification centers here and this was where our primary ossification center formed the diaphysis now each edge of the growth plate is called a name so right here on this edge of the growth plate we call that the diaphyseal edge or the diaphyseal side you'll see in some books they say the diaphyseal edge or the diaphysol side of the growth plate which would be the side touching the diaphysis the opposite edge of the growth plate is called the epiphyseal edge or the epiphyseal side of the growth plate because it's touching the epiphysis so when we go to write these steps out essentially here's what you need to know on the epiphyseal edge of the growth plate or on the epiphyseal side of the growth plate i'm just going to give you the words that are in the blanks of my note set for those of you that aren't in my class i'll sing all of this on the epiphyseal side of the growth plate some cells called chondrocytes or we could say chondroblasts and chondrocytes will continue to lay down cartilage they're dividing by mitosis and they continue to add cartilage to the process now as they're dividing by mitosis and adding cartilage simply what's going to be happening here is i'm going to add another line of cartilage and another line of cartilage and another line of cartilage and continue adding cartilage here and here we do not remove the bone what's happening is this i'm pushing this epiphysis out further so that now the edge is not here the edge is here and the same thing would happen here i'm pushing the epiphysis out for example if i put this chair here and i'm laying down cartilage behind me i don't remove the chair i'm pushing it behind me so we're pushing the epiphyses out away from the diaphysis and that's causing the bone to start to lengthen the problem is this cartilage here would be easily fractured or ripped so at the same time that we're adding cartilage on the epiphyseal side some cells called osteoclasts and osteoblasts are going to remove cartilage and replace it with bone and we will grow the bone tissue out further and add to the marrow cavity and we do the same thing at the other growth plate we're going to add some bone here and extend the marrow cavity so that now the diaphysis is keeping up with the growth and the way we would write this out is these new cells are going to lay down cartilage i just rewrote this this semester so i want to make sure i put it the way that it's in your note set and what that's going to do is push the epiphyses out i changed the way that i'm teaching this because our textbook changed it a little bit and i want to make sure that what i present is goes along with our textbook so that students can study this more easily it pushes the epiphyses out now in the third step it says at the same time on the diaphyseal edge these are just the words that are the blanks in my notes osteoclasts will remove some cartilage and osteoblasts will replace it with bone let me make sure that's how i have my yes so essentially osteoclasts are eating away the old cartilage and osteoblasts are filling in bone behind it and as we do this the bone grows longer but the growth plates don't get any thicker they remain relatively constant in their thickness okay now this bone growth will continue for quite a long time until we hit puberty and our sex hormones will rapidly increase the bone formation much faster than they increase the cartilage formation so over time essentially what would happen is this imagine if on this finger i'm laying down cartilage growing the bone longer this way and this finger is laying down bone behind it so that the growth plate is moving as we add tissue right but if bone formation if they're moving at the same pace the gap between them the growth plate stays a certain thickness but over time what if these cells the osteoclasts and osteoblasts increase their activity faster than the chondrocytes are working then as i'm growing the growth plate eventually we will start to remove cartilage and replace it with bone faster than we're laying down the cartilage and eventually the growth plates get replaced with bone tissue they close so to speak and then we stop growing in length we've reached our adult height for example i believe i've talked about this before but i'll talk about it again the fourth step is already filled in in my note set we continue to grow the bone out throughout most of our life until we hit late puberty and we close the growth plates and fill them in with bone but if i were to look at someone's distal radius when they're like you know 10 or 12 and the distal ulna it will look like this you'll see the radial and ulnar styloid but you'll see where the growth plate is on an x-ray there will be a gap in the bone that's where the cartilage is because cartilage doesn't show up on x-ray very well if i were to look at the same individual later on and you know a few years later say when they're 23 the bone would look like this there would be no more open growth plate that means that person stopped growing and if your x-rays are good enough sometimes you can see the faint shadow of a line across there that they now call the epiphyseal line the appearance of the epiphyseal line the closing of the growth plate indicates that you've stopped growing in length you're not going to get any taller so those are the steps for interstitial growth interstitial means between tissues and between the bone tissue and the cartilage tissue here we're growing longer okay now again if i grew my bones longer but not in diameter then they would start to flex and bow over time so that leads us to talk about what we call oppositional growth so i'm going to erase all this and we're going to talk about appositional growth which is bone growth in diameter now this requires us to do a cross-section of a long bone so if i have a long bone here and let's say i have some open growth plates i'm just going to draw a generic piece of bone here but i also know that i have this marrow cavity if i do a cross section through this if i cut it open and look down on top of it this way i would see a thick ring of compact bone filled with all those little osteons i would see some spongy bone right around the inner edge here i would have my perichondrium and my i'm sorry periosteum and endosteum here and here you have to remember from a previous lecture the periosteum and the endosteum have two layers the inner layer which is touching the bone is called the cellular layer the outer layer which is away from the bone is called the fibrous layer it's very fibrous and tough but the cellular layer is filled with osteoprogenitors and osteoblasts and some other cells and there's even some osteoclasts roaming around in here so now if we were going to follow along in the note set it's going to tell you interstitial growth is the process by which bones i'm sorry appositional growth i'm on another page we're on page 44 of my note set appositional growth is how bones grow in diameter it occurs at the same time that interstitial growth is occurring so that our bones can withstand more weight and essentially what's going to happen is that osteoclasts on the inside are going to continue to digest away some of this spongy bone and as they digest away the spongy bone they're going to increase the size of the marrow cavity and as they do digest us away as the marrow cavity increases the amount of spongy bone on the edge becomes less and less and less at the same time what's going to happen is some osteoblasts are going to migrate out of the inner cellular layer and they're going to lay down a long piece of circumferential lamellae those strut those plates of bone that grow all the way around the circumference here if i continue to add circumferential lamellae over time then it's going to push the periosteum out and if i continue to keep adding reams of bone out here it looks like the shaft of the bone would get very very thick but again at the same rate we're digesting away some of this bone here and increasing the size of the marrow cavity and essentially what happens is i end up with a ring of compact bone and i still have my spongy bone here and i have my periosteum in the endosteum and essentially the thickness of the bone will increase a little bit but again these two things are happening at the same time and as i do this in all directions the diameter of the bone has grown when i first started the diameter of the bone was about this far across now we've extended it out to here and the bone has grown much larger in diameter to support more weight spreading that weight out over a larger surface area so essentially we're increasing the size of the marrow cavity but we're adding circumferential lamellae keeping the thickness of the bone relatively constant and the bone grows in diameter so if we were to go over the steps here where all the blanks are let's do this for those of you that are enrolled in my class osteoclasts will continue to digest away the lining of the marrow cavity increasing its diameter at the same rate osteoblasts from the periosteum will migrate out and lay down another ring of bone and this is going to form what we call circumferential lamellae and as i add circumferential lamellae to the outside and keep adding but remove bone from the marrow cavity the dye again the diameter of the bone continues to grow the thickness of the bone remains relatively constant it gets a little thicker and this bone growth in both length and in diameter will continue until we reach our adult height okay so know that these osteoblasts and osteoclasts are always remodeling bone and growing bone and shrinking bone depending on dietary or depending on your diet how well you're eating and feeding your body the nutrients that it needs if you were in a third world country and starving to death then your bone growth and development would not be normal people don't grow as tall or as healthy if you're starving them and so their skeleton becomes thinner and weaker and more frail more susceptible to fractures and other diseases okay now i want to cover a couple of other topics but we're going to do this in another video we're going to talk about nutrition and bones hormones and bones and how to keep a healthy strong body we're going to talk about some interesting concepts that affect our bodies and now we can really directly start relating our anatomy and physiology to our body with our diet with our nutrition with exercising and things that we do that can impact the health of your skeleton and the health of other tissues of your body so i hope you learned something about interstitial growth and appositional growth growth and length and growth and diameter and i hope you know a little bit about intramembranous ossification it occurs within the dermis of the skin where some mesenchymal or stem cells convert into osteoblasts form some trabeculae of spongy bone and then we remodel some compact bone around it forming the flat bones of the body okay hope you had as much fun as i did i hope you learned something and i'll see you in the next lecture do this stuff until you can't stand it do it till you understand it and do it to you can teach it to someone else without looking at your notes thanks for watching