[Music] hey there folks welcome back and we're going to just continue on with our lecture material now as far as looking at the histology of our bone tissue there's a big difference between the hard outer compact bone and the porous inner spongy bone the compact bone Str structure well this needs to have a structure that can put up with a lot of stress there's a lot of strain going on our bones so the compact structure of the bone needs to be resistant to those stresses and withstand a lot of forces so when we're looking at the structure of our compact bone and this is looking at a crosssection of the bone so here's the outer compact bone and then in here this is where you're starting to see some spongy bone but the compact bone they're made up of these circular structures those are known as an oston the oston structure well each oston consists of between four to 20 different lamell lamell those are just the layers found within an osteon and they're arranged in these rings so a single Aon kind of looks like when you cut down a tree and you see the rings of a tree each of those Rings well that is a lamell making up a layer of an osteon and the strong Lamar Arrangement will this is allowing for this stress resistance aspect of the compact bone there's also collagen fibers that are running throughout these lameli and they run in opposite directions so notice here they kind of pulled out an osteon so you can see the individual lelli and you see these lines are representing how our collagen fibers are running so you've got them running in One Direction and this outermost Lamela you got them running in the opposite direction in the next Lamela and then you got them running in the the opposite direction again in this innermost Lamela running down the very center of our osteon this is a hole that's known as the central Canal also known as the herian canal and this is an indium line hole remember the ostium that's an inner membrane lining so it's found in the center of each of the osteon and this is where you'll see the blood vessels and nerves running as they're running through the osteon and running through the compact bone the osteocytes those can be found in the launi which I already mentioned when we talked about bone formation so you can see different launi here throughout our Lamela layer and those cavities those are where we'll find our osteocytes and you'll also find intracellular fluid within the Lacuna as well by the way Luna is singular Luni that's plural now the neighboring Luni are actually connected to each other through these small canals and we call those small canals canaliculi canulas that is the singular canaliculi that is plural so here you can see the individual Lacuna and they're connected by these lines and those lines are the canals that's the canaliculus look how it starts with Canal so canul liuli are canals there's these cytoplasmic extensions of the osteocytes and they actually extend through these canals as well and that allows these osteocytes to share resources with each other this is just another way to see how osteocytes interact with each other how they're found within a Lacuna and how you have the canaliculi that connect one Lacuna to another and the neighboring osteocytes able to interact with each other through these openings that are called Gap Junctions so overall the compact bone structure you've got these oons that are not permanent structure because remember the bone B is dynamic it's constantly being broken down by osteoclasts and being rebuilt by the osteoblasts and so as this Dynamic building and breaking down of the bone occurs it leaves behind some common features found in the compact bone those things that we find Left Behind are known as interstital lamell they're found in the space between our Circ C osteon so here you see two circular osteon and in between you'll have interstital lelli remember that word interstital that simply means an interval or an intervening space we also have circumferential lamell those are the lamell that are found on the outermost layer of the compact bone and it's also in the inner layer of the compact bone so in this image you're only seeing the outer layer but that's going all the way around all of the osteon that's the circumferential lamell they don't show it here but there's also a layer of circumferential lamell on the border between the Compact and this internal spongy bone as well and what these circumferential lameli do is they help to add strength to the Bone now also running through the compact bone we have what are known as Perforating Canal also known as folkman canals they originate from the blood vessels in the periostium remember that periostium that is that outermost membrane lining the outside of our bone so they originate in the periosteum and they're traveling at right angles or perpendicular to the Central Canal of the neighboring oston so these represent the central Canal of an osteon and running perpendicular to that you have your Perforating canals and they're helping to connect the oon to each other this is just another view of it this is a cross-section view but it'll show you here what I mean by these Perforating or vman's canals here you have one osteon here is another osteon you got the central Canal this big open area in the center of the osteon and then connecting this Central canal through to the neighboring one that is the Perforating Canal or the vman's canal this also provides a good shot of what our interstital lelli look like found between the osteon as well as the concentric lamell running with in the oston now unlike the compact bone the spongy bone that's not the weightbearing part of our bones so it's a lot less densely packed than the compact bone the spongy bone is actually made up of a network of these struts and what that's doing it's providing a reinforcement for stresses coming in from a variety of different directions but also remember it's within this spongy bone that we find the bone marrow tissue now the struts of the spongy bone those are called Tuli another name for spongy bone is actually tricular bone so the Tuli these are covered with the ostium that is the membrane where we find our osteoblasts unlike our compact bone bone the spongy bone is not actually made up into those osteons you do not see a central canal and you don't see all of these osteon all around you do however see the concentric lamell that are being formed and these concentric lamell they're made up of launi that are containing osteocytes and the launi they do connect to each other via or canaliculi now as I said there's no Central canal and there's no Perforating canals because well there's no osteon that need the central or Perforating canals to supply the blood the Tula they actually obtain their blood supply from the vessels that are found in the bone marrow so just a bit of a review here we have our compact bone the compact bone is found on the outer surface of the bone this is made up of osteon that have concentric lamell you've got interstital lamell between the osteon you've got a central canal in the middle of the osteon that's carrying the blood supply and you've got Perforating canals going between the central canals of neighboring osteon you've got the Luni that house the osteocytes and you've got the canaliculi connecting the lacuni you also have the outer circumferential lelli surrounding the compact bone and finally you have the periostium which is the outermost membrane and that is carrying the arteries in the veins for the tricular bone or the spongy bone you do have your lamell those concentric lamell but you don't have a central Canal you don't have Perforating canals you've got the Luni housing the osteocytes and you have the canaliculi connecting the launi oh and there's my Archie now I'm not sure if he's trying to tell me he's tired it's time to go to bed or it's time to play ball and to be honest I don't think Archie knows either but what I do know is that we're done with this section so I'll catch you guys next time [Music] bye