this chapter is going to be on the skeletal system um it's going to predominantly concentrate on bone and tissue of bone so we're going to talk a lot about histology now the skeletal system is actually made up of two separate parts we have the axial skeletal system and the appendicular skeletal system alog together in the adult we have approximately 206 bones it may vary between individuals but in general the average number is 206 the axial skeleton think of the word axis is going down the middle of the body that's going to be your skull mandible vertebral column and thoracic cage as well as a tiny bone called the hyoid bone the appendicular skeleton is going to be basically the outer portions of your body your pectoral girdle so your sh shoulder girdle your upper appendages your lower appendages and your pelvic girdle so your hips now within the skeletal system you are going to have different shapes of Bones so you can see in this picture we have long bones and long bones get their name because they're going to be longer than wider we have short bones short bones are going to be a more compact shape um it's not really safe to call them Cub like because some might have this variance of a shape but they're basically much more compact relatively equal on all sides we have flat bones flat bones are going to be thin and Broad so you have the sternum scapula and the parial bones on which are top bones of your skull irregular bones those are bones that don't have any particular shape so vertebrae are a good example your ethmoid bone which is within your skull your zygomatic bone which is your cheekbones and then sesm moid seso gets this name for the sesame seed shape and everyone's going to have the patella for the sesm moid bone and then you have your pisor which is a tiny bone in your wrist if people form extra Bones based off a manual labor um many times the shape will be a cosmoid bone now regardless of the shape all bones in the body are going to contain both types of bone so two types of bones are going to be spongy and compact as you're looking in this picture what you can see is that the compact bone is very solid and dense while the spongy bone is really porous so regardless of the bone shape we will see both types of Bones so this is a long bone we can see that the spongy bone is predominantly at the top the compact bone is predominantly through what we call the shaft of the bone so let's talk a little bit more about Compact and spongy some of this will be a review from chapter 4 compact bone again gets its name because it's very dense and solid it's going to be made up of unit called osteons so we see this kind of tunnel that is lifted that is one osteon so in compact bone these osteons will repeat themselves osteons are going to be made up of rings of salt called Lamela within the Lamela we're going to have our pits our pits are the Lacuna inside the Lacuna we're going to have osteocytes the cells that maintain bone and those OST ocytes since they're living they're going to need nutrients and they will produce waste so capillaries are going to Branch off from these blood vessels within the perversion Canal also known as the central canal and those capillaries are going to actually Channel themselves into the canaliculi which are tiny tiny channels that allow osteocytes and cap and blood vessels to meet now spongy bone is not going to have as compact of a of a disposition it's going to be very porous very light and with spongy bone it is going to be made up of units called tabula tabula I call it lattice work it's basically these little bony Spurs or columns and when you open up a tracular when you slice it open you'll see that a lot of it same components that are in compact bone are present in spongy bone so we can see that inside this little tracula box we have our rings of salt we have the Lamela we have our pits the Lacuna you have the cells within the pits the osteocytes and then you have the tiny little canals that bring nutrients and take away waste from the osteocytes the canaliculi so really they have very similar Parts what a tabula is missing is that uniform circular shape and in the center we don't have that herv verion Canal so tracula since they're not as compact they're much lighter less dense and since that and since the structure is these columns going in different directions we really strong in all the different directions because the tabula are putting tension in force in those different directions if you go back up and look at the osteons the osteons are running lengthways of the bone so even though osteons are pretty strong they're going to be strongest in the direction that they run whereas tabula since they go in all different directions they give you a little bit more strength and stability it's very similar to when you think about dense irregular and dense regular now what we have to remember is that bone is a connective tissue and like all connective tissues it's going to be made up of two major things The Matrix and the cells so think for a second what are the cells that produce the Matrix okay if if you said osteoblast last you're correct so with bones what's going to happen is we're going to have a precursor cell we call this precursor cell an osteogenic cell if you think of Genesis it means to begin so what are we beginning we're beginning bone the osteogenic cells will become osteoblast and remember blast secrete so the osteoblast are secreting The Matrix and then the osteoblast will become the osteocytes we also are going to have the cells that break down bone and these are called osteoclast but you can see I don't have it in a linear pattern because osteoclasts do not differentiate from osteocytes they come from basically your bone marrow now once we have our osteoblast secreting The Matrix our Matrix is going to have two major parts the organic part and the inorganic part the organic part just means that carbon is present so bone is mostly going to be made up of collagen and then salts the collagen other fibers such as elastic in reticular and then some sugars are all going to be found within bone and that's going to be the organic Matrix now what's really important about the collagen is that collagen's function is strength so bones strength comes Prim arily from the collagen fibers but we also have the inorganic portion and this is going to be those calcium salts bone is going to be made up of quite a few different minerals obviously calcium and phosphorus are going to be the most abundant but we'll have some magnesium some magnes we also have a little bit of fluoride so there's other minerals present besides calcium and phosphorus but calcium and phosphorus are the the most abundant what happens is the calcium salt will actually crystallize on the collagen so collagen is given us the strength but we have to remember it's relatively flexible so we have to have something to make bone also hard and that's going to be those inorganic salts the calcium phosphorus salts are actually known as hydroxy appetite so hydroxy appetite is the combin of the different types of the calcium salts so let's go over the actual cells again so we can talk a little bit more about the Matrix so the bone lineages we're going to start off with osteogenic cells basically these are mesenchimal cells that are differentiating to become bone the osteogenic cells are going to form into an osteoblast osteoblasts are the parts of the cells that are going to secrete The Matrix osteoblast are capable of producing collagen fibers but they're also going to form the hydroxy appetite and remember that's just basically calcium salts as soon as the osteoblast have secreted The Matrix and kind of cocon themselves or isolate themselves in a pit that is when they become Osteo sites now we have to remember that sites jobs are to maintain the tissue so they do daily upkey nutrient exchange waste exchange we do not see osteocytes until they are fully isolated within a pit within a Lacuna now at this point the lineage will stop but we haven't covered all the cells yet we've gone over the mesenchimal cells that develop in into osteogenic cells osteogenic cells form blast and once osteoblasts are surrounded in a Lacuna they're going to turn into osteocytes so our last cell are going to be osteoclast and as we can see they're going to be from your bone marrow basically modified white blood cells and their major function is to help break down remodel bone so why osteoblast secrete bones Matrix Osteo class are actually going to break it back down so they basically have opposite jobs so this is just another way to view how bone cells arise we can see that over here we have osteogenic cells which turn into osteoblast osteoblast will eventually become osteocytes when do osteocytes show up if you said when they are isolated in the Lacuna you're correct but we also see that we have the bone marrow cells right here that are going to produce our osteoclast osteoclast are basically 50 monocytes merged together to make up a relatively large cell and what happens is if you look at the Osteo classes border kind of looks like a ghost from Pacman that border is going to be very ruffled so we can see the Ruffles better in this picture and those Ruffles are going to be able to cover a lot of surface area so the osteoclast will release enzymes those enzymes will go onto the Matrix of the bone these ruffled edges will work those enzymes in which helps actually Break Down The Matrix so the calcium salts will go back into your intracellular fluid and then we'll go into the plasma now the next thing is the collagen what we can see in this picture is that collagen is going to be forming our Lamela so what happens is we have those calcium salts and they're going to deposit on the collagen we can see that the collagen is going to form the Lamela in different directions so this Al out side one is basically going from left to right the inside one is going from right to left at an angle and then the middle or the most inner Lamela is almost going straight up and down since the collagen fibers are all facing different directions it helps give us more strength and support but what's also great is that since collagen fiber is are relatively flexible even with the calcium salts crystallized on it it allows bone to have different types of force created so because bone can actually be moved out basically stretched a little bit not like Gumby or Pokey or Silly Putty but it does give a little bit of movement we call that tensile force basically being pulled longer because bone can be compressed we call that compress compressional force and because these collagen fibers do run in different directions bone does allow some twisting which is called torsional Force remember it's not moving in large increments but it does give some flexibility which helps Aid in more strength more Force so just for another little recap I just want to talk one more time about the makeup of bone bone is going to be made up of collagen fibers and calcium salts the salt will crystallize on the fibers in rings that we call Lamela since the fibers are going to always be going in a different direction with each layer of Lamela it helps add to different types of strengths so remember the calcium salts are kind of like the candy that will harden on the sticks which are like the collagen fibers