we're now beginning the skeletal system now there's a lot to talk about in the skeletal system so you will see that this is divided over three chapters in your textbook we're just completing the first chapter now which is where we focus on bone tissue and bone structure later when we move to the next chapter we will talk about the individual bones that make up the skeleton and lastly when we get to the third chapter we will talk about joints that's where two are bone more bones meet like at the elbow joint for example within the skeletal system now as we introduce you to the skeletal system itself in this chapter keeping in mind anytime we have an organ system like this it's made of organs that work together now of course the main organs in the skeletal system are your bones but in addition to that we have cartilage which forms a padding on the ends of most of your bones for instance we took your knee joint here and zoomed in on it and if you look at that bluish material in the picture that is representing some cartilage there at the end of the bones so when they meet up with each other in the knee joint we have some cushioning some protection also in the skeletal system we have ligaments like this white structure here a ligament is what's connecting one bone to another bone so we can actually hold all of these bones together forming your overall skeleton now each of these structures we talked about the bone the cartilage and the ligament is mostly made out of connective tissue so that's the most abundant type of tissue we have here in the skeletal system what we're going to do first glancing down your outline is talk about the bone tissue in more detail now this is again a type of connective tissue and we talked a little bit about bone tissue back in chapter four your tissue chapter or i might have the number wrong but whichever chapter was the tissue chapter but we're going to look at bone tissue in a lot more detail now with any type of tissue we have a group of similar cells of course here we would have the bone cells but there's more than one type of bone cell in your outline listed first is this guy the osteogenic cell now osteo referring to bone angenic meaning to generate to create so this is the cell that makes all the other types of bone cells this is a type of stem cell and as we've learned in the past that means the cell is able to continuously over and over and over again make a baby cells by dividing recall also when a stem cell divides into two one of the new cells will remain a stem cell in this case specifically an osteogenic cell so we can do this process over again the second cell will then specialize in this case the second cell will specialize into this guy here which is an osteoblast now the osteoblast job is to secrete the bone matrix now if you pause and go to your outline you'll see the bone matrix is our next topic but since this is connective tissue remember matrix in any type of connective tissue is basically this background material that we find in between the cells so all that background material there is produced by those osteoblasts now once the osteoblast has done its job making the matrix and it's actually completely surrounded by the matrix then that osteoblast develops into the sky the osteocyte osteobone site cell that's just your typical bone cell his job is now that the bone tissue has already been formed we have the cells and we have the matrix his job is just to maintain that bone tissue keep it going keep it healthy etc and then our last type of bone cell is an osteoclast notice this cell is multi-nucleated as we have in the other bone cells as with most cells in our body there's just one nucleus inside the cell so he has a little bit of a unique structure there being multinucleated the job of the osteoclast is actually the opposite of the osteoblast where the osteoblasts made the bone matrix the osteoclast breaks it down so i think of the osteoblast is like the construction worker building the bone to begin with i think of the osteocyte like the maintenance man just doing repairs to keep everything updated then i think of the osteo class like the demolition crew he's going to come in and break stuff down completely now later on in this chapter we will return to all these different types of bone cells and talk about how we use them together as a group to both create your bones from you know back when you're a fetus before birth including maintaining and repairing your bones throughout your lifetime so we will be talking about these cells in more detail later in the chapter now if we look at that bone matrix in more detail the bone matrix is made up of minerals and collagen minerals are what makes the bone hard like a rock there's different types of minerals here but the most abundant mineral is calcium i'm sure you guys are aware of your bones are mostly calcium now this is also what causes the bone to be a whitish color like we see in the bone there the collagen as we've discussed in previous topics in our class is the protein that gives connective tissue strength so that's this is what keeps the bone so strong so it does not easily break especially as we're applying forces to it like standing with on our leg bones holding up our body weight for instance now because the matrix that is around these cells is so hard the cells could then easily become crushed to prevent that from happening within the matrix we have cavities called lacunae those cavities are where the cells sit and think of it as like a protective shell around the cell so again they don't get smushed by the surrounding hard tissue so if if i could pop that cell out of the picture i would see a dent underneath him a cavity a depression and again that's called the lacunae now we have two different types of bone tissue if i were to cut open a bone like we did here this is showing the top of your thigh bone your femur as it fits into the hip socket here of your hip bone your oscoxa we made a frontal cut remove the front section this is the back section we're looking into you can see the outer bone tissue appears solid going around the edges here like where this arrow is pointing whereas the deeper bone tissue has a whole bunch of little tiny holes in it like where that arrow is pointing so in each bone we're going to find one type of outer and a different type of inner bone tissue now this outer bone tissue is referred to as compact bone think of like a compact car where everything here is smushed tight together in this case the cells the minerals the collagen etc everything in this compact bone tissue are smushed so tight together it gives it that solid appearance we don't see any cracks or spaces in there we'll come back to that compact bone tissue in a moment the deeper bone tissue is referred to as spongy bone because visually it looks like a kitchen sponge with all these small irregular sized and shaped holes throughout it but using that name spongy bone don't get confused it is not soft like a sponge all bone tissue as we discussed earlier is hard like a rock now if we go back to that solid appearing compact bone tissue and look at it in more detail if i took a chunk of this compact bone and put it underneath a microscope i would see this so microscopically it's actually not solid but has a whole bunch of holes inside of it each of these holes is in the middle of an osteon an osteon is made up of that central hole and look at how it has like basically rings of bone matrix around it so for instance looking at that picture inside the area that i circled would be one osteon you can see that there are several of these present another these are called osteons because again osteo they're in the bone they're also as you can see in your notes named haversian systems that would be named after the initial scientists who first discovered these saw them underneath the microscope so that hole in the middle is referred to as the central canal within that central canal we will find blood vessels and nerves for instance if we take that osteon i have circled and if i remove a chunk of it like i just traced there and drew a cartoon picture of that chunk like you see here there's the opening the central canal and red and blue are the blood vessels and yellow is the nerve that i find there now because this bone tissue is compact everything is so smushed tight together without having this central canal it's sort of like a hole drilled in the bone for these vessels to pass through i would never be able to get you know nervous system messages to my bones i would never get to blood supply to my bones now each of the rings going around the central canal are called the lamellae for example here's a piece of one of those rings there's another there's another and there's another in the light tan colored area this is where we have the matrix of the bone tissue so that's where again the minerals are and the collagen is along with the lacunae which are in orange here those are the spaces or as you can see the smaller holes throughout now within those lacunae are where we find the bone cells the purple dot would be the nucleus of each one there again the bone cell when it's completely surrounded by the matrix like we see here is known as the osteocyte now lastly and it doesn't show up quite as well on this image but you can see it better in my cartoon picture you see those little tiny cracks those are named the canaliculi basically the word canal so with their passageways with iculi meaning teeny tiny they're very small passageways these are radiating from the central canal out through the lamellae this allows the blood now to pass from the central canal basically through these cracks to get to the bone cells now if we look at spongy bone in more detail i take a chunk of the spongy bone tissue i put it underneath the microscope i have a completely different picture i have much larger openings large enough that i can even see them without the microscope so in this case blood has no problem flowing through the nervous system has no problem getting its messages through so notice i don't have any of those ring-shaped osteons here i don't need them instead of the bone matrix being arranged in the lamellae the circles here in spongy bone it's arranged in these random bars those are called trabeculae so for instance in my picture i've circled one of the trabeculae there here's another of the trabeculae i've circled there's another one you guys get the idea they're just random bars and because of that random arrangement i now have these large gaps between them within those large gaps we the bone is storing red bone marrow now this gets its name because in real life it is a bright red color again that's filling all of these holes here if this were living bone within that red bone marrow we find a type of cell called a hemocytoblast chem referring to blood and again you know sight is a cell this is another type of stem cell so every time it divides into two new cells one remains a stem cell the other one will develop into any one of these specialized type of blood cells so it can divide into a red blood cell also called an erythrocyte or all of these guys here are different types of white blood cells also called leukocytes or lastly it can divide into a platelet specialize i should say into a platelet also called a thrombocyte you might remember talking about your blood cells back in our tissue chapter because again this is found in those type of connective tissue the blood so that red bone marrow filling the holes is where we are making all of our blood cells so your red bone marrow found inside the spongy bone tissue in deep inside all of your bones is very important because it is making your blood now we will be learning that some bones have more compact bone versus the spongy bone but in general all bones have as you see in both of these here compact on the outside and spongy on the inside at least some of both types of tissue are going to be present okay taking any bone and looking at its overall structure for our example bone we're going to look at one of your vertebrae that was a backbone we took out and zoomed in on now there's different types of markings you may also see these referred to as landmarks that we find within the bone one type of marking we have are openings like this big hole in the middle here those openings will let other structures pass through the bunk openings have different names depending on their shape their size etc just for an example this is a fairly round shaped opening as these are also and they are referred to as foramen another type of marking we have is a depression like this dent you see along the edge of the bone right here now that depression is going to allow another bone or some other structure like a ligament whatever but allow something to lay right next to the bone basically it can kind of spoon right in here cuddling up to this bone i think of it as fitting in like a puzzle piece again different types of depressions have different names depending on their size shape etc and then we have projections like this guy here it is projecting it is sticking out of the bone like a bump these guys basically act as handles just like the door handle sticks out the front side side of the door allowing you to grab onto it this allows some other body part to grab onto the bone for example it might allow a muscle to attach to the bone here so when the muscle contracts it moves this particular bone and again different projections have their name based on their size shape appearance etc now i chose this bone as our example because it happened to have all three types of markings but looking at this bone for example notice there's no opening here so my point is you're not always going to see all three types of openings but these are the three possible types of markings we find on each bone now we can classify our bones by their overall shape looking at your outline we have five shapes listed we'll talk about each of these each bone of your skeleton then is classified as one of these shapes so using the ordering your outline some bones or shapes are have a flat shape like your sternum bone that's the anatomical name of your breastbone we find in the front center of your chest here if you rub your hand over the front center of your chest you'll feel it feel that it's fairly flat there we say that these bones are platelike meaning think of a dinner plate compared to the bowls and the cups in your set of dishes you guys know the plate is much more flat than the other types of dishes but just like that dinner plate these bones are not necessarily completely flat like that dinner plate was completely flat you know how your peas would roll off instead that dinner plate just has a little bit of a curve to it same with our flat bones next we have a long bone which gets its name because it is longer than it is wide now these bones though have more of a 3d like a cylindrical type of shape to them also the example here is your upper arm bone refer to that anatomically as your humerus then like this guy we have short bones short bones are not exactly but they're about as long as they are wide so like the one picture here they kind of sorta have a cube shape to them but again they're not perfect squares the one we have here is one of your carpal bones from the wrist area next we have round bones like my picture shows can also be called sesamoid bones you see that it does have a rounded shape but just like a sesame seed you know the things you find on the top hamburger bun sometimes they do have a pointy tip to them our example here is the patella more commonly known as your kneecap now side note about these round or again you can call them sesamoid bones they are always found in a tendon and by the way a tendon is what connects a muscle to a bone so that means your kneecap will be inside of a tendon and then lastly we have irregular shape bones that's basically a nice way of calling them weirdos they have very odd shapes they might be even a combo you know part of it is kind of like a flat bone another part is kind of like a short bone etc they just don't fully fit into any of the other categories so that vertebra which again is one of your backbones is in that classification this is looking at that backbone from a side view here we're looking at the same backbone from a top view either way it has just a kind of weirdo shape to it what we're going to do next is we're going to take one of these long bones and we're going to look at its anatomy and more detail remember anatomy refers to its structure now before we go down that list we could also look at the individual anatomy of each of the other shapes but since all bones regardless of their shape have a similar anatomy not exactly the same we're just going to pick the long bone and work with that in detail so looking at my picture basically the bottom half of the bone i've left it intact and the top half of the bone we've cut it open remove the frontal section so we can see inside of it all right looking at your list of long bone structures we start with the epiphysis that refers to the rounded end you can see i have a rounded end on each end of the bone circled in green here once more here's looking at it from the outside view we've cut this one open and looking at it from the inside view now since there's two of these we refer to one of them as the proximal epiphysis that's the end of the bone that's going to be again closer to the trunk the core part of your body and the other end would be the distal epiphysis that's the one farther away like closer to fingertips or tips of your toes depending if this is in the upper lower extremity the remaining portion so the skinnier middle area that i did not circle is the diaphysis basically the shaft of the bone like the shaft of a golf club we then have compact bone tissue once again that appears solid that's going to be found on the surface of the bone or even when we cut it open and look inside closer to the outside here spongy bone is deeper inside we cannot see it from the outside view we can only see it when we've cut it open and looked inside and as you see here it has the appearance of a kitchen sponge we have the medullary cavity medullary kind of like the word middle means toward the center cavity of space so that'd be this space here and that space runs down most of the diaphysis region we have the periosteum periperimeter osteobone this is a membrane that wraps around the bone that line you see there or you can see they've peeled it off here to show you that it's an outer covering we also have an endosteum endo it's on the inside this would be an inner lining it lines the cavities they didn't peel that off so you can't tell that that's a separate tissue but imagine like the you know inside lining of your winter coat kind of the same idea there now both the periosteum and the endosteum are storing osteoblasts remember those are the construction workers the bone building cells and osteoclasts recall those are the demolition crew they break down the bone tissue so those cells are being stored here until we need them once more later in the chapter that's actually our and we'll get into that in our next topic i will talk about when we need them and how we use them now the red marrow would fill these spaces they re of the spongy bone they removed the red marrow from our picture so we could actually see the holes of the spongy bone tissue but again in real life that would be filled with that bright red colored bone marrow the yellow marrow as we see here they just removed a chunk of it but that yellow marrow is going to fill that medullary cavity now this yellow marrow is made of adipose tissue do you guys recall adipose is fat uh it is basically just filling this cavity and by the way we need that cavity to be present to lighten the weight of this bone if that medullary cavity that hollow space were not there and instead it was filled with bone tissue like the rest of the bone is bone tissue again like a rock would make this overall bone very heavy so like the humerus your upper arm bone we're using as an example here if that medullary cavity were not present and instead this was all bone tissue by noon you'd have a hard time holding up your arms because they would be so darn heavy so when again that medullary cavity is there to lighten the weight and then the yellow marrow is basically just stuffing filling that space now a side note about this yellow marrow and this is kind of neat if needed that yellow marrow can actually turn into red marrow now as we discussed earlier the red marrow has the stem cells that make your blood so anytime i need extra blood for example let's say i had an injury where i'm losing a lot of blood or i have some type of disease where my blood cells are being attacked that yellow marrow can temporarily turn into red marrow helping me make the additional blood cells i need until i've now replaced the lost or the damaged cells bringing my blood back to normal all right next on our list is articular cartilage now an articulation refers to a joint so articular cartilage would be at a joint in our picture this is the blue material just covering the ends of the bone again forming some padding there so when this end of the bone would hook up with the end of another bone we have some protection in there so the bones don't actually rub against each other if they did it would be very uncomfortable and it would also decrease movement in that joint so that cartilage again is a protective cushion there we also have a nutrient foramen that is a hole or there could be more than one of these in the side of the bone and that allows like you see here blood vessels and not pictured but also nerves to pass through that hole and actually get inside the bone and then again those blood vessels can branch spray along with the nerves branching too spreading a blood or nervous system messages throughout the bone now our next topic is osteogenesis osteo referring to bone genesis to generate to create we're going to talk in this topic about how we make bone glancing down your outlying you'll see that there's different types of osteogenesis there's different ways we make bone and also we do it for different purposes we're going to begin with endochondral ossification endo we're going to go inside chondral cartilage we call it chondrocyte with a cartilage cell chondroitin means cartilage when you ossify something you turn it into bone so again putting all that together and endochondral ossification we're going to go inside of cartilage and turn it into bone now this is how we originally form most of our bones so this process starts when you are still a fetus before birth first that fetus will form this cartilage model it's basically there's no bone here yet it's basically just a chunk of cartilage that's all the blue stuff in this picture is representing cartilage and it's specifically made out of hyaline cartilage you guys remember there's a elastic cartilage and fibrocartilage as other types but this is made out of hyaline then the fetus forms a periosteum which they've started to make represented in brown here that's a membrane that will eventually surround this whole thing and as we stated earlier the periosteum is where we store our osteoblasts and osteoclasts so those types of bone cells are found here in this periosteum then right in the middle represented by that white spot the fetus will form a primary ossification center primary meaning this is the first one to form ossification this is where we're going to turn this tissue into bone center well duh it's right in the center of the picture right now in this primary ossification center the first event to occur is the chondrocytes dye cartilage cells die that's why we don't have blue tissue like we did here cartilage made out of cartilage cells even though that blue tissue would have originally been there those cartilage cells have now died now that the cartilage cells are gone there's room to start making bone to do that we take osteoblasts our construction workers the bone building cells that are stored in the osteo excuse me stored in the periosteum and they invade they come into this area now they could not invade before because there is no room for them but since the chondrocytes have died there's now room for them to come in once those osteoblasts invade they do their job they make the bone matrix as we can see and brown here the bone has started to form this area will then spread let me clear my arrow there out of the way meaning more cartilage cells right around the edges of the primary ossification center die we now have room for more osteoblasts to come in we can make more bone like we did here and this just continues to spread you guys can see how more and more and more of that has been turned into bone now around the time of birth the bone's going to look like this secondary ossification centers are now also starting to form at each end of the bone secondary the primary form first now the secondaries are going to form the same events what happened here however meaning first of all chondrocytes die you can see these white spots i'm adding guys i now have room for the for more osteoblasts from the periosteum to invade but now they're invading at the ends also producing bone so you guys see how i now have also bone at the ends notice though at the time of birth again when my bones looking like this look how much blue cartilage is still present has not yet been turned into bunk this is actually very advantageous cartilage again like rubber as we've discussed before has a little bit more flexibility compared to bone which is more like a rock so this makes it easier for the bones to have just a little bit of bend to them as that fetus is fitting through that birth canal so that makes it easier on mom's body makes it easier on baby's body now following birth the each of the ossification centers continue to spread you guys see how how the primary has become more and more filled with bone and less and less filled with cartilage same with the secondaries more and more bone less and less of that blue cartilage this bone that we're left with here is still developing it's not done fully forming because notice there's still at least a little bit of cartilage in blue here inside the sponge but notice this bone is almost all bone tissue so this bone for example would have come from a teenager by the time we reach our early 20s notice i'm not giving you a specific year because it might be different than you and a classmate but in general in our early 20s ossification is complete all the cartilage will have been turned into bone and therefore there'd be no more blue stuff using our picture here no more cartilage present it would all be bone like we saw on this picture here notice i have no blue cartilage left inside the bone this would be showing us a fully developed and adult bone it would have come from someone older than their early 20s like me for example now while this bone is in the developing process as we see occurring here at the same time we have been using the osteoblasts from the periosteum to invade and build the bone tissue we're also using the osteoclast from the periosteum to break down not the entire bone but small areas to give our bone its shape for example we carved out the diaphysis here to make it more narrow we rounded off the ends of the epiphyses here to make them more rounded now we carved out a nutrient foramen a hole for the blood vessel to fit through now in my outline and in my description to you i use the word sculpt because these osteoclasts act like a sculptor like michelangelo you gave michelangelo a block a stone like granite he would not take a sledgehammer to it and destroy the whole piece of rock instead he took that little tiny chisel chiseling little holes and little depressions in it to give it a specific shape that's what these osteoclasts are doing so i know i called them the demo crew earlier to continue with my you know building and breaking down analogy but think of there being a very precise demo crew again like michelangelo with his little chisel just breaking down little areas to give us our full shape so just like the bones are not completely made of bone tissue until you're an adult they're also not fully shaped until you are an adult now at the same time these are bones are developing by producing the bone tissue and by carving our shape the cartilage that's inside these bones will be stimulated by growth hormone growth hormone is made by the pituitary gland which is found in your brain we'll learn more about that pituitary gland in another chapter growth hormone i mentioned stimulates the cartilage here specifically it turns on the cartilage cells chondrocytes causing them to undergo mitosis the cartilage cells make baby cells it also tells the chondrocytes to undergo hypertrophy hyper they get larger bigger in size that's how the in my picture the blue representing the cartilage expands causing the bone to grow longer and therefore the person to grow taller now looking at this bone here like i said would have been found in a teenager notice there's not much cartilage left for the growth hormone to stimulate so this person would not be able to get very much taller at this point or going back to our previous picture looking at this fully formed bone with no cartilage at all inside of it there's now nothing here for a growth hormone to stimulate so this bone would not get any taller this person could not get any excuse me the bone would not get any longer this person could not get any taller so like i'm using myself for an example i have adult bones like the one pictured here no matter how much growth hormone i personally produced in my pituitary gland or even took as a drug type of medication i have no way of getting taller now because there's no cartilage left inside for this bone to expand now the chunk of cartilage that is present during development where i'm pointing to here and here that's in between the ossification centers is referred to as the growth plate because this is where most of the cartilage is remaining therefore where most of the lengthening growth of the bone will occur it's also anatomically named the epiphyseal plate because being closer to the ends of the bones it's in the epiphyseal region whereas if we go back again to the adult bone fully formed with no cartilage left at all there is no epiphyseal plate presence but instead notice this line of compact bone between the two regions of spongy that is called the epiphyseal line where the initial secondary and ossification centers have met and basically fused melted together to become all bone so it's like a remnant of what used to be the growth plate okay now again endochondral ossification in this top picture we've been studying that is how most of your bones will form the remaining bones formed by the method we're going to look at along the bottom here which is called intramembranous ossification intramembranous we're going to go inside of a membrane ossification turn the inside of that membrane into bone now this process will also first begin in a fetus and it will also be completed in your early 20s so about the same time frame is endochondral only here we start with cartilage and here we start with a membrane this process is forming most of your bones this intramembranous process we're going to start looking at now though however mainly just forms your flat bones like that sternum breast bone we use as an example earlier today of a flat bone so we have a connective tissue membrane we start with this is known as a fibrous membrane because look at all the little sticky things in there a bunch of collagen fibers present now it does not show in the picture here so we will draw it in the first thing that will form is a periosteum around this fibrous membrane hold on a second i'm getting my drawing tools there so that line i'm drawing around it we're going to say that's the periosteum now again anytime we have a periosteum that's where we're going to store the osteoblasts and the osteoclasts now since these stringy thing these fibers are spread out with lots of room in between them that's going to allow the osteoblast the bone building cells to easily come in and invade those are represented by the orange cells in the picture here as those osteoblasts invade they now start forming the matrix so this is the tan colored stuff that those cells have built as we discussed earlier once an osteoblast completely surrounds himself with matrix like notice this guy is completely surrounded he then matures into an osteocyte so here's an osteoblast he's still making matrix here's now an osteocyte completely surrounded he's just going to maintain it this process continues continues continues but it's random so we might form some bone here we might form some other bone here we might form some other bone here so as you can see we are mostly making spongy bone and it just continues so notice more osteoblasts have come in they're going to continue to make more bone tissue so the picture we're left with here would once more like the picture we stopped with here be from a teenager where most of that blue membrane has now been replaced by bone but notice there is still some left so we still have some more bone building to do also just like endochondral ossification at the same time we were building the bone the osteoclasts were also breaking it down to shape it that process will happen here like for example it's the osteoclast that carved that hole in the outside edge there for the blood vessel to be able to get in now notice here though no cartilage was discussed no cartilage cells since there's no cartilage present in these bones there's nothing for growth hormone to stimulate therefore these bones do not have much of an overall effect on our height once our bones have began forming a fracture like seen here may occur that's just the term we use for a broken bone now we're not going to go into a lot of detail but if you look in your book you will see different types of fractures described for example in this particular fracture the break went all the way through dividing the bone into clearly more than one piece i could instead have a fracture where it's basically instead just like a crack in the bone but it's still a one whole bone or it could have been shattered into many many pieces or if it broke into two like this one its ends are still in alignment but instead one could have gotten out of place and for example that pointy edge could actually be sticking through your skin each of these different types of fractures i'm describing have their own name so again you can look at that in your book if you would like more information about that but in this discussion we're just going to look at fractures in general so regardless of what type of break occurred the first event following the damage is to form a hematoma heme referring to blood the whole area at the fracture at the break fills with blood now we want all of this blood to come in because that's bringing in helpful materials that we will be using for the repair process for example the red blood cells are bringing in oxygen which we can use to make a atp aerobically for energy to heal the white blood cells can attack any germs that may have gotten in here in the injured injury process the platelets can clot blood if any blood is actually leaking out of us again due to that injury the plasma the liquid part of the blood can transport in nutrients like glucose which again we can use to convert into atp for energy the blood plasma can bring in calcium which we're going to use as our actual building materials and i could go on and on so the point is it's beneficial to bring extra blood to this area that's going to help us out quite a bit now remember that outside covering that kind of tan colored line they've shown there is the periosteum storing the osteoblasts and osteoclasts well first the osteoblasts like we see here will invade come into the damaged area and we'll start building bone like we see happening here however at the same time this is happening osteoclasts from the periosteum will then come in along the outside and like you can see here how we kind of smoothed out the edges as we filled it in with the new bone so instead of it being you know like all rough and jaggedy because those osteoblasts kind of cover outside at color outside the lines those osteoclasts kind of act as sandpaper then smoothing off the edges so when we're done our bone is basically like new another reason we will be producing bone tissue is for calcium homeostasis we want to maintain our set point our normal amount of calcium in our blood as we've talked about homeostasis in the past if we're in balance like our seesaw here everything's good we're in a state of health if we have too much of something that can cause a problem if we have too little of something that can cause a problem so if one of these changes occurs to maintain homeostasis we need to put it back to the way it should be so your notes first describe the process of hypercalcemia hyper meaning more than calc referring to calcium and emia is in the blood this is when i have more calcium in the blood than normal my seesaw is too high now this event would normally happen anytime you eat calcium you guys know calcium is in dairy products along with some other types of food too so let's say i have a yogurt for my snack that's a dairy product it has calcium as i eat the yogurt and it passes through my digestive tract the calcium along with the other nutrients from that yogurt get absorbed into my blood so as i'm adding the calcium to my blood my blood calcium levels rise the rise in blood calcium levels hypercalcemia turns on my thyroid gland this is an endocrine gland found near the front of your neck it causes him to make a hormone calcitonin calcitonin turns on my osteoblasts osteoblasts do their job to build bone but they get the building materials mainly calcium out of your blood to do so so they're using up all of this extra calcium to build the bone as a result the bone gets thicker and stronger and the blood calcium levels now go back down to normal if this process has occurred but there was so much extra calcium in the blood that even though we brought it down it's not yet all the way down to normal that calcitonin can also stimulate your kidneys to excrete taking the remainder of the extra calcium out of the blood putting it into your urine so you pee it out one way or the other calcium levels are back down to normal as the added benefit i now have some extra calcium that i've stored in my bones like putting your extra clothes in your closet even though you're not using these clothes right now they're available to you later so even though my blood is not using this calcium now it's available later when i need it when i need it would be when i'm instead experiencing hypo calcimia hypo less than kaus calcium emia in the blood i have lower than normal levels of calcium in my blood this event would normally occur if i have not eaten any new calcium for a while so i've been using up what was present uh also this would occur if i have been extra active like exercising because we will learn in another chapter when we get to the muscular system that muscles use calcium to contract so the more active i am the more muscle contracting i'm doing the more calcium i'm using that way so again either or or both i've not been eating calcium i've been doing a lot of activity using my muscles my blood calcium levels are going to drop below normal that turns on my parathyroid glands which are found on the back side of the thyroid those parathyroid glands produce parathyroid hormone pth which stimulates my osteoclasts as the osteoclasts get turned on they will do their job they break down bone now remember they're not breaking it down like sledge hammers but rather like little tiny chisels as they break down the bone that releases from the bone the calcium that was being stored there that release calcium enters my blood bringing my blood levels back up to normal so this is how i get that stored calcium out of the closet when i'm ready to use it now if i've done this process and even though that brought my calcium levels up i'm still not all the way up to normal that pth can also tell my digestive system to absorb even more calcium the next time i eat food with calcium in it and again as i'm absorbing more calcium from my food that's going to bring my blood levels up also so eventually i'll be back in homeostasis so on a typical day in your own body sometimes osteoblasts are building bone and sometimes osteoclasts are breaking it down you just go back and forth back and forth during the day just like a seesaw going back and forth back and forth trying to maintain your normal levels all right we have one more topic to discuss before we finish this chapter of the skeletal system and we're just going to look at overall functions of that skeletal system so one of the functions is to provide support for the body again bones are hard they're not going to bend underneath your weight so they hold you up they support you the bones also give us our body shape just for an instance not only does it give us the overall human shape but think of a male human compared with a female human from the backside without having to look at any facial features or anything else we can in general tell who's a male and a female by their bone structure men having the wider shoulders but females having more narrow shoulders females having wider hips but males having more narrow hips males overall having larger bones more mass bigger frame females smaller or if we are looking at the face regardless of gender one of the main ways we tell a single human from another single human individual is by looking at their uh facial bone structure you know this person has a higher cheekbone this person has a bigger forehead this other person has a wider nose this person has you know whatever overall a bigger head etc we can also use bones for storage this includes the bone tissue storing minerals mainly calcium like we just finished talking about acting as the closet we can put the calcium in we can take it out as needed and also the bone marrow specifically the yellow marrow there storing lipids fat it's made of adipose tissue hematopoiesis refers to blood production this happens in the red bone marrow that's stored in the spongy bone tissue again that's where we have the stem cells the hemocyte hemocytosis wait a minute hemocytoblasts that are making all the blood cells not just the red blood cells that are pictured here but recall also the white blood cells and the platelets protection like in the picture here the skull bones forming this protective shell around the brain inside of them or like the bones of the thoracic region forming a protective shell around the lungs and the heart which would be inside the joints which again is where two or more bones meet like the knee joint they've zoomed into from a side view here allows movement to occur now keep in mind we're not saying it produces the movement because that's the job of the muscles pulling and pushing on the bones but if we did not have a joint and instead your skeleton would be is one solid bone there be no area within the body to move but having the joints like the knee joint gives us a place where movement can happen because again it's not solid bone there we have a gap between the bones and then as we discussed earlier uh the majority of your bones those formed by endochondral ossification like this femur which is a long bone you see here uh when would these bones grow which occurs remember not at the bone tissue but the develo the cartilage inside of that developing bone the bone gets longer you then get taller so we need our skeleton uh it's for growth of our height as we develop okay when we move into the next chapter guys we will then get to the individual bones of the skeleton but this finished your bone tissue and structure function so i'll see you for the next part of the skeletal system bye guys