Full transcript
0:02foreign
0:10so continuing on with chapter six bones
0:13and skeletal tissue part two we're going
0:16to start with Section 6.5 so when we're
0:18looking at section section 6.5 there's a
0:21new term we're going to talk about
0:23which is going to be called ossification
0:26and ossification is going to be the
0:28process of bone formation you may also
0:32see the term
0:34osteogenesis which essentially means the
0:37same thing but these two terms are
0:39synonymous for this whole process of
0:42bone tissue formation so what's
0:44interesting about this bone tissue
0:46formation is when we have this bony
0:49skeleton that's going to form it's going
0:51to form around month two of development
0:54so that is when we're going to start
0:57this process so
0:59as we go with this forming skeleton we
1:01are talking about in utero so
1:04the formation of the bony skeleton is
1:07what it's called
1:09so as a reminder what we said at the
1:11very very beginning was that the
1:13skeleton is not hardened cartilage but
1:17that cartilage is converted and
1:19transferred into replaced by bone so
1:23we're going to start with this process
1:24so you'll you'll hear cartilage and bony
1:27skeleton quite a few times so this will
1:30actually
1:31occur at week eight so up to
1:35week eight
1:38the fetal skeleton
1:44is going to be made up of cartilage
1:48so up into
1:50um fetal skeleton is going to be made up
1:53of cartilage and then at this particular
1:55process it will be replaced with bone
2:00so the process that does this where it's
2:02going to be replaced with bone is going
2:04to be endochondral class ossification so
2:07with endochondral ossification we are
2:10replacing our bone
2:13um or sorry where our bone is replacing
2:16our hyaline cartilage and when this
2:18happens there's going to be a series of
2:20bones that are going to be called
2:21something kind of different which can be
2:22cartilage endochondral bones because
2:24it's going to be a mixture of the two
2:25tissues and this is going to occur for
2:28most of the skeleton so this will be
2:30almost all your bones
2:33we'll go through this endochondral
2:35ossification where the intramembranous
2:38ossification is a different process
2:39these bones are going to be called
2:41membranous Bones and this is primarily
2:43going to be for
2:45um
2:46tissues that are going to be
2:49um your skull your clavicle or your flat
2:53bones so the bigger priority to really
2:55understand and know is this endochondral
2:57classification so we're going to start
2:59with that
3:01endocondral remember anything that is
3:03conj is going to say cartilage or
3:07connective tissue so endochondral
3:09ossification
3:12we are converting our cartilage to Bone
3:14so this is going to be essentially all
3:16bones except for those clavicles which
3:18will go through that other process and
3:20it will begin at month two so this will
3:22begin around
3:24week eight week eight and month two so
3:27what it's going to do is it's going to
3:28replace hyaline cartilage specifically
3:32and the way it will do that is through a
3:35very sequenced step process of about
3:37four to five steps so as it's going to
3:40do this it's going to start at the very
3:42middle which is going to be called the
3:45primary ossification Center and it's
3:47going to be the center of the shaft so
3:49as we're going through this process we
3:51are starting there so there are five
3:53main steps to the process of
3:55ossification so this is a breakdown a
3:57shorthand version but I'm actually going
4:00to go down to the five steps in image
4:03form so this is the picture of them so
4:06we're going to talk through this
4:08endochondral ossification and a long
4:11bone so when we said that the um
4:14ossification Center was going to be the
4:16center of the bone essentially what we
4:18mean is if you have the bone where the
4:21diaphysis looks like this and the
4:22epiphysis looks like this we're going to
4:25start around right here this is going to
4:28be the primary ossification Center so
4:31this is where the process is going to
4:32start is in the center of a long bone
4:36so knowing that we're going to go down
4:38to the next step
4:40so with this the first step is going to
4:43be starting at the bone collar it's
4:45going to form around the diaphysis of
4:47the hyaline cartilage model so we're
4:49going to start with this primary
4:51ossification Center so as a reminder
4:52right now this is actually going to be
4:56um cartilage so the structure is there
4:58but what you're going to get is you're
5:01going to have let me get a little color
5:03for it
5:04a bone collar so I'm going to do all of
5:07my bone as green
5:08so a bone color will start to form
5:11around the diaphysis of the hyaline
5:13cartilage model so this is going to be
5:15our bone collar
5:18so what's happening with this bone
5:19collar is we are essentially going to
5:21start hardening from the middle and then
5:23we're going to go outwards so what's
5:25going to happen in step two
5:27is with our bone collar we now have our
5:31epiphyses our diaphyses we're starting
5:33to get this bone collar
5:36you're going to actually next have the
5:38center of your diaphyses the cartilage
5:41that will be in the middle will start to
5:43calcify and you will develop a cavity so
5:46the space inside the middle will
5:49actually start to open up and develop
5:51this cavity
5:52it's going to start decaying around it
5:55in order to make a larger cavity so
5:58we're going to start doing this but
5:59remember we also have this bone collar
6:02that is around the outside of our bones
6:05so then in step three
6:08what we're going to have is that we are
6:10going to have here's our diaphysis our
6:12epiphysis
6:13we've got the inside that is starting to
6:18become a little bit more of a cavity and
6:22what's happening here is something
6:23called a periosteal bud so a periosteal
6:26but
6:28is going to be made up of blood supply
6:32it's going to have artery vein nerve
6:35tissue and it's going to essentially be
6:38the incoming blood supply that will then
6:40go into and essentially invade the
6:44internal cavity this will occur
6:48around month three
6:51is where you will have this process so
6:54from the end of month two to the around
6:55month three you're going through steps
6:58one and two so now we've got our our
7:01wider medullary in the middle
7:03we've still got the bone collar around
7:05the outside but we have this essentially
7:07new supply of nutrients and oxygen
7:11coming through the blood supply so
7:13that's going to increase the growth so
7:14if you're trying to remember the
7:15sequence of steps you have to have the
7:17periosteal bud before you really convert
7:19everything to replace it with bone
7:23okay so then the next step what we're
7:25going to do with our endochondral
7:26classic ossification is we have our
7:29diaphysis our epiphysis it is all
7:32cartilage right now
7:34we've got our medullary shaft in the
7:36middle
7:37that's been hollowing out this whole
7:38time and we have our periosteal Bud that
7:42is now in the middle of this but what's
7:45happening in step four this is already
7:47kind of been here you're going to have
7:49your diaphysis elongate and as you
7:53elongate it'll essentially start to
7:56cavity out or create a larger medullary
8:00cavity so as this epiphysis or the
8:03diaphysis starts to elongate
8:05what it will actually do is as it does
8:08that it will convert the or it will
8:11break down the cartilage and replace it
8:13with bone so your bone collar will get
8:15larger and actually do the entire
8:18diaphysis first
8:20so as it's doing this your Osteo
8:23clasts are breaking down the cartilage
8:27and are essentially creating new spongy
8:30bone
8:31and then surrounding it with compact
8:33bone so as this is happening when your
8:35epiphyses are um still cartilage but
8:38your diaphysis is going to be um bone is
8:43going to be the end of step four so this
8:45will happen from
8:49this will happen from week nine
8:55to birth
8:57is this process will happen so when
8:59you're actually at Birth your epiphysis
9:04are still considered cartilage
9:08so they are still going to be made up of
9:10a totally different type of tissue that
9:12needs to be replaced by bone so week
9:15nine your epiphyses are cartilage but
9:17your diaphysis so the center is going to
9:21be bone
9:22so this is kind of what you'll get at
9:24week
9:24nine all the way up through birth
9:28and then when you actually after you
9:30have birth then you'll go through the
9:31final step which is going to be step
9:33five and this is when your epiphyses
9:36will actually ossify and ossify means
9:39they are going to be replaced by bone so
9:42now at this point if this is my
9:44um
9:45bone I've got my medullary cavity
9:48this is where we were with replacing our
9:51bone but now we have replaced the whole
9:53thing
9:54with our bone we have a large medullary
9:58cavity we have our periostal Bud that
10:01has turned into the artery in the vein
10:04completely and your epiphyses have
10:06ossifieds this way you will have the
10:08entirety of your bone replaced into
10:10cartilage this is going to happen at
10:14post-birth and then as growth will occur
10:17this step step five will actually stay
10:20and continue from childhood to
10:22adolescence but this process is
10:24different than bone growth in
10:26adolescence this process is bone being
10:30replaced by a cartilage by from
10:32cartilage to a bone so it's essentially
10:34you've made a mold of cartilage that now
10:37you are replacing by a bone so this is a
10:40very important process but these five
10:42steps do a very good job of explaining
10:44what's happening
10:45okay when you actually have the uh the
10:49neck the other process which was
10:50intramembranous ossification remember
10:52this was really only going to be for
10:54some of the bones of the skull which are
10:55these guys and your clavicle so the way
10:58this works is we're not going to spend a
11:00lot of time on it this intramembranous
11:02ossification but this is the summary of
11:05all of the events right here so
11:07basically what's happening with this
11:08intramembranous ossification is it is
11:11also starting
11:13um with an ossification Center but it's
11:15not necessarily starting with cartilage
11:18it's just going to be an ossification of
11:20cartilage tissue and cartilage cells
11:23then what they're going to do is those
11:26um fibrous connective tissue and your
11:28osteoblasts are going to secrete an
11:31osteoid so we're essentially just going
11:33to form the process we've already talked
11:35about it does not go from a cartilage
11:38model to a bone structure so we have our
11:41ossification center it's going to be a
11:43little bit different it's going to be
11:44made up of osteoblasts and our
11:46connective tissue and we've got our
11:47osteoclasts which will then secrete all
11:50of that osteoid to surround it and then
11:52what you'll have is you'll have an
11:54immature spongy and periosteum so you're
11:56still going to have that input of the
11:58blood supply come in but you're going to
12:00have this immature kind of spongy bone
12:02and then finally you will have the
12:04compact bone come alongside and Surround
12:06all of that so that is a slightly
12:08different process but the global one to
12:11know is going to be the intramus
12:13ossification
12:15okay so that's what happens when you are
12:18creating your bony skeleton for the
12:19first time what's happening with
12:22growing actual bones during development
12:26so this is going to be considered
12:27postnatal bone growth so what's
12:30happening with this is visible long
12:31bones will grow lengthwise
12:33but they will also increase in thickness
12:36so there's going to be another type of
12:38growth that we'll call that we'll talk
12:40about called a positional growth and
12:42then bones will stop growing at some
12:44point during adolescence and they all
12:46stop at different places in time point
12:49and development they stop different
12:50points for males versus females but they
12:53do eventually stop and if they don't
12:54then there's an issue with hormones but
12:58how do you actually have growth in your
13:00long bones
13:02so this is a
13:04um
13:04and also a kind of not five step process
13:07but five area process so this is going
13:10to be both in Long grounds that's long
13:12bones it's going to be post natal so
13:14what's going to happen here is this
13:16thing called the epiphysilial cartilage
13:18in the epiphyllium plate so we briefly
13:22talked about when we said at the very
13:24beginning here was our epiphyses
13:27here is our diaphysis
13:30and then in between the where these two
13:33connected
13:34was something called an epiphyseal plate
13:38so that is what we're talking about
13:39right here this guy and this guy
13:42this is your epiphysilial plate
13:45this is where bone growth will occur and
13:48what will happen is there is epithelial
13:51cartilage at the epiphysilial plate so
13:56essentially the green line I drew is the
13:58cartilage and what it's actually going
14:00to do is this cartilage or this plate
14:02will maintain its constant thickness but
14:05you will actually develop and grow the
14:06bone and push this up so then it will
14:10grow larger
14:13and your epithelial plate will grow
14:15higher and then it'll essentially just
14:17push everything making the long bone
14:19longer so this will actually occur at
14:21both ends it's not just one
14:25so this is how you're going to get bone
14:27growth it's essentially going to push
14:29the epiphicillate
14:32further away from the middle of the bone
14:34so how does it do that there are five
14:37zones to the epiphosilial plate
14:40so as we're looking at this overall
14:43picture right here with these five zones
14:47the first zone is going to be the
14:49resting or the quintessent quintessent
14:52zone and the last zone is going to be
14:54the ossification zone so with this
14:58resting Zone
14:59this is going to be the top
15:03of your plate
15:06whereas this is going to be
15:08the bottom
15:10of your plate so that means the resting
15:13or the quenescent zone is going to be
15:15closest to the epiphyses whereas the
15:18ossification zone is going to be closest
15:20to the diaphysis itself so that's what
15:24we want to talk about so this resting
15:26zone right here is the air is the area
15:30of cartilage that is on the epiphysilial
15:33side of the epiphosilial plate and is
15:37inactive all of that means that is a lot
15:40of epiphysilial okay I'm just going to
15:42draw one diaphysis and one epiphysis if
15:45this is the top of my epiphysillial
15:47plate and this is the bottom of my
15:49epiphosilial plate within this area I am
15:53going to have Zone
15:55that is my resting Zone
15:58which is going to be the top then I'm
16:01going to have my proliferation Zone
16:04then I'm going to have my hypertrophic
16:06then I'm going to have my calcification
16:08and then this last zone right here is
16:11going to be my ossification so what we
16:13mean with our the resting zone is that
16:16it is on the epithelial side so it's on
16:19this side
16:21of the epiphosilio plate this side right
16:24here is the epiphysillial side the other
16:27side
16:28is the diaphysis side this one
16:32so that's how you know which side of the
16:34plate you're on it is not top and bottom
16:37because if we were to continue down our
16:39bone and draw another epiphysis like
16:42there is for every long bone it also has
16:45an epiphysilial plate however this is
16:47going to be flipped
16:49so your diaphysis side is the one that
16:51is closest to the diaphysis that's this
16:54one so it's not top and bottom as much
16:57as it is the one towards the middle and
16:59the one towards out so the resting zone
17:01is on the epiphosilial side the next
17:04zone is going to be your proliferation
17:06and your gross Zone
17:07so this is exactly what the name says
17:09this is where you will have rapid
17:11division so it'll be constantly dividing
17:14in this proliferation zone so the
17:17proliferation zone is important for
17:22rapid division
17:24you're going to have a lot a lot a lot
17:26of cells dividing proliferation that's
17:28exactly what that means as these cells
17:31are dividing they are going to push
17:34the epiphysis
17:37away from the diaphysis
17:40so as they create new cells they are
17:43going to push this
17:46Up and Away
17:48as they form new ones they're going to
17:49keep doing this this will cause the
17:51lengthening of the bone
17:53so the next zone is the hypertrophic
17:56zone so this is where you're going to be
17:58slightly closer to the diaphysis and
18:00you're going to have your cartilage
18:01erode
18:02and you're going to form spaces
18:05so this section right here this
18:07hypertrophic if this is my
18:11medullary cavity right here essentially
18:14we have to create this medullary gravity
18:16so it will start to break down and form
18:18spaces break down lacuni
18:22enlarge them erode them and then create
18:24spaces and then what will happen in the
18:27calcification zone is that these spaces
18:29in the cartilage Matrix will start to
18:31classify and die and deteriorate so we
18:36essentially are going to erode then
18:39we're going to calcify and kill off and
18:42then the last step is we will actually
18:45ossify and replace with spongy bone so
18:50all of that to get to this guy right
18:54here
18:54so this is the top of your epiphycelial
18:57plate you can see right there how it's
19:00um this is the epiphysis side
19:05and this is the diaphysis side of this
19:08bone right here
19:10so if you look right here we've got our
19:12resting Zone and then our four other
19:14zones so five total if you'll notice
19:17right here
19:18how there is calcium calcification and
19:23there is
19:24a matrix
19:26essentially there is going to be the
19:28actual holes
19:31this is the inside
19:35this is the top end
19:37of that medulla so right now that's what
19:40you're kind of seeing so that's really
19:41important and really cool to be able to
19:43see how you're going to elongate that
19:45medulla medullary cavity
19:47okay so as that's going your
19:50epiphastilial plate is actually going to
19:52maintain its constant thickness
19:54throughout all development so the plate
19:56itself does not change but what will
19:58happen is that as it keeps growing and
20:01the cartilage keeps getting replaced
20:05um you will essentially at some point
20:07have what is called bone closure or
20:10epipio plate closure and that is when
20:13the two will actually fuse so rather
20:16than having your epiphyses and your
20:19diaphyses separated by this epiphosilial
20:22plate whenever those actually fuse
20:26together you just get this this will be
20:29no more growth
20:32so this is what's going to happen with
20:34adults
20:35when we no longer have any lengthening
20:37to our long bones this is going to be
20:40with any type of bone growth during
20:42childhood and Adolescence so essentially
20:45the epiphys and the diaphyses just fuse
20:48like I said it does happen at different
20:50places for different um genders females
20:53their diaphysis and epiphysis will
20:56actually fuse earlier so that way around
20:5818 years of age they stop growing
21:00whereas males it's around 21 years of
21:04age so that's why they say men hit their
21:06growth spurt a little bit later but they
21:08also technically just stop growing a
21:10little later so everything is just
21:11slightly a couple years behind for that
21:14one okay so that was growing the length
21:16of your bone but you can also grow bone
21:19width
21:20so if you were just to grow the width
21:23the length of your brown
21:24from a two-year-old to a 20 year old and
21:28it maintained its same thickness
21:30if this is your two-year-old
21:36this is your two-year-old and you
21:37maintain that same thickness as a 20
21:39year old you essentially have done this
21:42that does not actually support the
21:45entire body what you need to have is as
21:48the bone grows the thickness of the bone
21:52actually grows as well to be able to
21:54maintain the entire trunk body tissues
21:58everything to be able to protect and
22:01support so bones will actually widen as
22:06they lengthen and this is going to be
22:07called a positional growth
22:10so a positional growth is going to be
22:13both
22:14um bone widening
22:17this will continuously happen throughout
22:19life this does not pause with
22:21adolescence it is important because the
22:24reason we need this is because if we
22:26have a lot of increase in strength
22:28stress from muscle activity let's say
22:31you actually go to the gym and you work
22:32out and you are building muscle mass
22:34your bones will actually thicken in
22:36response to that muscle mass being
22:38increased or if you actually do add
22:40weight to your overall body then your
22:42bones will actually thicken in response
22:44to that so the way this is going to work
22:46is the bone the bone cells we've already
22:48talked about your osteoblasts will do
22:51what they do best which is secrete bone
22:53matrix and then the osteoclasts will
22:56then break down and remove the bone
22:58so essentially what you're doing is
23:01you're building up and breaking down
23:04your bone you're not just adding new you
23:07are building up and then you're breaking
23:09down and this leads to thicker stronger
23:11bones so you're not just replacing more
23:13bone on top of bone you're actually
23:15breaking down and replacing so here's an
23:17example of long bone growth and
23:18remodeling
23:20okay so what actually controls
23:24your bone growth postnatal
23:27so what controls
23:30your bone growth
23:32there's a primary way your bones are
23:34going to be controlled and that is going
23:36to be through a hormonal control
23:39so your hormones are responsible for
23:42controlling this entire process there's
23:44a couple hormones we're going to talk
23:45about
23:45first one is growth
23:48hormone growth hormone is exactly what
23:51it's called and it helps grow and
23:53stimulate growth which is really going
23:55to stimulate the epiphysilloplate
23:58activity so that's how you're going to
24:00get that bone growth it's going to
24:01stimulate that epithelial plate to do
24:03what it needs to do as a reminder when
24:06we talk about the first the functions of
24:08bone we said that growth hormone was
24:10actually stored in the bones so that's
24:12just full circle on how that process
24:14works
24:16um the next hormone is going to be
24:18thyroid hormone
24:22and thyroid hormone will also be
24:25responsible for helping out our growth
24:27hormone so it will actually modulate it
24:29so that way it makes the growth hormone
24:31work correctly in the correct
24:33proportions
24:34and then we have a couple other hormones
24:36that are responsible for bone growth
24:37they're going to be the reproductive
24:39hormones
24:40you're in androgens your estrogen
24:44for primarily for males in your estrogen
24:47primarily for females and what these
24:51guys are actually going to do for um
24:53males and females is they're going to
24:55happen at puberty but they're going to
24:58end the growth by closing the
25:00epiphosilial plate by triggering that
25:02process so this is how you're going to
25:04have essentially
25:06the closure and this is why it makes
25:08sense why they're at different rates for
25:10male versus female because they happen
25:12with under the control of different
25:14hormones
25:15okay so the next section we're going to
25:18talk about is called bone remodeling and
25:20this is a very cool process
25:22so bone remodeling is different than
25:25bone
25:27development or bone
25:29growth as I spell that out
25:31bone remodeling
25:33so what bone remodeling is is this will
25:36actually occur just to replace your bone
25:40mass so it will actually recycle your
25:43your bone mass essentially your will
25:45place
25:46seven to five percent of your bone mass
25:49every week so everyone is probably
25:51familiar with your skin being able to or
25:53needing to have a new layer of skin
25:56because
25:57um a little gets left off it'll get
26:00um scraped off but you need to have that
26:02replacement of your external skin you
26:04also need to replace your bone and just
26:06to make sure that it is super super
26:07strong so you bone remodeling is a
26:10process of recycling your bone
26:14you're going to break down the old
26:16and add in new just to make sure it's
26:19super super super strong so this means
26:22if we have spongy bone replaced about
26:24every three to four years
26:26our entire skeleton our compact bone and
26:29our spongy bone will be finished every
26:3110 years so about every 10 years
26:35you have a new skeleton from what you
26:36have before
26:38so bone remodeling has two steps
26:42and these two steps are going to be
26:44first
26:47bone
26:49resorption
26:53and then
26:55bone deposit I know it is out of order
26:58from what the slide says but I find it
27:01easier to
27:03um
27:04talk about them in this order
27:11so with bone resorption we're going to
27:13talk about that first
27:14this will occur both on the periosteum
27:18and the endosteum so it's going to be on
27:19inside of the cell and the outside of
27:21the cell and these are the two cells
27:23we're going to talk about a lot
27:24osteoblasts and osteoclasts so make sure
27:27you know those guys so first step
27:31bone
27:32resorption
27:34so bone resorption is going to be
27:37primarily responsible for being
27:40completed by your
27:42osteoclasts so whenever you think of
27:44resorption
27:46osteoclasts so as a reminder osteoclasts
27:49break down things so what these are
27:52technically doing with bone resorption
27:54is they are actually breaking down your
27:57bone
27:59so that's in a nutshell what these guys
28:01are actually doing for bone resorption
28:04the way they are doing it is because
28:06they are actually secreting an enzyme
28:09that is acidic
28:11and the acidic of nature of the enzyme
28:14will actually convert the salt to Ace of
28:18soluble form that can be dissolved um by
28:21water so essentially they are going to
28:23release an acid
28:25and the acid will break down the bone
28:29specifically the calcium salt which
28:31gives the bone its hardness so that's
28:34really important so just remember bone
28:35resorption is osteoclasts
28:38after the osteoclasts break down
28:41everything they're then going to
28:44phagocytase and essentially eat up and
28:47get rid of all of the destroyed mineral
28:50Matrix and all of the um dead osteocytes
28:54so it's going to digest everything so
28:56once it happens this is this digestion
28:59is what is called
29:01resorption so the digestion is
29:04essentially going to be this resorption
29:05concept right now so if it's helpful to
29:08think about that go for it but once this
29:10digestion of everything is complete your
29:13osteoclasts are destroyed
29:16so at the whole end of the whole process
29:20your osteoclasts will undergo
29:24apoptosis which means that they will
29:26destroy themselves
29:29and as they undergo apoptosis
29:32they will then trigger the next part of
29:35the process
29:38so resorption is breaking down the bone
29:42it's done by osteoclasts when it's done
29:45they destroy themselves
29:47this whole process is going to involve
29:50parathyroid and immune T Cell properties
29:53so these are going to be important so
29:56it'll be
29:58it'll be done with parathyroid
30:01hormone
30:03and with T Cell proteins will be
30:06responsible for making this process work
30:08so that's important to note okay then
30:10the step two is now that we've broken
30:12down part of the bone we have to lay
30:15down nubed bone essentially we broke up
30:17the highway now we have to lay down the
30:18new highway
30:19so bone matrix is going to be deposited
30:22by osteoblasts
30:25so the first one was clasps this one is
30:28blasts remember the blasts are the ones
30:30that secrete the osteoid so at this
30:33point your bone deposit is going to be
30:34done by osteoblasts and they will
30:36essentially just go through a process
30:40that will
30:43lay down new bone so it'll form there'll
30:47be a new area of Matrix that will
30:49actually be put together the connection
30:51between the old and the new is going to
30:54be the osteoid seam
30:56um
30:57and then that calcification front is
30:59going to be that transition point from
31:01the Osteo osteoid seam to the old bone
31:05so bone deposit is laying down new bone
31:07because the osteoblast will secrete The
31:09Matrix outside and essentially Harden so
31:12that is what's happening with bone
31:14deposit
31:15so some things that's happening with a
31:17bone deposit
31:19um it may be triggered the reason we
31:21might have this happen is because a
31:23couple things
31:24science is still trying to figure all
31:26this out but bone deposit may happen
31:28because mechanical signals there's
31:30increased levels of stress there's going
31:33to be increased concentration of
31:36um minerals that need to be actually
31:40laid down Matrix proteins that need to
31:43be bound
31:44or an appropriate amount of enzymes so
31:48why the bone deposit y bone deposit may
31:52or may not occur may be related to these
31:55things okay so when we actually control
31:58our bone growth we talked about hormones
32:00like growth hormone thyroid hormone and
32:02then the androgens of testosterone and
32:05estrogen but there's also a control of
32:08modeling
32:10so there's a process of hormones as well
32:14that will control our remodeling process
32:16of resorption and deposit so the first
32:19way that you'll have control of
32:20remodeling is going to be hormones
32:23so just like bone growth hormones are
32:26going to control this but it's different
32:27and it's a much more complicated process
32:30than the one before so some of the
32:32hormones that are controlling the
32:34process of remodeling are going to be
32:36related to calcium
32:39calcium is a big one so how calcium
32:43actually relates or controls your
32:47hormonal levels it is a negative
32:49feedback cycle
32:51so the negative feedback cycle is
32:54something that we have talked a lot
32:56about in our
32:58chapter one it came up on exams so just
33:01make sure you're always keeping that
33:02process in the back of your head so
33:04we're going to go through that process
33:05in a second
33:06but negative feedback loop is going to
33:08control calcium levels and this is
33:10really going to be around
33:14the reason we have this calcium it's
33:16responsible in many processes but really
33:19this is going to be for about 99 of the
33:22calcium you have in your body is going
33:23to be found in the bone so that's
33:25actually really really really important
33:27so your hormonal control is going to be
33:29responsible with blood calcium levels
33:33what controls your blood calcium level
33:36are going to be
33:39these two guys right here so this is my
33:43feedback cycle so remember a negative
33:46feedback cycle is going to do a opposite
33:49so that's what we're looking for
33:51we're looking for that cease on the
33:52middle so how you actually have
33:55Paratha your calcium levels controlled
33:58are going to be by the hormone
34:00parathyroid
34:02so the hormone control is going to be
34:04primarily
34:05through the parathyroid hormone
34:11and what this will do is it will control
34:15blood
34:17calcium
34:19levels
34:21so hormonal controls will actually
34:23regulate the blood calcium levels and
34:25it's going to be parathyroid hormone so
34:27we're going to draw a
34:29negative feedback cycle so here we go
34:32here's an example of a negative feedback
34:34cycle the first thing you're going to
34:35have is your stimulus
34:37so our stimulus is going to be a
34:39decrease of calcium
34:42in the blood
34:45if I have a decrease of calcium what I'm
34:47going to have the next step is I will
34:51have my parathyroid hormone pth will be
34:54released
34:56and it is going to be released from the
34:59parathyroid gland
35:01so this will live in your throat
35:05and when you have a decrease in calcium
35:07levels in your blood your parathyroid
35:09hormone is released if I release a
35:12hormone guess what it's going to do it's
35:14going to increase the levels of
35:15parathyroid in my blood
35:18because we just released it it'll go up
35:21parathyroid hormones are very very cool
35:24because what perithyroids do is they
35:27will actually cause your osteoclasts to
35:31work so if I increase the level of
35:33parathyroid hormone in my blood my
35:36response
35:38that I'm going to get from these guys is
35:40going to be my osteoclasts
35:44will degrade
35:48or resorb
35:52um
35:52the bone
35:54and as it does that it will release that
35:58calcium
35:59into
36:02the blood
36:05so if it
36:07if my osteoclast degrade and started to
36:10resorb and break down bone it'll release
36:11calcium into the bone into the blood
36:14what will my calcium levels do my
36:17calcium levels will increase in my blood
36:21so this process started with
36:24a decrease in calcium levels and ended
36:28with an increase of calcium levels All
36:30Because by releasing parathyroid hormone
36:33I'm going to start degrading my bone and
36:36getting that mineral out so this is a
36:39really cool product I do need to know
36:41about this is this is a stimulus of Inc
36:43of decreased calcium in the blood so
36:45that is the stimulus right there what I
36:48want you to be able to do is do the
36:50stimulus what if
36:53there's an increase
36:57of calcium in the blood
37:01What process happens there this is what
37:03I want you guys to be able to do because
37:05it's a negative feedback cycle which
37:07means if the blood levels go down they
37:10can also go up but what happens if we
37:12have too high of calcium levels then you
37:15have to go through a process and be able
37:16to figure that out so go through and
37:18look at that because that's going to be
37:19helpful information for you to know
37:22okay another hormone that is responsible
37:25for controlling
37:27um bone remodeling is going to be this
37:30calcitonin hormone and calcitonin is
37:33something that we're still trying to
37:34figure out exactly how it does but it
37:36will also be responsible for blood
37:38calcium levels so we do know
37:41both of these are going to be
37:43responsible for calcium levels
37:45so one thing to keep in mind is there's
37:47some issues if we increase our calcium
37:51levels too much and this is going to be
37:53homeostatic imbalance so now that we're
37:56into this systems of the body we're
37:58going to start talking through what
38:00happens when they go wrong so what
38:03happens if you have hypo
38:05calciumia so this is going to be low
38:09calcium
38:11can cause hyper excitability of your
38:13muscles what happens if you have hyper
38:16calcium calcium this is going to be high
38:19hypo is always going to be low hyper is
38:22always going to be high calcium
38:24you can actually cause your muscles to
38:26not respond at all because there's too
38:29much so just because calcium is great
38:32and we need it you can have too much and
38:34you can have too little so you need to
38:36have the piece right in the middle
38:39there's two more hormones that are going
38:42to be controlling this whole process and
38:44just to briefly run through those one is
38:46leptin and one is serotonin and leptin
38:50is released by adipose tissue and
38:52serotonin is going to be a
38:53neurotransmitter that regulates mood and
38:56sleep both of these are going to play a
38:58role in bone density so you just need to
39:00know that there are four total hormones
39:02parathyroid hormone calcitonin but also
39:05leptin and serotonin that do control
39:08remodeling of bone but there's a second
39:11way that you can control Remodeling and
39:14that's going to be mechanical stress
39:17so mechanical stress essentially means
39:19your bone will need to remodel because
39:22something is telling it that it needs to
39:24because there's some sort of stress that
39:26is put on it basically bones will
39:29reflect the stress that they actually
39:31encounter so if you were to pull down on
39:35one end of a bone it would bend that's
39:37what happens and that's what we're
39:38talking about with stress so there's
39:40this gentleman named wolf who came up
39:42with a law and his law is going to be
39:45called Wolf's Law
39:49and Wolf's Law is that the bone will
39:52actually grow
39:54or it will remodel
39:58in response to stress
40:01so it will affect whatever it
40:05um whatever affects it it'll actually
40:07change the bone itself so some examples
40:10of Wolf's Law is going to be stretched
40:14um
40:15will tend and break and they will
40:17actually compress on one side so
40:20this is a very interesting part right
40:23here so when we said that they will
40:25actually
40:25Bend this is the natural point of
40:29tension you'll notice that the bones
40:31actually look like this they don't just
40:33look like this so this is going to be
40:35the connection between your hip and your
40:37upper leg your femur and your hip bone
40:38so it's not just up and down like this
40:40it actually has to do this Bend right
40:43here in order to get the
40:47stress because the entire weight of the
40:49body resting on that one joint
40:52so Wolf's Law is actually really cool
40:54because it explains
40:56handedness
40:58the right or the left-handed whichever
41:00one you typically use to write with that
41:02hand will have a thicker and stronger
41:04bone that arm will have a thicker and
41:07stronger bone because you're using it
41:09more
41:10wherever you're going to have bones that
41:12are going to be likely to buckle that's
41:15they will be thicker in that particular
41:17place so if I have a bone that is likely
41:21to buckle
41:23that is a very bad one let's try that
41:25again
41:26I have a bone that will be lightly
41:28likely to buckle right here what you'll
41:31actually have is the bone will bump out
41:34and be slightly thicker in that space
41:38you'll have trabeculae form along lines
41:40of stress
41:42and then whenever you have places where
41:44large heavy muscles attach you'll
41:46actually have little projections for
41:49them to Anchor onto
41:51and what's interesting is that bones of
41:54um
41:55fetus and Bones of people who are in
41:58nursing homes who don't have the ability
42:00to get up out of a bed or bedridden are
42:02considered featureless there is no bumps
42:04there is no thickness they are smooth
42:08because there is actually no stress
42:11being put on them
42:12so it's an interesting way that we know
42:13that Wolf's Law actually does occur
42:17okay
42:18so then the last section that we're
42:20going to focus on
42:23um is going to be what happens when your
42:26bones go wrong
42:27so that's going to be bone repair
42:30so you've got bone growth during
42:32development well first of all you've got
42:35bone formation during development then
42:37you've got bone growth during Adolescent
42:39and then you've got bone
42:41remodeling that occurs just during life
42:44in order to replace and break down and
42:46give you new bone but what happens if
42:48you actually damage the bone then you
42:51have to repair the bone and so that's
42:52what this section is going to be
42:53covering so fractures are breaks so
42:58whenever you hear the term fracture it
42:59means the bone has broken
43:02we can classify fracture a couple
43:04different ways
43:06so when we actually classify fractures
43:10the first way we're actually going to
43:12classify them is based on the position
43:15of the bone ends
43:17so it's going to be the position of the
43:19epiphyses
43:22and what we mean by the position of the
43:24epiphysis is
43:26are they in their normal position or are
43:28they out of their normal position so
43:30this is going to be non-displaced or
43:33displaced so if we have a non-displaced
43:36fracture
43:38foreign
43:40end is in its typical spot what we mean
43:43by that is that the end of the bone is
43:45still connected and in the same
43:48organizational structure that it was
43:50that it should be
43:51um it has not moved out of the socket
43:54or you can have displaced which is where
43:57you have essentially just broken it and
43:59it has moved completely and it's no
44:00longer in alignment with the next bone
44:03or we can classify fractures based on
44:06the completeness of the break
44:08essentially how good at you how good
44:10were you at breaking the bone if we
44:13Blake it break it and it's complete
44:16the brown the bone was broken
44:18essentially all the way through so that
44:23means you slice that bone
44:26all the way through
44:34this is my bone
44:35you've sliced it like that it is going
44:38to be broken
44:39all the way through whereas if you have
44:42a incomplete bone
44:45this is only breaking a bone halfway
44:48through
44:50so this is going to be where you
44:52essentially have gone halfway but you
44:53haven't gone all the way through
44:55and then you can also classify a break
44:58whether or not
45:00um it goes through the skin
45:02and if it goes through the skin it's
45:04going to involve a lot more external
45:06blood
45:07um that would be an open or sometimes
45:11called a compound fracture
45:13means that it has gone all the way
45:15through the skin or you can have a
45:17closed sometimes called a simple
45:19fracture which means it is still within
45:22the skin and is intact so here's some
45:24examples
45:26um
45:27of some types of fractures
45:30so common types of fractures that we're
45:33going to have
45:34we're going to run through these real
45:36quick
45:37so this is how you're going to classify
45:38the um
45:41bone-ins the completeness and whether
45:43the skin is penetrated but you can also
45:46just look at the external structure of
45:49the there's a couple other things so
45:51these are going to be common fracture
45:53types
45:59you can have culminated this is
46:02essentially going to be where you have
46:04more than three three or more places
46:06that you have broken it you can have a
46:08compression which is essentially you've
46:10pressed the bone and it's crushed this
46:13will happen invertebrate a lot of the
46:14time you can have a spiral which was
46:17done because there was a great twist
46:19that was put to it so it actually breaks
46:21on the diagonal you can have the
46:24epithelial break which essentially just
46:26means it breaks right across the top of
46:28that epithelial plate and it just breaks
46:31right down that spot right there
46:33or you can have a depressed fracture
46:35which means that it is going to press
46:37inward kind of like if you were going to
46:39hit something it would make an indention
46:42or you can have a green stick fracture
46:45and this is going to be the bone that
46:47does not break completely so if you ever
46:50um have lived in the South and have gone
46:51outside and pulled a twig that still is
46:54green or fresh or New Growth and you try
46:57to bend it in half it doesn't snap in
46:59half completely it'll actually Bend with
47:02you and that's called a green stick
47:03because it doesn't break completely it
47:05will bend that's kind of what happens
47:07with this green stick fracture okay so
47:12I'm not going to cover what happens with
47:15repairing a fracture but essentially
47:18what you're going to have to just do is
47:19create new bone and it's going to happen
47:22through your intervention of your um
47:25blood supply but we're not going to
47:27specifically talk about that nor is it
47:29going to be on the exam so the last
47:32section I do want to talk about is go
47:33going to be what happens when all of
47:35this goes horribly horribly wrong
47:38these are bone disorders
47:40so like every part of the next couple of
47:42chapters we're going to talk about
47:44diagnoses or things where things will
47:46actually go wrong bone disorders are
47:48going to be an imbalance between the
47:50processes usually bone deposit and Bone
47:53resorption are going to underlie nearly
47:55every disease on the human skeleton so
47:59the three major bone diseases that we're
48:00going to talk about
48:01osteomalacia osteoporosis and peugees
48:05disease so first off
48:07osteomalacia
48:13you may have also heard this called
48:15rickets but that is going to be
48:16specifically just in children so the
48:18overarching diagnosis is osteomalacia
48:21and these are going to be bones
48:24that are poorly mineralized
48:27so there's not a lot of hard calcium
48:30phosphate in order to make them a very
48:33hard bone so they're poorly mineralized
48:36so what's happening with this is the
48:39osteoid is produced
48:42so you will actually have the structure
48:45in place
48:47but what will actually happen is that
48:49the calcium salts
48:52are not adequate so you will be doing
48:56what you should be doing but it's not
48:58doing it with the right amount of salt
49:00amount right amount of calcium salt so
49:03what you'll actually end up with is
49:05something called a soft bones you just
49:08do not have enough of the calcium salts
49:10in order to make it hard
49:12so
49:13what you're going to see is the symptom
49:15of this is actually going to be pain
49:18when you actually apply weight to the
49:21Bone because the bone is soft so it'll
49:24be pain with weight-bearing
49:27that is going to be the primary
49:30symptom that you will see so all of this
49:33for osteomalacia you need to know but
49:35for rickets whenever it's osteomalacia
49:38in children the same process applies
49:42except what it is since it's
49:44specifically in children this is going
49:46to affect growth a little bit so what
49:49you'll actually see is bone deformities
49:52and bowed legs so I don't know if
49:55there's a picture there is not so if I
49:57had a sweet little kiddo
49:59who should have hips who look like this
50:02what you'll actually get with these soft
50:05bones is you will get bones that look
50:08like this and the reason is is because
50:11all of their body weight is pushing down
50:13on these bones these femurs that are
50:16soft and not adequately able to support
50:18it so they'll Bend outward because it's
50:21stress Wolf's Law in action so that's
50:23going to be rickets it's the same thing
50:25it's just going to cause bone
50:26deformities
50:27so the primary thing that you'll see
50:29kids were diagnosed with rickets in 50s
50:32and 60s is because they had the bowed
50:34legs so the next one we're going to talk
50:36about is osteoporosis
50:40and so osteoporosis is probably one of
50:42the most common and it's actually a
50:44group of diseases but what is happening
50:47with osteoporosis is bone resorption
50:51so the taking up of old bone will
50:54actually exceed
50:57bone deposit
50:59so the ability to break down your bones
51:02is greater than laying down new bone so
51:06what you'll actually get
51:08is bones are going to be
51:12um
51:14the composition of the bones
51:17is going to be fine so your bone mineral
51:21composition is totally appropriate
51:25however what it is is it will actually
51:28decrease the bone mass
51:33so you've broken down a bunch of bone
51:35but you have not replaced it so that's
51:39what we mean by bone mass
51:42so it's going to be essentially bone
51:44resorption is exceeding bone deposit
51:46you're going to get kind of a spongy
51:48very very light bones is what these are
51:51called
51:52but not only will you have light bones
51:54you will have porous
51:57bones this is what is known as
51:59osteoporosis when you look at the
52:01microscope so this is what you see right
52:03here with all of the little holes in
52:06these pieces
52:07so some risk factors for osteoporosis
52:11is going to be
52:12usually female most often a
52:16post-menopausal women usually affects 30
52:19percent of women around age 60 and then
52:21that increases by age 80 to 70 percent
52:24but estrogen does play a role so that
52:28will come into play with hormones and
52:31all the bone deposit pieces okay so
52:35that's osteoporosis some additional risk
52:37factors are everyday life through
52:40smoking or
52:43poor diet
52:45um where you don't have enough minerals
52:46of calcium and protein insufficient
52:48exercise but then also some things like
52:51genetics hormone related conditions
52:54um and consumption of alcohol
52:57and there's how we treat it you can do
52:59it a couple different ways
53:01based on the severity
53:03I'm not going to focus on
53:06the drugs for osteoporosis but what I
53:09want to get to is Paget's disease
53:13so we had osteomalacia
53:16osteoporosis and now
53:18Pages disease so Paget's disease is
53:22where you are actually going to have ex
53:24excessive
53:28bone deposit and resorption so this is
53:33going to be a little bit different so
53:34you will actually have both
53:36you will have excessive
53:40bone deposit so you're laying down a lot
53:42of bone but you're also going to have
53:45excessive resorption so essentially
53:48you're doing the normal process but
53:51you're just doing it on Hyper Speed so
53:54this is actually going to be it's just a
53:56fast process so what you're going to get
53:59is you are going to have poorly
54:01developed bones
54:05because essentially the process happened
54:07too quick they have not been able to
54:09develop correctly and really the reason
54:12you're going to have poorly developed
54:13bones is because there will be a high
54:16ratio
54:19of spongy to compact bone
54:25so it's not going to be the normal ratio
54:27that you're going to have with this
54:29Paget's disease
54:30so a high ratio this is usually going to
54:33occur in your spine your pelvis your
54:35femur or your skull and it really
54:37happens before 40 but you can see this
54:40right here is Paget's disease where you
54:43essentially you're having your normal
54:44everyday process it kind of looks like
54:46osteoporosis underneath the microscope
54:48but there is the ratio of spongy to
54:52compact bone is what they're looking for
54:53not holes in the bone which would be
54:56what they're looking for with
54:57osteoporosis so when you're reviewing
54:59these three diseases osteomalacia
55:01osteoporosis and Paget's disease know
55:04the relationship between the bone
55:06remodeling and the bone resorption for
55:08each of these sections
55:11as we're going through with development
55:14of your bone we've already talked about
55:16most of this but at Birth most long
55:19bones are ossified except for the
55:21epiphyses this will continue with the
55:24epiphysilial plate doing
55:25um its uh
55:28its thing through childhood and
55:30Adolescent and then females and males
55:33will close off and ossify that
55:35epithelial plate at different ages but
55:37by age 25 skeletal growth should
55:40actually decrease so this is a really
55:43cool image to be able to show you the
55:45skeletal
55:48um bones
55:50versus the cartilage so this is weak
55:5410 so at week 10 we said at week nine
55:58you were starting to ossify and replace
56:01the bone
56:03um replace the cartilage across all of
56:05your bones so you'll actually can see if
56:07you look right here on the hand the
56:10these bones right here that are in the
56:12Palm are have been
56:14um replaced by bone however the
56:16connection point right here the ends of
56:19the bone and the ends of the bone right
56:22here
56:23are still cartilage cartilage is mainly
56:26made up of water so that's why in a
56:29image like this you can see through
56:33things that are made of water so they
56:35look clear where you can't see through
56:37harder structures like bone so another
56:39place that's really good to see it is
56:42the femur right here
56:44you can actually see
56:47this right here is going to be the
56:49actual
56:51diaphysis but what you are lacking right
56:55here
56:56is there is no hardened epiphysis so you
57:00can actually see straight through the
57:01ends of the bones because they are still
57:03cartilage and will continue to be
57:05cartilage up until birth
57:07so that's going to be the wrapping up
57:09this LAX section of uh chapter six