Bone Physiology Lecture, June 8

0:03good morning everybody thank you so much

0:07for joining me this morning if you guys

0:09had a great weekend and can really

0:13appreciate the fact that you guys are

0:14halfway through this experience already

0:17so good job I know that this is a lot of

0:20information I throw at you all at the

0:22same time as I said on the first day

0:24that we had together this is a strenuous

0:28course even during a semester and you

0:30guys are taking it in just a few weeks

0:32so she has a rockstars and definitely

0:36pushing through I know there was a lot

0:40going on this weekend I'm kind of a tie

0:43over from last week are there any

0:45questions comments or concerns that I

0:47can address at this point in the entire

0:50class okay and I'm sure you guys saw

1:00that I did post grades or at least what

1:02I was able to get through on grades in

1:05general the grades are actually higher

1:08than they would normally be an in person

1:10either spring or fall semester or even

1:13over the summer so that is fantastic

1:15news to me

1:17and hopefully it is to you guys as well

1:21at this point you know there are only

1:23really grades for the first quarter of

1:25the semester and so if you aren't

1:27exactly where you want to be at this

1:28point no worries there's still plenty of

1:32time right there's still three more

1:33exams to practicals including the one

1:36that opens today and so there's a lot of

1:38opportunities to bring up your grade and

1:41perhaps you guys saw the little analysis

1:44that I did of the videos and their

1:47effect on multiple choice scores and so

1:49it does seem like there is a link

1:52between making those videos at least you

1:56know studying them enough so that you

1:57can talk about it but actually doing

1:59better on the multiple choice section so

2:01that is interesting to me and hopefully

2:07validates the experience and so even if

2:11going forward we don't do those types of

2:13videos anymore

2:14I definitely

2:14I would like to point out that that is a

2:16really great study tool for you guys

2:19even going forward into a mp2 and into

2:21your graduate programs eventually again

2:25I'll pause just in case anyone has

2:27anything they want to throw out for the

2:30good of the order okay and I'm actually

2:37really enjoyed watching those videos it

2:40is wonderful to see and hear you guys

2:43like really wonderful but also you're

2:46doing just such a phenomenal job it is

2:50incredible that you guys can you know

2:52sit at home and learn these things to

2:55such a third degree so you really should

2:58be proud okay so this week we are

3:02wrapping up information for lecture exam

3:06two for ya so wrapping up lecture exam

3:11two we're going to take that on

3:13Wednesday so this is the last time we

3:17will meet before Wednesday we are also

3:20wrapping up the first half of the course

3:22worth of laboratory structures and so of

3:26course I am in the lab today and so I'm

3:28more than happy to show you guys models

3:31just that you can see them one more time

3:32and ask questions about them before you

3:35take the test before you take the lab

3:38practical and so the lab practical will

3:42be available on blackboard starting at

3:44two o'clock today and it is due by

3:47midnight tomorrow so before we get into

3:54lab stuff I do want to wrap up with the

3:56lecture so that you have full 48 hours

3:59to kind of come to terms of this

4:00information I did post goodness I did

4:06post lecture notes for you guys

4:09and we're just going to walk through

4:11that at this point him and as always

4:18this is going to be on YouTube just in

4:21case you missed something okay so on

4:27these

4:27are the lecture notes for today these

4:30are the different topics that we're

4:31going to talk about so we just wrapped

4:34up muscle physiology now we are going to

4:38talk about bone physiology pretty much

4:40how do they grow how do they change over

4:42time both in the good normal ways right

4:46adapting to our lifestyle and also how

4:48they might start to break down given

4:50what you choose to do with your life so

4:52this is what we're going to be going

4:55through on remember that bone is just

4:58another type of connective tissue then

5:00for connective tissues have mostly

5:02extracellular matrix that is there's

5:04lots of proteins there is always ground

5:07substance and there you know there's a

5:11possibility of having other types of

5:13substances as well and in the case of

5:15bone and cartilage which we're going to

5:17talk about because it is very similar to

5:19bone essentially there are inorganic

5:23molecules as well that can actually

5:25strengthen that extracellular matrix

5:27right so bone of course is a living

5:29tissue

5:30it is very vascular and we have these

5:33cells that are constantly building them

5:34up and breaking them down just to give

5:37you guys a little preview here I have a

5:41short animation for you guys

5:46[Music]

5:48a short animation on that we will watch

5:52see I think think you can see this at

5:55this point hopefully and so here we go

6:01this is an overview of everything that

6:04we're going to be talking about

6:14other loans consists of an outer shell

6:17compact bone and an interior of spongy

6:20bone compact bone is dense and strong

6:24and provides an attachment site for

6:26muscle punching foam is lightweight rich

6:29in blood vessels

6:30highly porous and contains bone marrow

6:33blood cells are formed while bone

6:36resembles periglacial

6:37the collagen fibers of bone are hardened

6:40by deposits of calcium phosphate there

6:43are three types of Elna cells

6:45osteoblasts called informing settles

6:48osteocytes but surer bone cells and

6:52osteoclast on dissolving so on producing

6:57osteoblasts form a thin layer covering

7:00the outside of the bone osteoblasts

7:02secrete a hardened matrix of bone and

7:05gradually become interact with it they

7:08then stops a training matrix and become

7:10osteocytes

7:12osteocytes are nourished by nearby

7:14capillaries that are connected to one

7:16another by thin extensions osteocytes

7:19sent out to each other from narrow

7:21channels in the bone although I able to

7:24produce more bone osteocytes secrete

7:26substances and control the continuous

7:29remodeling of bone each year five to ten

7:43percent of all the wound in your body is

7:46dissolved away and replace this allows

7:49where skeletons is subtly alter its

7:51shape response to the demands placed

7:53upon it for example by increasing the

7:56thickness of bones that carry heavy

7:58loads or are subjected to extra stress

8:01bone remodeling allows one to be

8:04replaced as it ages and becomes brittle

8:06as people age the remodeling process

8:09slows and bones tend to become more

8:12fragile as a result the continuous

8:15turnover of bone also allows the body to

8:17maintain constant levels of calcium in

8:20the blood calcium from bones is retained

8:23in the blood if blood calcium

8:25but returned to loan what calcium levels

8:29are adequate or high this process is

8:32regulated by two hormones

8:34calcitonin which causes the bones to

8:37retain calcium and parathormone which

8:40causes bones to release calcium into the

8:42blood bone remodeling is the result of

8:46the coordinated activity of osteoclasts

8:49and osteoblasts

8:50osteoclasts in crank acids and enzymes

8:53that dissolve the hard bone matrix

8:56working in small bruise osteoblasts

8:59tunnel into the bone creating channels

9:02that are invaded by capillaries and

9:04osteoblasts downstairs last Hill the

9:07channel the concentric deposits of newly

9:10born country's leading only a small

9:12opening for the capillary as a result of

9:15this process in cross-section hard bone

9:18is made up of tightly packed units

9:20called haversian systems each consisting

9:24of concentric layers of bone with

9:26embedded osteocytes the concentric

9:29deposits surrounded a central canal

9:31through which a capillary runs go back

9:42to our lecture here so again as the

9:46video showed you bone is continually

9:49being remodeled it's being built up and

9:52it is being broken down and so that

9:54course allows us to not only remember

9:57bonds based on what we choose to do with

9:59their lives but also it helps us to

10:02maintain a really important balance of

10:03calcium within our blood right of course

10:06we just finished talking about muscles

10:07and of course before that neurons and so

10:10hopefully at this point you guys can

10:11appreciate just how important calcium

10:13actually is for the function of our body

10:16right in order to exercise those

10:19neurotransmitters we need just the right

10:21amount of calcium in our body that is

10:24circulating freely in our body in order

10:26to contract our muscles right our

10:30muscles have to have a certain amount of

10:31calcium inside of them right in order to

10:34release that and therefore bind to

10:36troponin remove true

10:38Mison and ultimately form the cross

10:40bridges and so on maintaining calcium

10:43levels are between a particular or

10:45within a particular range is really

10:48important part to the functioning of our

10:52bodies

10:53bones in general are classified into

10:57categories based on their shape we will

10:59be learning all 206 bones of the body

11:02and you know generally we can appreciate

11:05in these different shapes for the

11:08upcoming lecture exam as well as a lot

11:10of practical the only ones that we are

11:12focusing on are the axial bones of

11:14course - the skull that's at the very

11:16end of the class and so hopefully this

11:19serves as a nice introduction to what

11:22different shapes are possible okay so um

11:26the long bones oops sorry about that

11:29on the long bones here you can see this

11:36better so the long bones are of course

11:37longer than they are wide we have lots

11:40of lots of those and we're going to

11:41spending most of our time today talking

11:43about how they work we have lots of

11:46short bones right so these are kind of

11:48cube shaped and ultimately have little

11:52indentations for the formation of joints

11:54or articulations we have some flat bones

11:57mostly in our axial skeleton so our

11:59sternum for example is a flat bone of

12:03course it is flattered that it is wide

12:05or tall

12:07we have irregular bones right which just

12:10have no particular pattern whatsoever

12:12our vertebrae are a great example of

12:14your regular bones and sesamoid bones um

12:17we really have a pair of them using your

12:20kneecaps right so they actually form um

12:22not in the same way that all of your

12:24other bones form they actually form

12:26within a tendon so we are going to be

12:30talking for the most part about how flat

12:33bones form as well as long bones form um

12:39so all bones have some basic structures

12:43in common whether they are long or short

12:46or flat they all have a periosteum

12:50right so remember we talked about this

12:52model right here this outer coating on

12:55the outside of the bone is the

12:57periosteum around the perimeter peri of

13:00the Aust the bone okay and so no matter

13:03what bone you're talking about all of

13:05them have a periosteum um this is a

13:09membrane that we're going to talk about

13:11a little more detail in a couple slides

13:12here but essentially this fuses to the

13:16bone and this is where your muscles or

13:18your tendons attach to your muscles is

13:20actually going to attach and so it's

13:22really important that this periosteum

13:24stays attached to the bone so that our

13:27muscles don't come off and also we have

13:31stem cells in this layer and so anytime

13:33we need to break down bone or build it

13:36up maybe we have we've had an injury or

13:38whatever um we need that periosteum and

13:41so it has to stay securely fastened to

13:44the surface of the bone and in order to

13:46do so it uses what are called

13:48perforating fibres okay so these are

13:50actually embedded within the bone and of

13:54course if you take a look at this model

13:56here we can see the perforating fibers

13:58attaching the periosteum right here of

14:03course the bone itself contains both

14:06compact bone as well as spongy bone the

14:09compact bone is the hard outer shell the

14:12spongy bone also called trabecular bone

14:14also called cancellous bone right wine

14:16and something once um that is the spongy

14:19bone inside and so here we can see a

14:21flat bone of our skull this is the

14:23compact bone and the spongy bone is kind

14:26of sandwiched in between um so let's

14:30talk a little bit more about the

14:31periosteum here um the entire surface of

14:34the bone is covered by the periosteum

14:36except for where the joints are okay so

14:39actually I'm you know at the top of your

14:42tibia the bottom of your femur for

14:45example um our knee comes together and

14:48so those bones don't rub against each

14:50other and kind of grind and cause a lot

14:52of pain a lot of discomfort

14:53we have cartilage that protects the ends

14:56of those bones so everywhere else except

14:59for the joint surfaces are covered with

15:01periosteum there are actually two

15:03layers of tissue within this membrane on

15:06the first of all we have the fibers

15:08layer that is on the outside it is made

15:12up of dense irregular connective tissue

15:13so that we can push and pull on it in

15:15every which way and it doesn't become

15:17damaged so if you look down here in this

15:20image we can see that there are two

15:25different layers here's the fibrous

15:27layer on the outside and the inner the

15:29deeper layer that's actually touching

15:31the surface of the bone is the cellular

15:34layer and so we can see that these cells

15:36look a little bit like squamous cells

15:37all right so nice and flat um these are

15:40in fact osteogenic cells so osteo for

15:44bone genic for can generate anything

15:47that will ultimately become a bone or

15:49like both that is these cells can become

15:53those bone building cells osteoblasts

15:55they can become bone breaking down cells

15:58osteoclasts they can ultimately become

16:01osteocytes all right mature bone cells

16:04and I'll spell all these out for you

16:06here soon and they can also become

16:08cartilage cells will see that bone and

16:10cartilage is very closely related and so

16:14yes we have stem cells right so just

16:16like in our stratum basale

16:18we are continually able to make more of

16:20these cells and they can differentiate

16:22that is they can express different genes

16:25to become either bone building or bone

16:28breaking concept on the periosteum also

16:32delivers about of us about a third of

16:34the Bloods of the bones blood supply

16:37right so we can see lots of blood

16:43vessels right so again going back to

16:45this model we see these perforating

16:48canals and these blood vessels

16:49ultimately distributing blood to all of

16:51the osteons we're getting there today

16:53but these are all coming from the

16:55periosteum also there's lots of nerve

16:59fibers so essentially the bone is a very

17:02is very much alive in general long bones

17:08are broken down into the ends of the

17:11long bones and the shaft of the long

17:14bones okay so on either end

17:17proximal end or distal end we have a

17:20fatter region of the bone and this is

17:23where the bones are going to form joints

17:27right so for example this is a femur

17:29which we'll get into a couple days

17:31actually but this entire structure here

17:34is going to form a joint with your hip

17:36right with your hip bones on and so

17:39these ends are fatter so that

17:41essentially the the weight and the

17:44pressure can be distributed over a

17:46larger surface and therefore not so much

17:48pressure on the bones themselves okay

17:51also within these structures the

17:55epiphysis on we have spongy bone right

18:00so here up here um we have taken a

18:04section through the epiphysis we can see

18:06lots of spongy bone inside and so spongy

18:09bone of course forms a latticework and

18:11within that lattice is stored our red

18:15bone marrow as we're going to see or as

18:18you're going to see you next semester

18:19whether it's the summer or in the fall

18:21red bone marrow is where we make all of

18:24the formed elements of our flood so the

18:26red blood cells the white blood cells

18:27the platelets all of these things which

18:29are so very important to our existence

18:31are made within our bones right so bones

18:34are a lot more important than just

18:35keeping us standing upright and allowing

18:37us to move they maintain calcium

18:39homeostasis they maintain our blood

18:42supply epiphysis also remember that they

18:48form joints or articulations it's the

18:51official word for a joint because of

18:53that they are covered with cartilages

18:55anytime you see this blue color here or

18:57this blue color that is showing it's

18:59cartilage the tissue type is high lean

19:03cartilage right one of three different

19:04types of cartilage that we learned about

19:06previously the structure is called

19:09articular cartilage right so Hylian

19:12cartilage is found all over the body

19:14right our costal cartilages for example

19:16are made of pileinn cartilage that's the

19:18tissue type articular cartilage is the

19:22structure it is helping to protect the

19:24end of the long bone within an

19:26articulation okay so that's a really

19:28important distinction to make

19:29okay so Lucia

19:31these um in between the two fatter ends

19:35of the long bones there is what is

19:38commonly called the shaft of the long

19:39bone but more specifically is they the

19:41diathesis of a long bone um during the

19:45development of our long bones on this

19:48structure ultimately hollows out and

19:51forms a cavity within it yes this cavity

19:54is called the medullary or medullary

19:56cavity it's essentially where the bone

19:59more the yellow bone marrow is going to

20:01provide mr. yellow bone marrow is

20:03different than red in that in

20:07adolescents or adults on this

20:09essentially just stores some extra fat

20:11all right so it's not the kind of fat

20:13that you go to jannat try to get rid of

20:15on this is just extra energy supply I'm

20:18just in case we're running low right so

20:21you always have this unless unless you

20:24are literally starving okay um you guys

20:29might have actually seen this in real

20:31life

20:31um so if you've ever um you know gotten

20:35soup bones from from the grocery store

20:37to cook up for your dog or to me you

20:39know soup for yourself or whatever or

20:41even like the little slice of bone

20:43within a hand on there's that like gooey

20:45stuff inside the ring of bone that gooey

20:48stuff is yellow bone marrow lining this

20:53medullary cavity is another membrane

20:56that is very similar in structure to the

20:59periosteum but this is called the

21:01endosteum so endo meaning on the inside

21:03inside of what the asked the bone okay

21:07so in general when in doubt um if you

21:09can't remember on a structure having to

21:12do with the bone tell me Aust and that

21:14will probably be partially correct all

21:18right a couple more features of the long

21:20bone that are essentially remnants are

21:24kind of like scars

21:25residual from the developmental process

21:28first of all we have these epiphyseal

21:30lines all right so we can see that

21:32within the compact bone or sorry within

21:35the spongy bone there are these lines

21:37that look like compact bone and in fact

21:39they are on these used to be your growth

21:42plates okay so

21:45when your bones were first growing you

21:50know this is all spongy bone there were

21:51stem cells in here there is actually

21:52cartilage and ultimately your growth

21:54plates closed but those like the

21:58location of those growth plates never

21:59actually disappears it stays with you

22:02throughout your adulthood as a line of

22:04compact bone we'll talk about that in a

22:07few slides here also uh there is a

22:12nutrient foramen or foramen this word

22:16foramen means hole and so this is a hole

22:18for nutrients to get into the bone so if

22:21we take a look over here we can see that

22:24there is a blood vessel that passes

22:27through the periosteum and is actually

22:29going to go all the way inside the bone

22:31into the medullary cavity here this

22:34blood vessel penetration into the bone

22:37actually happens within the first eight

22:40to ten weeks of your life in utero

22:42all right so eight to ten weeks after

22:44fertilization these blood vessels

22:45penetrate into the kind of preliminary

22:50bone it's not a bone yet it's more

22:52cartilage but essentially that blood

22:55vessel stays there and it's going to

22:57continue feeding you're feeding your

23:00bones for the rest of your life

23:02all right so the periosteum supplies

23:03about a third of the blood to the bone

23:05the nutrient frame and with its

23:07associated blood vessels supply the

23:08other two-thirds and so some histology

23:13of bone tissue at this point we have

23:15seen bone actual slides right so in

23:19histology lab we looked at some images

23:22of bone tissue that was probably some of

23:24the easiest tissue to identify just

23:26because of those nice little ring

23:27structures right the compact bone just

23:34like we have seen in our model here

23:36consists of these cylinders and the

23:39structural unit of the compact bone are

23:42these osteons right asked for bone on

23:44cylinders of bony tissue are osteons and

23:48so we can see that essentially each one

23:50of these osteons is like a little tree

23:52like a tree trunk even with those little

23:54rings inside called lamellae and they're

23:56very densely packed

23:58the compact bones are very densely

24:00packed forests of these little osteon

24:02trees and so this makes the compact bone

24:05incredibly strong um in fact about as

24:07strong as steel can be so very strong

24:11indeed um therefore we you know the

24:17structure matches the function right so

24:18we have essentially a shell around the

24:21outside of our bones that needs to be

24:23really strong because this is the

24:25weight-bearing structure of our bone in

24:28fact the weight-bearing structures of

24:29our body so it has to be as strong

24:31physically possible okay um each osteon

24:35contains four to twenty lamellae

24:37remember lamellae are these these layers

24:41here concentric layers um we can see if

24:45we kind of pull those layers out like in

24:47this image over here to the right that

24:49the collagen fibers and the other things

24:51that are about to talk about on in these

24:53layers are arranged in a somewhat

24:57parallel fashion but each layer has

25:01parallels or has fibers going in the

25:03opposite direction alright so here we

25:05can see fibers coming up here in the

25:08next lamella we can see fibers going in

25:09this direction it so this isn't by

25:12accident on this actually makes the

25:14osteons even stronger yet so not only

25:17are these or is this compact bone

25:19resistant to kind of like crushing more

25:22stress factors here also we get a

25:24certain degree of twisting in our bones

25:27particularly if you're younger but a

25:29certain degree of twisting is possible

25:31because these fiber arrangements are

25:36strong to withstand that twisting motion

25:38okay also all the way on the inside of

25:43these of these osteons as we know from

25:46the lab there is a central canal and

25:49this central canal is where blood is

25:51delivered use blood or deoxygenated

25:54blood is drained away and there are also

25:57nerves as well it's actually controlling

26:00what's happening within the bone okay

26:04just like that little video clip showed

26:06you

26:07each ASEAN houses many what are called

26:11osteo

26:12sites now when we learned about

26:14connective tissue for the first time I

26:15told you that these suffix of the cell

26:20names would tell you kind of what it

26:22does um and that is absolutely the case

26:24so the root site just means cell or

26:27mature cells of what of the osteo of the

26:31bone and so the osteocytes live within

26:35these little lacuna right still lives

26:37within these little cavities here

26:41throughout you know the entire life of

26:44the cell and so again

26:47double duty here we took a look at this

26:52model here before right so here's the

26:56osteons here's the central canal each of

26:58these are lamellae these little holes

27:03here are look yearning and they house

27:07within them osteocytes and so

27:10essentially where do these come from

27:12well these osteocytes used to be

27:16osteoblasts okay so they used to be bone

27:20building cells right again just like the

27:22video showed you that we're so good at

27:24what they do

27:25that's so good at secreting these bony

27:26matrix that they actually secrete it in

27:30front behind and all around themselves

27:32so they actually get trapped in the very

27:35matrix that they themselves are

27:37secreting alright so once they can't

27:40move anymore because they just buried

27:41themselves at bone then they become

27:44osteocytes okay so again bone building

27:47cells are osteoblasts right the blast

27:50here indicates building building up

27:53making more bony tissue they will become

27:57osteocytes sites live within lacunae

28:02remember that on these lacuna or these

28:06little cavities here are connected by

28:08what are called canaliculi it's a little

28:11tiny canals and so essentially in order

28:14to get nutrients and oxygen right from

28:17down here for example from this blood

28:20vessel glucose for example has to be

28:24taken into

28:26this cell passed through the cell to the

28:29next cell pass through the cell to the

28:30next cell and ultimately these kind of

28:34like you'll I allow these cells to

28:36communicate and pass substances back and

28:37forth so this is just another way of

28:43showing you this you know these

28:46structures remember here are the

28:49perforating canals attaching the

28:51periosteum which consists of dense

28:54irregular connective tissue as well as

28:55stem cells their stem cells can be

28:57osteoclasts osteoblasts osteocytes

29:01osteoblasts build up bone they get

29:03trapped in that bone and ultimately

29:04become osteocytes those osteocytes live

29:07in lacunae little cavities which are

29:09connected by canaliculi it's lots and

29:12lots of terms when I repeat them

29:14multiple times today not to be redundant

29:18although I know it is but most of these

29:21terms are also on your practical exam so

29:23I threw them at you guys last week um

29:25and just you know kind of learn these

29:27for now but now you have a little bit

29:29more of the physiological background on

29:31these structures so hopefully you can

29:34start to visualize them and recognize

29:36them a lot more easily if we look

29:42closely at the compact bone we can see

29:44that there are not only these concentric

29:46lamellae of the osteons but also there

29:49are lamellae that go around the entire

29:51periphery of the bone right so these are

29:55called circumferential lamellae which

29:58sounds so complicated but they literally

29:59go around the circumference so when you

30:01calculate the circumference of a circle

30:03you're calculating you know essentially

30:06the perimeter of it right so the

30:08circumferential lamellae just add girth

30:11right they add diameter to on the

30:14Longboat and so this adds a lot of

30:17strength and it is formed by something

30:20called appendicular growth or

30:22appendicular both bone deposition that's

30:27one of the things that we talked about

30:28I also another structure that we talked

30:33about in the lab right little models are

30:36these perforating canals right so here

30:38are the

30:39vessels and in order to get blood all

30:41the way in here on a bungee bone for

30:44example we need to have these tunnels

30:48board through right transversely through

30:52the osteons okay

30:56and so that's compact bone on let's like

30:59that spongy bone now I'm so spawn G bone

31:02is not actually spongy it's not squishy

31:05like a sponge it be but of course it

31:07looks like a sponge and if you look at

31:09this kind of honeycomb lattice type

31:11structure right here it looks super

31:13spongy and so spongy bone is always

31:17protected by the compact bone the

31:19compact bone is the really rigid really

31:21strong part of our bones because of the

31:24densely packed osteon arrangement um

31:28spongy bone is not quite as strong but

31:33it's not weak either and so if you think

31:36about um you know we're on campus and

31:41you went into big blue and you look up

31:42and you can kind of see those rafters or

31:44even just in the main academic spine or

31:47even if you haven't ever been sucked and

31:49if you've been to any kind of like

31:51gymnasium like High School gymnasium if

31:53you look up you'll see that there are

31:55these like this lattice type structure

32:00on the roof these are called trusses and

32:02essentially they are designed in such a

32:03way that they distribute the weight

32:06along these angles here and therefore

32:09they can be super strong but they don't

32:12have to be like a solid block of iron

32:16right so this is great news right we can

32:19save resources right we don't have to

32:21either manufacture more of these thick

32:25iron beams or manufacture more

32:27trabecular bone for example um but we

32:31still get the same benefits of the

32:32strength of a solid piece a solid

32:36structure okay and so in the same way

32:39that roofs can sustain a heavy snow load

32:44with this kind of structure here that is

32:47exactly how our spongy bones work okay

32:50so these this lattice work here that

32:52Rebecca

32:53they themselves are distributing weight

32:57in a very organized fashion it looks

32:59super disorganized but it is nearly just

33:04as strong as the compact bone because of

33:09the particular arrangement of these

33:11trabeculae okay also it is more

33:15organized than you would think just

33:17looking at it over time our trabeculae

33:21actually kind of arrange themselves

33:22right it's continually remodeling so it

33:25arranges themselves to distribute the

33:29weight well sorry to align along the

33:33lines of stress okay so that's what this

33:35image is showing you up here on this

33:37again is a section for a steamer on the

33:40weight of the body via the hip here is

33:42going to be borne by the femur your

33:45thigh bone and so in your knee you don't

33:48want the entire weight of your upper

33:50body as well as your thighs coming down

33:52on like some little tiny space so the

33:55the region of the joint the epiphysis is

33:58super fat right in comparison um and the

34:02trabeculae within that epiphysis

34:04distribute the weight relatively evenly

34:07throughout your knee joint alright if

34:09anyone's had any issues or no people

34:11with knee issues which I'm sure

34:12everybody you know just how crummy it is

34:17to have knee problems and so our body

34:19really tries to prevent that as much as

34:22physically possible so again the tissue

34:28itself the type of bone is spongy bone

34:32or trabecular bone or cancellous bone so

34:37that's the type of bone versus compact

34:39bone the structures themselves so the

34:41structural unit of the spongy bone are

34:43the trabeculae right as opposed to the

34:47structural unit of the compact bone

34:49which is the osteon okay so that's

34:52really important and that kind of sounds

34:53like a test question Jane tat

34:56nudge-nudge so the structures the

34:59trabecula the type of bone is the spongy

35:02bone okay um these are not arranged into

35:06Theon's but you do actually get these on

35:08lamellae right you also have osteocytes

35:12within their lacunae as well so really

35:14similar in that way okay remember that

35:19they're that housed within the spongy

35:22bone is your bone marrow right so you

35:27actually don't need a really big clunky

35:30or sorry you don't really need um blood

35:35vessels through a central canal because

35:38this tissue is essentially surrounded on

35:40all sides and so just to remind you all

35:47bones have these basic features in

35:49common they all have compact bone on the

35:52outside and spongy bone on the inside

35:54right whether you're talking about a

35:56flat bone or a long bone like this and I

35:59do want to point out that in pretty much

36:02all of your spongy bone you have bone

36:06marrow right but if you need to have

36:13your bone marrow sampled right so if you

36:16need to have it tested on you know

36:19physician suspects that you might have

36:21leukemia this bone marrow sample is

36:24taken usually from your iliac crest so

36:27from your hip bone like we can see down

36:29here even though we have bone marrow in

36:33you know pretty much all of our bones

36:34right so um this makes sense right it's

36:37not just some random decision random

36:39bone to take it from of course if you

36:42try to take it from a flat bone your

36:44flat bones are super skinny and of

36:45course if you miss a hunger rate through

36:47um there's a lot of really important

36:51stuff that you might hurt around around

36:54those flat bones

36:55um right your long bones are really

37:01strong they have a really thick layer of

37:03compact bone and that can be a lot more

37:06difficult as well and of course mobility

37:08of leg muscles and whatnot and so kind

37:11of the easiest places to get bone marrow

37:14or your hips right which of course are

37:16ready to service in the back there

37:18as well as your sternum your sternum is

37:21an option however just like with the

37:25skull if you miss on either side there's

37:29a lot of really important stuff in your

37:30chest that you don't want to poke okay

37:32um so this is why generally bone marrow

37:36is taken from your hips just so you know

37:39so that's the general structure of your

37:43bones let's zoom in a little bit further

37:46what are all of these lamellae made up

37:49when is compact bone and spongy bone

37:52actually consisting of at the tissue

37:54layer at the tissue level Bo and it's

37:58also called osseous tissue we've been

38:00talking about ask us ask us OSs is

38:03another group that means bone

38:07essentially the small population of

38:10cells are all called osteo something are

38:13surrounded by a ton of extracellular

38:15matrix just like any other connective

38:17tissue

38:18however this this type of extracellular

38:21matrix includes in an organic matrix and

38:24inorganic matrix so about two-thirds of

38:28the weight of your bones is actually

38:30made of as you might imagine calcium and

38:33phosphorus so these salts they actually

38:36spontaneously form little crystals

38:38around the existing proteins on these

38:41crystals are called hydroxyapatite

38:42crystals they they can be super super

38:49strong in a direction but also pretty

38:53brittle right there's no flexing

38:55whatsoever really strong but can shatter

38:59when twisted for example and so the

39:03organic matrix actually allows our bones

39:06to be a little bit flexible on as well

39:10as strong and so the organic matrix

39:12about a third of your bone weight is

39:15made up of something called osteoid

39:17crust or bone this is a lot of collagen

39:22just like the dermis skin for example

39:24and a couple other types of proteins

39:26that really give rise to strength as

39:29well as flexibility on so here

39:32um these are two fibula so part of your

39:35calf um if you treat the bone in such a

39:41way that you can get rid of the organic

39:44matrix you have a strong bone that's

39:46super brittle if you remove the

39:49inorganic matrix

39:50um you essentially have skin right so

39:54you have lots of collagen can be pretty

39:57flexible and give it a lot of different

39:59ways but of course this isn't going to

40:01keep your body upright okay so it is the

40:04combination of these two about

40:05two-thirds inorganic one-third ish

40:08organic and that comes together to form

40:11your bone tissue so we've used these

40:14words a little bit but let's actually

40:16kind of walk through it in more detail

40:20at this point the osteoblasts are the

40:23bone building cells um when the body

40:29needs bone to be built we'll talk about

40:31different scenarios for this case but

40:33when we need bone building osteogenic

40:36cells of course are found within the

40:38inner layer of the periosteum as well as

40:41the inner layer of the end ostium coming

40:45from both directions here um they are

40:47signaled right so a ligand is going to

40:50bind to receptors on these osteogenic

40:52cells that is going to trigger a

40:54pre-programmed response genes are turned

40:56on they make new osteoblast cells

41:01okay so osteoblast cells talked about

41:07that um build bone by secreting some

41:13stuff right specifically they're going

41:16to secrete osteoid right so essentially

41:18the organic component of bone is

41:20literally made by osteoblasts right so

41:24we can see in this image here borrowed

41:26from a peer-reviewed article

41:28these are osteoblasts they are going to

41:32transcribe translate and ultimately

41:35process these collagen proteins then

41:38they are going to secrete the collagen

41:41as well as all the other types of

41:42proteins in osteoid out of the cell

41:45I saw some exocytosis going on here so

41:49secretion and these proteins essentially

41:52are going to weave together and arrange

41:54themselves in the optimal direction

41:58right based on the needs of the body at

41:59the time and at the same time these

42:04proteins are organizing themselves into

42:07the appropriate direction there are the

42:11the osteoblasts are also going to be

42:14secreting enzymes again transcription

42:17translation processing through the or ER

42:19the Golgi secretion via exocytosis of

42:22enzymes into the extracellular

42:24environment and so these enzymes are

42:27actually going to be modifying the

42:30extracellular environment such a way

42:31that it essentially like calls over more

42:35salts that's a salt being calcium and

42:38phosphorus that spontaneously

42:41crystallize around these existing

42:45protein fibers so again

42:47osteoblasts secrete collagen and other

42:51types of structural proteins called

42:53osteoid they also secrete enzymes which

42:55call more salts to the scene which then

42:58spontaneously ossify around the osteoid

43:02right so now we have a third osteoid

43:05two-thirds hydroxyapatite crystals as we

43:14know these osteoblasts are just so good

43:17at what they do that they are you know

43:19secreting their oxygen which is then

43:21ossified and this isn't just happening

43:24like in front of or behind them it's

43:25also happening in front of them as well

43:27it's they ultimately bury themselves in

43:29this bony matrix okay and of course once

43:33they're trapped there they become

43:34osteocytes so they're no longer building

43:37bone no longer secreting osteoid instead

43:40they are merely maintaining it and

43:45finally the third type of bone cell are

43:50the osteo class right so bone breakdown

43:53seems really scary it seems like a

43:55really bad thing but on

43:57we absolutely need phone breakdown we

44:00need to continually remodel our phones

44:01and of course take calcium out of

44:03reserves in our bones and dump it into

44:06the blood necessary and so if we need to

44:10break down some bone again we'll talk

44:12about those conditions later but if we

44:15need to break down bone essentially

44:17those osteogenic cells the stem cells

44:21turn on particular genes which make them

44:23osteoclasts what do odds do class do or

44:26what they look like well essentially

44:27they are these big multinucleate globs

44:30with well and so anytime you see a lot

44:34of nuclei this essentially means that

44:36there's an even greater capacity for

44:39transcription and translation therefore

44:41lots and lots and lots of proteins can

44:43mate and so if we zoom in here to the

44:47edge of this osteo class we can see that

44:50there are tons of enzymes that are being

44:52secreted onto the surface of the bone on

44:55these enzymes as well as acid right so

44:58extra hydrogen ions is actually going to

45:01eat away it's going to break down that

45:03bone therefore mobilizing

45:07things like calcium and phosphate back

45:10into the blood okay so um again in this

45:14image here we can see the periosteum

45:16this cell is just differentiated into an

45:19osteoclast and now it is going to be

45:21spitting acid and enzymes onto the

45:23surface of the bone and essentially

45:24burrowing farther and farther and

45:26farther into that ball

45:28of course these mobilized substances can

45:31be released into the blood so if your

45:34blood calcium levels drop below a

45:36particular threshold we need to start

45:40breaking down our fault

45:43and so this there's always some degree

45:47of bone building by osteoblasts and bone

45:50breaking down by osteoclasts and as long

45:52as we maintain this balance we will have

45:55both strong bones as well as enough

45:57calcium in our blood it is only when you

46:01start to shift this balance between

46:03osteoblasts lastik clasts that you can

46:06start passing trouble okay so let's talk

46:10about

46:10where bones come from to begin with

46:12right you know all ties back to those

46:14three types of cells those are the main

46:17players in these stories the general

46:20process of making bone can be called

46:24either ossification it which is

46:26literally the you know forming of

46:29crystals on osteoid or more generically

46:32we can say osteogenesis that we are

46:34generating osteo or regenerating bones

46:37this process starts when you're an

46:42embryo actually so very early on in

46:47development and most of your bones exist

46:53by the time you're seven years old seven

46:56years post birth of course but they

47:02don't stop growing they don't stop

47:03changing okay so again this initial

47:06development of your bone starts very

47:10early on in your development and then

47:12it's going to continue throughout your

47:13life

47:14the very first thing that happens is

47:16pretty much just like quick and dirty we

47:20need some kind of model for our bones it

47:24doesn't have to be perfect it doesn't

47:25even have to be strong yet right so a

47:27fetus isn't actually experiencing any

47:32pressure and it's floating in amniotic

47:35fluid and therefore the bones don't need

47:37to be strong we just need to have some

47:39kind of bones and so the very first

47:41thing that happens is we form this

47:43really HAP hazard lee almost thrown

47:46together primary or immature or woven

47:49bone so essentially like spongy bone but

47:51without the kind of a thought put into

47:54it there are two different processes

48:00that start with this and then proceed

48:04from there to actually reorganize the

48:06bone and increase its strength first of

48:09all we have intramembranous ossification

48:13so ossification right so calcifying your

48:17osteoid

48:18and intramembranous so this is happening

48:20inside a membrane what membrane I'm

48:24remember that all connective tissue is

48:25derived from Mezen kind connective

48:27tissue that's a way back to exam one

48:30material in intramembranous ossification

48:34we build our flat bones and our sesamoid

48:37bones from like directly from a

48:40connective tissue sheet and in this

48:43image of an embryo here we can see some

48:46of the skull bones forming literally

48:49there was a membrane around your

48:52soon-to-be brain and bones literally

48:54formed within that membrane the other

48:58bones might see your long bones for

49:00example form via something called

49:01endochondral ossification it's again

49:04this process of crystallizing calcium

49:09and phosphorus but this time instead of

49:11forming directly from a membrane they

49:13form from a cartilaginous model so endo

49:17inside

49:18Kandra remember means cartilage so

49:21inside the cartilage in this image down

49:24here we can see very early bones we

49:30could also see our tail right that's a

49:32thing we had that so these here aren't

49:38bones yet they're just cartilaginous

49:40models of a bone and so in both of these

49:48we intramembranous and anacondrai we

49:51start with just irregularly arranged

49:53collagen bundles osteocytes osteoblasts

49:56building bone as much as they possibly

49:58can as quickly as they can just to get

50:02the models there and you know this

50:04process is going to continue to remodel

50:06them over time okay usually that really

50:10disorganized model is almost immediately

50:14broken down by osteoclasts and arranged

50:19much more strongly by osteoblasts and so

50:28intramembranous and endochondral

50:29ossification are both forming bones out

50:32of existing mesenchyme or cartilaginous

50:34tissues on appositional growth

50:37is increasing the Gertz increase in the

50:39diameter of the bones that already

50:43exists so oppositional can only happen

50:45to an existing bone not too membrane not

50:49too cartilage only to existing bone so

50:52let's walk through briefly the steps of

50:57intramembranous ossification alright so

51:00um here we see a fetal skull um if we

51:05zoom into that fetal skull we can see

51:08mesenchyme tissue right so here are stem

51:13cells right that can ultimately

51:14differentiate into any of the connective

51:19tissue shell cells and we can also see

51:22lots of like collagen fibers are one

51:23right here so you know generic old

51:26connective tissue given a particular

51:29signal you're not going to get into you

51:31but you know ligand binds the receptor

51:33these stem cells then differentiate into

51:37osteogenic cells right so this is

51:40actually turning on particular genes

51:44that essentially say I'm going to become

51:46something that has to do with bone or

51:48cartilage and nothing else gonna become

51:50a blood cell I'm not going to become an

51:55adipocyte or anything only bone or

51:58cartilage cells from here on out okay so

52:01then these osteogenic cells would

52:02further differentiate into osteoblasts

52:05okay and so this is actually happening

52:07in a couple different places on

52:09throughout this membrane that is

52:11covering your soon-to-be skull and so we

52:14can call these little areas of

52:17osteoblast differentiation we can call

52:20them ossification sites or ossification

52:22centers and so osteoblasts are going to

52:26start doing what osteoblasts do they're

52:29going to start secreting osteoid

52:30which is that organic matrix they're

52:33going to secrete those enzymes and

52:35essentially spontaneous ossification is

52:37going to form of course trapping some of

52:40those osteoblasts in the process so what

52:43we can see here is one of these

52:45ossification centers we started off with

52:48just normal old stem cells then

52:50made us eugenics sounds then we made

52:52osteoblasts alright and now we're

52:54starting to form this bony tissue

52:55immediately trapping the austin

52:57osteocytes inside we can also see that

53:07on all sides of this little ossification

53:10center there are more osteoblasts right

53:14so these osteoblasts are continuing to

53:16differentiate and they're kind of moving

53:18out in all directions I just like that

53:21video showed you that they kind of like

53:22tunnel through this is there for

53:26building bone out in all directions if

53:28we look at this prandtl bone right here

53:30and ossification Center might happen or

53:33occur within this the very middle and

53:36then osteoblasts are going to start

53:39moving out building bone in all

53:41directions and therefore the bone gets

53:43bigger and bigger hey hum

53:49intramembranous ossification as a

53:51process begins at about ten weeks post

53:54fertilization that's important because

53:57on between 810 weeks post fertilization

54:00your cardiovascular system really starts

54:03to develop and differentiate and so

54:05after ten weeks you have blood vessels

54:08and so connective tissue is generally

54:12very vascular and so as these

54:14osteoblasts are building their bone

54:17outwards and all directions from their

54:19Asti or from their ossification centers

54:21they actually have to weave around the

54:23existing blood vessels and so this

54:26naturally forms something that looks a

54:30heck of a lot like spongy bone so it's

54:32naturally forming trabeculae right so

54:34that's what these images over here

54:35showing you weaving around the blood

54:39vessels forming a lattice trabeculae now

54:44while these trabeculae are forming we

54:48essentially differentiate some more of

54:51those men and kind of stem cells into

54:53what is going to become the periosteum

54:55rights over here we can see that these

54:58blood vessels are organizing and that

55:00these extra cells here have

55:02differentiate

55:03into periosteum cells and so they are

55:07going to actually start forming bow and

55:12right so more osteoblasts forming

55:13compact bone sandwich on either side of

55:17the spongy bone okay so again we form

55:21periosteum the deeper layer the

55:23periosteum contains stem cells those

55:25stem cells become osteoblasts and start

55:28secreting osteoid into this nice compact

55:31bone structure here so this entire

55:37process is happening in all of your flat

55:40bones simultaneously and so your flat

55:42bones like continue to grow towards one

55:44another right so out from the

55:46ossification center but towards the

55:48other bones and so this here hopefully

55:54will help you to visualize that here is

55:57a parietal bone here is one of one half

55:59of the frontal bone this might be an

56:01oxidation center this might be an

56:03oxidation center and so essentially this

56:05bone building by osteoblasts as well as

56:08the simultaneous formation of the

56:10periosteum it's going to happen out in

56:12all directions and so this bone is

56:16growing towards the front this bone is

56:19growing towards the back right so there

56:22you know the bones themselves are

56:24getting bigger and they're also getting

56:25closer together this process absolutely

56:30does not stop when you're born and I'm

56:33sure that you guys can all appreciate

56:34this babies have soft spots these soft

56:37spots are actually called fontanelles

56:39and what the soft spot is is the

56:44mesenchymal

56:46that is still being converted into or

56:51having bone formed inside of it

56:56intramembranous ossification is still

56:59occurring within this mesenchyme tissue

57:01and so this of course is really

57:04important because baby's head is not the

57:06size of an adult head and so you still

57:08need you know your bones to be able to

57:12grow to accommodate your current brain

57:14um also um

57:16the particular position of these joints

57:20right so where this membrane is as

57:21opposed to bone is really important in

57:25the birthing process so essentially the

57:27fact that there is a joint that isn't

57:29filled in right so it's still membrane

57:31as opposed to bone means that those two

57:34halves of your skull when you're being

57:36born can actually pass over one another

57:40to make baby's head a little bit

57:41narrower to ease its passage through the

57:45vaginal canal and then after birth you

57:48can watch it just pops right back out

57:51right so kind of a cool side effect of

57:56incomplete intramembranous ossification

58:00okay so that is probably this simpler

58:04simplest process here the next process I

58:10want to talk about is endochondral

58:11ossification

58:12this is happening in pretty much the

58:14rest of your bones this process starts

58:19at about eight weeks post fertilization

58:22so in fact before intramembranous

58:25ossification is going to begin

58:27and this also differs in that this

58:31process has to start from an existing

58:33cartilaginous model alright so in utero

58:38you form cartilage vague shapes that

58:42look kind of sort of like bones or what

58:44going to be bones but it's just part

58:47llege and so endochondral ossification

58:51starts at eight weeks post fertilization

58:54and it's going to continue through

58:55puberty and beyond and pretty much those

59:00cartilaginous models are going to be

59:01replaced by bone with some exceptions

59:04that is we keep some heileen cartilage

59:07we don't turn into the bone in our chest

59:10okay so this allows us to flex our

59:13ribcage and therefore inhale and exhale

59:16more easily also the ends of the long

59:18bones maintain that cartilage right so

59:21just like I mentioned before that

59:23cartilage is made of hyaline cartilage

59:25tissue and it is called articular

59:27cartilage okay so I'm

59:30we have looked at cartilage under them

59:32under the microscope before but really

59:36what is this type of tissue so cartilage

59:40is a gel of proteoglycans so essentially

59:43different proteins different

59:44carbohydrates and they form this like

59:48brush like structure here and this is

59:51important because these brushy

59:53structures trap water molecules and

59:56essentially um creates a nice cushion

1:00:01flexible cushion that is still really

1:00:03strong surrounding the cartilage cells

1:00:07in this structure is highly resilient

1:00:11right so again it covers our long bones

1:00:13right you jumping jacks and your femur

1:00:16would grind against your tibia if not

1:00:18for this cartilage

1:00:21unlike most connective tissue cartilage

1:00:25is a vascular that is it doesn't have

1:00:28blood vessels or many blood vessels if

1:00:32any in some places and it has very

1:00:35little nervous control as well and so

1:00:39what that means is that in order to get

1:00:41nutrients oxygen etc to for example this

1:00:45cell these substances have to diffuse

1:00:51from this cell through the matrix to

1:00:55this cell through the matrix in that

1:00:57cell through the matrix of that cell

1:00:58right so this is a very time-consuming

1:01:01process and so these chondrocytes these

1:01:06cartilage cells can't really have a big

1:01:08energy demand if you damage your

1:01:10cartilage they take a really long time

1:01:13to get the materials they need to

1:01:14actually repair that cartilage and so if

1:01:17you wreck your cartilage if you grind

1:01:19that cartilage away it will take a

1:01:23really long time to heal or it won't

1:01:26heal at all um again cartilage and bone

1:01:32are pretty similar in a lot of ways one

1:01:35of those ways is that there is a

1:01:36membrane surrounding the entire

1:01:38structure however the perichondrium

1:01:41right superior perimeter Kandra for car

1:01:44this perichondrium might appear to be

1:01:48like the periosteum but it also has a

1:01:53function of essentially keeping that

1:01:55gooey gelatinous matrix in shape right

1:01:58the bone has its own shape right if you

1:02:00happen to rip off the periosteum it's

1:02:02still gonna look like a phone

1:02:03perichondrium essentially is acting like

1:02:05a girdle

1:02:06right so when femur comes down on tibia

1:02:09when you're doing jumping jacks the

1:02:11reason why that cartilage doesn't lose

1:02:13out to the side is because of this girl

1:02:16because the perichondrium is keeping

1:02:18that cartilage in the crotch shape also

1:02:22the perichondrium just like the

1:02:23periosteum contains blood vessels so

1:02:25this is the only source of blood that

1:02:28the cartilage is going to get and again

1:02:32just like the bone we have these

1:02:35specialized cells that live within

1:02:38cavities that are essentially sustaining

1:02:40the surrounding tissue and so it's not a

1:02:43bone so we can't call it osteo whatever

1:02:45instead we have to call it condor oh

1:02:48whatever

1:02:48it's a condor for cartilage chondros

1:02:51lasts build cartilage just like

1:02:54osteoblasts they get stuck in that

1:02:56cartilage and then we call them

1:02:58chondrocytes a mature cartilaginous

1:03:00cells and again just like we can see

1:03:03here there are little cavities called

1:03:05the Kunik there's a lots in common again

1:03:10we looked at these tissues for the last

1:03:13the last lecture exam these things are

1:03:18still applicable to your practical exam

1:03:20which opens up this afternoon and also

1:03:23we're expanding on this a little bit

1:03:25because it's so very relevant it's

1:03:27chapter three types of cartilage most

1:03:30common is highly and cartilage we also

1:03:33have fibrocartilage and what's different

1:03:34about fiber cartilage is that we can see

1:03:36not only are there these proteoglycans

1:03:40those nights like brushy protein

1:03:42carbohydrate conglomerations but also we

1:03:46have a lot of collagen right so these

1:03:47big dark lines here are collagen fibers

1:03:51this is super strong and particularly

1:03:55resistant to damage on

1:03:58so fibrocartilage is found in places

1:03:59that get a lot of wear and tear such as

1:04:03your intervertebral discs and also the

1:04:06discs of the knees so the menisci are

1:04:09the meniscus is of your knee which we'll

1:04:11look at beginning of next week

1:04:16and finally elastic cartilage same deal

1:04:19as the other two but instead of just

1:04:22playing proteoglycans instead of

1:04:24proteoglycans with with collagen now we

1:04:28have proteoglycans with elastic

1:04:30cartilages with elastic fibers at it and

1:04:34so your external ears right are nice and

1:04:36flexible and really strong and whatnot

1:04:38because it's made of elastic cartilage

1:04:41but you guys already know that from last

1:04:44section

1:04:45and of course hylene cartilage is just

1:04:47pretty so in endochondral ossification

1:04:55we begin before weeks post fertilization

1:04:59with cartilaginous models made of Hylian

1:05:03cartilage we are going to be walking

1:05:05through these steps over here and of

1:05:08course I am number them for you here

1:05:10unfortunately I've never found a great

1:05:12animation of this if you find one by all

1:05:14means let me know but we're just going

1:05:17to walk through the diagrams ok so we

1:05:19start with this blue thing that looks

1:05:23kind of like a long bone in that it has

1:05:25fact epiphysis ends and a skinnier

1:05:28diathesis shaft in the middle it's also

1:05:33blue which implies cartilage and so the

1:05:38very first thing that happens about

1:05:39eight weeks plus fertilization is that

1:05:41some of those chondrocytes that are

1:05:43trapped within their lacunae are going

1:05:46to grow right so as they grow they are

1:05:49going to be pushing that lacuna bigger

1:05:51and bigger and bigger and so you can see

1:05:53down here there are like tiny little

1:05:54dots those are normal old lacuna when

1:05:57some chondrocytes start to get bigger so

1:06:00to do their cavities and so on bigger

1:06:03and bigger and bigger cavities and then

1:06:05the chondrocytes dot it's essentially

1:06:07babysitting great leaving these big

1:06:09gaping holes

1:06:11in the very middle of this cartilaginous

1:06:13model okay at the same time this is

1:06:17happening we're getting more blood

1:06:20vessels I remember I told you that

1:06:22between eight and ten weeks we start to

1:06:23get more and more blood vessels and

1:06:25that's important in our intramembranous

1:06:27ossification but also during this period

1:06:30we are growing blood vessels around the

1:06:34diathesis of each and every one of these

1:06:36cartilaginous soon-to-be bones okay when

1:06:40the blood arrives it brings with it not

1:06:42only oxygen not only nutrients but also

1:06:45a lot of chemical signals and these

1:06:47ligands are going to trigger the

1:06:51differentiation of stem cells within

1:06:54this connective tissue that is ligand

1:06:58binds to receptor triggers certain genes

1:07:00to turn on and essentially what we're

1:07:02going to get here um is stem cells that

1:07:06were in the perichondrium this girdle

1:07:09around the long bone or soon to be long

1:07:11bone they are going to turn on different

1:07:13genes to become osteoblasts so as soon

1:07:18as we get cells that turn on the

1:07:20osteoblasts genes we can now call this

1:07:23membrane the periosteum okay and so just

1:07:28like osteoblasts are prone to do they're

1:07:30going to start secreting osteoid which

1:07:33is then ossified on specifically around

1:07:36the diathesis so what we have now is a

1:07:40cartilaginous bone shaped structure in

1:07:43the diathesis you have lots of big

1:07:46gaping holes where chondrocytes died and

1:07:49also you have this shell of bony tissue

1:07:52surrounded by periosteum just around the

1:07:56diaphysis right remember this all

1:07:58happened because the blood vessels

1:08:00brought chemical signals that said hey

1:08:03this needs to be a bone not cartilage

1:08:06and so we continue from here the blood

1:08:11of course doesn't stay on the outside as

1:08:13we talked about earlier today the

1:08:15nutrient foramen is what allows blood

1:08:18vessels to enter into the axis of long

1:08:20bone that happens now and so here we

1:08:24have

1:08:24blood vessels actually penetrating

1:08:26through that nice shell of bone around

1:08:29the diathesis okay and of course with

1:08:33the blood comes ligands those ligands

1:08:37are going to trigger stem cells inside

1:08:40the diaphysis to differentiate into

1:08:44osteoblasts and of course the

1:08:47osteoblasts are then going to start

1:08:50creating osteoid which is that ossified

1:08:53remember that there are all these big

1:08:55old holes in the diathesis as a result

1:08:58there's space for bone tissue to

1:09:01actually grow right so we start filling

1:09:03in those holes you know sending out

1:09:05osteoblasts in all directions they're

1:09:07just sloppily throwing down any osteoid

1:09:10in any direction we want to convert this

1:09:12into bone as quickly as possible we'll

1:09:14go back and reorganize them later and so

1:09:19this process is going to continue right

1:09:22in all directions right so out towards

1:09:25the edges right towards that shell of

1:09:28bone and up towards the epiphysis and

1:09:30down towards the epiphysis while this

1:09:36and a primary or immature bone is being

1:09:39laid down as quickly as possible

1:09:41we simultaneously get the

1:09:44differentiation of osteoclasts and

1:09:47osteoblasts again in the diathesis so

1:09:51what's happening here is that

1:09:52osteoclasts are going to break down that

1:09:55sloppy bone and allow new osteoblasts to

1:09:59more slowly reorganize that diathesis

1:10:04and so this is going to lead to the

1:10:07formation of the medullary cavity so the

1:10:09medullary cavity in adults is filled

1:10:12with yellow bone marrow as a fetus and

1:10:16as a young child this is actually filled

1:10:18with even more red bone red bone marrow

1:10:20because of course growing takes lots of

1:10:23lots of energy and lots and lots of

1:10:24blood and so we need as much bone also

1:10:29kids have to eat a lot all the time they

1:10:32don't have a lot of extra energy stored

1:10:34in these places yet and so they need to

1:10:37take it

1:10:39all right so while this reorganization

1:10:41is occurring within the diaphysis it's

1:10:44the formation of the medullary cavity

1:10:46now filled with red bone marrow soon to

1:10:48be filled with yellow bone marrow we are

1:10:51going to get the formation of the

1:10:53secondary ossification centers so for

1:10:57the primary ossification center was the

1:10:59entrance of this blood vessel into the

1:11:01diathesis formation of bone here

1:11:04now we are going to get more blood

1:11:06vessels and couple into each epiphysis

1:11:08that again bring these osteoblasts

1:11:13osteoblasts are going to start secreting

1:11:15osteoid which has been ossified and of

1:11:18course this is happening in all

1:11:19directions spreading out towards the

1:11:21edges of the epiphysis okay so bone

1:11:26growth bone formation is still happening

1:11:28here and now it's happening in the ends

1:11:31of the long bones of spot okay and so

1:11:35soon these ellipses are going to fill

1:11:36with spongy bone we can reorganize that

1:11:39as we go along and we're still getting

1:11:44bone formation within the diaphysis and

1:11:46so if we look at this next image over

1:11:48here we can see that there is actually a

1:11:51separation between bone formation here

1:11:54and bone formation up here and so there

1:11:58is purposely maintained a thin layer of

1:12:03high lean cartilage between these two

1:12:06bony structures this cartilage line is

1:12:11cartilage plate is called the epiphyseal

1:12:14cartilage or the epiphyseal plate or

1:12:17you've surely heard it referred to as

1:12:19the growth plate okay so remember that

1:12:22endochondral ossification has to start

1:12:25with cartilage before we can form bones

1:12:28so even when the entire initial little

1:12:31tiny fetal bone is replaced by or fetal

1:12:35cartilage is replaced by bone we still

1:12:38need to get bigger bones and you know

1:12:40these were low thanks so growth is going

1:12:43to continue from the hyaline cartilage

1:12:46that is maintained between the

1:12:49epiphyseal bone and

1:12:51the bone in the diathesis and so let's

1:12:56zoom in on this even more on keep in

1:12:58mind that we are just looking at for

1:13:00example the proximal epiphysis but this

1:13:02is also happening in the distal that is

1:13:04bone growth is occurring up making you

1:13:07taller by going up but also making you

1:13:09taller by growing down as well so it's

1:13:11happening on both ends on the long bone

1:13:13simultaneously

1:13:15how do growth plates work well on the

1:13:19epiphyseal side we have the growth of

1:13:23hyaline cartilage it's essentially we

1:13:26have chondrocytes that are dividing and

1:13:30going mitosis making more of themselves

1:13:31these are going to build more cartilage

1:13:36up towards the epiphysis or down towards

1:13:39right so towards the epiphysis so we're

1:13:44building cartilage on this side right

1:13:45here just like we saw in the very

1:13:49beginning existing chondrocytes which

1:13:52are trapped within their little acute a

1:13:55that they themselves did they're gonna

1:13:57die they're going to die they're going

1:14:00to decompose leaving these big open

1:14:02holes these holes are very convenient

1:14:05for the osteoblasts keep in mind that

1:14:07the osteoblasts are chugging on up the

1:14:10diathesis towards the epiphysis laying

1:14:13down sponging or Langdon osteoid and is

1:14:16then ossified they are trapped within

1:14:18this bony matrix okay and so they are

1:14:22proceeding towards the epiphysis they

1:14:25encounter this big gaping hole which

1:14:28used to contain and chondrocyte they are

1:14:30going to fill it with bone and they

1:14:32themselves become trapped we make more

1:14:35osteoblasts and they continue working

1:14:37their way up so essentially the

1:14:40chondrocytes are going to be building

1:14:42more and more and more cartilage up

1:14:44towards the epiphysis while the

1:14:47osteoblasts are coming behind them

1:14:49filling all of that cartilage in with

1:14:51bone and so for a good portion of your

1:14:54childhood

1:14:55both of these are growing and

1:14:58approximately the same rate so we build

1:15:00cartilage we replace it with bowling

1:15:02villa cartilage we replace it with ball

1:15:05and so this is just another way showing

1:15:08you this if you were to look at some

1:15:09Estella gee this is what you would see

1:15:11alright so the proliferation zone we

1:15:14make more chondrocytes which make more

1:15:16cartilage those cartilaginous cells die

1:15:20leaving big holes and those holes will

1:15:23then be filled in by osteoblasts and so

1:15:28ultimately this is going to allow our

1:15:31bones to grow in both directions so you

1:15:33know on Monday your bone is this length

1:15:36and because the cartilage has built on

1:15:39this side the bone is built on this side

1:15:41essentially Monday the next week your

1:15:45bone is this tall so again this is going

1:15:49to continue you know the the speed of

1:15:54the chondrocytes is approximately the

1:15:55same speed as the osteoblasts and both

1:15:57are going to be growing in both

1:15:58directions as we're all surely familiar

1:16:03there are certain periods where growth

1:16:05spurts are pretty darn common

1:16:07particularly when you hit puberty right

1:16:11so you know you might go home in June at

1:16:17the end of a school year in the seventh

1:16:18grade and come back in the eighth grade

1:16:20the next year and all of a sudden you're

1:16:21six inches taller oh my gosh what the

1:16:23heck just happened

1:16:24hormones are going to ramp up this

1:16:28process quite considerably and so as I

1:16:31said normally chondrocytes and

1:16:33osteoblasts move out that approximately

1:16:34same rate sex steroid so the hormones

1:16:37that are associated with the process of

1:16:40puberty are going to ramp up

1:16:42particularly in the activity of

1:16:44osteoblasts and so the chondrocytes are

1:16:46still going to be doing their thing at

1:16:48approximately the same rate but now the

1:16:50osteoblasts are going to hurry up and

1:16:52they're actually going to meet those

1:16:54chondrocytes before that you can die

1:16:57right and so what this means is that

1:17:00there's no more cartilage being laid

1:17:02down okay I'm without cartilage we

1:17:06cannot complete endochondral

1:17:07ossification so when your osteoblasts

1:17:09catch up to your condo sites this is

1:17:13when your growth plates close

1:17:16is when there is no more cartilage to

1:17:19convert and therefore we're left with

1:17:22this little epiphyseal line this scar

1:17:24that used to be the cartilaginous

1:17:26epiphyseal plate and now it's not and so

1:17:31of course if your osteoblasts are just

1:17:34charging through making bone super fast

1:17:36that is how you can get several inches

1:17:38of growth that are relatively short I'm

1:17:40okay I also want to point out this x-ray

1:17:44right here

1:17:45you can see the growth plates open keep

1:17:48in mind that this is cartilage cartilage

1:17:50doesn't show up on an x-ray and so it

1:17:52looks like the epiphysis is actually

1:17:54separated from the diathesis you can

1:17:58tell when your growth plates are open or

1:18:00closed and of course the other thing I

1:18:04want to point out here is that this

1:18:06isn't just happening in your femur

1:18:08coming in your legs or your arms this is

1:18:11happening in every long bone of your

1:18:13body and so each and every little

1:18:16fellings here has its own growth plates

1:18:20and so as I said puberty really ramps

1:18:24this process up and makes you grow super

1:18:26fast but different bones

1:18:31epiphyseal plates are going to close at

1:18:34different times and so this just gives

1:18:37you some very basic ranges I'm you'll

1:18:40have to put these numbers out at me I

1:18:41just want you to kind of keep in mind um

1:18:43that maybe some of your growth plates

1:18:46aren't even closed hum at this point and

1:18:48so you know maybe your ankles will close

1:18:52when you're a teenager right within a

1:18:54few years of puberty your osteoblasts

1:18:56finally catch up to your collar sites

1:18:58but then others other bones like your

1:19:01clavicle here might not close until

1:19:03you're like 30 all right so um at the

1:19:08beginning of this class I had a little

1:19:11image that said you know pretty much you

1:19:13are what you eat literally what you put

1:19:15into your body is going to affect your

1:19:18bones right what you're doing at this

1:19:20point is affecting how much your bones

1:19:22are growing how much you know what's

1:19:27going into them okay so just

1:19:29just a little side note there okay so

1:19:32intramembranous ossification forms your

1:19:35flat bones and sesamoid bones from a

1:19:37membrane from a mesenchyme membrane

1:19:41endochondral ossification forms your

1:19:43long bones from cartilaginous models we

1:19:46need cartilage in order to make phone

1:19:49and endochondral ossification there is a

1:19:51third type of bone growth or bone

1:19:53deposition in this case that occurs only

1:19:58from existing bones so this is happening

1:20:01throughout your life right whether you

1:20:04are you know your growth plates are

1:20:05closed or not it is always happening

1:20:08it's an oppositional bone growth allows

1:20:11your bones to grow in diameter and not

1:20:13just in length right so if you can

1:20:15imagine a fetal femur for example is

1:20:18probably like this wide but that is

1:20:21certainly not wide enough to sustain the

1:20:24weight of an adult body and so we not

1:20:26only need to grow in length we need to

1:20:28grow in width and so what we can see

1:20:31down here is a positional bone growth

1:20:33here is an infant bone what we do is we

1:20:37you know have a course removed bone with

1:20:41osteo class on the inside this widens

1:20:43your medullary Kathy I'm at the same

1:20:45time we have deposition bone growth by

1:20:51osteoblasts around the perimeter and so

1:20:55remember that the periosteum contains

1:20:56stem cells they're there throughout your

1:20:58entire life and so if your body is

1:21:01putting more weight on your bones than

1:21:03your bones can withstand essentially

1:21:06osteogenic cells will differentiate into

1:21:08osteoblasts and they will deposit

1:21:11osteoid in a ring around the outside of

1:21:15your bone okay now of course your bone

1:21:18is wider now and so we can clear out a

1:21:20little bit more space on the inside with

1:21:22osteoclasts and so this process happens

1:21:23over and over and over again until we

1:21:25end up with an adult bone big wide

1:21:28yellow marrow filled medullary cavity

1:21:31with lots of these extra rings or

1:21:34lamellae around perimeter right so I'm

1:21:37we've actually already seen evidence of

1:21:39oppositional bone growth for

1:21:42okay so going back to this model here we

1:21:45have the osteons and the osteons have

1:21:48all these lamellae but also around the

1:21:51outside around the perimeter we have

1:21:53multiple layers of bony tissue and these

1:21:56are called circumferential lamellae all

1:21:58right so they're going around the

1:21:59circumference and again they are made by

1:22:01a positional bone growth

1:22:04and on the other thing is image shows

1:22:06you is the fibrous layer of the

1:22:08periosteum and the osteogenic layer of

1:22:12the periosteum

1:22:13which is where the osteoblasts come from

1:22:14and so that's why when they

1:22:16differentiate they can lay down bone

1:22:18right here once again your bones don't

1:22:26just grow and then stop changing as the

1:22:30video showed your bones are continually

1:22:32remodeling themselves and oftentimes

1:22:34continually repairing themselves again

1:22:39there is usually a balance of bone

1:22:40building and bone breaking down or bone

1:22:43deposition and bone resorption we can

1:22:47change this balance if we have mineral

1:22:52needs that is if we need more or less

1:22:54calcium if we need more or less

1:22:56phosphate we can actually dip into the

1:22:59reserves in our bones to help the body

1:23:03maintain homeostasis if there's damage

1:23:06right so if you break a bone you need to

1:23:08fix it all right so obviously you don't

1:23:10want to have equal amounts of bone

1:23:12breaking down and building you want to

1:23:14have a lot more building to repair that

1:23:17gap and of course disease is is an

1:23:22unfortunate imbalance of these two

1:23:25processes so let's talk about

1:23:27homeostasis first on this pie chart here

1:23:30shows you what is actually in your bone

1:23:32it is a reserved for the overwhelming

1:23:36majority of your body's calcium as well

1:23:38as the body's phosphate as I talked

1:23:43about earlier today calcium is so

1:23:45important for your neurons for your

1:23:47muscles for everything that we need to

1:23:49have just the right amount of calcium

1:23:51okay we have lots of calcium

1:23:55and within our bones so that we can

1:23:58always break down more bone to increase

1:24:01the levels in our blood okay um this is

1:24:05a classic homeostasis diagram it shows

1:24:08you calcium homeostasis so when the body

1:24:11is within its target range right we have

1:24:15a balance right so the target range is

1:24:17nine to eleven milligrams per 100 mils

1:24:19of blood all right so we're shouldn't

1:24:21pretend it's right if we have a ton of

1:24:25calcium right so you just had a glass of

1:24:28milk your digestive system pulls calcium

1:24:31into your blood and so now you have

1:24:33increased your blood calcium levels over

1:24:36eleven okay what do we do we that's also

1:24:39bad okay um so if there is an imbalance

1:24:44where there's too much calcium our

1:24:47thyroid gland detects this okay the

1:24:51thyroid gland in response to high

1:24:53calcium is going to release calcitonin

1:24:55because there's a ton of calcium

1:25:00calcitonin is a hormone that is detected

1:25:03on several different target tissues

1:25:04including our bones in response to

1:25:07calcitonin bones are going to take more

1:25:09calcium out of the blood and build more

1:25:12both ultimately this should bring

1:25:14calcium back down to about ten okay on

1:25:18the other hand if you don't drink milk

1:25:21in a while on but of course you're still

1:25:23using calcium in your body this is going

1:25:26to decrease the calcium levels in your

1:25:29blood below nine and this is detected by

1:25:32your parathyroid glands all right which

1:25:34are actually kind of on the posterior

1:25:35side of your thyroid which is like right

1:25:37here in your throat

1:25:39in response parathyroid glands release

1:25:42PTH or parathyroid hormone or

1:25:45parathormone as the video said on PTH is

1:25:48another hormone that is also detected by

1:25:50many target tissues including your bones

1:25:52if we don't have enough calcium in our

1:25:55blood we can tell osteoclasts to start

1:25:58spinning out more acid enzymes and break

1:26:01down that volunteers faster so let's

1:26:04dive into this just a little bit more

1:26:06and we'll start with low

1:26:09calcium levels again if you don't have

1:26:13enough calcium in your diet right you

1:26:15forgot to take your vitamins this

1:26:16morning whatever your calcium levels

1:26:19might drop below this target threshold

1:26:22all right there is a negative feedback

1:26:23process which involves the parathyroid

1:26:26gland releasing parathyroid hormone or

1:26:30PTH or parathormone and you those would

1:26:34be okay for me

1:26:35of course this hormone circulates

1:26:37throughout the entire body but there are

1:26:39only receptors for PTH on certain organs

1:26:42and these organs all have some kind of a

1:26:45role in maintaining calcium first of all

1:26:49on the most relevant to us right now is

1:26:51the bones right so our if our bones bind

1:26:58to PTH what that's going to do is

1:27:01trigger osteoclasts to start working

1:27:04more to break down the bone right so

1:27:07essentially immobilizing that calcium

1:27:09that has been ossified onto the osteoid

1:27:12and that calcium is released into the

1:27:14blood therefore increase in the calcium

1:27:16a little bit all right but that's not

1:27:17our only response to low calcium levels

1:27:19we can also tell the kidney that we have

1:27:23too low calcium kidney cells also have

1:27:26PTH receptors in response to binding to

1:27:31PTH the kidney is going to do two

1:27:33different things first of all it's going

1:27:35to reduce how much calcium we pee out

1:27:38for example all right so we actually are

1:27:42reabsorbing more calcium from our

1:27:44filtrate or our soon-to-be urine back

1:27:46into our body and therefore back into

1:27:49the blood all right so we stop losing so

1:27:52much calcium in the urine and instead we

1:27:55put it in the blood right

1:27:57also the kidneys secrete more of its own

1:28:02hormone the kidney actually has tons of

1:28:04hormones that it detects and it produces

1:28:07one of those is cows at trial and calso

1:28:09trial tries to increase calcium it's

1:28:13actually a derivative of vitamin D and

1:28:16so cows a trial as well as parathyroid

1:28:20hormone are both DTAC

1:28:22did on the cells of the intestines when

1:28:26these are detected I'm actually past

1:28:29trial are actively has a role in this

1:28:31process on it is going to increase how

1:28:34much calcium we absorb from our food

1:28:37right so if your calcium levels are

1:28:39super low you want to make sure that

1:28:42every little ion that is in your food

1:28:45actually comes into your blood

1:28:48okay so again all of these target

1:28:50tissues are working towards increasing

1:28:53the calcium in your blood by breaking

1:28:56down bone and immobilizing stored

1:28:57calcium by taking more calcium from your

1:29:00food and by releasing less calcium in

1:29:05your yard and so on that note calcium as

1:29:12I said is a derivative of vitamin D so

1:29:16you've all surely seen that whole milk

1:29:20for example now has vitamin D in it well

1:29:23the cow is not putting vitamin D in the

1:29:25milk for you that has actually been

1:29:27added as a supplement because you

1:29:31absolutely mean vitamin D in order to

1:29:34absorb calcium from your diet right so

1:29:38even if you're drinking milk constantly

1:29:41if you don't have vitamin D / positive

1:29:43trial you're not actually going to get

1:29:45that calcium into your body and so it's

1:29:47a couple different places where you can

1:29:49get vitamin D as I said from your milk

1:29:51for example that has been added there

1:29:54somewhat recently but of course there's

1:29:57other ways of getting it as well so from

1:29:58your food you can get vitamin D which is

1:30:03called house overall um you can also get

1:30:06vitamin D from being the Sun as you

1:30:09probably heard of before

1:30:10essentially the UV rays from the Sun

1:30:14configure a steroid that is in your skin

1:30:17in a particular way then it actually

1:30:19forms automatically this particular

1:30:23substance holy cow so for all that is

1:30:25vitamin D this molecule is then

1:30:28processed by the liver to a certain

1:30:31extent which is then sent kidney and the

1:30:33kidney finally released

1:30:34this product again derivative of vitamin

1:30:38D without vitamin D you don't get kalsa

1:30:41trial without kalsa trial you cannot

1:30:43pull calcium out of your food and into

1:30:47your blood even if it's in your diet

1:30:50you're not actually able to get it so

1:30:52why do we put vitamin D in the milk well

1:30:56for a long time calcium and balances on

1:31:01such as rickets were a fairly regular

1:31:04occurrence so rickets is a condition

1:31:08where there's either not enough vitamin

1:31:11D you're not getting enough vitamin D

1:31:14you're not getting enough calcium or

1:31:17some kind of a genetic issue where you

1:31:19can't actually use it but essentially

1:31:21you're not able to use vitamin D to get

1:31:23calcium without enough calcium

1:31:25you cannot strengthen your bones so

1:31:28essentially you end up with more

1:31:31frequent fractures right because we

1:31:34don't get this awesome vacation as

1:31:37strongly I mean also another

1:31:40characteristic rickets symptom our bowed

1:31:43femurs bowed legs in general on remember

1:31:48a few slides ago we took a look at what

1:31:51you could do with a bone with organic

1:31:54matrix versus without or inorganic

1:31:56matrix and so essentially if your bones

1:31:59don't have enough calcium they

1:32:00essentially become more like skin rights

1:32:02they're super flexible and so they can't

1:32:04support the weight of your body and so

1:32:06they actually grow bowed out side

1:32:09unfortunately with the lack of calcium

1:32:14alright so on the other hand what

1:32:16happens if we have too much calcium yes

1:32:18we can have that problem as well so if

1:32:22there is high calcium you just have lots

1:32:24of milk and it had lots of vitamin D in

1:32:26it or even out in the Sun a lot lovely

1:32:28you're gonna have lots more calcium in

1:32:30your blood and so the organ responsible

1:32:33for detecting this is the thyroid gland

1:32:36in response to high calcium we release

1:32:39calcitonin right so when there is a ton

1:32:42of calcium using these calcitonin a ton

1:32:46and calcitonin

1:32:48another hormone is going to be detected

1:32:50on the same three target tissues and

1:32:52produce like the opposite effect as PTH

1:32:56calcitonin is going to stop the n' osteo

1:33:00class from breaking down your bone all

1:33:02right so we don't need to keep

1:33:03mobilizing more more calcium we've got

1:33:05plenty okay so we stop having bone

1:33:08breakdown we might increase bone

1:33:10deposition a little bit right start

1:33:12pulling more calcium out of the blood

1:33:14and putting it into the bones just in

1:33:16case you stuck drinking lots of milk

1:33:18with vitamin D you will still have a lot

1:33:20of calcium in research calcitonin is

1:33:23also going to tell the kidney that

1:33:24there's a ton of calcium in the blood

1:33:26and as a result the kidney is going to

1:33:28pee out more calcium we don't need it in

1:33:31our blood so we can put it into into the

1:33:34urine and it is going to release less

1:33:38calcitriol remember calcitriol tries to

1:33:41increase calcium and so with less

1:33:45calcitriol we are absorbing less calcium

1:33:48from our diet and more is released

1:33:50thisis it's ultimately more calcium

1:33:53exits in the feces in urine more calcium

1:33:57is deposited in the bone and the blood

1:33:59levels are going to decrease another

1:34:05time when we want this balance between

1:34:09osteoclast activity to shift is when we

1:34:14break a bone it's a fracture is a crack

1:34:17or break in the bone and so this process

1:34:19very much resembles endochondral

1:34:22ossification and it requires the stem

1:34:25cells excuse me within the periosteum

1:34:28end or end

1:34:30Asya I'm gonna try to play this from

1:34:32here just a short clip set super-helpful

1:34:41just kidding every time I think it's

1:34:43gonna work so let me show you the other

1:34:50way guys we are almost

1:35:02almost done today

1:35:05all right so pressures how do we heal

1:35:09them how do we replace that bone when

1:35:19the moment breaks it pleads or massive

1:35:24hematoma is rich in stones that are

1:35:27capable of guarding your cartilage these

1:35:31cells sent to work foreman at Calais to

1:35:33hold the bone fragments together the

1:35:36countless visit first more cartilage and

1:35:38bone missus melanism SOT Calais the soft

1:35:42callus gradually begins to fill with

1:35:44bone all in different more stable are

1:35:47cows after the hard calluses born the

1:35:51bone may not may look slightly fruity it

1:35:56probably has a large bony callous over

1:35:59months and even years the bone begins to

1:36:03model based on the stresses remodelling

1:36:07allows it to take on the shape similar

1:36:09to its original shape if there is too

1:36:14much displacement or angulation meaning

1:36:17that the bone fragments are pushed too

1:36:19far apart for the protein spend too much

1:36:21remodeling may not be sufficient the

1:36:24phone bank yield proven or may not

1:36:27appeal at all this is why fractures

1:36:29sometimes able to be reduced or said

1:36:32once the fracture is what I learned is

1:36:35important to keep it fun displacing it

1:36:37is also important to prevent too much

1:36:40movement possible at your site so with

1:36:42McAllister and so fractures are often

1:36:45treated with immobilization this can be

1:36:48better than asked plants or a surgical

1:36:51fixation ok so this again connects back

1:37:02to this balance between

1:37:05osteoclasts and osteoblasts activity and

1:37:07it's going to connect to what we already

1:37:10know about the periosteum so let's walk

1:37:12through this again on

1:37:13the first thing that happens after a

1:37:16fracture is bleeding um you guys will

1:37:19learn more about this at a p2 but in

1:37:21general you form a blood clot right

1:37:24these blood vessels in your bone are

1:37:26broken and therefore blood is allowed to

1:37:28exit your blood vessels and so through a

1:37:31chain reaction platelets are going to

1:37:33join together in this positive feedback

1:37:35scenario and essentially start creating

1:37:38this network of proteins and blood cells

1:37:43and platelets that forms you know that

1:37:48this fibrous network so first of all it

1:37:52stops the blood and it starts forming

1:37:55the scaffolding for the formation of

1:37:58that callus so very first thing that

1:38:01happens right within minutes in the

1:38:03first hours is the formation the

1:38:05hematoma which is a blood clot um next

1:38:09over the next few days you start to form

1:38:11the soft callus right and of course at

1:38:15the same time there's a lot of

1:38:16inflammation right so your body is

1:38:18cleaning up all that damaged tissue and

1:38:20also um you know that the swelling

1:38:23around that break inherently immobilizes

1:38:28the healing tissue right it hurts and

1:38:30like it's soft and you you kind of like

1:38:32you know even if it's not immobilized

1:38:37with a splint or something you naturally

1:38:40don't want to move it you naturally

1:38:42don't want to damage it even more so

1:38:46inflammation is actually a pretty

1:38:48important part of this process and is a

1:38:49natural splint essentially but again the

1:38:54hematoma forms this fibrous network

1:38:56which is then used by the chondroblasts

1:38:59or the Condorcet and so what we can see

1:39:02here in this fractured bone is that the

1:39:06periosteum thank goodness is still

1:39:08intact it is still there and so what

1:39:10this means is that there are a lot of

1:39:12stem cells which when they detect that

1:39:16there is damage in the tissue these stem

1:39:18cells are going to turn on chondroblasts

1:39:20genes which of course forms

1:39:23chondroblasts which then start secreting

1:39:26cartilage

1:39:27those pretty of likens trapping water

1:39:29molecules and therefore creating that

1:39:31nice flexible yet fairly durable

1:39:35cartilaginous callus so again these

1:39:41cells came from the periosteum that is a

1:39:44huge huge importance here it was out the

1:39:49periosteum right so the periosteum is

1:39:51damaged if it is torn off or you know if

1:39:55a burn accompanies a break and goes that

1:40:00deep essentially it takes a lot longer

1:40:03to heal if at all and so just like with

1:40:08endochondral ossification we have

1:40:11osteoblasts that can come in and they

1:40:13can start secreting us loyd which is

1:40:15that ossified within that cartilaginous

1:40:18model right so this used to be the soft

1:40:20callus right just cartilage now it is

1:40:23the hard callus it is spongy bone just

1:40:27like when we are first building our

1:40:28bones the osteoblasts just row down as

1:40:31much bony tissue as they possibly can as

1:40:33quickly as they can just so that this

1:40:37person can get back to normal only then

1:40:40do we have osteoclasts come along tunnel

1:40:44you know small tunnels into this bone

1:40:47and so we can get the slow remodeling

1:40:49process okay so over the next months

1:40:53over the next year's this callus is

1:40:56going to be remodeled back into what it

1:40:59used to look like before the break and

1:41:02so here is or here a couple x-rays here

1:41:06here is a fracture of the fibula here is

1:41:11six weeks later so we can see that the

1:41:13fibula is or has this extra bump where

1:41:17the break used to be you know that this

1:41:21is not only you know just a side effect

1:41:23of how a bone heals itself it also is

1:41:27helpful to have a slightly fatter maybe

1:41:31you know a slightly fatter region of

1:41:34bone here right if this spot was weak

1:41:37to break before maybe we want to have a

1:41:40larger bone in this place so that we

1:41:43don't get a second break and of course

1:41:46the video talked about on the importance

1:41:48of setting bones as I'm sure you're all

1:41:50familiar with if there's too much

1:41:53displacement in the bone like in this

1:41:55radius over here the bone will heal

1:41:58probably but it won't look normal right

1:42:02and so oftentimes you have to re-break

1:42:06it reset it in order to get it back to

1:42:09the original shape of course sometimes

1:42:11this requires surgical efforts so this

1:42:15here is a femur that has been absolutely

1:42:17shattered I'm going to put back together

1:42:19surgically other types of damage besides

1:42:25just fracturing the bone an example here

1:42:30is osteo arthritis

1:42:31so essentially you can break a bone at

1:42:34any time but what is also happening over

1:42:39your life is that you are putting so

1:42:42much wear and tear on your joints okay

1:42:45so this here it happens to be a knee

1:42:47this is your femur since your thigh bone

1:42:49this is a tibia and so if you are if you

1:42:58are athletic and constantly you know

1:42:59playing sports and everything maybe

1:43:01there's a lot of grain being on on your

1:43:04joints in this way obesity is linked to

1:43:08you know a lot more pressure on this

1:43:10cartilage and so over time you get this

1:43:14wearing down of the cartilage the

1:43:17articular cartilage at the end of your

1:43:19joints so remember that cartilage is a

1:43:22vascular it can't fill itself very

1:43:24quickly if at all and so if you're

1:43:26continually exerting the stress on your

1:43:29joints it's just going to get worse and

1:43:31worse over time until as we can see here

1:43:33the cartilage can completely wear away

1:43:35and you get this grinding sensation what

1:43:39can also happen here right in addition

1:43:42to the wearing way the cartilage is that

1:43:44now there is less space between those

1:43:47bones and so the edges of the bones

1:43:51start to rub together as well so

1:43:54remember earlier in this talk I told you

1:43:57that the periosteum covers everything on

1:43:59the bone except for where the articular

1:44:02cartilages well now if the articular

1:44:04cartilage is rubbing away now maybe the

1:44:06edges of the femur get to rub on the

1:44:09edges of the tibia here which is

1:44:12essentially scraping at that periosteum

1:44:16what do you think is telling the

1:44:19periosteum cells these osteogenic cells

1:44:21that they need to divide besides

1:44:24abrasion right actual mechanical stress

1:44:27and so when there is rubbing on those

1:44:30osteogenic cells stem cells say oh my

1:44:32gosh like there is damage here I need to

1:44:34replace this bony tissue the stem cells

1:44:38differentiate into osteoblasts and they

1:44:40start laying down more bony tissue right

1:44:41that's what you would do if there was a

1:44:43break right if there was a mechanical

1:44:45stress on the periosteum the problem

1:44:48with this however is that we're not

1:44:51supposed to have extra bone here we're

1:44:54not supposed to have osteoblasts laying

1:44:57down more bony tissue on the edges of

1:44:59your poor joints and so now you have all

1:45:01these little sharp spicules called bone

1:45:03spurs because of that rubbing on the

1:45:07periosteum because of the damage to they

1:45:09are taking their cartilage and so bone

1:45:13spurs really are just a positional bone

1:45:16growth right stimulated by a lot of

1:45:19stress on your joints and so this isn't

1:45:22just something that happens in your

1:45:24knees it can also happen on for example

1:45:28on this is your heel bone and your

1:45:30calcaneus if you are on your feet all

1:45:32day if you're wearing lots of high heels

1:45:34uncomfortable unsupportive shoes

1:45:37essentially that puts a lot of stress

1:45:40right here on your calculus and so you

1:45:45know rubbing of the periosteum and

1:45:47ultimately getting bone spurs on your

1:45:50heels or heel spurs now this is not only

1:45:54particularly uncomfortable because of

1:45:56course you're standing on your feet now

1:45:58you have bony spurs on your feet but

1:46:02also on there is a lot of connective

1:46:04tissue that

1:46:05on the plantar side of your foot

1:46:07essentially stabilizing all of those

1:46:10bones and muscles of your feet on now if

1:46:12you have bone spurs here where do you

1:46:14think they're going besides in the

1:46:16fleshy connective tissue and muscular

1:46:19tissue on the bottom of your foot and so

1:46:21it is continually rubbing on that and

1:46:23maybe fraying those tissues and causing

1:46:25a lot of inflation a lot of pain and so

1:46:28plantar fascitis so is inflammation of

1:46:33the fashio

1:46:33on the bottom of your foot can be linked

1:46:36to bone spurs as well and here in the

1:46:40cervical spine you can see that their

1:46:42bone spurs actually on the bodies of the

1:46:45vertebra actually the images that I gave

1:46:47you guys of the vertebra models in the

1:46:52left have bone spurs okay also there's

1:46:57some crazy Spurs on the ribs as well

1:46:59that's not how normal bodies of

1:47:02vertebrae are supposed to look but the

1:47:05bone clone models that we have our

1:47:07actual castings of real people's bones

1:47:10so whoever whoever's bones you know

1:47:14these models were made from had some

1:47:17pretty rough bone spurs on the bodies of

1:47:21their vertebrae

1:47:22right so that can also be associated

1:47:24with the degenerative disc disease where

1:47:27now there's less space in between the

1:47:28bodies of the vertebrae so when you bend

1:47:30your neck there's a lot of rubbing on

1:47:32those bodies right so not only like a

1:47:35pinched nerve kind of thing but also

1:47:37bone spurs as well so just another plug

1:47:41for strengthening those stabilizer

1:47:46muscles to hopefully reduce this a

1:47:47little bit okay um disease right so bone

1:47:51remodeling an imbalance due to disease

1:47:55on osteoporosis is the most common bone

1:47:57disease the United States often linked

1:48:00to these issues down here so an

1:48:05inadequate amount of calcium or vitamin

1:48:07D estrogen kind of fights bone

1:48:12deposition and so it actually decreases

1:48:15the activity of the osteoblasts and so

1:48:18just being

1:48:19email increases your chances of getting

1:48:21osteoporosis as you get older not only

1:48:25are your sex steroids shifting but also

1:48:31as you get older as the video said your

1:48:36repair processes in general just kind of

1:48:39slow down and as a result osteoclast

1:48:46activity is still working about

1:48:47osteoblast activity just can't keep up

1:48:50um lack of exercise right so if you

1:48:54don't move it you lose it or even as I

1:48:57said before if you go into space and you

1:48:59are not needing to withstand the force

1:49:02of gravity you don't need very strong

1:49:06bones and so your osteoblasts aren't

1:49:08going to replace that bone as quickly if

1:49:10you're just not using it and of course

1:49:12there's a lot of genetic factors but

1:49:14ultimately osteoporosis is just porous

1:49:17bones associated with more grown

1:49:20breakdown than bone and that oh I'm not

1:49:28gonna do open-ended practice because

1:49:31that is not something we need to do for

1:49:34this upcoming exam so oh my gosh so much

1:49:38information any questions I know I flew

1:49:42through that quickly all right so at

1:49:51this point that is the end of the

1:49:52lecture information on exam number two

1:49:57your exam number two is going to be this

1:50:00Wednesday I will have zoom essentially

1:50:03office hours to let you guys come and

1:50:05ask questions I don't really have

1:50:09anything planned for you know an

1:50:11official review but if you want to come

1:50:13and like hear what we're talking about

1:50:14by all means you can join for that your

1:50:18lab practical is going to be posted on

1:50:22blackboard right under the exam two

1:50:25resources folder it's open at 2:00 today

1:50:29through midnight tomorrow

1:50:32same format I'm pretty much going to

1:50:35have a picture something like this and

1:50:39say you know what is this entire region

1:50:41of the bone and you'll tell me that's

1:50:43the epiphysis all right what is this

1:50:45whole region of the bone emphasis what

1:50:48is this

1:50:49substance inside the medullary cavity

1:50:52right so that's the yellow bone marrow

1:50:54right all of those terms on the

1:50:57practical one terms list are fully fair

1:51:01game for this test

1:51:02there are reused questions all right so

1:51:06it is in your best interest to go back

1:51:07and take a look at the practice

1:51:11practical as well as your lab quiz

1:51:13because you will see some of those

1:51:16questions again there are or this is 50

1:51:21points and so there will be 25 stations

1:51:27or questions with two structures bones

1:51:34whatever each some of those questions

1:51:37might have like two parts right so for

1:51:43example going back to this you know the

1:51:48cell like I could point to this and say

1:51:51what is the cell and what is the cavity

1:51:55right so the cell in here would be the

1:51:58osteo site the cavity would be the

1:52:00lacunae and as always try to use the

1:52:04words exactly as they are on the on the

1:52:08list if there are two structures so for

1:52:11example the ventral root versus the

1:52:13anterior root that is we're looking at

1:52:20this a little difficult to see but the

1:52:28dorsal root the ventral root dorsal root

1:52:33ganglion spinal nerve within the spinal

1:52:38cord we have the white matter right

1:52:40myelinated axons we have the gray matter

1:52:42on myelinated axons we have the

1:52:45posterior or

1:52:46dorsal root the lateral root or horn oh

1:52:49my gosh posterior or dorsal horn ventral

1:52:55or anterior horn right so on the list

1:52:59you see that it's like posterior

1:53:01parentheses dorsal horn pick one of them

1:53:04and tell me that don't give me both

1:53:06don't give me lots of crazy slashes just

1:53:09posterior horn that's it and that will

1:53:13allow blackboard to make the right call

1:53:16and so you won't have to wait for me to

1:53:18go back in and make a judgment call

1:53:21about whether it's actually right or not

1:53:23so that will expedite your grades

1:53:26Shirley let's see on the spine remember

1:53:38that there are three regions so if I'm

1:53:41asking for the region of a vertebra its

1:53:44cervical it's there assic its lumbar if

1:53:47I give you a picture of the actual spine

1:53:50I know the lighting here is not the

1:53:51greatest for you to see this but you can

1:53:54actually like count down if I give you a

1:53:57picture that you can write see one two

1:54:00three four five six and seven

1:54:02right so c7 c6 c5 right no - no spaces

1:54:07just the letter C the number five

1:54:10so from c7 t1 t2 t3 t4 and so on and so

1:54:15forth alright so I'm asking you for the

1:54:17letter number combination

1:54:19I want t3 I'm asking you for the name

1:54:24for example right remember that the

1:54:27vertebra prominence c7 that's the name

1:54:31and it's letter number vertebra

1:54:34indicator okay let's see you guys are

1:54:40more than welcome to speak up or ask

1:54:43questions via the chat feature by all

1:54:46means

1:54:49questions are great if there aren't

1:54:52questions I'm just gonna point out a

1:54:53couple more things for you guys

1:54:59all right I remember that there are

1:55:01seven pairs of true ribs five pairs of

1:55:06false ribs two of those ribs are

1:55:10floating and or false ribs right so you

1:55:13could tell me floating or false and that

1:55:15would be okay for these two but for the

1:55:17other three pairs of false ribs they are

1:55:20just false they're not floating right

1:55:21again you can count right one two three

1:55:24four five six and seven trips one two

1:55:28three four false and one two or eleven

1:55:32and twelve rather for floating so this

1:55:47we now know all sorts of things about

1:55:49this hooray hopefully you guys enjoyed

1:55:54or hopefully at least got something out

1:55:56of this most recent open ended video but

1:56:01muscle cell right remember this is the

1:56:04motor neuron that is a cell this is a

1:56:07Schwann cell a cell right this here is

1:56:11the sarcolemma of the myocyte or

1:56:13myofiber right that is a cell right on

1:56:17the back here we see connective tissue

1:56:19that is the endomysium

1:56:21you know the endomysium surrounds each

1:56:23and every cell the spiderweb looking

1:56:32thing is the sarcoplasmic reticulum

1:56:34don't tell me sr tell me sarcoplasmic

1:56:36reticulum right and of course the Triad

1:56:41is all three of these sarcolemma the

1:56:45specific part of the sarcolemma that is

1:56:48essentially covered with receptors for

1:56:52ACH from the motor neuron that is the

1:56:55squiggly little motor endplate right so

1:56:57just just a couple reminders that you

1:57:01may or may not see we'll see

1:57:08any questions for me alright I'm happy

1:57:21to show you any of the models I'll hang

1:57:23out for a few more minutes you can stay

1:57:26behind and uh you know chat more

1:57:31privately if you'd like if not I will

1:57:33see you maybe

1:57:35it's optional on Wednesday to come to

1:57:38our zoom meeting okay so if not um I

1:57:41will see you or at least see your names

1:57:43on a black screen next Monday oh and

1:57:48remember that what is it a week from

1:57:51today we are doing our chicken leg

1:57:53dissection so make sure that you have

1:57:56access to a chicken leg for that so I'm

1:58:02gonna stop the recording I'll get this

1:58:04posted on YouTube as soon as I can

1:58:06I hope you guys all have a lovely lovely

1:58:09day good luck on the practical and if I

1:58:12don't see you on Wednesday good luck on

1:58:13the exam