Full transcript
0:00for Chapter six we're gonna focus in on
0:01bone tissue this is going to be looking
0:03at the functions of the skeletal system
0:05as well as the structure of specifically
0:07long bones we're gonna take it closer
0:09look at the tissue of compact and spongy
0:11bone the nerve and blood supply bone
0:13formation we're talk a little bit about
0:15fractures and repair and calcium
0:17homeostasis exercise and aging as it
0:19relates to bone tissue so the skeletal
0:22system does include bones cartilage
0:24tendons remember tendons are gonna hold
0:26muscles to bone and ligaments which hold
0:29bone to bone each individual bone is
0:32considered an organ why would this be
0:34well
0:35it's composed of different tissue types
0:37each muscle is gonna have a different
0:40combination of tissues therefore it's
0:42gonna be its own organ examples of
0:45tissues associated with bone are gonna
0:47include of course bone tissue connective
0:50tissue osseous tissue cartilage dense
0:53connective tissue adipose blood and
0:57nervous now if you'll notice the first
1:00five of these are going to be types of
1:03connective tissue then you have the
1:05nervous tissue also present now
1:07osteology is the study of bone structure
1:10and treatment of bone disorders so let's
1:13look at the functions of the skeletal
1:15system the functions are going to
1:17include support it's to support your
1:19body and provide a framework for you to
1:22is it's going to protect it's going to
1:24protect some of your internal organs
1:25from damage specifically when we talk
1:27about the ribcage it's just support your
1:29heart and lungs your brain case is to
1:31support your brain we also see the
1:33spinal column is there to support the
1:35spinal cord they also are going to
1:38assist in movement skeletal muscles
1:40attached to these bones through the
1:41process of tendons and this allows you
1:43to be able to move these bones the bones
1:46also store and release minerals
1:48primarily calcium and phosphorus those
1:50are the minerals that contribute to the
1:52bones hardness and they are used in
1:54metabolic processes throughout your body
1:56as well blood production also takes
1:58place in the bone tissue this is called
2:00hemopoiesis or hematopoiesis this occurs
2:03in the red bone marrow this is where
2:04you're gonna have erythrocytes red blood
2:06cells made leukocytes which are white
2:08blood cells and thrombocytes which are
2:10platelets other cells can be produced in
2:12the bone marrow
2:13well like fibroblasts and macrophages
2:15the bone is also going to be a place for
2:18triglyceride storage and this is going
2:20to be where we make a Patou sites in
2:22yellow bone marrow so the red bone
2:24marrow is there to make more debate the
2:25stem cells for blood
2:26the yellow bone marrow is gonna be
2:28storage of fat so when we look at red
2:31bone marrow this is gonna be the place
2:33where hematopoiesis or hemopoiesis does
2:35take place the red bone marrow contains
2:38stem cells these stem cells can undergo
2:40mitosis and then they can be
2:41differentiated into red blood cells
2:43white blood cells or platelets the
2:45yellow bone marrow is gonna be found
2:47more in the shaft of the bone this is
2:49going to be for lipid storage so a quick
2:52note in fetuses and newborns all bone
2:55marrow is red bone marrow to start with
2:57but as we age red bone marrow is
2:59replaced with yellow bone marrow and an
3:01adult bone marrow does remain in certain
3:03areas it remains in your ribs sternum
3:06and skull of like your flat bones the
3:08vertebrae and pelvis which are known as
3:10irregular bones and the ends of your
3:13femur and your humerus of your long
3:15bones so these are going to be the areas
3:17that are going to continue to contain
3:19red bone marrow in adults now the types
3:22of bones are classified by their shape
3:24these include long bones short bones
3:26flat irregular and so on
3:28so guys when we look at a long bone a
3:30long bone is greater length than width
3:32so it's longer than it is wide the outer
3:35layer of a long bone is made of compact
3:37bone and the inner layer has spongy bone
3:40and the spongy bone is also going to be
3:42at the ends of the what we call
3:44epiphysis there's going to also be a
3:46medullary cavity or shaft so the
3:49epiphysis are going to be on the ends
3:51and you're going to see that there is
3:52going to be spongy bone in this area the
3:54medullary cavity is in the middle or the
3:56shaft of the bone and it's going to have
3:58the compact bone mostly examples in the
4:01lower limb are gonna be your femur tibia
4:03and fibula your upper limb has the
4:06humerus radius and ulna your digits your
4:09fingers and toes are also known as long
4:11bones they are short long bones in the
4:13sense that they're small but they are
4:15longer than they are wide that is why
4:17they are part of the long bone group now
4:19short bones are nearly equal in length
4:21than width so they are going to be more
4:23cube shaped the inner layer spongy bone
4:26is
4:26gonna be covered with a thin layer of
4:28compact bone and there is no medullary
4:31cavity in these short bones now if
4:34you'll look here you can see the spongy
4:36bones in the middle and compact bone on
4:38this side
4:38the only openings are present in the
4:40spongy bone structure some examples are
4:43going to be your carpals your wrist
4:44bones and your tarsals which are your
4:46ankle bones flat bones have a thin inner
4:48layer of spongy bone which is sandwiched
4:50between outer layers of compact bone
4:53they still also have no medullary cavity
4:55as well so their structure is going to
4:57be similar to what we saw with these
4:58short bones however they're not going to
5:00be cube-shaped
5:01some examples of your flat bones are
5:03gonna be the bones that make up your
5:04cranium or your skull your sternum which
5:07is known as your breastbone and your
5:08scapula your shoulder blade now your
5:11regular bones are odd shaped they do not
5:13fit into any of the other categories
5:14they will have various amounts of spongy
5:17bone on the inside with of course
5:19compact bone on the out and they still
5:21have no medullary cavity now these bones
5:24are irregular odd shaped and so because
5:26of this this vertebrae are eggs a great
5:28example of irregular bones a lot of your
5:31facial bones as well the coxal or hip
5:34bones and what we call the calcaneus
5:36which is the bone that makes up your
5:38heel now sizemode bones are going to be
5:41bones that are contained within tendons
5:44they're not always completely ossified
5:46and they can typically be very small
5:48like millimeters in diameter the whole
5:51point of these bones is to prevent wear
5:53and tear on the tendons one of these
5:55sizemode bones that we do see as has a
5:58name is what we call the patella or the
6:00kneecap
6:01now sutural bones are small bones
6:04between your cranial sutures this is
6:06where your cranial bones are going to
6:08attach these bones are going to be known
6:11as Wimmer and bones and they are going
6:13to be in their own unique structure as
6:15well so short flatten irregular bones
6:17are composed mainly of inner spongy bone
6:19with an outer layer of compact bone this
6:23spongy bone is also located in the
6:25epiphysis or the ends of the long bones
6:29so if we take a look here we'll see
6:32spongy bone is going to be the inside
6:34part and the compact bone is going to be
6:36the outside part about 80% is going to
6:39be compact
6:40the other 20% is the spongy now the
6:43spongy bone is known as cancellous bone
6:46in the whole point of this structure of
6:48compact with the spongy bone on the
6:49inside is to help reduce the weight of
6:52our bones if they were compact bone all
6:54the way through they'd be super-heavy
6:55some spongy bones are filled with red
6:58bone marrow this is to allow for
6:59hematopoiesis or the production of red
7:01blood cells to occur so let's take a
7:04look at the structure of the long bone
7:06now this is the gross anatomy meaning
7:08the large anatomy of the long bone and
7:10in this case they picked the humerus to
7:12take a look at we do see that the
7:14diaphysis is what we call the shaft of
7:16the body of the bone we also see the
7:19epiphysis this is going to be the distal
7:21end or the proximal end of the bone so
7:24remember way back when we talked about
7:25in Chapter 1 we had those directional
7:27terms where we had proximal and distal
7:29the proximal epiphysis is gonna be the
7:32one closer to the trunk or where the
7:34limb attaches and the distal will be
7:37further away metaphysis is going to be
7:40in between the epiphysis and the
7:41diathesis it's gonna be the area that
7:43joins these two this is the area where
7:46your growth plate is located when your
7:48bones are still growing this does turn
7:50into a growth line in adults when we
7:53talk about the growth plate this is one
7:55to be we're growing boats are gonna add
7:57links and when we say length it's the
7:59interstitial growth they're gonna grow
8:00this way this is gonna have hyaline
8:02cartilage but when it fuses and it
8:05becomes aligned in adults the cartilage
8:07is going to be converted to bone and
8:09therefore there's gonna be no more
8:10growth of that bone long ways we also
8:13see that there's going to be cartilage
8:15on the ends on the epiphysis these are
8:19going to be with hyaline cartilage in
8:21the whole point here is for articulation
8:22with the joints it's to reduce friction
8:25so that's not bone on bone in a joint
8:27and also to absorb some shock the
8:30periosteum is going to cover the bone
8:32surface you can see it's kind of like a
8:34sheet you can kind of think about if
8:35you've ever taken a leaf and you've
8:37pulled that waxy layer off of the leaf
8:39that's kind of like how the periosteum
8:41is on the bone it's a little thin layer
8:43of that but on the bone this is where
8:46ligaments and tendons will attach to the
8:48bone it's to protect and nourish the
8:50bone as well the outer layer of the
8:52periosteum is
8:53dense connective tissue but the inner
8:55layer is gonna be what we call
8:57osteogenic osteogenic means that it has
9:00these cells called osteoblasts who are
9:03gonna help produce bone so this is gonna
9:06actually help what we call promote
9:07appositional growth and repair so where
9:10the bone can grow and repair outwards
9:12okay where it's gonna give it more girth
9:14the medullary cavity is inside the
9:16diathesis it's gonna be a hollow space
9:18which contains fatty yellow bone marrow
9:20this area also is gonna be vascular you
9:23can see how the blood vessel is running
9:24through this canal or cavity the
9:26endosteum is gonna be on the inside part
9:29of the bone this is going to be a thin
9:31membrane that lines the medullary cavity
9:33it also has a layer of osteogenic cells
9:35and connective tissue tissue to help
9:38with repair and growth the appositional
9:41growth of the bone so let's look at the
9:43histology of the bone tissue the
9:45microscopic study now the bones hardness
9:48depends on the crystallized inorganic
9:50mineral salts that we call calcium
9:52phosphate and calcium carbonate and so
9:54on if you remove the mineral salts from
9:57a bone it will become rubbery now you
9:59can do this not bones that have been
10:01cooked but you can put them in type of
10:03acid and it's going to cause the calcium
10:06to leave and it makes the bone very
10:08rubbery on the other hand we do see the
10:12calcification is the process of this
10:14crystallization of the mineral salts in
10:16order to cause those cells to bind and
10:20build together and so again this gives
10:22the hardness now the strength of the
10:24bone this flexibility comes from the
10:27collagen fibers okay it's going to make
10:30it where the bones can be a little bit
10:32flexible okay so they flex a little bit
10:34before they'll actually break kind of
10:36like when you take a celery stick in you
10:38and it flexes first before it actually
10:40breaks now we can actually remove these
10:43collagen fibers by baking the bones and
10:45this is what makes the bones then very
10:47brittle now bone or osseous tissue is a
10:50type of connective tissue which means it
10:52does have cells but the majority of it
10:55is going to be made out of that matrix
10:57now the first kind of cell that we do
10:59see that's part of this bone tissue is
11:01what we call osteoprogenitor cells or
11:03osteogenic cells these are the
11:06unspecialized
11:07cells that we would call stem cells they
11:10can undergo mitosis and they are going
11:12to ultimately produce what we call
11:13osteoblasts these are going to be
11:15concentrated in the inner layer of the
11:17periosteum now osteoblasts are not
11:21capable of mitosis anymore so they've
11:23matured enough to where they can't do
11:25mitosis but they are gonna be the ones
11:27who actually build the bone so if you
11:29can remember osteoblasts with the be
11:30there the bone builders they're gonna be
11:33the ones who secrete the extracellular
11:34matrix specifically the collagen fibers
11:37they're gonna initiate calcification the
11:40blasts are gonna then become walled off
11:42and they will mature into the next cell
11:44that we call osteo sites okay osteocytes
11:48are going to be mature bone cells
11:50they're gonna be found in a lacunae so
11:52what happens guys is this osteoblast
11:54starts building the extracellular matrix
11:56and it builds it around itself all right
11:59so it's like almost building a fence
12:00around itself continuously until it's
12:03completely walled off this walled off
12:06area is called the lacunae it's like a
12:07little lake area for it it no longer can
12:10secrete extracellular matrix and it's
12:12just there to maintain the area it's
12:16just to make sure that everything is
12:17gonna stay healthy in that area this is
12:20the actual bone lineage this is where
12:22bones go from the beginning which is
12:24going to be the prosti Oh Jen tore cuz
12:26Ghent means beginning here so beginning
12:29to osteoblasts then they mature into
12:31osteo sites there's also going to be
12:33osteo class Osseo class are derived from
12:36white blood cell stem cell lines these
12:39are going to be the bone destroying
12:41cells so osteoblasts build bone
12:43osteoclasts break it down they do this
12:46by releasing very powerful hydrolytic
12:48enzymes and the whole point is to break
12:50apart the calcium and release it back to
12:52the blood
12:53this results in bone reabsorption and
12:55these are concentrated on the in the
12:58endo ostium now one thing to note about
13:00this guys is normally the amount of bone
13:02being broken down should equal the
13:04amount of bone building up this is a
13:06continuous process in your body your
13:08bones are constantly being remodeled the
13:11problem is whenever the osteoclasts
13:14start to tear down bone faster than the
13:16bots blast can build this can ultimately
13:18cause issues like osteoporosis
13:21and remember the osteoclasts are going
13:23to come from the white blood cell
13:24lineage the matrix is going to be 15%
13:27water when we talk about bone 30% will
13:30be the collagen fibers and 55% will be
13:33those crystallized mineral salts now
13:36remember the collagen provides
13:37flexibility but the salts provide the
13:40hardness
13:41so remember osteoblasts are going to
13:42make the matrix osteocytes are going to
13:46maintain the matrix
13:48so guys bone remodeling is a normal
13:50continuous process it's going to use
13:53this process to renew the bone
13:55continuously throughout your life now
13:58bone deposition is associated with the
14:00osteoblasts on the periosteum side of
14:03the bone whereas the bone reabsorption
14:05is associated with the osteoclasts and
14:07they are concentrated on the endosteum
14:09part of the bone the inside now when
14:12reabsorption occurs when we break the
14:14bone down calcium and other minerals are
14:16released into the interstitial fluid
14:18these can then get moved to the plasma
14:20which is in the blood and they can be
14:22used for metabolic functions by your
14:23muscles your muscles need the calcium
14:26for contractions they can also be sent
14:28to your nerves because your nerves need
14:30calcium for nerve impulses and you also
14:32need calcium for blood clotting so there
14:34is a purpose for removing this calcium
14:36if your body needs it for other
14:38processes so if you take a look here's
14:41some of that remodeling of a compact
14:43bone it shows you the child's bone
14:45versus the adults bone you'll notice
14:48that the bone is getting bigger in the
14:49sense of it's getting wider but you'll
14:51also notice that the medullary cavity
14:53that hollow portion is also getting
14:55wider
14:57now this remodeling is going to take
15:00place again using the idea of the
15:02osteoclasts breaking the bone down and
15:04osteoblasts building the bone back up
15:06let's take a look at the structure of a
15:09compact bone ok the different parts that
15:11we see have a compact bone now remember
15:13the periosteum is the bone covering
15:15which again you can see here it's a thin
15:17layer this is made out of dense
15:19connective tissue on the outside and the
15:21osteogenic layer on the inside the
15:23compact bone is going to be located here
15:26now the compact bone is going to be
15:28composed of what we call osteons osteons
15:31are repeating structural units and they
15:33run parallel to the die
15:35offices so if the diaphysis runs this
15:37way they're gonna run the exact same way
15:39all right so they run parallel we also
15:42see that there's what we call the
15:43lamellae this is calcified matrix the
15:46lamellae can have a couple of different
15:48forms all right so when we look at the
15:50lamellae it could be concentric meaning
15:52it goes around the osteon okay so the
15:56osteon has the lacunae in the middle and
15:58it's building its walls around itself
16:00and so this can be the concentric we
16:03also have the interstitial the
16:05interstitial is gonna fill in the spaces
16:07between the osteon and guys the
16:10interstitial lamellae is the oldest
16:12lamellae that started to be remodeled
16:14but we don't remove all of it so that we
16:15don't just have holes in the bone as
16:17we're remodeling we just remove pieces
16:19of it and so on and it's gonna
16:20constantly be changing filling in the
16:22spaces between the osteons the last one
16:26is what we call the circumferential it's
16:27the one that goes all the way around the
16:29bone this is the new appositional growth
16:31of the bone all right and so this is
16:33gonna be the outer circumference part of
16:35the bone the lacunae is the space within
16:37the lamellae where the the osteocytes is
16:40going to be found so if you'll notice
16:42here in this picture that's showing you
16:44where that osteo site is and it's in
16:45this kind of like ish looking area
16:47called the lacunae we then have the
16:50osteo side of the mature blood cell the
16:53mature blood cells going to communicate
16:55with other individual cells and blood
16:58vessels and stuff outside of its little
17:00lake through what we call cannula Q lie
17:03these can you lick you lie are
17:04interconnected channels of extracellular
17:07fluid that are going to connect one
17:09lacunae to the next this is gonna
17:11provide nutrients to the osteocytes but
17:13also allow the waste to leave the area
17:15as well there are gonna be some canals
17:18running through these bones these canals
17:20are going to either be periphery tting
17:22canals or Volkmann canals these are
17:23gonna run transverse remember a
17:25transverse cut is side-to-side these
17:27contain blood vessels and lymph vessels
17:30as well as nerves and they are going to
17:32connect to the central canals these
17:34central canals are known as haversian
17:36canals these are gonna run parallel up
17:39and down with the osteons and they're
17:41gonna contain blood vessels lymph
17:43vessels and nerves as well make sure you
17:45study this picture of the compact
17:48now the spongy or cancellous bonus
17:50towards the interior this is gonna be
17:52the area that contains the red bone
17:54marrow we do see that it's protected by
17:57the contact bone there are going to be
18:00some special structures that you can see
18:02here in the spongy bone one being the
18:04trabeculae the trabeculae are thin
18:06columns of lamellae which are arranged
18:09in a regular pattern so this is
18:10different than the compact the compact
18:12is very structured in those osteon
18:14structures whereas a spongy is not these
18:17osteocytes and the lacunae will have
18:20connecting can cannula collide just like
18:22they do in the compact bone but their
18:24organization is just more disorganized
18:26the way they build this bone is more
18:29disorganized
18:29there's no osteons and there's no
18:31peripheral or central canals in the
18:33spongy bone because there's already
18:35holes present okay because that's why
18:37it's called the spongy bone just like a
18:38sponge it has spaces present
18:41all right this brings us to the blood
18:42and nerve supply to the bone there are
18:44going to be arteries and veins that come
18:46into the bone and leave the bone and
18:48these are going to be found in certain
18:50areas they get named based on where
18:52they're entering so we have the Epistle
18:54artery and vein we also have the Met
18:57official artery and vein the periosteal
19:00artery and vein and then the nutrient
19:03artery and vein and guys the nutrient
19:05already an artery in veins the one
19:06that's going to go into that medullary
19:08cavity the periosteal artery and vein is
19:11going to service the periosteum and the
19:13outer layers of the compact bone with
19:15the diathesis they're going to do this
19:17via those Volkmann channels we saw in
19:20the compact bone structure the nutrient
19:23for Rhema is a hole in the bone this is
19:26where nutrient large arteries and veins
19:28are going to enter into the periosteum
19:30they're gonna then go into the diathesis
19:33to the medullary canal this service is
19:36the inner bone tissue and also the
19:38spongy bone okay so it's very important
19:41that it's gonna go inside to get those
19:43inside layers of the bone there are
19:45going to be proximal and distal branches
19:47again depending on which side of the
19:49bone you're looking at now these are
19:51just some wing bones that you can get
19:53like when you eat wings at Buffalo Wild
19:55Wings or whatever you can find the
19:58nutrient foramen which is a hole through
19:59the bone this is where the artery
20:01vane would enter in into the medullary
20:04cavity alright so now let's talk about
20:06bone formation how does the bone form
20:08this is also known as osteogenesis
20:10Genesis means the beginning and osteo
20:12means bone so the beginning of bone this
20:16process can also be called ossification
20:18because we're hardening those bones in
20:20the process the support occurs in four
20:23principal situations so an embryo is up
20:27to two months that's what we call an
20:28embryo a fetus is the third month to
20:31birth the bones are forming in this
20:33process so this is the first kind of
20:35situation you see this ossification the
20:38second is growth of bones during infancy
20:40to adulthood this is going to be two
20:43forms of growth we're gonna see
20:45interstitial growth this way and
20:47appositional growth from infancy to
20:49adulthood
20:51remodeling does occur throughout life
20:53this is the whole idea of bone
20:55deposition with bone reabsorption
20:56happening all at the same time and last
20:59is repair of bone fractures if the bone
21:02does break we need the ability to repair
21:04it we need those bones to be able to go
21:07through that process of ossification
21:09again alright so this is just showing
21:11you the different situations that
21:13ossification or osteogenesis can take
21:16place now the formation of a bone in an
21:20embryo and a fetus is gonna be a little
21:22different than when we look at like
21:24repairing and growth after birth so
21:26embryonic skeletons are made of what we
21:29call Mezen kind this is the embryonic
21:31connective tissue it involves
21:34replacement of a connective tissue with
21:36bone so we are going to replace this
21:38mesenchymal with bone tissue now this
21:42type of replacement and ossification is
21:45called intramembranous ossification this
21:48is going to occur in the flat bones of
21:49the skull these bones form in a sheet so
21:52they form in a sheet within the Mezen
21:54kind and they are going to have a
21:56certain process it's gonna start first
21:58with the Mezen time the embryonic
22:00connective tissue this will then
22:02differentiate cuz remember embryonic
22:04means it's more like stem cells it will
22:06differentiate into what we call
22:07osteoprogenitor cells these are
22:09unspecialized bone stem cells these are
22:12going to mature into what we call
22:14osteoblasts or
22:15remember the osteoblasts are gonna be
22:17the ones who build the bone they're
22:19gonna provoke promote the calcification
22:21they're gonna make the matrix once these
22:23mature and wolof they are known as
22:25osteocytes okay so once they're walled
22:28off they can no longer secrete any more
22:30matrix they become osteocytes spongy
22:34bone develops using the trabeculae form
22:36and the whole idea of the vascular
22:39realization the adding of the blood
22:40vessels do occur the periosteum the
22:43outer bone covering then is formed and
22:46then compact bone later develops during
22:49a remodeling process alright and so we
22:52see spongy bones gonna get made first
22:53and then compact bones going to remodel
22:56to where it gives it more structure now
22:58this is why babies have soft spots
23:01okay these are called fontanelle's these
23:03soft spots are in newborn skulls and
23:05they are gonna have that connective
23:07tissue that remains so that
23:08intramembranous ossification has not
23:11completed here this allows for easier
23:14birthing processes the whole point of
23:16having these soft spots is so that the
23:18cranial bones can slide past each other
23:20so that the child's head can fit through
23:22the birth canal this is why some babies
23:24actually if they've spent a lot of time
23:26in the birth canal come out looking like
23:27they have a conehead and it's because
23:29those those bones have had the ability
23:31to move it will not stay that way these
23:34soft spots will allow it to move back to
23:36normal and the soft spot starts to grow
23:38and go through ossification as the baby
23:40grows this allows for them to have a
23:42little more space for their brain to
23:44continue to grow also after birth all
23:47right so now we're gonna move on instead
23:48of that intramembranous ossification
23:50where it does it in sheets we're gonna
23:52talk now about endochondral ossification
23:54which occurs in our long bone so what
23:57happens here is this is still going to
23:59have that mesenchyme embryonic tissue
24:01like we saw with the intramembranous
24:03this however is then gonna get replaced
24:06with hyaline cartilage it's going to be
24:08a mold form where it's gonna give the
24:11shape of the bone but this is done by
24:13chondroblasts so these are cells that
24:15produce the cartilage the bone will
24:18start to become replaced with actual
24:21bone cells so the cartilage will start
24:23to be replaced in the shaft area that
24:26diaphysis area with osteoblasts
24:29we then see that spongy bone is gonna
24:33form first followed by compact bone in
24:36the medullary cavity will then form due
24:38to osteo class now spongy bone formation
24:45will happen by the same events during
24:47primary ossification however they will
24:50not create a medullary cavity so when
24:53we're looking at that spongy bone area
24:54they're not gonna work on making that
24:55medullary cavity but they are going to
24:57still go through this process of going
24:59from mesenchyme to cartilage to bone
25:01articular cartilage does form on the
25:04ends of the long bones and again this is
25:07to help where it's not bone on bone in
25:08our joints the epiphysis ol growth plate
25:12will remain cartilage throughout their
25:14growing years allowing it the bone to be
25:16able to grow in length so when we look
25:18at endochondral ossification the bone
25:21forms from highland cartilage okay and
25:24so this process we see there's a
25:25development of a cartilage model first
25:28this is going to happen of course with
25:30the mesenchymal in Brianna
25:31tissue it will differentiate though into
25:34the chondroblasts first these are
25:36immature cartilage cells and this gives
25:39us the kind of model of whatever the
25:41bone supposed to look like now the
25:44growth of this model is going to cause
25:46those chondroblasts to mature into
25:48chondrocytes okay these are mature
25:50cartilage cells the matrix starts
25:53becoming more calcified and they do
25:55start to die as they start to die we do
25:58see that this is where the bone is gonna
26:00start for me so the bone or osseous
26:03tissue will then start to replace the
26:05cartilage this is gonna first start with
26:07those osteoprogenitor cells those
26:09unspecialized bone stem cells they're
26:12gonna go through the process of then
26:14specializing into osteoblasts and
26:16building the matrix this will form the
26:19trabeculae in the spongy bone we see the
26:22formation of the medullary canal debt or
26:24cavity does happen here with the
26:26osteoclast activity it's going to
26:27destroy some of those bone cells making
26:30an actual hollow cavity the compact bone
26:33then is laid down on the inner wall
26:34starting from the diathesis moving
26:37towards the epiphysis
26:38so it starts in the middle of the cavity
26:40and moves towards the ends now
26:42secondary ossification is going to be
26:45where there's the development of
26:46secondary ossification centers in the
26:48epiphysis of the bones this is the same
26:50process however the spongy bone remains
26:53with no medullary cavity the formation
26:56of the articular cartilage does occur on
26:59the ends as well as the cartilage
27:01staying in the Epistle growth plates ok
27:04now this only does remain through the
27:06growing years okay so the epistle growth
27:09plate will only remain through the
27:11growing years so when we look here at
27:13this bone formation we see the
27:15intramembranous ossification is going to
27:18be with the flat bones like those of the
27:20skull whereas the endochondral
27:22ossification is going to be the process
27:24used to produce a majority of the other
27:27bones from cartilage really specifically
27:29the long bones but most of the other
27:32bones besides these skull bones now when
27:35we look at bone growth from infant to
27:37adult we see that there's the
27:39interstitial growth which is going to
27:41add a link to the bone this is going to
27:43happen at those epistle or growth plates
27:46we also see there's going to be a
27:47positional growth which is going to add
27:50thickness or girth to the bone so when
27:54we talk about interstitial growth this
27:56is going to take place within those
27:58growth plates in these growth place
28:00there's going to be some layers of
28:02cartilage so the resting cartilage is
28:05going to be the closest to the epiphysis
28:07this is the area where there's no growth
28:10it's going to anchor the plate to the
28:13epiphysis the proliferating cartilage is
28:16just below that and this is going to be
28:17chondrocyte chondrocytes in stacks the
28:21hypertrophic cartilage is going to be
28:23the chondrocytes that are mature and
28:25then on the inner most part close to the
28:29medullary cavity is going to be the
28:31calcified cartilage this is where the
28:33extracellular matrix around the
28:35chondrocytes starts to calcify and
28:37becomes more like bone so you'll notice
28:40you have the resting cartilage the zone
28:43of poor freighting cartilage
28:44hypertrophic cartilage and calcified
28:47cartilage so this is where we can
28:50actually see some structural differences
28:52if there's a growth plate or not this
28:55question says which
28:56which x-ray is that of an adult and how
28:58did you know
28:59well the adult one is actually a and the
29:02reason being is if you look right here
29:04it's missing this line that B has B here
29:08is showing you that they have a growth
29:09plate in an ace the growth plates are
29:12closed now for appositional growth that
29:16was where when we were talking just a
29:17second ago we're talking about growth on
29:19the ends making the bones longer now
29:21appositional growth is going to be more
29:23girth so this is a type of surface
29:24growth this process is going to start
29:27with the osteoprogenitor cells remember
29:29these are the stem cells they are going
29:31to generate to form the periosteum the
29:34outer bone layer ok these will mature
29:36then into the osteoblasts the
29:39osteoblasts will start secreting the
29:41bone matrix
29:42they are then going to be when they get
29:44walled off and mature they will be
29:46osteocytes the osteocytes are going to
29:49produce those osteon structures and you
29:52can see them here in the picture
29:53basically while themselves off they
29:55create this osteon structure they do
29:58need an actual central canal here which
30:00is going to enclose a blood vessel
30:02meanwhile we do see osteo class are
30:05going to be destroying bone on the
30:07inside through the medullary cavity ok
30:10promoting reabsorption so again we're
30:12building on the outside of the bone
30:14making it wider but on the inside the
30:17medullary cavity is also getting wider
30:18due to the osteoclast activity so as a
30:21result the medullary cavity also starts
30:24to enlarge while the bone thickness also
30:26increases like you see here in this
30:28picture now bones do need to undergo
30:31remodeling this remodeling is going to
30:33be a lifelong process where mature bone
30:35tissue is removed from the skeleton and
30:37new bone tissue is going to get formed
30:39now deposition is going to be done by
30:42those osteoblasts because this is where
30:44they're depositing the calcium coming
30:46from the blood and they're gonna deposit
30:48into the new into this new bone tissue
30:50now reabsorption is going to be done by
30:53the osteoclasts and this is the reverse
30:55this is where they're gonna break down
30:57the calcium that's been packed into the
30:59bone tissue and they're gonna release
31:01these minerals back to the blood to be
31:03transferred so when we look at this
31:05guy's bone remodeling is controlled by
31:07some hormones these hormones are
31:10going to be calcitonin and parathyroid
31:12hormone calcitonin is going to be
31:15released if there's high levels of
31:17calcium in your blood and it's going to
31:20tell your bones hey go ahead and build
31:22some more bone we've got all this extra
31:24calcium you need to store it on the
31:26other hand if your body needs the
31:28calcium for your muscles or your nerves
31:31parathyroid hormones gonna get released
31:32and this is going to stimulate the
31:34osteoclasts activity and they are going
31:37to release the minerals back to the
31:39blood
31:39so here calcitonin product promotes a
31:42bone deposition Bastia blast it
31:45increases the uptake of calcium into the
31:47bone decreasing the calcium in the blood
31:50the parathyroid promotes both bone
31:53reabsorption so the osteoclasts are
31:55going to be triggered they're gonna
31:57decrease the calcium in the bone and
31:59increase it in the blood so these these
32:01hormones are opposites now there are
32:04lots of factors that can actually affect
32:05brow bone growth and remodeling of
32:08course the amount of minerals that are
32:09present can be part of this if we aren't
32:12taking in enough calcium or phosphorus
32:14it could cause issues vitamins are also
32:16important and specifically vitamin D
32:19vitamin D deficiency causes rickets
32:21which means the bones start to get very
32:23weak and they start to bow they're more
32:25flexible but they don't have that
32:27hardness that's there now this is due to
32:29the fact of not being able to absorb the
32:32calcium in their diet and this could be
32:34due to a vitamin D deficiency others are
32:37gonna be hormones so the human growth
32:38hormone is going to promote growth in
32:40all body tissues which include the bones
32:42sex hormones also can be released from
32:45the ovaries and testes and they can
32:47actually stimulate the osteoblasts to
32:49grow suddenly and remember parathyroid
32:52hormone and calcitonin are the two
32:54hormones we just talked about on the
32:55previous slide so what happens when
32:59creation of new bone or deposition does
33:01not keep up with the removal of the old
33:03bone or the reabsorption this is what is
33:05called osteoporosis which bone type is
33:08affected first by osteoporosis well this
33:11is actually going to be the spongy bone
33:13okay so spongy bone is actually going to
33:16be affected first now osteoporosis does
33:19affect men
33:20women however it affects women more at a
33:23higher risk especially after they've
33:24gone through menopause this is due to
33:27estrogen levels dropping so drastically
33:29during menopause that they are not able
33:32to then help continue stimulate
33:33osteoblasts activity so I'll see you
33:36class are still doing their job at
33:37osteoblasts or not are not working as
33:40much medication healthy diet and
33:43weight-bearing exercise can help prevent
33:44bone loss or it can also help strengthen
33:47the weak bones already all right so this
33:49brings us to repairing and fractures
33:52what is a fracture a fracture is going
33:55to be where the bone is broken now there
33:57are different types of fractures so one
34:00can be an open or compound fracture this
34:02is where the bone actually protrudes
34:04through the skin okay simple on the
34:07other hand is the bone is broken but it
34:10does not protrude through the skin so
34:12it's known as a closed fracture commuted
34:14fractures are going to be where the bone
34:16is broken into multiple pieces and
34:19fragments this is called a commuted
34:21fracture greenstick fractures are going
34:24to be where the bone did not break all
34:25the way through it's a partial break and
34:28this happens a lot of times in kids
34:29because their bones are gonna be more
34:31flexible than ours are as adults and so
34:34because of this it causes them to be
34:36more where they just break on one side
34:38this happens a lot of times too with
34:39kids if there's a twisting action it
34:42takes a lot of force to break a child's
34:44bone all the way through impacted
34:48fractures are going to be where the bone
34:49gets pushed up against itself this can
34:52also cause a commuted fracture where
34:54there's gonna be pieces but the bone has
34:56been impacted and pushed driven back
34:58together Potts fracture is what takes
35:01place with the fibula it's where the
35:03fibula breaks at the distal in by the
35:06ankle okay it breaks off down at the
35:08distal in another very specific fracture
35:12is called a colles fracture and this is
35:14found on the wrist
35:15this is when the radius breaks at its
35:17distal end at the wrist section now
35:20stress fractures are microscopic bone
35:23injuries this is normally due to
35:24repeated strenuous activities this can
35:27happen with running jumping dancing it
35:29can cause these stress fractures a lot
35:31of times individuals will talk about
35:33this happening
35:34they're shins and they call them shin
35:35splints but that is kind of the
35:37beginning of stress fractures all right
35:39so this picture right here is showing
35:41you how the bone actually gets repaired
35:43when a fracture or break takes place so
35:46the first thing that has to happen is we
35:49have to have the formation of a hematoma
35:51we have to have the formation of a blood
35:53clot once the blood clot is formed then
35:56we can go to the next stage this is
35:58where the fibrous cartilage is going to
36:01start to form a callus these are going
36:03to create a callus that bridges the two
36:06areas of the bone that are broken now
36:09this callus that needs to be replaced
36:11with bone so this more cartilage fibrous
36:14callus is going to be replaced with bone
36:16in the next stage we then see remodeling
36:19takes place now if you will notice the
36:22bone and the area where the break took
36:24place does not look exactly like it did
36:26before the break there is remodeling
36:29that takes place and there's also going
36:31to be some evidence of that break still
36:33on their bones later in life now you're
36:36gonna be responsible for reading and
36:37understanding certain material like the
36:39bones roll in calcium is on page two
36:41forty five exercises talked about on teh
36:44page two forty one and then the hormones
36:46were found on two forty three in your
36:49textbook