Full transcript
0:01hello everyone this lecture
0:03is going to be covering chapter 6 from
0:06your mayor of text
0:07which is on bones and skeletal tissue
0:11um so we're not actually going to be
0:12talking about like all the bones
0:14in our skeleton i'll name a few of them
0:17but you will be spending time in lab to
0:21learn
0:21the names of all of the bones and all
0:24the little markings on the bones
0:26um so in lecture we're really just
0:27talking about um the gross anatomy
0:31of just bones the structures of bones
0:32themselves some microscopic anatomy
0:36and then physiology of how bones are
0:38made developed
0:40and how they regrow and repair
0:43themselves
0:45okay so we're going to start off by
0:48talking about
0:49just bone and cartilage anatomy
0:53and obviously this is the skeletal
0:55system so it makes sense that bone
0:56is included in here but some of you may
0:59be saying well why
1:00do we have cartilage anatomy we already
1:03talked about that in the histology
1:05chapter
1:06but cartilage is really important to the
1:08skeletal system because the human
1:10skeleton
1:10initially is just made of cartilage
1:14okay and as the fetus develops
1:18that cartilage structure blueprint if
1:21you will
1:21um is going to be changed into bone
1:26okay so cartilage is the precursor for
1:28all the bones in our body
1:30um which makes sense because they're
1:31both a type of connective tissue they're
1:33both derived from the same
1:36embryonic tissue mesenchyme so the
1:38mesenchyme becomes cartilage first
1:41and then eventually will become bone
1:43okay so some areas are going to remain
1:45cartilage
1:47to require it to give the bones
1:50themselves a little bit more flexibility
1:53more articulations at the joints but the
1:55most of the cartilage in our embryonic
1:56skeleton is going to be
1:58converted into bone okay so just kind of
2:01review on
2:02the just types of cartilage and how they
2:04may
2:05relate to the skeletal system just
2:08besides the embryonic skeleton
2:11so we have hyaline cartilage right which
2:14functions to provide support
2:16flexibility and resilience resilience
2:18it's the most
2:19abundant type and contains a lot of
2:22collagen fibers
2:24you're going to find it a lot of places
2:26in the skeleton
2:28so you're going to see it as articular
2:31cartilage
2:32and think of where your arms and legs
2:36are articulating anywhere there's a
2:38joint you're going to have
2:40articular cartilage okay and it's just
2:42going to kind of cushion
2:43the bones as they're rubbing up against
2:45each other to make sure that
2:46you know you're not damaging the bones
2:48themselves so articular cartilage of the
2:50joints
2:52you have costal cartilage which is the
2:54cartilage that's connecting
2:56your ribs to the sternum okay so that is
2:59cartilage
3:01you have in your respiratory system some
3:04respiratory cartilage in the larynx
3:07which is shown up here which is really
3:08not important for this chapter
3:10um and then nasal cartilage right so
3:12your nose isn't
3:13actually a bone it's made up of hyaline
3:15cartilage
3:17and hyaline cartilage ii is the
3:18cartilage that's going to make up
3:21embryonic skeleton
3:26okay so your fetal skeleton will be made
3:28up of hyaline cartilage
3:30that will eventually be turned into bone
3:33you also have
3:34obviously elastic cartilage um similar
3:36to highland but contains the elastic
3:38fibers which gives it the
3:40stretch um an elasticity that it has
3:43it's found in the external ear and
3:45epiglottis
3:46um the epiglottis if you don't know is
3:49at the top
3:50of your trachea and the ear
3:53is on the side of your head um and then
3:56finally fibrocartilage
3:58has really thick collagen fibers and
4:01really
4:01good tensile strength and you can find
4:04it in the meniscus
4:05of your knee so you have articular
4:08cartilage at the joint but in the
4:11meniscus the meniscus itself
4:13is fibrocartilage and then also the
4:16intervertebral discs
4:18so this red between your vertebrae
4:22all those little red discs between all
4:24of the vertebrae are fibrocartilage
4:27okay and you're also i don't know it
4:28doesn't say it here but in the pubic
4:30symphysis
4:32i'm going to add that
4:38your pubic symphysis between your two ox
4:41coxae or hip bones
4:43is also made of fibrocartilage so
4:45fibrocartilage is really in areas that
4:46have a lot
4:48of tensile stress on them so think about
4:51all of the stress that's in your knee
4:53joint all the pressure and weight put on
4:56in between the vertebrae and then also
4:58between your two um hip bones
5:01okay all right so that's a little bit
5:03about cartilage we're going to
5:04talk about especially hyaline cartilage
5:07throughout the rest of the chapter but
5:09there
5:09are all these types of cartilages found
5:12within the skeleton you could say but
5:15for bones bones obviously have
5:17a lot of important functions so
5:21um support for the body
5:24and soft organs just holding everything
5:26up
5:27protection so it covers
5:30a lot of really important organs such as
5:34your spinal cord so your spinal cord
5:36runs
5:36through your vertebrae your brain is
5:39housed within
5:40your cranium and then other vital organs
5:43like your lungs are under the rib cage
5:45your heart's under the rib cage right
5:47things that you don't want to get
5:48damaged are behind that hard bone
5:52functions in movement so provides places
5:54for
5:55muscles to attach and
5:58with those attachments the muscles when
6:00they contract will actually move your
6:02skeleton
6:04mineral and growth factor storage so
6:07calcium phosphorus and other growth
6:10factors
6:10um can be found within bone so it's kind
6:12of like a reservoir
6:14holds extra um of those things
6:18blood cell formation actually happens
6:21within your bones
6:22so the process of blood cell formation
6:25is called
6:26hematopoiesis um it occurs in red bone
6:30marrow
6:30cavities which are not in every bone but
6:33in certain bones you're going to find
6:35red bone marrow and the red bone marrow
6:38is responsible for
6:39hematopoiesis or the making of red blood
6:42cells
6:44functions in triglyceride which is fat
6:47storage
6:48is stored in bone cavities in yellow
6:53bone marrow
6:57right so red bone marrow is responsible
7:00for blood cell formation
7:02yellow bone marrow is fat storage
7:05and then finally some hormone production
7:07also happens within bones
7:09um so osteocalcin is secreted
7:12by bones and it helps insulate um helps
7:15regulate insulin secretion glucose
7:17levels and metabolism
7:19so a lot of different stuff going on um
7:22kind of cool bones do more than you'd
7:24think okay we have 206
7:27named bones in the human skeleton
7:29there's a whole lot of them and we can
7:30divide them into two groups based on
7:32location and these locations or
7:34um sections whatever you want to call
7:37them
7:38um we have to discuss before and a lot
7:41of people got these wrong on the first
7:43exam um so first you have your axial
7:46skeleton
7:48right the axial part of the body is
7:51this skull vertebrae
7:54um and your rib cage okay so the trunk
7:58of your body the appendicular
8:02skeleton are the appendages
8:05okay so we talked about before about
8:08your arms and legs
8:10are appendages right when we're talking
8:12about the skeletal system
8:14the girdles that connect your appendages
8:17to the trunk
8:17are considered appendicular as well so
8:20your
8:21pelvis attaches your legs to your
8:23vertebral column
8:25and your pectoral girdle which is your
8:27shoulder blades
8:29and clavicle which we'll talk about in
8:31the lab
8:32attach your arms to your trunk as well
8:35okay so appendicular skeleton
8:37are the arms appendages legs
8:40as well as the girdles that attach the
8:43limbs
8:45okay we can classify bones also
8:48according to their shape
8:50so there's four different
8:51classifications long bones
8:54are longer than they are wide which
8:56that's the name
8:57so that should make sense um these are
8:59mostly going to be the bones of your
9:01limbs your appendages
9:04short bones are going to be short so a
9:06lot of times they're
9:07cube shaped um so the bones in your
9:10wrists and ankles
9:11so your your bones in your wrist are
9:13your carpals
9:15and your ankles are your tarsals
9:19which you'll learn the names of all
9:20those again in lab
9:22sesamoid bones are a specific type of
9:25short bone
9:27that forms within a tendon so you have
9:30some of these in your hand
9:33but the main one that we're going to
9:34talk about is the patella but
9:36technically
9:37the pisiform is a sesamoid bone as well
9:39because it's within a tendon
9:43okay we have flat bones that are going
9:46to be
9:46flat thin flat and oftentimes
9:50curved so your sternum
9:53scapula the your ribs and
9:56most of your skull bones so the bones
9:58that make up your skull are all flat
10:02and then finally we have irregular bones
10:05so those are the bones that don't really
10:06necessarily fit into the other
10:07categories
10:08so they're just kind of weird shapes so
10:11for example your vertebrae
10:13and your hip bones okay
10:17um also you have a bunch of little tiny
10:19bones in your ear
10:21the stapes um malice incus
10:25they're known as your ossicles
10:30those are also considered an irregular
10:32bone
10:34okay so here's an image that just shows
10:38that again
10:39long bones are going to be longer than
10:41they are so humerus
10:43um the phalanges in your finger
10:46are also long bones
10:50short bones we have um this one is
10:53showing your talus which is a tarsal
10:56a bone of your ankle but also the bones
10:58of your wrist the carpals
11:02flat bones sternum um your scapula
11:06which you can't see in this picture but
11:07scapula
11:09um cranial bones your ribs are also
11:12considered flat
11:14and then irregular the weird shape ones
11:18so your
11:19[Music]
11:20vertebrae pelvis so on and so forth
11:25okay bones are considered organs because
11:28they contain different types of tissues
11:30remember tissues are a group of cells
11:33with a common function
11:35organs are a collection of different
11:37types of tissue that are working
11:39together
11:40okay so bones are made up of different
11:42types of tissue so there are considered
11:44an organ
11:46bone tissue also known as acis
11:50ashes osseous
11:53tissue um predominates but you also have
11:57nervous tissue within bones cartilage
12:00different connective tissues
12:02um muscle epithelial cells
12:05and blood vessels and stuff so there's a
12:06lot of different types of
12:09um tissues that are associated with the
12:12bones that bones couldn't survive
12:14without
12:15okay and we can talk about bones with
12:17three levels of structure
12:19so these we talked about in chapter one
12:21but the gross structure what you can see
12:23with kind of the naked eye bigger
12:25picture items
12:26microscopic the small stuff and chemical
12:29um
12:29even smaller okay so let's start with
12:32the gross
12:33level of structure okay so i put that up
12:36here just if you needed that
12:38um so gross anatomy of short irregular
12:41and flat bones first
12:43okay so what you'll see is there is
12:46actually two different types of bones
12:48you have spongy bone and compact bone
12:52and if you look at this image really
12:54quick um you can tell
12:56you know it's kind of intuitive this
12:58part in the middle is spongy bone and
13:00then on either side
13:02is compact bone here right you can see
13:03the difference pretty easily
13:05so spongy in the middle compact on
13:07either side
13:08so all flat short and irregular bones
13:12have a setup where you have a compact
13:16bone
13:16on each outside with a spongy bone in
13:20the middle so i kind of like to think of
13:21it like an ice cream sandwich
13:23okay and that spongy bone in the middle
13:26of this type of bone
13:27is has this fancy name the dipoli
13:30dipole don't know how to say it i don't
13:32know how to say a lot of things
13:34sorry um but that is just
13:37this part in the middle right the spongy
13:39bone
13:40in this little ice cream sandwich is
13:42called the dipole
13:44okay um the compact bone is
13:47also sandwiched okay so you have compact
13:50bone spongy compact
13:51but if you were to get close enough to
13:54the
13:55um spongy bone or the compact bone you
13:59would see that you have
14:00two types of membranes um sandwiching
14:04it okay so you have the periosteum
14:07that covers the outside of the compact
14:09bone
14:10and the endosteum which covers the
14:12inside of the compact bone
14:14okay so i'm going to zoom in again so we
14:16have complex bone on the outside
14:18on the outside of that compact bone is
14:21the periosteum
14:25and the inside would be the endosteum
14:29okay so you have the same thing on the
14:30bottom on the inside endosteum
14:33outside would be periosteum
14:36okay so you have like three ice cream
14:38sandwiches
14:40in this flat bone okay within the spongy
14:44bone
14:45in the dipole you have bone marrow
14:48so there's no defined marrow cavity it's
14:51just going to be within
14:53the spongy bone itself because you can
14:55see these little holes so it's going to
14:57be within there
14:58when you look at the bones well you're
15:00not going to be in lab so never mind
15:02in lab we have um actual bones and
15:05you'll see that you can't
15:06these look like actual holes they're not
15:08filled in and that's because the bone
15:10marrow
15:11you know goes away in those bones but if
15:14if you were to see a living bone the
15:16spongy bone those holes would be filled
15:18with marrow
15:19okay um and then you have
15:23hyaline cartilage that's covering areas
15:25of the bone that's part of the movable
15:27joint
15:28and remember that's called articular
15:32cartilage okay and you'll see here
15:36i think i mentioned in a later slide but
15:38just to i'll reinforce it
15:41the spongy bone that's covering it but
15:43you can see there's
15:45those um spongy areas called trabeculae
15:48okay so all of this spongy part these
15:51little
15:53whatever you want to call them are
15:54trabeculae
15:57okay okay so now let's look
16:00at long bones
16:06which i don't know i didn't put that on
16:07there so the other gross anatomy was for
16:09short flat and irregular bones long
16:12bones have a little bit of a different
16:13structure
16:15so they're still going to have compact
16:16bone um
16:18that is going to be on the outside layer
16:21of the entire bone and it's going to
16:24have spongy bone
16:26on the inside so it's kind of hard to
16:29see at the top of the bone but you're
16:31going to have compact bone
16:32all around the outside and then all that
16:35stuff
16:36in the middle is spongy bone and in some
16:38areas you're gonna have
16:39thicker compact bone okay and it's
16:42always gonna look smooth and solid where
16:44spongy is gonna be
16:45spongy looking okay
16:48um the spongy bone like i said these
16:51little
16:52needle like or flat spongy looking
16:54pieces are called tribeculae
16:56and again i said this in the last side
16:57but the trabeculae are
16:59filled with um some sort of bone marrow
17:02so it can be yellow marrow or
17:04red marrow we'll talk about the
17:05differences and where you can find them
17:08a little bit later on okay
17:13so more about the long bone so like i
17:16said it has the compact bone on the
17:18outside a spongy bone on the inside
17:21um but the log bone also has some
17:23different areas that you need to know
17:24so the first is the diaphysis
17:28okay the diaphysis is the tubular shaft
17:30that forms the
17:32long part of the bone okay so this very
17:34long middle part
17:36is the diaphysis of the long bone
17:40okay it's going to be compact bone with
17:43that
17:44um surrounds actually
17:47on the ends you'll see um spongy bone
17:50but in the very middle you're gonna see
17:52um here where did it go the medullary
17:55cavity
17:56okay so if i zoom in a little bit on
17:58this bone you see in the middle of
18:00diaphysis
18:01you have the medullary cavity
18:05which is this cavity here that is
18:08filled with yellow bone marrow
18:11okay so the medullary cavity yellow bone
18:14marrow is going to be in
18:15the diaphysis okay
18:19the epiphyses epiphysis epiphyses
18:22because there's two of them are going to
18:24be at both ends
18:25okay so i'll do this in a different
18:27color epiphyses
18:29are at both ends so we have the proximal
18:31epiphy epiphyses
18:32epiphysis which is going to be the part
18:35of the bone that's attaching
18:37um closer to the bottom body and the
18:40distal epiphysis
18:41which is going to be further away from
18:43the body
18:45okay again you have compact bone on the
18:47outside
18:48spongy bone on the inside and like i
18:50mentioned
18:51previously articular cartilage is going
18:53to cover any
18:55kind of area that's going to be involved
18:56in a joint
18:58okay so that's hyaline cartilage that's
19:00going to
19:01be in areas of joint surfaces to help
19:04protect the bone
19:06okay between the epiphysis and the
19:10diaphysis
19:11you have a structure called the
19:13epiphyseal line
19:16i'll change my color again epiphyseal
19:19line
19:20which i'll zoom in here it's epiphyseal
19:23line
19:24is this can you see that kind of line
19:28that goes through there
19:29that's the epiphyseal line okay
19:32um and it's important because it's
19:34actually remnant of a childhood
19:36structure
19:37called the epiphyseal plate the
19:40epiphyseal plate is where bone growth
19:42occurs
19:43so obviously children have small bones
19:45or bones need to get a lot longer
19:47so when children are developing you know
19:51the baby is born
19:52now they're a child um the epiphyseal
19:56plate is made up of cartilage
20:00and the cartilage is going to grow
20:03into bone and lengthen the bone okay so
20:06epiphyseal plate is really
20:08a cool structure and if you see the line
20:11where that it's no longer cartilage but
20:13it's ossified
20:14solid bone that tells you that the
20:17individual is done
20:19growing okay
20:23all right there are two types of
20:25membranes that we can find i already
20:28mentioned these but periosteum and
20:30antioxidant
20:31so periosteum is a white double layered
20:34membrane
20:35that covers the external surfaces of
20:39the um bone so you can see periosteum
20:42here
20:42this membrane that's covering the whole
20:44outside okay so be right up tight with
20:47the surface of the
20:48exterior layer of the bone there's
20:50actually two
20:51layers to the periosteum we have the
20:55more superficial fibrous layer
20:59that is dense irregular connective
21:01tissue
21:04consisting of sharpay's fibers
21:07that secure the
21:11osteogenic layer to the bone matrix
21:14okay so sharpay's fibers are just kind
21:16of connecting
21:18the membrane with the bone
21:22and then we have the osteogenic layer
21:25which is the inner layer
21:27that contains osteogenic stem cells
21:32and these types of cells we'll talk
21:34about in a little more depth later on
21:36but osteogenic cells are going to um
21:39give rise to pretty much all bone cells
21:42so they're going to be the stem cells
21:43that are going
21:44through mitosis right mitosis
21:48and dividing and creating um the bone
21:51cells
21:52okay within the periosteum you have a
21:55lot of nerve fibers
21:57you have blood vessels um perforating
22:00um and they
22:03go into the shaft through these things
22:06called nutrient
22:08foramens okay so foramen is just a hole
22:12but the inside of the bone needs um
22:15blood
22:15so there's these little holes in your
22:17bones that these vessels and nerves are
22:19gonna go through to get into the
22:21the bone matrix itself okay and those
22:23are called nutrient foramen again
22:26foramen just means holes
22:29okay and the periosteum is going to be
22:31an anchoring point for tendons and
22:33ligaments so where
22:34those are actually going to attach
22:38okay so that's the periosteum on the
22:40outside
22:42of the bone the endosteum
22:45is going to be on the inside okay so
22:47this whole
22:48inside layer right there right lining
22:52in this case the medullary cavity would
22:54be the endosteum
22:56okay so it's covering the whole
22:59medullary cavity
23:01in the inside of compact bone but it's
23:03also covering the trabeculae of the
23:04spongy
23:05spongy bone okay so it's gonna be all on
23:07the inside of the bone so anywhere
23:09there's gaps or
23:10the places that um bone marrow would
23:14reside
23:16um you'll see the endosteum
23:19okay there's gonna also be a bunch of
23:20canals that are passing through compact
23:23bone that we'll talk about in a minute
23:25and it's going to be lining those as
23:26well so literally any holes
23:28or spaces gaps within the bones are
23:30going to be lined with the endosteum
23:33okay and endosteum also has those
23:36osteogenic cells
23:38that are going to be responsible for
23:40differentiating and creating
23:42new bone cells
23:46okay so those are the membranes of the
23:49bones
23:51um and then we can also talk about
23:54the hemo
23:58hematopoietic there you go tissues and
24:01bones which are the
24:02tissues that are making um making blood
24:09okay so red bone marrow is found within
24:12the trabecular cavities of spongy bone
24:16and the dipole of
24:19the flat bones which have the trabecular
24:22cavities as well
24:24such as your sternum okay
24:28in newborns you're actually going to
24:29find red bone marrow
24:31in the medullary cavities
24:34in adults the medullary cavity
24:37turns into yellow bone marrow right
24:41so that yellow stuff is a medullary
24:44cavity
24:45so in adults you're only going to find
24:47red marrow
24:49in the trabeculae of
24:52certain bones so the femur and humerus
24:55you're going to find a lot of red bone
24:57marrow but most of it is going to occur
25:00in flat bones dipoles okay
25:03so the flat bones with those little
25:05sandwiches the dipole spongy bone in the
25:07middle
25:08is going to be responsible in adults for
25:09most of the red
25:11bone marrow um and the
25:15hemapuedic hematopoietic tissue
25:19it's getting harder to say okay um and
25:23yellow bone marrow can actually convert
25:24into red
25:26um if a person is anemic or is not
25:28producing enough
25:29red blood cells um you can see that
25:32their yellow marrow as act
25:33actually can turn into red mirror which
25:35is interesting
25:37okay and then the last bit of gross
25:40anatomy here is just
25:41bone markings um so bones aren't just
25:44gonna be perfectly smooth they're gonna
25:46have little divots
25:48and ridges and crests and those are what
25:50we call bone markings and they're
25:52important because of the site
25:54of attachment for muscles
25:57ligaments tendons and
26:01they can also be involved in joint
26:03formations
26:04so where other bones are going to join
26:06together
26:07or little holes conduits for blood
26:10vessels and nerves to get through
26:12okay so there's a lot of different types
26:14of markings
26:16we have what we call projection which is
26:18an outward bulge
26:20okay um which happens naturally on the
26:23bone
26:24but it can also happen due to increased
26:27stress
26:28from muscle pulls or modification for
26:30joints
26:33we can see depressions which are just
26:35divots so some sort of bowl or groove
26:38that can serve as passageways
26:41for vessels and nerves or also play a
26:44role in
26:45joints so in our hip bone we're going to
26:47have a depression
26:48called the acetabulum acetabulum
26:53which is going to be in the hip bone and
26:55it's going to be where the head of the
26:57femur connects
26:58okay and we can also have openings in
27:01the bones which are holes or canals
27:03that serve as passageways for blood
27:05vessels and nerves
27:07okay so those need to get through the
27:08bone um
27:10so our um a one that
27:14comes to mind is we have a what we call
27:17the jugular foramen
27:20it's my favorite one
27:23i don't know maybe not but your uh
27:26jugular
27:28vein is going to go through the jugular
27:30foramen
27:31okay and the carotid canal your carotid
27:33artery goes through
27:35you have um the external acoustic
27:38meatus that your ear canal goes through
27:40so there's a lot of different holes in
27:42the bones that
27:43stuff's gonna go through and you'll talk
27:45about this in a lot more detail in lab
27:47so i'm not going to get into all of
27:49these right now and waste your time
27:51because you're going to learn all of
27:52these in lab but these are all the
27:54different
27:55markings that you're going to need to
27:56know so you should know
27:58on the description of them of the
28:00different terms
28:01and then also in lab you're going to
28:03need to know the specific ones so
28:05um like i mentioned earlier you have
28:08the um external
28:12acoustic meatus
28:16okay which is where again your ear goes
28:18into your skull your ear canal goes
28:20through your skull
28:21um to your brain so a meatus is just a
28:24canal
28:25like passageway okay so if you know
28:28these
28:28general terms now it's going to help a
28:30lot when you have to memorize the
28:32specific ones later on
28:36okay so that's the gross anatomy now
28:38we're going to move on and talk about
28:40the microscopic anatomy so
28:44compact bone we'll start there also
28:47known as
28:47lamellar bone consists of a few
28:51different microscopic structures that
28:53you need to know
28:54um so we'll go into detail like we
28:56always do on all these but you have the
28:57osteon
28:58you have a few different canals and
29:00caniculi
29:02and interstitial and circumferential
29:05lamellae okay so let's start with the
29:08osteon
29:09so the osteon is the structural unit of
29:11compact bone
29:14and it is an elongated cylinder
29:17that runs parallel to the long axis of a
29:20bone
29:20okay so this whole thing over here
29:23is kind of showing you what an osteon
29:25looks like
29:27okay so it's a kind of rings of bone
29:31on top of each other and they run um
29:34parallel with the bone so if this is
29:36like your femur
29:38right your other femur you'd have a
29:40bunch of these running along the length
29:42of the femur
29:43if that makes sense with the bone long
29:45ways
29:47okay the cylinder itself consists of
29:50several
29:50rings of the bone matrix that are called
29:53lamellae
29:54so you can see here the lamellae so each
29:57one of these rings that goes around
29:59the osteon is a lamellae
30:02okay the lamellae have collagen fibers
30:06that are going to be running in
30:07different directions to provide
30:09different types of strength so you can
30:11see the collagen fibers
30:13going all different ways to make sure
30:15that
30:16your bones are strong and resistance to
30:19any kind of stress no matter what the
30:21direction it is
30:23so i just said that with stand stress
30:25and resist
30:26twisting um and you're going to find
30:29that between these collagen fibers
30:31you're going to have what we call bone
30:33salts
30:34which we'll talk about that a little bit
30:35more but those make up the matrix of the
30:37bone
30:38okay so that's an osteon kind of the
30:42structural unit of compact bone
30:45again you're only going to find this in
30:48compact bone okay
30:50spongy bone is made up of the sponges so
30:53you're not going to have this compact
30:54dense structure okay so if you take a
30:58bone and do like a little cross section
30:59here
31:00this is your femur looks like
31:04um so if you're looking again just at
31:06the compact bone
31:08so you can see you have spongy bone um
31:11more deep but on the outside is compact
31:14bone
31:15and you have these osteons okay so each
31:18one of these like little bullseye things
31:21is an
31:21osteon and it's gonna run down the
31:25length of this entire bone
31:27okay within the osteon like i said in
31:30the previous side you have the lamellae
31:33which are going to be the
31:34circumferential like rings
31:37so if we look i'm going to zoom in on
31:39this osteon here
31:40so each of like the bull's eyes of the
31:44osteon are the lamellae
31:47okay so those are all lamellae
31:52okay kind of cool in the middle of the
31:54ocean you're also going to have what's
31:55called the
31:56central canal so you can see that kind
31:59of hole right in the middle here
32:01um central canal and it's going to hold
32:04all the veins nerves arteries and all
32:07the different
32:08things that you know are running through
32:10the bone
32:13okay oops
32:17oops sorry um so
32:20like i said central or virginian canal
32:24runs through the core of the osteon
32:26contains blood vessels nerve fibers
32:29we have another structure called
32:31perforating or volksman's canals
32:34that line with the endosteum that occur
32:38at right angles to the central canal
32:40so i'll show you those in a second but
32:42basically they're just
32:43connecting all the central canals
32:45medullary cavity
32:46and the periosteum together so they're
32:49kind of
32:50connecting everything
32:54we also have structures called lacunae
32:57which we talked about when we talked
32:58about the um
33:00uh cartilage so lacunae translates to a
33:04little lake
33:06so they're gonna be little holes or
33:07lakes within that dense
33:09bone tissue that's going to contain
33:12osteocytes and osteocytes are
33:14bone cells and i'm going to write
33:18mature bone cells
33:22okay we also have structures called
33:25caniculi
33:26which are going to be little tiny canals
33:28that connect lacunae to each other
33:31and to the central canal right because
33:33all of
33:34our blood and nerves all that stuff is
33:36running through the central canal
33:38and the bone matrix is really hard so
33:41in order for the nutrients and stuff to
33:43get from the blood to
33:44the osteocytes the actual bone cells
33:48that need those nutrients
33:50we have to have these little caniculi to
33:51connect everything
33:54okay and i'll show you all of these in a
33:56second um
33:58and then we also have interstitial
33:59lamellae and circumferential lamellae
34:02so if you remember lamellae are the
34:04rings of the bullseye that make up the
34:06osteon
34:08okay so we have rings of bullseyes that
34:10make up the osteons
34:12so like that let's say right those are
34:15four osteons
34:18when we make those rings you can see
34:22in this middle area they there's nothing
34:25there we can't make another osteon
34:27that fills that space because there's
34:28always going to be spaces in between
34:31so we have what are called interstitial
34:33lamellae that are little
34:35rings in between the other
34:39um actual osteons so the interstitial
34:42aren't actually part of the osteon
34:43they're just filling in gaps
34:46okay then we also have circumferential
34:49lamellae
34:50that are just deep to the periosteum
34:52which means they're around the whole
34:54outside of the bone
34:58okay and i'll show you those right here
35:02so first let's start talking about show
35:04you these lamellae
35:06so again we have the
35:09um lamellae of
35:13the osteons themselves right
35:16this spot in the middle
35:19it's hard to see and those would be
35:23these interstitial lamellae that we
35:25talked about
35:27okay so between the spaces of all the
35:29osteons
35:31the circumferential lamellae are
35:34lamellae that are going to run
35:35all the way around the outside of the
35:38bone
35:39so all these are circumferential
35:41lamellae
35:43okay what else do we talk about we
35:44talked about our
35:46central canal running through the
35:48osteons
35:50right we also have perforating canals
35:54so this guy here would be a perforated
35:55canal this guy here would be a
35:57performing canal
35:58that runs perpendicularly to connect the
36:01central canals together
36:03and connect it to the medullary cavity
36:05in the middle
36:08and we talked about if we zoom in
36:14so again remember the lamellae are those
36:16hard
36:17bone matrix rings we have
36:20little gaps within those called lacunae
36:24so these little gaps in the lamellae are
36:27lacunae
36:28which remember are the little lakes
36:32and inside of the lakes you have your
36:35osteocytes so these the red little dots
36:38are the actual individual bone cells
36:40okay so it's a connective tissue so the
36:42majority of bone
36:44is that matrix right made of different
36:46fibers and
36:48minerals and all that stuff but you have
36:50actual osteocytes the bone cells
36:53within the lacunae um
36:56and then the caniculi
37:00are the little rivers i like to think of
37:01them these little canals are going to
37:04connect the lacunae together
37:06and connect to the um lacunae to the
37:09central canal as well
37:11okay so the kanikili i think of the
37:13little rivers leaving the lakes
37:17and i think that was everything was that
37:21yeah
37:23okay so that is the microscopic anatomy
37:27of compact bone
37:29right this is all just for compact
37:33spongy bone is a different story so
37:35spongy bone obviously we already kind of
37:37talked about this but we don't have
37:39those osteons like we do
37:41in compact bone because it's spongy and
37:43we have the trabeculae instead
37:46um it appears like it's just poorly
37:50organized
37:51but actually it's organized along the
37:53lines of stress to help
37:54bones resist um stress and breakage so
37:58the way that this like sponge is laid
38:00out
38:00actually is meaningful
38:04um all these little trabeculae add extra
38:07strength to the bone
38:10there are no osteons but the trabeculae
38:14do technically contain lamellae um
38:18just not in those nice pretty patterns
38:20in the concentric rings
38:23there are osteocytes that have
38:26there's caniculi all of that stuff in
38:28there um but you normally won't see
38:30diagrams of that
38:33okay and since we don't have central
38:36canals
38:37instead we have capillaries running
38:39through the endosteum
38:40which if you remember is the inner
38:42membrane
38:44lining the spongy the compact bone and
38:47also it's lining the trabeculae so
38:49all of the outside of this trabeculae be
38:51covered in an ostium
38:53as well
38:58okay so that's some microscopic anatomy
39:01um let's spend some time talking more
39:03about the types of
39:05um bone cells
39:08okay so there's five major cell types
39:11each have
39:12a specialized function and all come from
39:15the same
39:16basic cell types okay so there's going
39:18to be a slide for each of these but
39:19these are the five
39:21so osteogenic cells osteoblasts
39:26osteocytes which we've already talked
39:28about are those mature cells
39:31we have bone lining cells and then
39:34osteoclasts
39:36okay so osteogenic cells we also
39:39already talked about are the stem cells
39:43that are going to be making new bone
39:46tissue
39:46so they're called osteoprogenator cells
39:52they are mitotically active stem cells
39:55that are found in the membranes around
39:58the bone so the periosteum and the
39:59endosteum
40:02okay they are going to be able to
40:04differentiate
40:06into osteoblasts or the bone lining
40:08cells which we'll talk about
40:10in a minute some of them obviously are
40:12going to stay
40:13as an osteogenic stem cell so they can
40:15continue to form
40:17new bone cells when they need to
40:22okay osteoblasts
40:26are considered bone forming cells
40:29so osteogenic cells make bone cells
40:33these make bone cells i don't know why
40:36i'm writing in all caps
40:38osteoblacks blasts makes the bone
40:42matrix let's call it
40:46um which is known as the osteoid
40:49okay so osteoblasts are secreting the
40:52osteoid
40:54so the osteoid is made up of those
40:56collagen fibers
40:57right which we talked about in the
40:58lamellae are running in
41:00all different directions and then also
41:03different calcium binding proteins
41:08collagen makes up about 90 of the bones
41:10proteins though
41:12okay osteoblasts are also actively
41:14mitotic so they can divide and create
41:16new cells as well
41:20okay so we have osteogenic and
41:22osteoblasts
41:25our osteocytes are the cells
41:28i'm gonna say in lacunae
41:32right which are within the lamellae
41:36osteocytes of the mature bone cells oh
41:38it says it right there i didn't have to
41:40write it
41:41um that are no longer dividing right so
41:43they're mature not dividing
41:46they help to maintain the bone matrix
41:48and act as
41:49stress or strain sensors so if
41:52there's some sort of mechanical stress
41:54or stimuli
41:55um it will communicate that
41:58information to other cells to
42:02initiate bone remodeling
42:05okay so osteoblasts and osteoclasts are
42:08going to be
42:09responsible for bone modeling so we
42:11already talked about osteoblasts how
42:13they secrete
42:14bone matrix so i like to think of those
42:17osteoblasts
42:18build because they're secreting all of
42:21those proteins needed for the bones
42:24osteoclasts actually destroy bone so i
42:27like to think osteoclasts
42:29two blasts build clasts chew
42:33they chew up the bone and get rid of it
42:35okay so there's too much stress or force
42:37on the bone
42:38or there's some sort of damage to the
42:40bone osteocytes will
42:42sense that and send the information to
42:45osteoblasts and class
42:47to do some remodeling
42:52okay bone lining cells are
42:55ones that you're not going to hear about
42:57very often but they're flat cells
42:59that are on the bone surfaces believe to
43:02help maintain the matrix
43:06on the external bone surface are called
43:08periosteal cells
43:10by the periosteum internal surface and
43:12osteocells
43:14so they're just there also helping a
43:17little bit
43:18not super exciting and then finally
43:22osteoclasts which i just said class
43:24think two um
43:28they are derived from the same stem
43:30cells that become macrophages
43:33um i don't know if i said it in previous
43:35chapters when we talked about
43:36macrophages but macrophages
43:39macro is big phage means eater
43:43so macrophage is a big eater that's me
43:47i'm a macrophage so they're going to be
43:50responsible for chewing up and eating
43:53cells that are no longer needed or uh
43:55the tissue
43:57bone tissue that's no longer needed so
43:59they're giant multinucleated cells
44:01they function in bone reabsorption it's
44:04called
44:05which is just the breakdown of bone
44:09when they're active they're in these
44:10little depressions you can find in the
44:12bone
44:12called reabsorption bays
44:16they have ruffled borders that serve to
44:18increase surface area
44:20to help degrade the bone faster with
44:23enzymes
44:25and it also helps seal off the area from
44:27surrounding matrix so they can actually
44:29eat like a specific part of the bone and
44:31aren't just eaten the whole thing
44:37okay
44:40so osteoblasts are the matrix
44:43synthesizing cell
44:44responsible for bone growth remember
44:46blast
44:48build osteocytes are the mature bone
44:52cells
44:53okay they monitor the matrix
44:57osteoclasts think two
45:00they're gonna be the bone reabsorbing
45:02cell
45:03that's responsible for breaking down the
45:07bone
45:09okay and then on a very cellular level
45:13bone is made up of organic and inorganic
45:16compounds
45:16so this isn't super duper important but
45:19just
45:20to understand how bone gets its strength
45:23so organic compounds include the
45:26osteogenic cells osteoblasts osteocytes
45:28bone lining cells osteoclasts
45:31so all of the cells
45:34and also the osteoid okay so the osteoid
45:37again is that matrix
45:42that is secreted by osteoblasts
45:45so it's made up of ground substance and
45:47collagen fibers
45:49which contributes to the high tensile
45:52strength and flexibility of the bone
45:56okay there's actually things called
45:58sacrificial bonds this is just cool
46:00in bones between different collagen
46:03molecules that can stretch
46:04and are made to break to dissipate
46:07energy and prevent fractures
46:09okay so if you go through your land on
46:11your legs really hard or something jump
46:13off
46:14a building your bones don't break
46:17but i guarantee there's sacrificial
46:19bonds
46:20between the collagen molecules
46:24that will break to dissipate the energy
46:26to help protect
46:27the structural integrity of the bone
46:29okay and those
46:30little breaks um repair a lot more
46:33easily
46:34than bigger ones would
46:37like actual fractures
46:41okay and then inorganic compounds
46:45um mostly hydroacceptates
46:50which we're just gonna call mineral
46:51salts i butchered that
46:54um they make up about 65 of the bone by
46:57mass
46:57so a lot of your bone is just these
46:59inorganic um
47:01salts so different minerals calcium
47:04phosphate crystals
47:06um mostly that are found all around the
47:09collagen fibers
47:11um that are responsible for the hardness
47:13and resistance to compression
47:15okay so the bones hardness is from
47:19um the inorganic compounds these mineral
47:22salts
47:23the organic compounds remember with the
47:25collagen fibers and all that
47:27that is allowing more like flexibility
47:31in the bone which you don't think of
47:32bones flexible but
47:34it allows more tensile strength
47:37inorganic components
47:38make it harder and resistance to
47:40compression
47:43okay this is cool
47:46bones half as strong as steel and
47:49resistant compression
47:50and as strong is in resisting tension
47:54you don't need to know that and bones
47:57last long after death because
47:59of this mineral composition
48:03okay so i'm going to stop here for part
48:05one of
48:06chapter six um we'll talk about bone
48:10development and remodeling in part two