Full transcript
0:00hey everyone's dr. mark on this is
0:01chapter six on bones and skeletal
0:04tissues so before we get into bones we
0:09want to talk about cartilage and we
0:10covered cartilage in the first unit of
0:13lab we know that cartilage is found
0:18throughout the adult body we can see
0:20cartilage in the external ear and we
0:22know the different types of cartilage
0:24so the carlesha found in the external
0:26ear is elastic cartilage we know there's
0:29cartilage of the nose the articular
0:32cartilages and the costal cartilage as
0:34well as the cartilages in the larynx and
0:37the trachea and we saw cartilage in the
0:40intervertebral discs the pubic symphysis
0:42and articular discs so this figure shows
0:50you the types of cartilage that we have
0:53covered and where they are located in
0:55the body we have three types of
0:57cartilages we have Highland cartilage
1:00elastic cartilage and fibrocartilage and
1:03what's nice about this picture is that
1:05it's color-coded so you can see where
1:08the different types of cartilage are
1:10found throughout the body and we covered
1:12in lab we have elastic cartilage in the
1:16external ear the pinna I can't really
1:18see the epiglottis but then we have and
1:21blue the hyaline cartilages that we see
1:23in the nose the costal cartilages the
1:27small bronchi in the lungs as well as
1:30the trachea and the larynx and then we
1:33have my fibrocartilage --is found in the
1:35intervertebral discs as well as the
1:39articular cartilages and the joints
1:42specifically in the knees and the Menace
1:45kisses I'm in the sky so just some
1:51general characteristics of cartilage we
1:54have this structure called the
1:56perichondrium the perichondrium
1:58surrounds cartilages it helps resist
2:01outward pressure and helps function in
2:03growth and repair of cartilage it
2:05consists primarily of water and is a
2:08very resilient tissue it actually has
2:11this characteristics where it springs
2:12back
2:13it's original shape now all cartilages
2:18share some similar properties we know
2:22that the mature cell type is called the
2:24chondrocyte so anything with this root
2:29word Kandra is talking about cartilage
2:31so chondrocyte is a cartilage cell in
2:36this case it is the mature cartilage
2:38cell and we know the chondrocytes are
2:40located in spaces called lacunae so
2:43they're located within lacunae we know
2:46that because it's a type of connective
2:48tissue it has an extracellular matrix
2:51and we know the matrix contains fibers
2:54as well as the jelly-like ground
2:57substance and we know that the
2:59chondroblasts is the cell that helps
3:02produce the different types of fibers as
3:05well as the ground substance of the
3:08extracellular matrix the first type of
3:12hyaline cartilage that we've covered is
3:14Highland cartilage hyaline cartilage is
3:16the most abundant cartilage here we see
3:20that the chondrocytes do appear
3:22spherical collagen fibers so the
3:26collagen unit sidewall is the only type
3:27of fiber that is found in the matrix of
3:30Highland cartilage and we know that the
3:32ground substance actually holds a large
3:34amount of water which provides support
3:36through flexibility the second type of
3:40cartilage we have is elastic cartilage
3:42that contains many elastic fibers it is
3:45because of these fibers that is able to
3:48tolerate repeated bending and we can see
3:50elastic cartilage again in the
3:52epiglottis as well as the external ear
3:56in the peanut of the ear the third type
3:58of cartilage that we covered was
4:00fibrocartilage fibrocartilage actually
4:02resists strong compression and strong
4:05tension it's an intermediate between
4:07Highland and elastic cartilage and we
4:10can see fibrocartilage in the pubic
4:12symphysis again that cars that connects
4:15the two hip bones the ox coxae
4:19anteriorly you can also find fibro
4:22college in the meniscus
4:23as well as the annulus fibrosus in the
4:27intervertebral discs and in lap we saw
4:35histo preparations of the different
4:37types of cartilage we saw hyaline
4:40cartilage which had a ground-glass
4:43appearance you can see the chondrocytes
4:44in there lacunae we saw elastic
4:49cartilage with those lovely elastic
4:51fibers between the chondrocytes in there
4:54leepu day was very darkly stained and
4:57then we saw fibrocartilage
4:59fibrocartilage the chondrocytes are kind
5:01of in rows and you can see these lovely
5:04collagen fibers within the matrix so how
5:11does cartilage grow there are different
5:15types of growth within cartilage you
5:16have a positional growth this is when
5:19you have the chondroblasts
5:22in the surrounding perichondrium that
5:24will actually produce new cartilage and
5:27then you have interstitial growth the
5:31chondrocytes within the cartilage will
5:33divide and secrete new matrix now Carter
5:36stops growing when the adult skeleton
5:39stops growing so moving on to bones
5:49bones actually contains several types of
5:52tissues they are dominated by of course
5:55bone connective tissue also they contain
5:58nervous tissue as well as blood
6:01connective tissue
6:02they contain cartilage in the articular
6:05cartilages where the bones articulate
6:08with one another they also contain
6:10epithelial tissue that lines the blood
6:14vessels so there are different types of
6:16tissues that make up bone of course we
6:22have functions of bones functions abodes
6:26include supports bones provide a hard
6:29framework for the body movement skeletal
6:32muscles will use the bones as levers
6:35protection
6:37provide protection of underlying organs
6:39they are also also a site for mineral
6:41storage they are reservoir for important
6:45minerals also within bones we have blood
6:48cell formation hematopoiesis black bone
6:51contains red bone marrow where we have
6:55formation of new blood cells also bones
6:59participate in energy metabolism we have
7:02the osteoblasts that secrete osteocalcin
7:07osteocalcin is a hormone that stimulates
7:10pancreatic secretions that reduce blood
7:13sugar levels or through insulin
7:17osteocalcin also influences fat cells
7:20causing them to store last fat and to
7:22secrete a hormone that increases the
7:25insulin sensitivity of cells so these
7:28results will have clinical implications
7:31for the treatment of metabolic disorders
7:33that are related to blood sugar
7:35regulation such as type 2 diabetes so
7:42talking about bone tissue bone tissue
7:45has both organic and inorganic
7:47components the organic components of
7:49bone tissue include cells fibers and
7:52ground substance the inorganic home
7:55components include mineral salts that do
7:58invade the bony matrix the extracellular
8:04matrix of bone has a unique composition
8:08it gives the bone exceptional properties
8:11we know that the extracellular matrix
8:13about 35% of it is made up of organic
8:16components that help contribute to the
8:19flexibility and tensile strength of bone
8:21mm-hmm 65% of the extracellular matrix
8:26is made up of inorganic components that
8:28help provide hardness exceptional
8:32hardness and help with resistance of
8:35compressive forces the there are cells
8:40that make up bone so there are three
8:42types of cells in bone that produce or
8:45maintain bone we have osteogenic cells
8:48osteogenic cells are based
8:50stem cells that will eventually
8:51differentiate into osteoblasts again we
8:56see the word blast think immature cell
8:58however osteoblasts will actively
9:01produce and secrete bone matrix and bone
9:05matrix is osteoid osteoid is just a
9:09fancy term that means bone like so the
9:13bone matrix that is secreted by the
9:15osteoblasts is osteoid or bone like the
9:19third type of cells are the mature cells
9:21these are the osteocytes these cells
9:24help keep the bone matrix healthy we
9:33also have osteoclasts osteoclasts are
9:36found within bone tissue osteoclasts are
9:38responsible for resorption of bone
9:40meaning the breakdown of bone we want
9:45bone to be broken down in times when we
9:48need certain certain molecules if we're
9:54for example low on calcium or phosphorus
9:57osteoclasts actually break down bone to
10:00give our body a supply of these these
10:04minerals these molecules osteoclasts are
10:07derived from a line of white blood cells
10:09they secrete hydrochloric acid as well
10:12as lysosomal enzymes to help break down
10:14bone now osteoblasts build up bone
10:19whereas osteo class break down bone and
10:22usually these two kind of even each
10:25other out because you don't want one
10:28more than the other so if osteoclasts
10:31are breaking down bone we have
10:32osteoblasts that help build up bone so
10:41we can classify bones
10:42according to shape we have long bones
10:46long bones are longer than they are wide
10:49these bones have a shaft plus ends to
10:53the shaft there are short bones these
10:55are roughly cube shaped we have flat
10:58bones that are thin and flattened and
11:00usually curved and we have irregular
11:02bones base
11:03those that fall into the other that
11:06don't fit into the other categories so
11:08irregular bones are of various shapes
11:10and do not fit into these other
11:13categories here we just see examples of
11:17the different classifications of bones
11:19so for example a long bone that has a
11:21shaft plus the two ends example this is
11:24the humerus a short bone an example this
11:29is one of the bones in the foot or ankle
11:32this is the talus and then we have flat
11:37bones example this is the sternum in the
11:40thoracic cage and then we have irregular
11:43bones that are irregularly shaped
11:47example this are the vertebrae within
11:50the spinal column so we want to go over
11:56the gross anatomy bones bones are made
12:01up of compact bone compact bone is a
12:04dense outer layer of bone and then they
12:07are also made up of spongy or cancellous
12:10bone this is the internal network of
12:13bone we see structures culture Bakula
12:15Rebecca there are these little beams of
12:17bone if you actually kind of open up
12:19well you can see little beams with
12:22little spaces inside so open spaces
12:25between the trabeculae are filled with
12:27bone marrow and bone marrows importance
12:29and has some very important
12:31characteristics so a typical structure
12:36of a long bone it has these structures
12:40we has the diaphysis the diaphysis
12:43is the long shaft of a bone we have the
12:46epiphysis these are the ends of a bone
12:49with in a typical long bone of course we
12:52have blood vessels because bone is very
12:54well vascularized it does need a blood
12:56supply within the bone is the medullary
12:59cavity this is a hollow cavity filled
13:02with yellow marrow and then we have the
13:05membranes within a typical long bone we
13:09have the periosteum the periosteum is a
13:13connective tissue membrane that covers
13:15the entire outer surface of each
13:17except on the ends of the epiphysis
13:19where articular cartilage occurs we have
13:23perforating collagen fiber bundles
13:25called sharpey's fibres again these are
13:30thick bundles of collagen that will run
13:32from the periosteum into the bone matrix
13:34and we have the end ostium the end
13:38ostium is the internal bone surface our
13:43covering made up of a connective tissue
13:50so here we see the structure of a
13:53typical long bone again we have this
13:56long shaft which is the diathesis we
13:58have the two ends we have the proximal
14:01epiphysis and the distal epiphysis
14:04within the the bone we have a medullary
14:07cavity and then the outer connective
14:11tissue lining is the periosteum and then
14:14we have the internal and ostium that
14:16lines the medullary cavity and then
14:20within the medullary cavity there is
14:22yellow bone marrow and then we can see
14:25the two types bone we have a compact
14:28bone which is the outer covering and
14:31then we have the spongy bone within made
14:35up of these trabeculae or beams with
14:38spaces and within the spaces we have
14:41yellow marrow yellow bone marrow
14:48so um short irregular and flat bones
14:53also have a similar structure flat bones
14:57short bones and irregular bones contain
14:58bone marrow but don't have a marrow
15:01cavity like long bones do within these
15:04bones we have structures called deploy a
15:06deploy are the internal spongy bone of
15:09flat bones and here we see that spongy
15:14diplo way and then the outer compact
15:17bone again we have those structures that
15:19your Bakula that are like little beams
15:22and then spaces within the trabeculae so
15:30bone design and stress we note the
15:33anatomy of a bone will reflect the
15:36stresses that the bone comes in contact
15:39with
15:40we know that compression and tension are
15:43greatest at the external surfaces so
15:49here we see a figure of the bone anatomy
15:57and bending stress so we can see that
16:00body weight is transmitted through this
16:02is actually the femur but body weight is
16:05transmitted through the head of the
16:06femur which will threaten to bend the
16:08bone along this arc this dotted line
16:11right here so the strongest forces occur
16:14at the periphery of this long bone so we
16:17have two types of forces we have
16:20compression forces on this loaded side
16:24you can see that these forces compress
16:27the bone and then we have tension forces
16:29on the opposite surface so these forces
16:32are resisted by the outer compact bone
16:36and then we'll have actually a
16:39cancelling out so tension and
16:40compression will cancel each other out
16:42internally at the point of no stress as
16:46a much as a result much less bone
16:49material will be needed internally than
16:52superficially okay
16:56and this is just diagram of the stress
17:00the different types of stress
17:01trajectories through the proximal femur
17:03during loading and again these forces
17:06will cancel each other out of the point
17:09of no stress and compression lines are
17:12shown in red where as the tension lens
17:15are shown in blue and we can see these
17:18lines and we can see we compare this
17:21figure with the actual picture of the
17:24procs the inside of the proximal femur
17:28where the trabeculae kind of aligned
17:31with these forces these stress forces so
17:37much the last material is needed in this
17:42area of the bone because we know that's
17:46due to the structure of the bone the
17:49compression forces and the tension
17:51forces will cancel each other out so we
17:57talked a little bit about bone markings
17:59and the other day bone markings are just
18:02superficial surfaces of bones that will
18:04reflect the stresses on them there are
18:07three broad categories of goal and
18:09markings that you guys need to know bone
18:13markings provide projections for muscle
18:15attachments secondly and they are they
18:18provide surfaces that will form joints
18:20they can also be depressions and
18:23openings so this Table six point one is
18:29actually a really good table that you
18:31guys should study because it shows the
18:33three categories of bone markings and
18:36the different bone markings within those
18:37categories so make sure you know which
18:42bone markings are in which categories so
18:45the first category for bone markings are
18:49projections that are sites of muscle and
18:51ligament attachments so we have
18:53structures called tuberosities
18:55tuberosities are large rounded
18:58projections they may be roughened we
19:00have structures called crests so for
19:03example here the iliac crest right here
19:05the crest is a narrow ridge of bone that
19:08is usually prominent
19:09we have trochanter zandig Andrew
19:11Cantor's are very large blunt
19:14irregularly shaped processes that occur
19:17only on the femur so we have the greater
19:20trochanter and the lesser trochanter and
19:23then we have a line that kind of
19:24connects them so a line is a narrow
19:26Ridge of bone that is less prominent
19:28than a crest so for example the
19:31intertrochanteric line can see is
19:33definitely a lot smaller or less
19:35prominent than a crest and this line
19:37connects the greater trochanter would be
19:39less search or cancer but lines are
19:41found throughout others other bones in
19:44the body a tubercle is just a small
19:47rounded projection or process we have an
19:51epicondyle which is a raised area on or
19:54above a condyle
19:56when we talk about muscles will later
19:58talk about the medial epicondyle of the
20:01humerus and how all the flexor muscles
20:05within the forum can attach to the
20:07medial epicondyle of the humerus a spine
20:11is just a sharp slender often pointed
20:14projection and a process is just any
20:17bony prominence
20:21we have bone markings that have surfaces
20:25that form joints for example on the rib
20:27we have the head the head is a bony
20:31expansion carried on a narrow neck we
20:36also have facets facets are smooth
20:38nearly flat articular surfaces that
20:42articulate with other bones and then we
20:45have a contact a condyle is just a
20:46rounded articular projection which often
20:50articulates with a corresponding fossa
20:52of another bone and this again helps
20:56form and articulation with another bone
21:00then we have depressions and openings
21:02usually these openings or depressions
21:04are for passage of vessels and nerves so
21:08the first opening we'll talk about as a
21:10form and foramen is just a round or oval
21:13opening through a bone the plural for
21:15foramen is foramina we have grooves that
21:18are furrows where vessels can also
21:20travel along
21:22then we have fissures fissures are
21:24narrow slit like openings notches are
21:27indentations at the edge of the
21:30structure and then we have other bony
21:32markings that fall in this category we
21:34have fossa these are shallow base and
21:38like depressions in a bone that often
21:39serve as an articular surface or where
21:43you know muscles can can sit such as the
21:46subscapular fossa and then we have a me
21:50itis of me this is just a canal like
21:52passageway sinusitis is a cavity within
21:56a bone filled with air and lined with
21:59mucous membranes the sinuses that we'll
22:02be talking about are the paranasal
22:03sinuses within the skull so here we see
22:13a figure of the microscopic structure of
22:15compact bone this is a section from the
22:18diathesis of a long bone and we can see
22:22the different structures that make up
22:26the compact bones so under the mr.
22:32slides we saw the osteon which is this
22:37rounded structure within the bone tissue
22:41and then we saw those lines as well as
22:44the osteocytes in the lacunae we saw
22:47those thin spidery like lines called
22:52canaliculi which allow for communication
22:54between the osteocytes and we saw these
22:57concentric lines within the osteon
23:00called lamellae and then in the middle
23:02is the central canal where we have
23:04passage of nerves as well as blood
23:07vessels and we'll talk more about these
23:11structures so compact bone is the
23:17structure that makes up the outer part
23:19of the bone compact bone contains
23:21passageways for blood vessels lymph
23:23vessels and nerves within compact bone
23:26we have these rounded structures called
23:28osteons osteons are also called
23:30haversian systems osteons are long
23:33cylindrical structures that are or
23:35parallel to the long axis of the bone
23:38and to the main compression stresses
23:42functionally they are basically major
23:45weight-bearing pillars within compact
23:47bone osteons function and supports and
23:51structurally they resemble rings of a
23:53tree and cross-section we saw those
23:56concentric layers within the osteon so
24:03the osteon contains structures called
24:05lamellae each of the tubes within the
24:10osteon is a lamellae which is a layer of
24:13bone matrix in which collagen fibers and
24:15mineral crystals will align and run in a
24:18single direction and then each layer of
24:22lamellae alternates directions to kind
24:26of help with the twisting forces so
24:29osteons also contain a central canal
24:34central canal runs through the core of
24:36each osteon and also is called a
24:39haversian canal it's lined with
24:41endosteum and contains its own blood
24:43vessels and nerve fibers but going back
24:45to the lamellae the fibers and crystals
24:48of adjacent lamellae always run in
24:51opposite directions this alternating
24:53pattern is optimal for helping to
24:56withstand torsion or twisting forces and
24:59then we have a centralized central canal
25:01we also have perforating canals perfect
25:06these perforating canals are known as
25:08bulk mince canals these perforating fans
25:12will lie at right angles to the central
25:14canal and connect the blood and nerve
25:16supply of the periosteum to the central
25:21canals and marrow cavity then we have
25:26canaliculi which we talked about
25:28canaliculi are thin tubes also known as
25:32little canals that run through the
25:33matrix and connect neighboring lacunae
25:36to one another and to the nearest
25:38capillaries such as those in the central
25:40canal these canaliculi allow for
25:45communication between osteocytes and
25:47they form
25:48gap junctions between osteocytes so here
25:54we see the structures within the osteon
25:59or havisham system we have that central
26:02canal that allow for passageway of blood
26:05vessels and nerves then we have the
26:10outer lamellae again these lamellae are
26:15concent concentric structures that will
26:18run parallel so if the inner lamellae
26:20for example is going a clockwise
26:23direction the van lay on top of that
26:28will go in a counter clockwise position
26:33so the collagen fibers will run in
26:35different directions to help kind of
26:38help with the twisting forces that occur
26:41on the bone so these are the structures
26:44that make up compact bone spongy bone is
26:48less complex than compact bone we have
26:52those beam like structures cultured
26:53Bekele that will contain layers of
26:55lammle and osteocytes however they
26:58spongy bone and the tareq they are too
27:01small to contain osteons so you don't
27:04have those have ershon systems and be
27:05spongy bone in here again we see those
27:10beam like structures of the trabeculae
27:13and then the spaces within the
27:15trabeculae so we have a layer of and
27:17ostium again they contain osteoblasts
27:22that are important for forming new bone
27:25and forming matrix and then we have the
27:29mature osteocytes
27:30within the solid portions of the
27:33trabeculae so how does bone develop we
27:39have the process of ossification also
27:44known as osteogenesis which is bone
27:46tissue formation membrane bones are
27:51formed directly from Mezen kind and they
27:55ossify through what's known as interim
27:57membranous ossification
28:01so membranous bones form directly from
28:03Mezen kind without first being modeled
28:06in cartilage all bones to the skull
28:08except for a few at the base of the
28:10skull are of this category the clavicles
28:16are the only bones formed by
28:18intramembranous ossification that are
28:20not in the skull other bones will
28:24develop from a cartilage model so
28:27developed initially from Highland
28:29cartilage and this is known as
28:30endochondral ossification so all bones
28:35from the base of the skull down except
28:38for the clavicles are endochondral bones
28:40meaning they are first modelled in
28:42Highland cartilage which is then
28:44gradually replaced by bone tissue so
28:50again this is known as endochondral
28:53ossification so here we see
28:59intramembranous ossification again these
29:02are the bones of the skull except for
29:04the bones the base let's call and the
29:05clavicles so this occurs in the
29:10developing fetus we first have
29:13ossification centers that will appear in
29:15the fibrous connective tissue membrane
29:19so we'll have selected centrally located
29:22mesenchymal cells that will eventually
29:24cluster and differentiate into
29:26osteoblasts and form an ossification
29:29Center okay so we have our osteoblasts
29:32kind of coming together forming this
29:35ossification center so we know that
29:39osteoblasts secrete bone matrix which is
29:42osteoid so secreted within the fibrous
29:44membrane which will eventually calcify
29:48so osteoblasts begins to secrete osteoid
29:51which is then calcified within a few
29:54days trapped osteoblasts eventually will
29:57mature to become osteocytes so here we
30:01see newly calcified bone matrix so
30:06calcification basically is just the
30:10hardening of the matrix to come
30:14bone then woven bone and periosteum will
30:20form accumulating osteoid being secreted
30:23by the osteoblasts laid down between
30:26embryonic blood vessels in a random
30:28manner which will results of a network
30:32of trabeculae instead of lammle and this
30:35is called woven bone vascularized
30:38mesenchyme will condense on the external
30:40face of the woven bone and we become
30:43that outer periosteum again periosteum
30:47being that outer connective tissue
30:50membrane that will cover the entire
30:52outer surface except for any bends that
30:57might articulate so lamellar bone will
31:03then replace woven bone just deep to the
31:06periosteum and we have a red marrow that
31:08appears trabeculae just deep to the
31:10periosteum will thicken and will later
31:13be replaced with mature lamellar bone
31:15forming compact bone plates spongy bone
31:19also known as deploy will consist of
31:22distinct trabeculae which will persist
31:24internally and then it's vascular tissue
31:27becomes red marrow so then we also have
31:34endochondral ossification this includes
31:37all bones basically from the base of the
31:41skull except for the actual Bulge of the
31:46skull and the clavicles basically these
31:48bones are modeled in highland cartilage
31:51so are formed from highland cartilage
31:53this begins forming late in the second
31:56month of embryonic development and will
31:59continue forming until early adulthood a
32:03year we see the steps of the
32:06endochondral ossification of a long bone
32:09so first we have the formation of a bone
32:12collar so the bone collar will form
32:14around the diaphysis of the hyaline
32:17cartilage model then we have the
32:22cartilage in the center of the diaphysis
32:24will calcify and then develop cavities
32:29here we see areas of deteriorating
32:30cartilage matrix then we have the
32:34periosteal bud which will invade the
32:36internal cavities and formation of
32:40spongy bone beginning to form then this
32:45occurs about the third month of fetal
32:48life and then at Birth the diaphysis
32:50will elongate elongation of the shaft
32:54and a medullary cavity will form as
32:57ossification continues will then have
33:00secondary ossification centers that will
33:02appear in the epiphysis of the the
33:05different ends of the the long bone and
33:08then the epiphysis will ossify when
33:13completed hyaline cartilage remains only
33:15in the epiphyseal plates here as well as
33:18the articular cartilages so we want to
33:25talk about the anatomy of the epiphysial
33:28growth areas and epiphysial plates of
33:31growing bones cartilage is organized for
33:33quick efficient growth CARTER cells will
33:36form tall stacks the chondroblasts at
33:39the top of these stacks will divide very
33:41quickly the epiphysial plates will push
33:46the epiphysis away from the diathesis
33:49and then we have lengthening of the
33:52entire long bone older chondrocytes will
33:58signal surrounding matrix to calcify and
34:02then or older chondrocytes will die and
34:05disintegrates which will leave long
34:07trabeculae or beams or spicules of
34:10calcified cartilage on the diaphysis
34:12side trabeculae are partly eroded by
34:15osteo class again these cells that help
34:18break down bone they have the
34:20hydrochloric acid and the enzymes that
34:22help with breaking down a bone
34:26osteoblasts will then then cover
34:29trabeculae with bone tissue so they help
34:32with putting down bone or forming bone
34:36tissue trabeculae will then filing be
34:39eaten away from the tips by osteo class
34:41you have this kind of breaking down and
34:43building up a bone by the two different
34:45cells so osteoclasts kind of break down
34:50bone whereas osteoblasts versus Abby and
34:53osteoblasts build up bone so here we see
34:59an organization of these cells and
35:02cartilage cells within the epiphysial
35:04plate of growing long bone so we have
35:08the resting zone within the epiphysial
35:13plate and then we have the Pearl
35:14iteration zone this is where we have
35:16cartilage cells undergoing mitosis or
35:18cell division we have the hypertrophic
35:21zone this is where we have enlargement
35:24of the older cartilage cells then we
35:28have the calcification zone this is
35:31where a matrix becomes calcified
35:32cartilage cells will die and the matrix
35:36begins deteriorating and here we see the
35:39ossification zone ossificans the
35:42ossification zone is where we have a new
35:45bone formation
35:51so after birth we have Co sale growth of
35:56endochondral bones so during childhood
35:59and adolescence bones will lengthen
36:00entirely by growth of the epiphyseal
36:03plates cartilage is replaced with bone
36:06connective tissue as quickly as it grows
36:08and the epiphysial plate will maintain a
36:11constant thickness and the whole bone
36:13will lengthen as adolescence draws to an
36:20end
36:20Kadri bust will divide less often the
36:24epiphyseal plates become thinner cards
36:27which means the cars will stop growing
36:29and is replaced by bone tissue so long
36:32bones will stop lengthening when the
36:34diaphysis
36:35and the epiphysis fuse
36:41growing bones will widen as they
36:44lengthen again we have these cells the
36:45osteoblasts will add bone tissue to the
36:48external surface of the diaphysis
36:50whereas the osteoclasts will remove bone
36:54from the internal surface of the
36:56diathesis and now we have what's known
36:59as a positional growth acquisition
37:02growth is the growth of a bone by
37:03addition of bone tissue to its surface
37:11bone growth is regulated through
37:13hormones and you have different hormones
37:15that are included so we have the growth
37:18hormone which is produced by the
37:20pituitary gland specifically the
37:22anterior pituitary gland growth hormone
37:24will stimulate bone growth by
37:27stimulating the epiphysial plates we
37:29have thyroid hormone secreted by the
37:31thyroid gland that ensures that the
37:33smells and retains proper proportions
37:35and then we have sex hormones such as
37:37estrogen and testosterone that promote
37:40bone growth and later on it will induce
37:43closure of these epiphysial plates so we
37:50know that bone is a dynamic living
37:53tissue and participates in what's known
37:57as bone remodeling 500 milligrams of
38:00calcium may enter leave the adult
38:01skeleton each day so guys make sure you
38:05are getting enough calcium either in
38:07your diet or through supplements bone
38:10matrix and osteocytes
38:12are continually removed and replaced
38:16cancellous bone of the skeleton is
38:18replaced every three to four years and
38:20compact bone is replaced every 10 years
38:25bone deposit and removal occurs at the
38:28periosteum and endosteal surfaces so the
38:31outer and inner surfaces of the bone
38:33bone remodeling is done through bone
38:36deposition which again is done by
38:39osteoblasts are accomplished by
38:41osteoblasts and then bone reabsorption
38:44breaking down a bone which is performed
38:47by the osteo class
38:53so within the spongy bone for example we
38:59can see remodeling occurring so we know
39:02that the trabeculae of the spongy bone
39:04is covered with that inner membrane
39:06called the end ostium and if we kind of
39:11zoom in we can see resorption of the
39:14bone matrix by osteoclasts that are
39:19along that and ostium and then we have
39:24deposition of new bone by osteoblasts
39:29okay so we have osteoclasts and
39:31osteoblasts within the bone that either
39:35will reabsorb bone by breaking it down
39:37or the osteoblasts will deposit new bone
39:41all occurring along the end ostium so
39:48just talking about the different cells
39:49that participate in bone remodeling we
39:52have the osteoclasts which are our bone
39:54degrading cell it's a giant cell with
39:56many nuclei curls along bone surfaces
40:00will break down bone tissue through
40:03secretion of concentrated hydrochloric
40:05acid also there are lies of zonal
40:07enzymes that help break down bone that
40:10are released from the osteoclasts and we
40:15know that osteoclasts are derived from
40:19matter poetic stem cells and then
40:23finally these osteoclasts apparently
40:25take up collagen and dead osteocytes
40:28through phagocytosis so here we see an
40:35osteo class this is the ruffled border
40:41of the osteoclasts which will break down
40:45the bone and the bone matrix through
40:50release of hydrochloric acid as well as
40:54lysosomal enzymes so here is that
40:59osteoclast
41:04so how does bone repair itself we have
41:09different types of fractures that it can
41:11occur in bone we have simple and
41:14compound fractures now a simple fracture
41:18is a fracture in which the bone breaks
41:20cleanly but does not penetrate the skin
41:22whereas a compound fracture is when
41:25broken ends of the bone will protrude
41:28through the skin and we have other types
41:30of other common types of fractures that
41:32include comminuted fractures compression
41:35fractures spiral epiphysial depressed
41:38and greenstick fractures and you can see
41:41this in table 6.2 and we did which we
41:47treat bone fractures through reduction
41:50which is the realignment of the broken
41:53bone ends in close reduction the bone
41:56ends are kind of manipulated back into
41:59position by the physician physicians
42:02hands in open reduction the bone ends
42:05will be joined surgically with pins or
42:08wires so after the bone is immobilized
42:12I'm sorry after the broken bone is
42:15reduced it is immobilized by cast or
42:17attraction to help allow for the healing
42:20process to begin and healing takes
42:22usually about six to eight weeks for a
42:24simple fracture but it may be longer for
42:27large weight-bearing bones and for bones
42:30of older people so here we see the
42:36different stages in the healing of a
42:39bone fracture first we have hematoma
42:43formation so fracture is usually
42:47accompanied by hemorrhaging we have
42:48broken blood vessels that break in the
42:51periosteum and inside the bone that will
42:53release clots to form what's known as a
42:57hematoma and we can see the stages of
43:00inflammation in and around the clot so
43:03here is that hematoma that was formed
43:06then we have a fibrocartilaginous callus
43:09formation so within a few days new blood
43:11vessels will grow into the clots
43:14um the periosteum in the end ostium near
43:17the fracture sites show a proliferation
43:19of bone forming cells which will then
43:22invade the clot and fill it with a
43:24repair tissue called soft callus so then
43:33we have the soft callus being called the
43:38fibrocartilaginous callus then we'll
43:40have a bony callus that forms so within
43:43a week that you're back laid up new one
43:44bone will begin to form and the callus
43:46mostly through endochondral ossification
43:50the callus is now called a bony callous
43:53or hard callus and that trabeculae will
43:56grow thicker and stronger and become
43:57firm in about two months after the
43:59injury then we have finally bone
44:01remodeling that occurs so if over a
44:04period of many months the bony callus is
44:06remodeled excess bony material is
44:09removed from both the outer bone shaft
44:13and the interior of the medullary cavity
44:15compact bone is laid down to reconstruct
44:18the walls of the shaft the repair area
44:22will resemble the original unbroken bone
44:25region because it responds to the same
44:27set of mechanical stresses so these are
44:34the stages of healing of a bone fracture
44:36and again table 6.2 shows the common
44:39types of fractures which you guys should
44:42be aware of we have a comminuted
44:45fracture where grown fragments into
44:48three or more pieces and are common in
44:51the old elderly whose bones are more
44:54brittle
44:54we have compression fractures where the
44:57bone is crushed these are common in
45:00porous bones or osteoporotic bones that
45:05are subjected to extreme trauma as an
45:07AFOL so here we can see compression
45:10fractures occurring within the vertebrae
45:14we have spiral fractures where a ragged
45:19break occurs when excessive twisting
45:20forces are applied to a bone and these
45:22are common in sports fractures we have
45:25epiphysial fractures where the
45:27epiphysial
45:28epiphysis will separate from the
45:30diaphysis along the epiphysial plates
45:32occurs where cartilage cells are dying
45:34and the calcification of the matrix is
45:36occurring we have depressed fractures
45:40where the broken bone portion is pressed
45:44inward this is a typical type of skull
45:47fracture usually due to trauma green
45:50strip fractures this is when the brain
45:53bone breaks skin completely much like
45:57how a green twig will break only one
45:59side of the shaft will break and the
46:00other side bends
46:01these are usually common in children
46:04because their bones have more organic
46:07matrix and are more flexible than those
46:09of adults so here we can see a break in
46:13one side of the bone but the other side
46:16has only bent as it's still relatively
46:19intact so then we have disorders of
46:24bones we have a disorder - many of you
46:29may know about called osteoporosis and
46:31osteoporosis is characterized by low
46:34bone mass what happens is bone
46:38reabsorption by the osteo class will
46:40occur more quickly than bone deposition
46:44by the osteoblasts and this often occurs
46:46in most women after menopause usually
46:49due to the decreased effects of estrogen
46:52after a certain age in women so here we
46:57can see the trabeculae abnormal bone
47:01strong trabeculae beams of spongy bone
47:05and then in osteoporotic bone so we can
47:08see these pores kind of infiltrating the
47:11trabeculae making the bones less firm
47:17and this is you due to a decrease in the
47:21amount of calcium as well as the effects
47:25a decrease effective estrogen on bone
47:29osteomalacia occurs in adults this is
47:32basically a vitamin D deficiency in
47:34adults
47:35bones are inadequately mineralized
47:38rickets is just the
47:42vitamin D deficiency in children so
47:44rickets occurs to children and is
47:48analogous to osteomalacia so basically
47:51it's just the vitamin D deficiency in
47:53children versus adults and here we can
47:57see the pathognomonic bowing of the legs
48:02of a child with rickets and this is
48:05again due to a vitamin D deficiency
48:08osteosarcoma this is a form of bone
48:12cancer osteosarcoma primarily affects
48:16young people between 10 and 25 years old
48:19usually originates in the long bone of
48:21the upper or lower limb with 50% of
48:25cases arising near the knee so basically
48:31the sarcoma is any cancer arising from a
48:35connective tissue cell or muscle cell
48:39and we know that osteo means bone so now
48:47we're going to talk about what occurs to
48:49the skeleton throughout life cartilage
48:52grows very quickly in youth the skeleton
48:55shows fewer chondrocytes in the elderly
48:58and basically we can use the bones as a
49:01time table we have me as a derm that
49:04gives rise to embryonic mesenchyme cells
49:07and the messing times will produce
49:08membranes and cartilage membranes and
49:12cartilage will ossify so here we see the
49:16primary ossification centers in the
49:19skeleton of a 12-year 12 week old fetus
49:23and we can see you know the different
49:26types of bones that will eventually
49:29become adult structures the cells
49:34skeleton grows until about 18 to 21
49:37years old in children and adolescents
49:39bone formation will exceed the rate of
49:42bone reabsorption and young adults full
49:45information and bone reabsorption are in
49:48balance with one another and then in old
49:50age reabsorption will predominate and we
49:54know that as we get
49:55older bone mass declines that's why now
50:00you guys take care of your bones make
50:01sure you are getting enough calcium and
50:04vitamin D eating good healthy diets as
50:08well as getting enough exercise to build
50:10strong healthy bones okay and that is
50:13the chapter on bones