Full transcript
0:02hello everyone and welcome to another
0:03recorded lecture
0:04of anatomy and physiology 1 online
0:08today we will discuss chapter 7 which is
0:10on bone tissue
0:14bone is one of the major components of
0:16the skeletal system
0:17and we'll be talking about the skeletal
0:18system in the upcoming two chapters
0:21in addition to bones we also have
0:23cartilage
0:24joints and ligaments as part of the
0:27skeletal system
0:29the skeletal system has many functions
0:31uh one of the major ones is
0:33support so our limb bones and our
0:36vertebrae
0:36can support our body our jaw bones can
0:40support our teeth so the skeletal system
0:42functions as a support
0:44system our skeletal system also protects
0:47our organs such as our brain our spinal
0:50cord hearts and
0:51lungs our skeletal system helps us move
0:55around
0:55so whether it's limb movements and
0:57walking or even breathing
0:59all these kinds of movements depend on
1:01the skeletal system
1:03the skeleton can also play a role in
1:05acid and base balance and electrolyte
1:07balance to maintain homeostasis
1:09so depending on how much calcium and
1:12phosphate
1:13is in the blood the skeletal system can
1:15either contribute more
1:17or can take away so again make sure
1:19there's the right concentration
1:21of these minerals in our body similarly
1:23bone tissue can buffer the blood against
1:25excessive ph changes
1:27so this is the skeleton also functions
1:30to maintain
1:31homeostasis and finally the skeletal
1:35system is very important in blood
1:37formation because the bone marrow the
1:39red bone marrow
1:40specifically is the chi producer of
1:42blood cells
1:43including cells of the immune system
1:47so bone is made up of osseous tissue
1:50and bones are not just these brittle dry
1:54cracked things that we see in in the
1:56laboratory they're actually alive
1:58so bones are living organs and they're
2:00mostly composed of connective tissue
2:04many different kinds of different types
2:07of tissues are
2:08found within bone so we not only have
2:10bone tissue
2:11but we have bone marrow we have
2:14cartilage
2:15adipose tissue nervous tissue and dense
2:18regular connective tissue
2:20so all these different types of tissues
2:22we discussed already
2:23are found in bone and like i said
2:26bone is alive so there has to be a
2:28living component
2:30and those living components are
2:32osteocytes
2:33so osteocytes are cells of the bone
2:36osteo always means bone and site always
2:39means cell so osteocyte is a bone
2:41cell they're embedded in the non-living
2:45extracellular matrix extracellular
2:48matrix is just what's outside of the
2:50cells
2:50so this matrix of bone is a composite
2:54of minerals and proteins composite
2:57meaning it's a combination
2:59so the matrix of bone is not just
3:02minerals
3:03not just proteins it's approximately 35
3:05percent
3:06organic protein and about 65
3:09in organic mineral and
3:13the organic component is collagen
3:15specifically so we know that collagen
3:17provides a lot of
3:18flexible strength which is really
3:20important the
3:22inorganic component is composed of
3:24calcium
3:25and minerals and calcium phosphate
3:29called hydroxyapatite provides the
3:31weight-bearing strength required for
3:33bone
3:35also calcium carbonate is found as part
3:38of the inorganic component
3:39and other minerals like fluorine sodium
3:42potassium and magnesium so
3:46so far we said bone tissue has
3:48connective tissues
3:50plus cells
3:53and there's importance to both the
3:56inorganic and the organic components of
3:58bone matrix so what do you think would
4:00happen
4:01if we didn't have any of those minerals
4:03any of those hard
4:05minerals the bone would be
4:08pretty flexible it wouldn't have a lot
4:10of the strength required
4:13for bone and you can actually do this
4:15you can take a chicken bone and put it
4:16in vinegar
4:17and it will seep out all the minerals
4:19and you'll see that
4:20with just collagen bone is very flexible
4:24uh not very strong without collagen
4:27however
4:28bone would be very brittle and it would
4:30crack
4:31um in response to even very tiny amounts
4:34of stress
4:34so it's important that we have both this
4:36hardening this mineral
4:39the the mineral component but also the
4:42collagen
4:42the flexible component so we need both
4:44of these working together
4:47we can classify bones according to their
4:50shape
4:51so starting with flat bones such as the
4:54sternum
4:55right these are thin curved plates and
4:58generally function to protect
5:00soft organs so flat bones also
5:03um are part of like the skull bones for
5:05example the skull bones are flat bones
5:08as well
5:08and they protect our brain we also have
5:11long bones which are bones of the limb
5:15um such as the humerus the radius the
5:17ulna
5:18um so these are longer than they are
5:20wide
5:21and these serve as levers acted upon by
5:23muscles to enable movement
5:26those are long bones we also have short
5:29bones
5:30like those found in the wrist with the
5:32carpal bones those are approximately
5:34equal in length and width
5:35and they glide across each other in
5:37multiple directions we'll talk more
5:39about short bones uh when we discuss
5:41joints finally we have irregular bones
5:44that are kind of elaborately shaped that
5:46don't fit into the other categories
5:48so those can include like um these
5:50vertebrae or the sesamoid bone as part
5:53of the patella kind of looks like a
5:56um a sesame seed that's why it's called
5:58the sesamoid bone
6:00so each vertebra is an irregular bone um
6:02a seismoid bone of the patella isn't a
6:04regularly shaped bone
6:08so bones come in two different types
6:11when we're talking about the tissue
6:13itself bone can be either compact
6:16or spongy compact bone is very dense and
6:19very strong
6:20it's also called cortical bone because
6:22it forms the outer
6:24cortical layer of bone material so
6:27compact bone is very very compact and
6:30very
6:30dense spongy bone also called
6:35cancellous bone is a lot different
6:38this is more of a lattice work um and
6:40these have
6:42what's called trabeculae these are these
6:44little spaces
6:46in between so this gives a lot more of
6:48like a spongy appearance
6:50and this um is less dense than
6:54than compact bone but it's still very
6:55rigid so it still allows us to have the
6:57strength
6:58um but it's less dense so it doesn't
7:00take up as much
7:01doesn't weigh as much it's not as
7:04heavy to carry around the spaces in the
7:08spongy bone are filled with
7:09bone marrow and we see the spongy bone
7:14in the center and the ends of
7:17long bones and in the middle of nearly
7:20all other bones
7:24right so overall we're seeing the spongy
7:25bone can reduce the weight of bone so we
7:28still get the strength
7:29but it's not as dense so this is the
7:31spongy bone with those trabeculae
7:33and this is the compact bone so
7:36when we look at flat bones such as let's
7:38say the parietal bone
7:39of the skull we see a sandwich-like
7:42construction
7:43we see two layers of compact bone so
7:46here's
7:46compact bone and here's more compact
7:49bone
7:50but in the middle there's what's called
7:51diploi it's like a spongy
7:53middle layer of that spongy bone and
7:55again that's good for absorbing shock
7:58and that also stores bone marrow
8:03there's also this outer lining called
8:04periosteum
8:06so periosteum peri means outside right
8:09and osteum is bone
8:10so periosteum is the surface
8:13of the bone and we'll talk more about
8:15that in a bit
8:17so let's talk about long bones next
8:20so long bones are mostly composed of an
8:23outer shell of this
8:25dense compact bone um
8:28outside of that compact bone we have the
8:30periosteum which is a fibers outer
8:32membrane made of dense irregular
8:34connective tissue
8:37and then on the inside we have the
8:38spongy bone we said
8:41um the spongier bone the let's just
8:44talk about some parts of bone so the
8:47shaft of a long bone is called the
8:48diaphysis
8:49so this part is called the diaphysis and
8:52the two
8:52enlarged ends are called the epiphyses
8:56singular is epiphysis both are epiphyses
9:00so these are the heads of the long bone
9:01that could form joints or articulations
9:04with other bones the articular cartilage
9:09is a layer cartilage that covers and
9:11protects the joint surfaces to enable
9:13very smooth movements
9:16within here
9:19within the long bone we have a space
9:21called the medullary cavity
9:24and in the medullary cavity is where we
9:27see
9:27bone marrow specifically we find
9:31a yellow bone marrow inside the
9:34medullary cavity we'll talk a little bit
9:35more about that
9:37the endoscium is an inner membrane
9:40lining
9:41the medullary cavity so the endosteum
9:43endo means inside
9:45right so the endosteum lines the inside
9:49of the medullary cavity over here
9:53the endosteum has a very important role
9:55in helping to form
9:57and repair bone
10:00and it's actually a form of reticular
10:03connective tissue
10:08right so again this forms like a mesh
10:10for for the bone marrow to live in
10:14so we so so far we spoke about here's
10:17the diaphysis within the diaphysis we
10:19have the medullary cavity
10:21um and that's where we're gonna have
10:23yellow bone marrow as we'll soon see
10:25within the epiphyses we have spongy bone
10:29so spongy bone is in the epiphyses
10:32so here we're going to have spongy bone
10:34spongy bone
10:36and then again we have this compact bone
10:38for forming the cortical layer
10:44within the epiphyses of long bones
10:47we have red bone marrow
10:50so red bone marrow is found in the
10:52epiphyses of long bones
10:55also um in the pelvis
10:59sternum ribs and the skull
11:03so flat bones also have red bone marrow
11:05in them as well
11:06so flat bones have red bone marrow and
11:09the epiphyses of long
11:11bones have red bone marrow and red bone
11:14marrow can make
11:15blood cells right so it makes our our
11:18blood cells
11:19um which include all the cells of our
11:21immune system
11:23the yellow marrow is found in the
11:25medullary cavity and that functions to
11:27store fat so it's a very different
11:30function as the red bone marrow so
11:32yellow bone marrow
11:34is meant to store fat um children have
11:37red uh
11:38have more red bone marrow than adults do
11:41um
11:42and because as we age our red bone
11:44marrow gets converted
11:45into more yellow marrow interestingly
11:49yellow malware can become
11:50red red bone marrow if more blood cells
11:53are needed
11:54so the cells can um basically turn into
11:57the yellow bone marrow cells can turn
11:58into
11:59red bone marrow if more blood cells are
12:01needed for hematopoiesis
12:04so in this picture we can see the
12:06distribution of bone marrow in
12:08adults and we said that in adults most
12:11of the red bone marrow is replaced by
12:13the yellow bone marrow
12:14um which is usually found in the
12:17endosteum
12:18of long bones so that leaves adults
12:21um with red bone marrow just in their
12:23skull
12:25and their vertebrae and their ribs
12:28sternum and the pelvic girdle
12:32which is the hip and of course the
12:35proximal heads
12:36of long bones such as the humerus
12:40and the femur also have red bone marrow
12:45so that's red bone marrow we spoke about
12:47the functions
12:48and locations and again here
12:52is the red bone marrow and the proximal
12:54epiphysis
12:56of um of this bone so
12:59again proximal i didn't define that
13:01proximal epiphysis means the one
13:03closer to the point of attachment this
13:05would be the distal
13:06epiphysis of the humerus this is the
13:08proximal
13:09epiphysis of the humerus
13:12so the proximal heads of the humerus and
13:14the femur have red bone marrow
13:18so try to answer this question and pause
13:21uh the recording here
13:24so the answer is d
13:27right a long bone consists of a
13:29diaphysis
13:30um that extends between two epiphyses
13:35so read this question and please pause
13:36here
13:39and the answer is c red bone marrow
13:42right the spaces in spongy bone of an
13:44adult proximal epiphysis of humerus and
13:46femur like we just said
13:48has red bone marrow in it
13:52so now let's talk about the histology of
13:54compact bone
13:56so when we look at compact bone and
13:58again that's in the cortical layer of
13:59long bones
14:01we see subunits called osteons
14:05so osteons are the subunits of compact
14:08bone and here's one
14:09osteon over here and the osteon has many
14:13layers to it
14:15and within those layers in the very
14:16center we have what's called the central
14:18canal over here you can see this is the
14:21central canal
14:22and that's where blood vessels and
14:24nerves can run through
14:27so one osteon always has a central canal
14:31running through it so around the central
14:35canal of an osteon so here's one osteon
14:37again
14:38and here we have a central canal so
14:41within the
14:41osteon we have concentric rings of bone
14:44cells
14:46and bone matrix so let's zoom in
14:49here here's one osteon let's zoom in we
14:51have different concentric
14:53rings so we have a layer of bone
14:57and layer means a lamella lamella
15:00literally means
15:01layer lamellae is plural so we have a
15:04layer of bone and then we have a layer
15:07of bone cells
15:08osteocytes and then we have more bone
15:12and then we have another layer of
15:14osteocytes so it's almost like
15:16rings of a tree in a way so they go in
15:19concentric circles
15:21and we said that blood vessels um go
15:24through each
15:25central canal but they also can connect
15:27to neighboring osteons
15:29via perforating canals so here you can
15:33see
15:34this and here's one osteon and here's
15:36another osteon
15:38but these perforating canals can go from
15:42one central canal to another
15:46in addition there are also small holes
15:48in the outside of the bone through the
15:50periosteum
15:51that allows blood vessels to deliver
15:53nutrients
15:54and remove wastes from the medullary
15:56cavity
15:57so we need to get away we need um the
15:59bloodstream to have a way
16:00inside of the deepest part of the bone
16:03right even in the spongy bone
16:05and that's where we have these these
16:07nutrient foramina
16:10they're just holes a foramen a singular
16:13nutrient foramen is a singular whole
16:15nutrient foramina are plural
16:18and again these are holes in the
16:20periosteum
16:22and that outer layer surrounding bone
16:25that allows blood vessels to go inside
16:29and again we need a lot of blood supply
16:32for our bones to function
16:33so we get a half a liter of blood supply
16:36to our skeletal system every minute
16:39which is very significant so
16:42we have all these components we said we
16:44each compact bone is composed of osteons
16:48osteons have lamellae a bone with
16:50osteocytes which are the bone cells
16:52within each osteon we have a central
16:54canal
16:56um perforating canals can connect
16:59adjacent osteons and nutrient foramina
17:02allow blood vessels to go from
17:04outside into the bone
17:08so while it might not seem like it bones
17:10are constantly being broken down and
17:12being rebuilt
17:13at a microscopic level so this is called
17:16bone
17:16remodeling and we need specialized cells
17:19within the bone tissue to constantly
17:21build and break down bone as needed
17:24on average your entire skeleton is
17:26remodeled over about 10 years
17:29now we have to introduce some very
17:30important types of cells found in bone
17:33tissue
17:35the first we'll call osteogenic cells
17:37which are just bone
17:38stem cells and these bone stem cells can
17:41become
17:42mature bone cells or cartilage cells
17:46all right so that's the first so
17:47osteogenic cells
17:49are stem cells that can give rise to
17:51most bone cell types
17:54then we have osteocytes osteocytes
17:58are active bone cells they're
18:01responsible for maintaining
18:03the existing matrix they don't build
18:05they don't break down
18:07right so the osteocytes um are all
18:10connected
18:11uh to each other so they can pass
18:13nutrients and chemical signals
18:14from one another so those are the active
18:17bone cells
18:17osteocytes osteoblasts
18:21are bone forming cells that build new
18:24bone matrix so you can remember
18:26the build and b for blast builds new
18:28matrix
18:30um so these osteoblasts are non-mitotic
18:33they don't divide
18:35so the only source of new osteoblasts
18:37are those osteogenic cells
18:39so those can become more osteoblasts
18:42osteoblasts also secrete a hormone
18:44called osteocalcin
18:45which can stimulate insulin secretion by
18:48the pancreas
18:49um which can limit the growth of adipose
18:51tissue
18:52and make sure our our homeostasis is
18:54maintained so this could basically help
18:56us
18:58store or help us not store
19:01excess sugar as fat
19:04osteoblasts eventually get trapped in
19:07the matrix
19:07and become osteocytes so osteocytes are
19:11former
19:12osteoblasts that have been trapped in a
19:15matrix
19:16that they deposited themselves
19:20osteoclasts dissolve and break down
19:24old bone matrix so osteoclasts
19:27destroy or dissolve bone right in a
19:30process called osteolysis
19:33so osteoclasts dissolve um and degrade
19:36bone osteoblast build bone
19:38osteocytes maintain bone osteogenic
19:40cells can become any of these guys
19:44so what type of cell is responsible for
19:46building new bone
19:48pause here the answer is c
19:52osteoblast what about breaking down bone
19:57so you can pause here the answer is
20:01a osteoclasts so to build new bone it is
20:06important that you do
20:06weight-bearing exercise weight-bearing
20:09exercise stimulates bone remodeling
20:12you're basically telling your body that
20:14you're gonna have some more weight to
20:15withstand
20:16so you better build the bone stronger
20:18all right very similar to how
20:20the body um builds muscle right when you
20:23use your muscles more you're going to
20:25build it um so use it or lose it the
20:27more you use your bones
20:28the more they will be built so for
20:31example
20:32uh for astronauts or in space they
20:34actually lose a lot of their bone
20:36density
20:37because they don't have the ability to
20:39exercise the way that we do
20:41so people in space have to do certain
20:43kinds of exercises in order to maintain
20:45their bone remodeling
20:47otherwise their bones would just
20:48decompose
20:51so now let's talk about ossification
20:52which is the process of bone formation
20:55that begins during the sixth or seventh
20:57week of embryonic life
20:59and i'm going to talk very briefly about
21:02ossification
21:03there are two types of bone formation in
21:05development there's
21:07intra membranous that's how we get
21:11certain flat bones of the skull
21:14parts of the collar bone and part of the
21:15mandible and then we have
21:17endochondral ossification i'll talk
21:20about each of those
21:22first intramembranous ossification forms
21:25flat bones and flat bones forms
21:29between connective tissue membranes
21:32of the embryo so what this means is that
21:34there are connective tissues
21:36inside the membrane that become
21:39osteoblasts
21:40and make spongy bone remember that flat
21:43bones have spongy bone in the inside
21:46osteoblasts outside of the membrane
21:48deposit compact
21:49bone um so again we have the in
21:54inner part making spongy bone the outer
21:56part makes compact bone
21:58and it's called intramembranous because
22:01the bone forms between
22:02um two membranes
22:06microscopes are called intramembranous
22:07that forms in between membranes
22:11the next kind of ossification is
22:13endochondral ossification
22:16in endochondral ossification we see that
22:18bone
22:19forms over a hyaline cartilage model
22:23so it starts off as hyaline cartilage is
22:25replaced
22:27by bone and again this happens around
22:29the sixth week of field development
22:31and continues into a person's twenties
22:34and this is how most bones of the body
22:36uh develop um so most
22:39of your long bones uh your vertebrae
22:41your ribs sternum scapula
22:44um are all formed by endochondral
22:47ossification
22:49osteoblasts of the periosteum
22:52can make a collar around the diaphysis
22:56that starts to form compact bone so
22:59cartilage becomes calcified which
23:01hardens it
23:03and around the diaphysis we start seeing
23:06compact bone
23:07developing right and the c
23:10as the cartilage is calcified it is
23:13being killed so chondrocytes which are
23:15cartilage cells are being killed
23:18um and then osteoblasts will replace
23:21that
23:22inner cartilage with spongy bone
23:25so as the cartilage is being calcified
23:28we have spongy bone being formed
23:32instead of the cartilage the osteoclasts
23:37remove spongy bone to form the medullary
23:40cavity
23:41in the center and of course the
23:43medullary cavity allows us to store
23:46bone marrow so
23:49in this image you can see endochondral
23:51ossification of the long bones forming
23:54an intramembranous um ossification of
23:57the flat bones of the skull
23:59so pause here and try to answer this
24:01rapid response question
24:06the answer is b chondrocytes
24:09remember endochondral ossification
24:11starts off with cartilage
24:14so the chondrocytes the cartilage cells
24:16end up being
24:17killed by the deposition of calcium
24:19salts by osteoblasts
24:23so again i went through that very very
24:25quickly you don't need to know
24:26all the information contained in the
24:28textbook on
24:30ossification so try this one more
24:34question before we move on
24:36so you can pause here and the answer to
24:39this question
24:40is d
24:45so ossification does not stop at birth
24:48it continues throughout our life with
24:49the growth and remodeling of bones
24:52and bones need to grow in two directions
24:54both in length
24:56and in width so as we age up until a
24:59certain point
25:01about in our mid-20s our long bones
25:03continue to grow in length
25:06and we grow taller as a result
25:09this is responsible this is in response
25:11to the growth plate
25:13the growth plate also called the
25:14epiphyseal plate
25:16is a thin band of cartilage between the
25:18diaphysis
25:20and the epiphysis of long bones
25:23and this allows the shaft of the long
25:25bone to grow
25:26as well as the head of the long bone to
25:28grow
25:29and the way that this happens is at this
25:31epiphyseal plate
25:33it's made of cartilage so we have
25:35chondrocytes
25:37growing so cartilage cells being grown
25:39and
25:40as the cartilage cells grow they are
25:42then replaced by
25:43bone right so those chondrocytes
25:46um those cartilage cells can then be
25:49calcified
25:51um and then bone gets deposited as the
25:54chondrocytes die
25:56so again the way that bones grow is
25:59first it starts off as
26:00cartilage and at this epiphyseal plate
26:03we see cartilage grow um in length
26:07that will help us grow taller
26:10also the bones could grow in diameter
26:13around the periosteum bones can be built
26:16by osteoblasts and that gets our
26:19diameter of the diaphysis bigger
26:22so again all is because of cartilage
26:25what happens at around age 25 is that
26:28the growth plate hardens into bone
26:30and that's when growth permanently ends
26:33and we can see that in an adult bone as
26:35the epiphyseal line
26:37that's where the fusion of diaphysis and
26:39epiphysis happens
26:41so this was once the epiphyseal plate
26:44where that cartilage was
26:45that allowed the bone to grow and um in
26:48length
26:49as well as in diameter
26:54there are many factors that can affect
26:56bone growth and repair
26:58so just nutrition what you eat provides
27:00the raw materials to build bone
27:03so the calcium phosphorus of the
27:04proteins in your diet
27:06have a lot to do with how your skeletal
27:07system can be remodeled
27:10vitamin d promotes calcium absorption in
27:12the intestines
27:14so in order for our calcium to be
27:18taken from our intestines into our
27:19bloodstream we need vitamin d as help
27:22that's another um dietary requirement
27:26we need and we also need the sunlight to
27:28get proper vitamin d
27:30we also rely on growth hormones and sex
27:32hormones to promote the proper building
27:34of bone
27:36and like i mentioned before
27:37weight-bearing exercise is the stimulus
27:39to make bone stronger
27:41so bone stores the majority of calcium
27:44in our body
27:46our body contains about 1 100 grams of
27:49calcium
27:50and 99 of that is in our bones
27:53and calcium is required for many
27:55functions outside of the skeletal system
27:57right but a lot more than just the bone
27:59structure
28:00we need calcium uh to maintain our heart
28:02rhythmicity
28:04um we need calcium for muscle
28:05contraction we need calcium for our
28:08nerves to function properly
28:10um we need calcium also for our blood to
28:12clog
28:13and again this is a small subset calcium
28:15is also required in many other
28:17physiological processes
28:19and calcium is continuously exchanged
28:21between the solid form and bones
28:24and the dissolved form in blood
28:27the normal calcium concentration in
28:28blood plasma is about
28:309.2 to 10.4 milligrams per deciliter
28:33and that's a very narrow margin of
28:35safety
28:38if you have hypocalcemia that means you
28:41are
28:42deficient in blood calcium levels
28:45and that can cause excessive
28:46excitability of the nervous system
28:49um and what's called tetany which are
28:51muscle spasms
28:53um and if you had any of the muscles of
28:55the larynx
28:57that could cause death by suffocation
29:00so if you have a vitamin d deficiency or
29:02excessive diarrhea
29:04or thyroid tumors this could impact your
29:07ability to store calcium
29:09and that could cause a calcium
29:10deficiency and pregnancy and lactation
29:13increase the risk of hypocalcemia
29:18hypercalcemia a calcium excess
29:21could make ion channels less responsive
29:24and thus nerve and muscle cells are less
29:26excitable they're less able to respond
29:29to our brain signaling um and that
29:32is um a lot rarer um so hypercalcemia
29:37is rare but hypocalcemia um
29:40is a lot more common and again like i
29:43said pregnancy and lactation puts women
29:44at risk of
29:45hypocalcemia um because they need to
29:48have a lot of calcium to make
29:51milk and also to ossify the fetal
29:54skeleton
29:57so now that we understand just how
29:59critical blood calcium level is
30:01let's try to explain how the body
30:04controls calcium homeostasis
30:06and how do we make sure that we have the
30:08right amounts of calcium in our blood at
30:10all times
30:11well we have three important hormones
30:14that help our body regulate calcium
30:16homeostasis
30:17the first is calcitriol also known as
30:21active vitamin d
30:24and calcitriol functions to increase
30:26calcium in the blood
30:29so active vitamin d increases calcium in
30:32the blood
30:33vitamin d is produced by the skin liver
30:36and kidneys
30:37there's actually a multi-step process to
30:39get active um
30:41calcitriol we have like a precursor to
30:43vitamin d in our skin
30:46we need uv light to activate it
30:49then there's a little step in the liver
30:51and a final step
30:52in the kidneys to make it fully
30:54functional and once it's fully
30:56functional
30:57it can raise our blood calcium by
30:59increasing
31:00absorption by the kidneys
31:03and the small intestines what this means
31:06is
31:07absorption is helping keep calcium in
31:10the body
31:10so calcitriol can go over to the small
31:13intestines and make sure
31:15that it's keeping the calcium in it's
31:17not getting
31:18it's not going to excrete it right so
31:21calcitriol goes to the small intestines
31:22and say okay
31:24do not let it be excreted keep it inside
31:26the blood keep it in the body
31:28same idea at the kidneys it's telling
31:30the kidneys do not
31:31let the calcium be eliminated in
31:35in the urine keep it in the body right
31:37so absorption
31:39means keep it in the body and that's
31:40what calcitriol is doing
31:43calcitriol can also stimulate
31:45osteoclasts
31:47to increase calcium resorption from the
31:50skeleton
31:51what resorption means is we're going to
31:54take the calcium from the bone
31:56and put it into the blood
31:59calcitriol will be released when we need
32:02more
32:02calcium in the blood so what that
32:04calcitriol can do is it can activate
32:07osteoclasts
32:08to break down bone so the calcium could
32:11be then released into the bloodstream
32:13where we need it more
32:15so this is how calcitriol um
32:18acts to increase the concentration of
32:22calcium in the blood
32:23right it can act on bone resorption
32:25reduce excretion of calcium
32:28and increased absorption of calcium in
32:30the small intestines
32:34next we could talk about calcitonin
32:38calcitonin is produced by the thyroid
32:41gland and this is when blood calcium
32:43levels
32:44are high so this is another way so when
32:48blood
32:48levels are too high then we want to have
32:50calcitonin be secreted from the thyroid
32:53gland
32:55so calcitonin inhibits osteoclasts
32:59from degrading the bone matrix and it
33:02stimulates
33:03bone deposition by osteoblast so this is
33:06the opposite of calcitriol
33:09calcitonin inhibits osteoclasts so they
33:12can no longer break down bone
33:14so this will make sure that our blood um
33:17doesn't get any more
33:18calcium in it right we don't want any
33:21more calcium if it's already high enough
33:22so calcitonin will inhibit osteoclasts
33:25making sure they don't degrade
33:26any bone matrix and they will stimulate
33:30osteoblasts so the osteoblasts will
33:32start taking the calcium from the blood
33:35and putting it into bone so remember
33:38calcitonin
33:39we need when blood calcium levels are
33:41too high
33:43calcitriol we needed when the calcium
33:45levels were too low
33:47so these are doing opposite things and
33:50again calcitonin
33:51um is released from the thyroid
33:56so he said it inhibits osteoclasts and
33:59stimulates
34:00osteoblasts finally the third
34:04hormone we'll talk about is parathyroid
34:06hormone
34:07and this like calcitriol functions when
34:10blood calcium levels are
34:12low um parathyroid hormone is named so
34:16because it is secreted from the
34:17parathyroid gland
34:19um i should have showed this before uh
34:21but
34:22right right in front of the larynx we
34:24have the thyroid gland
34:26that's where the calcitonin is released
34:28from and then we have these
34:30four parathyroid glands where pth
34:34is secreted from um again those are just
34:38these little glands on the posterior
34:39surface of the thyroid glands
34:41so when blood calcium is low the
34:44parathyroid glands release
34:45parathyroid hormone and parathyroid
34:48hormone will stimulate
34:50osteoclasts to degrade bone matrix
34:53and release calcium into the blood very
34:55similar to what calcitriol did
34:59parathyroid hormone also helps with
35:01retention of calcium
35:03from the intestines and the kidneys so
35:05calcium isn't excreted
35:07so very similar to calcitriol active
35:10vitamin d
35:11you know is parathyroid hormone
35:15so let's review if we have too much
35:18calcium in our blood we can have
35:21calcitonin
35:22be secreted from the thyroid
35:25and what that will do well inhibit
35:27osteoclasts
35:29so they'll stop raking down bone
35:32they'll also activate osteoblasts so the
35:35osteoblasts will take the excess calcium
35:38from the blood and put it into the bone
35:41and together that will return the blood
35:43calcium back to normal
35:45we said if there is too little blood uh
35:47too little calcium in the blood
35:50pth gets secreted um into the
35:52bloodstream by the parathyroid
35:53glands and that does several things that
35:57increases osteoclast activity so they'll
35:59continue to break down
36:01bone so more calcium can get into the
36:03blood they will stop the osteoblasts
36:06from building more bone and they will
36:09also make sure
36:10that calcium is conserved making sure
36:12that calcium does not leave
36:14um in the urine does not get excreted
36:17and
36:17gets absorbed by the small intestine
36:20and all together that will make sure
36:22that our blood calcium is maintained
36:24we want to make sure that we have enough
36:28so let's answer a few of these rapid
36:29response questions so pause here
36:35the answer is
36:38c bone deposition is the building of
36:41bone
36:42what is the effect of vitamin d on the
36:44skeletal system
36:46so pause here right so the answer is
36:51a right so vitamin d
36:55functions to raise the blood calcium
36:57concentration
36:59and it does so by making sure the small
37:01intestine does not get rid of any of
37:03that calcium
37:06what is the effect of calcitonin on the
37:08skeletal system
37:10so you can pause here
37:14and the answer is d calcitonin inhibits
37:17the activity
37:18of osteoclasts because calcitonin is
37:21secreted when there's already
37:22enough calcium in the blood so we don't
37:25want osteoclasts to break down bone and
37:27put even more calcium in the blood
37:29right so calcitonin inhibits the
37:31activity of osteoclasts
37:34in response to low blood calcium which
37:36would not occur
37:38so pause here and try to use process of
37:41elimination for this one
37:43so the answer is a in response to low
37:46blood calcium
37:47osteoblasts would not build new bone
37:50right there's not enough calcium in the
37:51blood to begin with to even build a new
37:53bone
37:54but in response to low blood calcium a
37:56parathyroid hormone would be
37:58active and that would actually activate
38:01osteoclasts
38:02to break down um bone so we could get
38:05more calcium inside the blood
38:08and um calcitonin would not be active
38:12right because calcitonin inhibits
38:13osteoclasts
38:15and we want osteoclasts to break down
38:17bone so we can get
38:19more calcium in the blood so the answer
38:22is a
38:24so just to conclude so orthopedics is
38:28the branch of medicine that deals with
38:29the prevention
38:30and correction of injuries and disorders
38:33of bones
38:33joints and muscles osteoporosis is a
38:37disorder you've probably heard of
38:39already
38:39and that's a decrease in bone density
38:42and that leads to bones that are very
38:44weak
38:44and can be more easily fractured so
38:48osteoporosis really looks like pores
38:51within the bone and the risk of
38:55osteoporosis increases with age
38:57and women are at greater risk than men
39:01and osteoporosis is not just a calcium
39:03deficiency that can be fixed by taking
39:05calcium pills or
39:06having more milk it has a lot to do with
39:08the endocrine system
39:10and in women estrogen levels decrease
39:12after menopause and estrogen would
39:14normally help stimulate osteoblasts to
39:17build bone
39:18and would usually help to absorb more
39:20calcium
39:21so when you have less estrogen women
39:24have
39:24less osteoblast functioning to build
39:26bone and less ability to absorb calcium
39:30so there's always a dietary approach to
39:32make sure that there's adequate intake
39:34of calcium protein vitamins and minerals
39:36but there's also the exercise approach
39:38and weight-bearing exercise is known to
39:41promote stronger
39:42bones and that's often the suggestion a
39:44doctor might give
39:46to somebody with osteoporosis
39:49so you can watch a video contained in
39:51the ebook on connect about osteoporosis
39:55so finally i just want to talk about um
39:58types of fractures
40:00so a fracture is a break in the bone
40:02that can be caused by
40:03one of two things you can have a stress
40:05fracture
40:06um that's when you kind of you fall or
40:09something happens in an
40:10accident so it's an abnormal trauma to
40:13the bone it's a stress fracture
40:15you can also have a pathological
40:16fracture that's due to disease
40:19and that's more of a break that's due to
40:21bone cancer osteoporosis
40:23something that would not have normally
40:25broken a healthy bone
40:26so if the fracture breaks um when it
40:29norm
40:30if a bone breaks be when it normally
40:32would not have it's pathological because
40:34it was probably
40:35due um to the weakened bone itself
40:39fractures can be classified by their
40:40structural characteristics
40:42for example the direction of the
40:44fraction line
40:47um whether the skin is broken or not
40:50and how many pieces the fracture is
40:53broken into
40:54um so you can look at the book a little
40:56bit more about different types of
40:58fractures
40:59and they can be repaired um either
41:01closed
41:02or open so closed reduction is a
41:05procedure in which the bone fragments
41:07are manipulated without surgery
41:09so with a cast for example um open
41:12reduction
41:13involves surgical exposure of the bone
41:15and you can
41:16pin the bones back into position
41:19so you realign the fragments using
41:21plates or screws
41:23surgically so there's close reduction
41:26versus
41:27open reduction
41:30so an uncomplicated fracture can heal in
41:33about eight to
41:34twelve weeks but more complex fractures
41:36take longer
41:37and in older people all fractures here
41:40more slowly
41:42an uncomplicated fracture heals in about
41:44eight to twelve weeks
41:45but complex fractures take a lot longer
41:48and in older people
41:50all fractures heal a lot more slowly but
41:52fractures can be healed in a basic
41:55four steps so first we have hematoma
41:58formation which is a blood clot
42:01so a bone fracture would have severed a
42:03lot of those blood vessels of the bone
42:04and the periosteum
42:06which caused the bleeding and that
42:07formed a blood clot
42:10then we start having some osteogenic
42:12cells becoming very abundant within 48
42:15hours of the
42:16injury so osteogenic cells start coming
42:20in and those osteogenic cells start to
42:23become chondroblasts
42:25and they start making um fibrocartilage
42:28and um fibroblasts start making collagen
42:32so this is called soft callus formation
42:34we have collagen being made by
42:35fibroblasts
42:37and chondrocytes um are making this
42:40fibrocartilage
42:42uh so we have this soft callus being
42:45formed
42:46then we have the formation of a hard
42:48callus so the soft callus is converted
42:50to a heart callus
42:51as osteogenic cells differentiate into
42:54osteoblasts
42:56which deposit a bony collar around the
42:58fracture to unite all the broken pieces
43:02and that heart callus can be there for
43:04about three to four months
43:06um and during that time we have bone
43:08remodeling
43:09where small bone fragments are removed
43:11by osteoclasts
43:13where osteoblasts continue to deposit
43:15spongy bone
43:16and then convert it into compact bone
43:20so again these are the four basic steps
43:22to fractures being healed
43:25and that is the end of chapter seven uh
43:28we will continue
43:29um with talking about the skeletal
43:31system in the next chapters
43:33um and then followed by that we'll talk
43:35about joints
43:36uh so that is it for now i'll see you
43:39next time