Full transcript
0:00this is chapter 6 part a on bones and
0:02skeletal tissues so initially the human
0:05skeleton contains just cartilage which
0:08later will be replaced by bone during
0:10development except in a few select areas
0:13so remember from chapter 4 and the
0:15tissues we said cartilage is made up
0:17mostly of just water so there's new
0:19blood vessels or nerves we have a lot of
0:21this extracellular matrix or this
0:23water-based a matrix the perichondrium
0:25is a layer of dense connective tissue
0:28that surrounds the cartilage on either
0:29side so it helps the cartilage to resist
0:32any outward expansion and it will also
0:34contain those blood vessels to deliver
0:36nutrients to the cartilage since the
0:38cartilage doesn't have of its own blood
0:40vessels the cells in cartilage are
0:42called chondrocytes and they're
0:44contained within this extracellular
0:46matrix or goo of the tissues kind of
0:49suspended with collagen fibers and
0:51contra sites and elastic fibers there's
0:55three types of cartilage in the skeleton
0:57first type is hyaline cartilage so this
0:59is by far the most abundant it's also
1:01going to be the basis for the bone
1:03development in utero Highland cartilage
1:06provides support flexibility and
1:07resilience it's found in the joints or
1:10the articulations of the body at the
1:12ends of the long bones as well as the
1:14costal cartilages of the ribs the larynx
1:17in the respiratory tract and the tip of
1:20the nose so all your huiling cartilage
1:23here are shown in blue elastic cartilage
1:27is similar to Highland but it just
1:29contains more of those elastic fibers so
1:32we find elastic cartilage is shown in
1:34green in the external ear and the
1:36epiglottis so the epiglottis is just a
1:39flap that kind of flaps down to cover
1:41the trachea the windpipe to make sure
1:44food doesn't go down the wrong hole
1:46fibrocartilage shown in red is the most
1:49durable type of cartilage so remember
1:52from chapter 4 again we said you find
1:53this type of cartilage typically in
1:55places that are subject to you a lot of
1:58weight and compressive forces so I have
2:01thick collagen fibers and the greatest
2:03tensile strength so we find
2:04fibrocartilage in the discs or the
2:07menisci
2:07of the knee as well as the
2:09intervertebral discs in the vertebra
2:12there are seven important functions of
2:14bones
2:15one being support so it just helps to
2:17keep our body upright and maintain its
2:19shape protection is another function so
2:22the skull helps protect the brain the
2:25ribcage helps protect your vital organs
2:28movement is another function so the
2:31bones the skeleton serve as levers for
2:34muscles to act on number four is mineral
2:37and growth factors storage so calcium
2:40phosphorus and some other growth factors
2:42can be stored within the bone tissue
2:44blood cell formation is another function
2:47of bone so the process of blood cell
2:49formation is called hematopoiesis this
2:52occurs in the red bone marrow cavities
2:54of certain bones another function is fat
2:58storage or triglyceride storage so we
3:00use fat for energy and we can store
3:03excess fat nutrient reserves in the
3:06yellow marrow and I've been the hollow
3:08core of the long bones and finally
3:12hormone production some bones can
3:14produce a hormone osteocalcin just to
3:16help regulate insulin and glucose levels
3:19as well as metabolism so there are 206
3:23bones in the human body so for lecture
3:26we won't focus on naming and learning
3:28all of the bones you will do that in lab
3:30but we can divide the skeleton into two
3:32basic groups so the axial skeleton is
3:35the head and truck regions of kind of
3:37the central long axis of the body the
3:40appendicular skeleton consists of the
3:42appendages or the limbs the arms and the
3:45legs bones can be classified based on
3:47their shape so generally bones are going
3:49to fall into one of four shape
3:51categories your long bones are longer
3:54than they are wide so basically all of
3:57your limb bones will fit into this
3:59category short bones are shorter and
4:02more cube shaped so these are commonly
4:05found in the wrists and the ankles of
4:08the carpals
4:08in the tarsals sesamoid bones are a
4:12special type of short bone so it's a
4:15short bone that is suspended within
4:16tendons so the patella or the kneecap
4:19is an example of a sesamoid or a
4:21sesame-seed shaped bone flat bones are
4:25thin flat and maybe slightly curved so
4:29these include the sternum or the
4:30breastbone the scapula or the shoulder
4:32blades the ribs and most of the skull
4:35bones would be considered flat bones and
4:38then finally irregular bones have
4:40complicated shapes that don't really fit
4:42nicely into these other three categories
4:44so this would include your vertebrae and
4:47the hip bones or the coxal bones so
4:50looking at bone structure we send that
4:52organs are made up of different types of
4:54tissues working together so bones are
4:57considered organs because they contain
4:58different types of tissue
5:00so obviously bone or osseous tissue is
5:03the primary but it also contains nervous
5:06tissue cartilage on the ends of the
5:08bones and within the osteocytes
5:12connective tissue on the outside of the
5:15bone as well as muscle cells and
5:17epithelial cells within the blood
5:19vessels in the bone so we'll look at
5:21gross anatomy and then move on to you
5:24microscopic so there's two main textures
5:27of bone spongy and compact so contact
5:30bone is a very dense outer layer on
5:34every bone and it appears smooth and
5:36solid so the cells are more compact in
5:39this tissue spongy bone has more of a
5:42honeycomb type texture so it's made up
5:45of small little needle-like or flat
5:48pieces of bone called trabeculae
5:51so all of these open spaces this spongy
5:55texture will be filled with the red bone
5:57marrow we said red bone marrow was where
6:00all blood cells are formed sure
6:04irregular and flat bones consists of
6:06thin plates of spongy bone that are kind
6:10of sandwiched between compact bone so
6:14the periosteum is the connective tissue
6:16layer that's covering the outside of the
6:19bone and helps to serve for muscle
6:21tendon and ligament attachments and the
6:23endosteum is going to line the inner
6:26cavity of the bone so bone marrow will
6:29be scattered throughout that spongy bone
6:31it doesn't have a defined
6:33Oh cavity like we do with the yellow
6:35Barrow in that medullary cavity and then
6:38Highland cartilage will cover the areas
6:40of the bone that are part of a movable
6:42joint just to reduce that friction of
6:44the bone ends as they move across one
6:46another looking at the structure of a
6:48typical long bone so all long bones have
6:51a shaft or a long portion called the
6:54diathesis and they have two ends called
6:58the EP Phasis these member epi just
7:01means above so when we talk about the
7:02epidermis
7:03so the epiphyses are gonna be on the
7:06ends of the bone so you would have a
7:08proximal epiphysis so this would be the
7:11head of the humerus that would join with
7:13the shoulder and a distal epiphysis
7:17that's going to join and from the elbow
7:19joint the diathesis the tubular shaft is
7:22going to form the long axis of the bone
7:24and surround that central hollow
7:27medullary cavity so in adults this
7:29medullary cavity will be filled with
7:31that fatty yellow marrow the EP C's are
7:36more spongy bone texture so they have an
7:39outer layer of compact bone but
7:40internally they have the spongy bone
7:42arrangement and they will be filled with
7:44that red marrow the articular cartilage
7:47is a thin covering of Highland cartilage
7:49to reduce friction between the bones as
7:52at the joints so in between the
7:55epiphysis and the diaphysis we have
7:57what's called the epiphyseal line so in
8:00adults this is just a solid line of bone
8:03but in children it's still cartilage
8:06though we said the skeleton is
8:07originally cartilage that is gradually
8:09converted to bone so this is where long
8:12bones will grow from so children they're
8:13still growing so they still need that
8:15cartilage that will gradually turn into
8:17bone but as adults this epiphany line
8:20will close and become solid bone so this
8:24is how they can estimate the age of a
8:28body when they find it they look for
8:29that epiphany line so if it's still
8:31cartilage present then we're dealing
8:33with a young person if it's solid bone
8:36then we're dealing with an adult amount
8:38of poetic tissue and bone is just blood
8:41cell forming tissue so whenever you see
8:43poetic or Police's
8:45at the end of the word it just means the
8:46formation or forming hamato means blood
8:50cell
8:50so all blood cells are derived from the
8:53red bone marrow we said red bone marrow
8:55was found within that spongy bone the
8:58trabeculae or those little pores and
9:00holes within that spongy bone texture in
9:03newborns and infants the medullary
9:05cavity as well as their spongy bone will
9:08contain red marrow
9:09however as adults red marrow will be
9:12limited to the axial skeleton and the
9:15ends or the epiphysis of the long bones
9:18bone markings are sites of muscle
9:21ligament or tendon attachment on the
9:23external surface of the bone some areas
9:26involved in joint formation or conduits
9:29and channels for blood vessels and
9:31nerves to run through so again for
9:33lecture you're not going to have to
9:35learn all of the names of the parts of
9:37the bones but this will come in handy
9:39for labs so you not only need to know
9:41the names of the bones but you will need
9:43to know a lot of these bone markings so
9:46there are some bone markings that are
9:47projections that are typically going to
9:49be sites of muscle and ligament
9:51attachment you can also have bone
9:54markings that are surfaces to help form
9:56joints to allow the bones to fit
9:59together more nicely as well as
10:02depressions and openings for blood
10:04vessels and nerves to pass through for
10:06example whenever you see the word for
10:08Raymond for Raymond just means a hole
10:10whereas me ADIS is more of a canal like
10:13passageway so getting into the
10:16microscopic anatomy of bone tissue my
10:18five major cell types that we see in
10:21osseous bone tissue each of which has
10:23its own specialized role and function we
10:27have osteoprogenitor or osteogenic stem
10:29cells osteoblasts osteocytes bone lining
10:35cells and osteoclasts osteoprogenitor
10:39cells also called osteogenic stem cells
10:42are mitotically active in that
10:45periosteum in endosteum so the outer and
10:48inner linings of the bone so whenever
10:51they're stimulated they can
10:52differentiate into bone forming cells or
10:56bone lining cells
10:57and some will remain as those stem cells
10:59to make new bone cells in the future so
11:03whenever you see progenitor or progeny
11:05it means like offspring and genic means
11:08like Genesis so the beginning or
11:10formation of so these are all beginning
11:13to form other bone cells so all of our
11:16bone cells will be derived from these
11:18stem cells osteoblasts are bone forming
11:22cells that are going to secrete the bone
11:24matrix remember we said in chapter 4
11:26whenever you see blast at the end of the
11:28word that means that we're dealing with
11:30the immature or the forming type of cell
11:33osteocytes are your mature bone cells
11:36that no longer divide and are gonna work
11:39to help maintain the bone matrix these
11:41osteocytes are found within the lacunae
11:43or these tiny little cavities within the
11:47osteon in the bone structure so
11:49osteocytes help maintain the bone matrix
11:51by responding to different mechanical
11:53stimuli such as increased force or
11:55weight or even weightlessness so one
11:58issue that astronauts may have if
12:00they're in space in an antigravity
12:02environment for a long period of time is
12:04they can come back and lose a lot of
12:05their bone density because their bones
12:07have not been subjected to that
12:09mechanical stress or those forces of
12:11their weight osteocytes are also able to
12:13communicate with other bone cells so
12:15bone remodeling can occur the bone
12:18lining cells are flat cells on the
12:20surface that maintain the periosteum and
12:24the endosteum
12:25so we said the periosteum was lining the
12:28outside of the bone surface the
12:31endosteum is gonna line the internal
12:33cavities of the bone husky oak last
12:36function in bone breakdown or resorption
12:39so you never see class at the end of the
12:41word and we're dealing with a breakdown
12:43cell so these osteoclasts hafta there's
12:47a ruffled border just to increase their
12:49surface area for their enzymes to break
12:52down that bone compact bone is sometimes
12:55referred to as lamellar bone because
12:57it's made up of love
12:59la or these rings of bone tissue so
13:02compact bone consists of osteons
13:04sometimes referred to as a Hoover Seon
13:07system so kind of one tree trunk so if
13:10we were to cut down a tree and you have
13:12the tree trunk with the rings one tree
13:14trunk is one osteon compact boat also
13:17contains different canals and canaliculi
13:19for blood vessels and nerves to run
13:21through as well as interstitial and
13:23circumferential lamellae so willem la
13:26would be the individual rings in the
13:29tree stump
13:30so an osteon is the structural and
13:32functional unit of compact bone to
13:35consists of elongated cylinders or tubes
13:38within tubes that are gonna run parallel
13:40to the long axis of the bone so in a
13:44sense they act as these tiny little
13:46weight bearing pillars they give the
13:48bone a lot of its strength and
13:50durability
13:50so one osteon cylinder consists of
13:53several rings of bone matrix called
13:55lamellae so I always use the analogy of
13:57tears on the wedding cake you have a
14:00three-tiered cake
14:01each tier or level of the cake is one
14:04lamellae where if we were looking at it
14:06from the other view right each ring in
14:08the tree stump is one lamellae so each
14:12layer of de lamellae contain collagen
14:14fibers that are going to run in opposite
14:17directions this layer they're running
14:19counterclockwise and later they're
14:21running clockwise so this is just going
14:23to add some extra strength and
14:25durability to the bone tissue to help it
14:27stand stress and twisting forces the
14:30central or diversity and canal is going
14:33to run through the central core of the
14:35osteon right so it will contain the
14:38blood vessels and nerve fibers
14:41perforating or Volks means canals are
14:44going to run perpendicular to the
14:46central canals so they're going to
14:48connect all of the blood vessels and
14:50nerves between the periosteum the
14:52medullary cavity and the central canals
14:55so this is why these are sometimes
14:57referred to as communicating canals
14:59because they allow the different blood
15:01vessels and nerves to still be able to
15:03communicate with one another
15:05well the clean a are the small cavities
15:08between the lamellae where the
15:11osteocytes
15:12live right so those mature bone cells to
15:15help maintain the matrix are found in
15:17these little spaces between the lamellae
15:22canaliculi are small canals that allow
15:25the lacunae to be connected to one
15:27another so they can still communicate so
15:29these osteocytes are still able to
15:31communicate with one another so I like
15:33to use the analogy looking at this it
15:35looks kind of like a spider with the
15:37spider legs so the lacunae would be the
15:41spider body with osteo site in it and
15:43the canaliculi are all the little spider
15:46legs that are coming off interstitial
15:50lamellae are not part of the actual
15:52osteon so these are just kind of space
15:55filler lamellae and osseous tissue so
15:59see they're not actually part of that
16:00circular osteon structure
16:04circumferential lamellae who run the
16:07circumference of the osteon structure so
16:11they are part of that tree stump so
16:14looking at the microscopic anatomy of
16:16spongy bone it's much less organized
16:18than our compact bone so it does not
16:20contain any osteons but it does have the
16:24trabeculae to help withstand stress the
16:27trabeculae act like cables on a
16:29suspension bridge and help confer
16:31strength to the bone so again no osteons
16:34are present but they do contain some
16:36irregularly shaped lamellae and they
16:39still do have the osteocytes osteoblasts
16:42and osteoclasts