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  • >> This video is on bone

  • and the tissues of the skeleton.

  • The learning objectives

  • that we'll cover are here.

  • We'll cover a little bit

  • about what bone's made of --

  • cells and matrix.

  • We'll talk about bone growth

  • and remodeling.

  • And quite bit

  • about calcium homeostasis

  • which involves our bones.

  • The functions of bones --

  • support and protection are

  • probably pretty obvious

  • and moving our muscles around.

  • But also, don't forget

  • that new blood cells are formed

  • in our bone marrow.

  • Also, the bones are going

  • to play an important role

  • in calcium homeostasis

  • in maintaining our extracellular

  • calcium -- serving

  • as a calcium reservoir.

  • In the first learning objective,

  • we'll cover here is

  • to describe the cells, matrix,

  • and organization of bone

  • and associated tissues.

  • So we'll mention a little bit

  • here about cartilage

  • and ligaments.

  • But mainly we'll focus on bone

  • and bone marrow.

  • So if we look at bone --

  • so we've learned so far

  • as the osteocyte.

  • The extracellular matrix

  • around those cells is mainly

  • collagen protein as well

  • as the minerals calcium

  • and phosphate.

  • And so that's what gives bone

  • its sort of hardened

  • extracellular matrix is the

  • calcium phosphate and mineral.

  • If we look at tendons

  • and ligaments,

  • the cell we're interested

  • in is the fibroblast

  • which makes this dense

  • connective tissue of collagen

  • and elastin.

  • These proteins make

  • up these fibers, collagen

  • and elastic fibers.

  • A cell I don't think we've

  • learned yet is the chondrocyte.

  • Chondrocytes help maintain a

  • special connective tissue

  • called cartilage.

  • Cartilage is mainly collagen

  • and elastin proteins as well.

  • So cartilage is kind of famous

  • for making up things

  • like your ears and nose

  • and being on the ends of bones

  • such as our ribs.

  • So if you look at each of these,

  • the sort of thing they share is

  • that they're made

  • of extracellular matrix

  • of collagen built

  • by certain cells.

  • Okay, I just wanted

  • to mention ligaments.

  • Ligaments attach bone to bone.

  • And they stabilize our skeleton.

  • Tendons attach muscles to bone,

  • and they allow movement

  • of our bones.

  • Okay, ligaments

  • and tendons are basically just

  • dense connective tissue.

  • Cartilage, cartilage is

  • well-known for being at the ends

  • of our bones.

  • So wherever we form a joint

  • so that those bones don't clash

  • against each other,

  • it's protected by cartilage

  • and also our ears and nose

  • and things like that.

  • So to summarize, keep in mind

  • that when we talk

  • about the skeleton,

  • we're talking

  • about the different types

  • of cells that make

  • up the different type

  • of skeletal tissues.

  • And each of them shares collagen

  • as an important protein

  • and then slightly

  • different cells.

  • If we look at this picture

  • of bone here, and it's cut open

  • to show you

  • that inside the core,

  • deep inside bone,

  • are these marrow spaces

  • and it includes red bone marrow

  • and yellow bone marrow.

  • There's usually an outer sort

  • of shell of compact bone

  • and then an inner core

  • of trabecular bone

  • for these marrow spaces.

  • And what's interesting

  • about bone marrow is

  • in adults we have yellow bone

  • marrow in certain places filling

  • our bones with adipocytes --

  • kind of space filler,

  • packaging so energy.

  • The interesting stuff though is

  • the red marrow found

  • in certain parts of our skeleton

  • which gives rise

  • to all our new blood cells

  • whether they're leucocytes

  • for defense

  • or erythrocytes carry oxygen

  • around the body attached

  • to hemoglobin the protein inside

  • those erythrocytes.

  • And also, the bone marrow also

  • makes those little platelets

  • which help in blood clotting.

  • So red bone marrow gives rise

  • using these hematopoietic stem

  • cells to all the cells

  • of our blood.

  • If we look at real bone,

  • what we see is this outer shell

  • of compact dense bone covered

  • by a fleshy periosteum

  • which is sort

  • of like a connective tissue

  • cover of our bones.

  • And then deep

  • to the compact bone is this

  • trabecular bone.

  • Trabecular bone has these spaces

  • or sort of grooves

  • and little nooks and crannies

  • where we have our bone marrow.

  • And there's lots and lots

  • of living cells in our bone,

  • and so we need a rich blood

  • supply that feeds our bone

  • and helps keep it nourished.

  • We also have a nervous supply

  • as well so that's why

  • if you've ever broken a bone you

  • know it hurts so badly.

  • So sometimes your blood supply

  • can be interrupted to your bone.

  • And in that case,

  • we get a condition called

  • osteonecrosis

  • or avascular osteonecrosis

  • which can cause death

  • to your bone.

  • Again, we have this fleshy outer

  • cover of bone called

  • the periosteum.

  • It's mainly dense connective

  • tissue of collagen built

  • by fibroblast.

  • But there's a couple of layers

  • of fibroblast

  • and osteogenic stem cells

  • in there which will become

  • important when we talk

  • about fracture repair

  • in that periosteum.

  • Then there's compact bone just

  • deep to that.

  • The compact bone has mostly bone

  • matrix with some osteocytes

  • in there that maintain the

  • bone matrix.

  • And so again,

  • that bone matrix is collagen

  • protein with some calcium

  • phosphate mineral.

  • Then deeper

  • to that is the trabecular bone.

  • The trabecular bone you can see

  • has little spaces

  • that are filled

  • with bone marrow,

  • either red bone marrow

  • or yellow bone marrow filling

  • the trabecular bone.

  • Trabecular bone is hardened.

  • Some textbooks call it spongy

  • bone, which I don't really

  • like because that makes me think

  • of it as soft.

  • But it's really all hard.

  • I think the reason they

  • like spongy was

  • because there were spaces in it.

  • So we'll call it compact bone

  • and trabecular bone.

  • If we zoom in on compact bone,

  • what we see is very little

  • space, open space.

  • It's instead these compact

  • columns of bone matrix called

  • an osteon.

  • And you can see several osteons

  • in this little picture here.

  • The osteons have these little

  • rings of osteocytes which help

  • to build the osteon.

  • And then they help maintain it.

  • Each osteon has a little central

  • canal, a little tunnel,

  • that allows things --

  • soft things like blood vessels

  • and nerves to run

  • through the hardened bone.

  • So again, the bone matrix is

  • collagen and mineral.

  • And so we see several osteons

  • making up this compact

  • bone section.

  • If you look at trabecular bone,

  • you don't see any osteons.

  • Instead, you see marrow spaces.

  • And then in the hardened bone

  • matrix it's a little more

  • irregularly shaped.

  • It's still pretty much the same

  • stuff, osteocytes embedded

  • in a bone matrix of collagen

  • and mineral.

  • And then the other thing you'll

  • notice is that you see these

  • lining cells that cling

  • to the edge of the bone

  • in the marrow spaces.

  • This is called endosteum.

  • So endosteum is the cellular

  • lining in the interior spaces

  • of bone.

  • It includes cells

  • like the osteoclast,

  • the osteoblast

  • and osteogenic cells,

  • which we'll learn more about.

  • Again, if you look

  • at the marrow spaces

  • of trabecular bone,

  • you see all these little cells

  • clinging to the edge

  • of the bone.

  • And so we call those cells

  • endosteum as a group.

  • Okay, the fleshy outer cover

  • of bone we call periosteum.

  • And that's connective tissue,

  • dense connective tissue somewhat

  • similar to maybe the dermis

  • of the skin.

  • And it has cells