hello all this is Dr. Alsup and in this video we will be discussing the different parts of a long
bone so many of these terms and these structures that we're going to discuss are going to be
brought up in subsequent videos so do try to make sure that we get our bearings here in this area so
there will be different parts of the actual bone um but there'll also be uh accessory structures
that we need to to be aware of that are either attached to the bone or very closely associated
so as always after viewing and taking notes of the lecture
i would return to these learning objectives and make sure you can write these in your own words
all right so let's begin with just the term long bone in terms of what that means and it's
kind of exactly what it sounds like a long bone is going to be longer than it is wide and you'll
have these very closely associated with the appendages or the limbs so we're looking here
over over here we're looking at a humerus over here this is a femur these are the longest of the
long bones of the upper limb and the lower limb and there's really two major parts of a long bone
you will have the diaphysis which you can see here labeled this is also referred to as the shaft
or the body so this is really where that long comes in this is the longest portion of the bone
and then on the ends you will have the epiphysis or the epiphyses if you're talking about more
than one and these will be located on the ends of the long bone so often you'll have an epiphysis
associated with the proximal as well as the distal end of the bone sometimes you'll only have one
epiphysis sometimes you'll have more than two epiphyses but in general usually you'll have one
proximal and one distal as you can see see here in this cross section the epiphysis is going to
be made up of mostly spongy bone with an outer layer of compact bone on the end for protection
a more conceptually difficult region is the metaphysis and this literally is a region okay
so this is the region or the the region between an epiphysis and the diaphysis it is just going
to be that space in between and what the epiphys- or what the metaphysis actually is composed of
will differ quite wide wildly in terms of age in terms of individuals so one of the
things that you will find in a growing bone is a growing bone in terms of length is what's called
an epiphyseal or a growth plate and you don't really see an example of that here on this image
but what this is is literally like a plate-like structure that's composed of hyaline cartilage
and since it's actually attach this hyaline cartilage is actually attaching the epiphysis
to the diaphysis in a bone that's still growing in length this is actually an example of a joint
specifically this is a synchondrosis which is a type of cartilaginous joint
and what happens here at this epiphyseal plate is that the plate will actually grow so the cartilage
will actually grow and eventually it will be replaced by bone allowing for the bone to grow
in terms of length so very important in terms of during bony growth now eventually that hyaline
cartilage will be completely replaced by bone and what you will have left is what's referred
to as an epiphyseal line you can see that here I'm going to just kind of fill in the line right here
you can see an epiphyseal line in a young adult eventually with age that line does appear
to kind of occlude and you don't see that so it's really kind of a bony joint in this region
now on the ends of long bones so associated with the ends of those epiphyses on the ends
of the bone you will have a thin layer of hyaline cartilage so you can see a little bit of it there
you can see a little bit of it right here and this cartilage is not involved with bone growth
so that's an important differentiation here instead articular cartilage
is going to be associated with synovial joints for the most part and it's really an added layer of
shock absorption and protection to the bone but this cartilage is not what's actually attaching
the bone to another bone so it's not what's forming the joints it's a component of the
joint but it's not the part that's actually the connective tissue actually attaching the bones
also important to note in terms of the articular cartilage is that it is mostly avascular meaning
that if there's damage to this cartilage this is very slow to heal unlike what we have with bone
and so it's typically articular cartilage that's going to be affected in osteoarthritis
and we'll talk more about that when we get to talking about the joints
articular cartilage is actually a remnant of endochondral ossification
which is the major means through which the bones develop in a cartilage model
so you'll have cartilage throughout the entirety of this region eventually replaced by bone and
that's all that's left of that process are these this these remnants of this articular cartilage
next we have the periosteum the periosteum is going to surround
the bone almost the entirety of the bone it's a connective tissue layer that is going to be found
everywhere around the bone except where there's articular cartilage and except where tendons and
ligaments actually are going to insert on the bone but pretty much everywhere else you'll have the
periosteum it gives that kind of shiny appearance to the bone now it's actually composed of two
layers oftentimes these types of tissues will have two layers this outer layer as you can see
here does exactly what a good outer layer should do which is really going to protect the bone
it's going to serve as this outer fibrous layer it's going to be composed of mostly
dense irregular connective tissue and also you're going to have an inner osteogenic or cellular
layer you can see that here and that is going to be important in terms of appositional growth
or growth in um on the outside of the bone or bone width and so you'll have your osteogenic cells
in there you'll have osteoblasts associated with this inner layer of the periosteum
the the periosteum you can't really no i guess you can't really see
it well here but that periosteum is literally going to be attached to the bone it will send
certain fibers that are going to interweave with the matrix of the bone
that's referred to as these penetrating or perforating or Sharpey's fibers you'll hear those
uh three terms that that's the actual means by which periosteum attaches to the bone
all right now we're moving inside the bone so periosteum was surrounding the outside now we're
moving inside and one of the most prominent things that you'll see when you're looking at
the inside of a long bone or the diaphysis is the medullary or the marrow cavity medulla literally
means marrow and when we're talking about an adult bone this is going to contain yellow bone
marrow so very important in terms of triglyceride storage as well as allow for neurovasculature to
travel throughout the bone if you were to remove those structures it would appear completely hollow
in that region so that um that is not only important in terms of triglyceride storage
and neurovasculature but it also really reduces the weight of the bone think of this whole area
was just completely filled in with compact bone that would make that bone quite a bit heavier
that could affect movement but it would certainly affect energy consumption associated with movement
and then the last structure i want to talk about is the endosteum so endo- means within so we are
talking about this thin membrane of cells this is literally just um cells with a little bit of
connective tissue to kind of keep them together and so this is found within bone you will have
most of the bony cell types associated with the endosteum so you see the large osteoclast here
you'll have some osteogenic cells you'll certainly have osteoblasts as well
so most of the the bone cell types are going to be associated with the endosteum
and you'll have the endosteum lining the marrow cavity or the medullary cavity and then you'll
also see it associated with the trabeculae of bone as well so you can see the endosteum surrounding
the trabeculae that are within the bone all right excellent so those are the major parts of a long
bone and so let's take a moment to review with a question and as always i want you to pause the
video take time to answer this on your own and so the question here is articular cartilage is
typically located on what part of a long bone so pause if needed but if you're ready to answer i
hope that you went with b as the correct answer so it is the articular cartilage is going to be found
on the ends of long bones those ends are going to typically be associated with an epiphysis
that's going to form part of um be associated with articulating bones and form the joint
the diaphysis is going to be the shaft or the body of the long bone so it's not going
to have articular cartilage and that medullary cavity is actually within the diaphysis so also
wrong the metaphysis is a little trickier that you remember the metaphysis is the
region between an epiphysis and the diaphysis and you can actually have an epiphyseal plate
in the metaphyseal region and that is composed of hyaline cartilage so both the epiphyseal plate as
well as articular cartilage are made up of hyaline cartilage but they are located in different
regions as well as having very different functions as well so metaphysis while a little bit trickier
not the right answer either and lastly you have the periosteum which is going to surround
almost all of the long bone except for where there's articular cartilage
or insertions of ligaments or tendons so also not correct all right most excellent
thank you for your time and attention here and as always reach out if you have any questions