hello anatomy friends this is dr alsup and now that we are feeling a little more comfortable with
how bone forms remember through intramembranous and endochondral ossification let's talk about
how it actually will grow so we will discuss the differences between interstitial and appositional
growth and where these types of growth typically occur so we will spend a bit more time discussing
bone length growth and what is happening at the epiphyseal plate so we've introduced some
of these terms so now let's actually try to understand them in a little bit more detail
okay we've mentioned these in a few earlier videos and let's talk about the difference between
interstitial and appositional growth interstitial growth literally means growth from within so this
is the dominant process and bone growth in terms of length but remember that what is allowing this
to occur are those epiphyseal plates which are actually made out of hyaline cartilage so it's
the growth of that cartilage that is going to be very important in terms of interstitial growth
eventually it will be replaced by bone via that endochondral acidification
appositional growth means growth of the outer surface so instead of at that epiphyseal plate
it is occurring on the outer surfaces so particularly important in terms of growth of bone
width so what is happening just deep to the periosteum now during infancy childhood and
adolescence and even into a early adulthood for certain bones bones in the body grow in terms
of length particularly those long bones through interstitial growth as well as thickness through
appositional growth so both types of growth are needed to get the full skeletal full skeleton
and particularly in terms of appositional growth this will occur throughout your lifetime
so let's talk growth and length this occurs through two processes
first you will have that interstitial growth of the cartilage so that um
so that cartilage that's going to be found in the epiphyseal plates remember is hyaline cartilage
and it will also involve the replacement of that cartilage with bone and as we we know
from a previous video this is going to occur via endochondral ossification it is that activity of
the epiphyseal plate that allows for the diaphysis to get longer so the hyaline cartilage gets larger
at that epiphyseal plate and it will be replaced by bone on the diaphyseal side so
those new chondrocytes replace the old and that will eventually be replaced by bony tissue
now this is an important concept to get and that is that growth does not occur at the same rate
or time throughout the bones of the body or even on the same bone different ends of the bone can
ossify at different times and one end of the bone is always considered the dominant growing
end so the ends of the femur which you can see here as well as the tibia and the fibula which you
can't see the fibula very well on this particular donor the ends of these regions are going to the
dominant growing epiphyseal plates will be towards the knee so these are the ones that
will be growing faster than the ones opposite the knee whereas the ends that are opposite the elbow
in the upper limb are going to be the dominant growing epiphyseal plate so opposite the elbow
understanding these differences can be very useful in determining bone age and age at death and when
adolescence or early adulthood occurs those epiphyseal plates will close or in other words
the cartilage cells stop dividing and bony tissue will completely replace the cartilage and what
we're left with are those epiphyseal lines which indicate that bone growth and length has stopped
now bone growth and thickness or diameter can only occur through appositional growth and can
occur throughout life this type of growth occurs at the bone surface so just deep to the periosteum
is where this is going to occur once initiated and so those osteoblasts will begin to secrete
the organic materials of the bony extracellular matrix which will in this initiate calcification
so remember those osteoblasts will eventually eventually sufficiently surround itself and
trap itself and once it's trapped it becomes an osteocyte and so depending on how large and
how much bone growth will occur this process can continue to occur for forming numerous or maybe
only a few osteons additionally osteoblasts will deposit new circumferential lamellae so remember
there's a melee that will surround the entirety of the outer bone this process will continue
as long as the processes that initiate it continue so say there is a considerable weight-bearing
exercise in a certain area that could initiate those osteoblasts to secrete the organic material
now it's also important to note as these processes occur on the outer surface
these osteoclasts on the inner surface around the endosteum will break down the bone in that
region to maintain the proper amounts of compact bone because you don't want too much compact bone
and also maintain an appropriately sized medullary cavity all right so those are the basics of
interstitial appositional growths as well as bone length and bone width growths and similar to the
ossification processes these are very complex and you can have a whole course on these processes
but i just wanted us to be familiar with the very basics for this gross anatomy course but before we
part let's review a concept all right bone growth and width occurs through which type of growth is
it appositional or is it interstitial all right so recall that appositional growth is growth from the
outer surface so this is going to be outer surface whereas interstitial will be growth from within
so bone uh bone growth and width or diameter occurs on the outer surface so which one of
these would be correct i am hoping and thinking that you probably picked appositional and if you
did that is correct interstitial growth will be important in the growth of the epiphyseal plate
composed of hyaline cartilage which will be replaced by bone on the diaphyseal side
so that's important in terms of length and appositional will be important in terms of
width or diameter all right so that should wrap us up for this video thank
you for your time and attention here and as always have a great rest of your day