Hey guys, Dr. Brown here. Another little video in histology and this time we're
gonna be going over something that a lot of folks have a hard time wrapping their
head around, and that is the epistle growth plate. So we look at this picture
of a long bone you can see that we're kind of zoomed in on that thin band of
hyaline cartilage there in the epiphysis of the bone, thats why it's called an epistle
growth plate. And the growth plate is actually divided into five distinct
layers. There's a zone of reserve cartilage. Immediately beneath that a
zone of proliferation, meaning that's the area where we're gonna make new
cartilage tissue. The zone of hypertrophy, where the cartilage cells themselves the
chondrocytes are going to enlarge and then die off. The zone of calcification
where the holes left by the dead cartilage cells are going to be
infiltrated by osteoblasts, which are going to start to calcify the cartilage
tissue. And then finally deepest down the zone of ossification where the calcified
cartilage is a remodeled into lamellar bone in the zone of ossification. So how
these zones relate to the direction of bone growth is something a lot of people
tend to struggle with and so I've put together just a little animation that will
hopefully make this make just a little bit more sense. Let's look at just the
growth plate all by itself. The helices is called the zone of
proliferation for a reason, it's going to be making new tissue. So as
chondrogenesis begins in the zone of proliferation new cartilage tissue is
going to be made. Hey, zone of proliferation got a proliferate, right? Now what's going
to happen next is deep down in the zone of proliferation, lower, those are the
cells that are the oldest. Those proliferated the longest time ago, and
they're eventually going to begin to undergo hypertrophy. so these cells are
going to undergo a morphological change, they're gonna get bigger, they're gonna
get bigger. Right? They're going to continue to grow meanwhile underneath
these cells down here that were hypertrophied, they're going to begin to
undergo calcification. So these recently hypertrophied
cells begin to calcify. Notice that the zone of proliferation is still
pushing up. So these cells that were in the zone of proliferation have now
differentiated, and this has become the zone of hypertrophy. So the...the...bottom
part of the zone of proliferation is now not part of the zone of proliferation,
it's part of the zone of hypertrophy. Likewise the zone of hypertrophy has
become the zone of calcification, and then finally down here the zone of
calcification is going to be remodeled into new bones. So the calcified
cartilage is remodeled into bone, and now what was the zone of calcification is
the zone of ossification. So essentially as the zone of proliferation grows, the
cells that were left behind from the previous iteration of growth in the zone
of proliferation, become the zone of hypertrophy, the cells that were zone of
hypertrophy become zone of calcification, and the cells that were in the zone of
calcification become ossification. Let's kind of wrap this up with a side-by-side.
So here's our original cartoon of the epiphysis growth plate, and here's the
cartoon we ended up with at the end. So you can see that it has gotten longer,
but it has gotten longer by extending upward...right...toward the zone of
proliferation. So we can kind of think of the epiphyseal growth plate as like a
snail, and as the snail crawls along, it's gonna leave a trail of bone behind it. So
that the bones are gonna...gonna...gonna...gonna...gonna...pardon me...the zones are gonna...
..once more...the bone is gonna grow toward the Epiphanes. Meaning the bones
are gonna grow from the edges outward. A lot of people want to think that the
bone is growing inward but that is not the case. As cartilage is being produced
at the top of the zone of proliferation everything beneath it is being turned
into more bone. More cartilage is made at the top everything beneath it becomes
bone. So I hope that helped make some sense out of how those layers in the
epistle growth plate contribute to bone growth, and why bone is growing in the
direction it's growing. Alright I hope that helps
study hard. Have fun. See you later.