So, the structure of the bone is pretty simple.
Here we will talk about the long bone.
Now, please note that this is specific for long bone
and flat bones
may not have all of these different structures.
So, in the long bone, you have the shaft
or the long part of the bone.
This is referred to as the diaphysis.
At each end of the bone, you have the two epiphysis.
And the region that separates the diaphysis
from the two epiphysis are referred to
as the metaphysis.
The long bone also consist of other parts.
So, at the ends of each of the bones on the epiphysis,
you will have the articular cartilage.
This is going to be important for joints.
Also on the outside of the bone
you have a connective tissue layer known as
the periosteum.
Inside of the bone, there is a hollow space
that we refer to
as the medullary cavity.
And finally,
inside of this medullary cavity,
there is also a connective tissue lining
known as the endosteum.
So before we get started in talking about
the histology of the bone,
I first want to go over a little bit of vocabulary
that will help you navigate the following slides.
When you see the term Osteo,
think bone.
When you see the term Chondro,
think cartilage.
When you see Peri,
think peripheral
or the outside of the bone.
And when you see Endo,
think inside of the bone.
And for suffixes at the end of the word
when you see Blast,
especially when we're talking about certain types of cells,
these are normally precursor cells
that are going to secrete matrix
like collagen and ground substance.
When you see Cyte, think of those as mature cells.
So the bone is going to contain an abundant extracellular matrix
that is going to surround different types of cells
that are very widely separated.
The bone is mostly made up of three major components:
There's water.
There is a large amount of crystallized minerals,
those including
calcium phosphate,
calcium hydroxide,
and hydroxyapatite.
And finally, we have collagen.
The importance of collagen
is that calcification
or the hardening of the bone
requires the presence of collagen fibers
in order to occur.
So there are four main types of cells
found in our bones.
First we have, osteocytes.
which are mature bone cells.
Prior to that, we have the osteoblasts,
which are the precursor to osteocytes
and are going to secrete the matrix.
Prior to osteoblasts, we have osteoprogenitor cells.
These are a type of stem cell
that normally differentiate into osteoblasts.
And then we have osteoclasts.
Osteoclasts come from a different lineage
and are actually a type of white blood cell.
And this cell is going to be important
for remodeling
as this type of cell breaks down bone.
So in the bones,
we have two major types of bone tissue.
We have compact bone,
which is going to be good
for providing protection and support.
It is very thick and very strong.
And then we have
spongy bone.
Spongy bone is a lot more lightweight
and is also going to provide some support for the tissue.
Compact bone is usually found on the periphery of the bone.
Whereas, spongy bone is often found inside of the bone.
The epiphysis of the bone or the ends of the bone
are going to contain a large amount of spongy bone.
Whereas,
the diaphysis of the bone or the shaft of the bone
is made up of mostly compact bone
with a little bit of spongy bone also in the medullary cavity.
So, the bone does have a blood supply.
There are several different arteries and veins
that are going to go into and out of the bone.
In the periosteal area of the bone or that outer layer of the bone,
you have periosteal arteries.
These are also accompanied by periosteal veins.
Coming into the center of the diaphysis
or shaft to the bone
through a hole known as the nutrient foramen,
we have the nutrient artery.
This is going to be very important when we talk about bone formation.
Along with the nutrient artery,
exiting from the nutrient foramen,
we have the nutrient veins.
Also, in the metaphysis and epiphysis of the bone,
there will also be arteries and veins
associated with those areas as well.