00:02
In this lecture,
I'm going to talk about bone.
00:05
But I'm going to
concentrate on mature bone
and the function of mature bone.
00:11
In a later lecture,
I'm going to talk about bone formation
and bone growth.
00:19
Bone is a very specialized
connective tissue.
00:24
Like all connective tissues,
it's composed of cells,
fibers and matrix.
00:31
But in the case of bone,
the matrix is calcified.
00:35
And because of that,
it enabled bone
to have some very important
functions in the body.
00:43
It can protect vital
organs of the body,
the thoracic cavity protects
the heart and the lungs.
00:51
The cranium protects the brain.
00:55
Bone always forms the skeletal
components of the body,
and in unison with muscle
affects movement of the body.
01:07
It's also a very
important mineral reserve
for both calcium and phosphate.
01:14
And it provides a compartment for
bone marrow to form blood cells.
01:20
I'm going to talk about
these latter two functions
in a lecture later on.
01:28
Let's look at really what
I want you to understand
with this initial
lecture on bone.
01:37
First of all, I want you to appreciate
that there are two types of bone,
compact bone and spongy bone.
01:45
And I'll describe these two
types during this lecture.
01:50
The very fundamental structural
unit of bone is the osteon.
01:55
And I will also describe that,
and it's something that you
really should understand
because it will explain
to you really how bone
forms its functional
role in the body.
02:08
And equally important,
you must understand how bone
cells received their nutrients.
02:15
As I said earlier,
the matrix is very hard, it's calcified.
02:20
Unlike other connective tissues,
such as loose connective tissue
or even cartilage.
02:27
There is no aqueous component
of the extracellular matrix.
02:33
So nutrients, including oxygen,
cannot diffuse through that matrix.
02:39
So I'm going to
explain in this lecture
how bone cells get their
nutrients from the blood
when they're embedded in this
very firm calcified matrix.
02:51
So, again, let's look at
what characterizes bone.
02:58
First of all, it's vascular.
03:00
Unlike cartilage,
it has the blood supply.
03:03
It has a very
large blood supply.
03:07
If you break a bone, it bleeds.
03:10
Again, like connective
tissues, it has cells,
fibers and matrix.
03:18
The cells are called osteocytes.
03:22
And these osteocytes live
within the bone matrix.
03:27
And often you see just
a small clear space,
this is a lacuna.
03:34
And a lacuna is really, a space is
occupied by the bone cell or the osteocyte.
03:43
Normally, the osteocyte would
occupy the entire space.
03:47
But during processing of bone,
often the cell is completely
lost from its territorial area
in the bone matrix, and just a small
little space or lacuna remains.
04:01
Sometimes however,
in some of these little lacuna spaces,
you can see remnants
of the osteocytes.
04:09
Again, like cartilage, the most important
functional part of bone is the matrix.