Here is a number of images
of basically the same part of the body, a
wall through a blood vessel except for the
lymph node down below showing reticular fibres.
Using H&E, it is very difficult to tell the
different between smooth muscle, collagen and
elastic tissue. But if you use the Weigert's
stain, you see here, the elastic tissue is
now differentiated, and you can see the elastic
tissue from the smooth muscle and the collagen.
If you use the Masson stain, the green stains
collagen and the browny reddy component
stains smooth muscle. The Gomori stain down
below, the collagen stains blue and smooth
muscles stains the reddish colour. And you
can see a very shiny white line on the very
edge of the blood vessel that is elastic tissue.
It is the elastic lamina, we will talk about
when we talk about blood vessels later
on. So we can use these stains in certain
tissues to differentiate the sorts of fibres
in the tissue from smooth muscle and from
each other. And the reticular fibres are shown
here using a silver stain.
Well, let's have a look at the extracellular constituents
of connective tissue, the matrix. The extracellular
matrix is really a combination of three components,
collagen we know that from what we have seen
so far but also non-collagenous glycoproteins.
Remember I said collagen is a glycoprotein.
Well, there are a lot of other glycoproteins
in the extracellular matrix and they have
a very important function or a numbers of functions.
They actually combine the cells to the fibres.
They can regulate a lot of the activity of
the cells, signalling of these cells.
They have a role in dictating lots and lots of
functions to the cells. I am not going to
talk about it in great detail, but the cell biologists
and the physiologists will certainly emphasize
the role of these special glycoproteins when
you talk about the physiology and the cell
biology of the extracellular matrix. The major
component of the extracellular matrix that
has a real important function are the proteoglycan
aggregates. They are called glycosaminoglycans
and here is a diagram illustrating one of
these highly organised, highly complex proteoglycan
aggregates. And I am not going to go through
all the detail of these again. I emphasized the
cell biologists will talk to you about
these in cell biology courses, but have a look
at the diagram and the main features is to
understand that you have these huge molecules
running through the extracellular matrix.
In this case, hyaluronic acid, the hyaluronan
molecule, the blue one running through this
diagram. And attached to this hyaluronic acid
molecule, this huge molecules are different
sorts of core proteins shown in green. And
on those core proteins, you see glycosaminoglycans.
These are the most important functional components
or molecules of the extracellular matrix.
Here is a diagram shown on the left-hand side
and here in the middle is an Australian
Bottlebrush. You know when you talk about
Australian wild flowers, everyone knows the
bottlebrush. But why am I showing you is bottlebrush
in this lecture? Well it really looks like a
glycoaminoglycans because if you look at the
core protein in the diagram, it is just like
the stem of the bottlebrush, and the glycoaminoglycans
projecting off that core protein are like those
red fine lines making up the bottlebrush flower.
Now, the most important role that these glycoaminoglycans
have, is that they are all negatively charged.
So all those little fine fibres you see making
up the bottlebrush, if they are negatively
charged, they repel each other as they do
in the extracellular matrix. And that creates an
enormous space for water. It attracts water
and therefore the connective tissue extracellular
matrix is very turgent. It is a gel like viscous
strong structure because of this ability to
attract and hold lots of water in. And on the
far right-hand side, that strange looking
structure illustrates the importance of the
extracellular matrix. We don't seem to appreciate
the importance much when we think about it in
the lamina propria for instance, but yet it
is very resistant to compressive forces. Well,
this structure on the right-hand side is an
umbilical cord consists of two arteries
and one vein. It is not important.
We identified these components here, but they're
surrounded by extracellular matrix, a special mucous
connective tissue that is called Wharton’s jelly.
Now that extracellular matrix has lots and
lots of these glycosaminoglycans within it,
attracting water, holding the water in and
making this umbilical cord not at all compressive.
And that is important because the umbilical
cord is a lifeline when we are developing
in the womb. It twists and turns and we do
not want it to be compressed. Otherwise, blood
flow to and from the developing foetus is
retarded. So this extracellular matrix has
a very important role in making sure the umbilical
cord does not become compressed. Again it
illustrates the important role of these very
special molecules in normal connective tissue