Well, it is important to, first of all, start off by
looking at the properties of connective tissue
and these properties are varied. As I mentioned,
connective tissue consists of cells, matrix
and fibres, and various connective tissues
have various proportions of these three components.
One usually dominates and dictates the function
of that connective tissue. When you think
about epithelia, epithelia is supported by
a basement membrane and underlying connective tissue.
We call that underlying connective
tissue, the lamina propria, and that lamina
propria is dominated by cells. Sure, there
are some connective tissue fibres there, collagen
fibres to support the epithelium. But remember
epithelium forms the surface of body cavities.
Body cavity such as the respiratory system,
the digestive system, parts of the urogenital
system and also the skin. So epithelia is
a perfect place for pathogens to try and access
the body. So it makes sense that lamina propria
is dominated by cells that can identify pathogens
and then alert the body about the presence
of those pathogens and then commence an Immuno-response.
In contrast to lamina propria, bone
is very hard, and that is because the matrix
component dominates. The matrix is calcified,
makes it hard and that is perfect for what
bones need to be. They are the framework of
our body, the support of all our body organs
and they form limbs and enable us to move. A tendon
imparts the force of muscle contraction onto a bone.
So in tendons, the fibres dominate.
The collagen fibres as we will see during
this lecture are arranged in parallel sequence.
So they can impart the force of contraction
directly to the bone and be very effective
in doing that. So, connective tissue is very
different to epithelium. When you look at
this image of connective tissue, you find
that, first of all, the cells are isolated.
They are separated apart. They are surrounded
by the clear stain part you see there, which
is ground substance or matrix.
Unfortunately, in normal H&E sections, you don't see the
real components of that matrix. It just appears
as a clear space because a lot of the components
are lost during processing. But those cells
are very isolated from each other. Running through
the connective tissue, there are always going
to be fibres of some sort, most likely collagen
in most parts of the body. Collagen is the
most abundant protein in the body. And of
course as I mentioned earlier, connective
tissue is the pathway in which blood
vessels reach their destination and also
where nerves reach their destination.