Let's first of all look
at the red blood cell,
the erythrocyte. Erythrocytes contain as I
mentioned before hemoglobin that binds oxygen
and carbon dioxide. They are shaped like a
biconcave disc. They have no nucleus.
They are very small. They are about 7 to 8 microns
in diameter and they have a central area that
is very thin of only about 0.8 microns, so
they are shaped like a biconvave disc. They
have a edge thickness of roughly 2.6 microns.
Now that biconcave disc shape is very important
because it allows the hemoglobin, the packages
of hemoglobin within the cell to have the
greatest exposure to the surface of the red
blood cell and then be able to very effectively
transport oxygen to the tissues. It has a
very very elaborate cell membrane as you can
see in the diagram. In the diagram, the cell
membrane is represented by a very thin surface
on the top of the diagram. You can see certain
structures projecting from that surface, the
surface proteins. Well on that surface, those surface
proteins have a number of roles, one is to
house the specific blood group antigens of
the red blood cell. And those proteins can
also, as you can see interact with the underlying
peripheral network of the cytoskeleton. And
that is important because the cytoskeleton
maintains the shape of the red blood cell.
It maintains the shape of it, the stability
of that shape and the flexibility.
You know red blood cells are very flexible although
they appear as biconcave discs when you see
them in sections of blood, they actually can
squeeze through very very fine narrow capillaries
and become elongated sausage-shaped structures.
That is because that cell membrane is very
flexible. Well, later on of course, as those red
blood cells aged, that flexibility is lost.
The red blood cells only lasts for about 120
days and hence that flexibility is lost, then
they find that they cannot work their way through
certain organs particularly the spleen. As
we will learn later on, the spleen is controlled
or least structured by having lots and lots
of reticular cells and reticular networks
through the spleen. And these aged red blood
cells when they leave blood capillaries in
the spleen and wander through the spleen,
sometimes they found it very hard to find
their way to navigate their way, pass this
reticular network into other blood vessels
to return back to blood system. So they get
stuck in this reticular network because they
have not got the flexibility anymore to get
through it. And so then they're phagocytosed by
macrophages. Let us now move on white blood cells, the
leukocytes. They are granulocytes or agranulocytes.
And the terminology we use is based on the
fact that they are to have granules within
them or they do not have granules within them.
So they are called granulocytes having granules
or agranulocytes without granules. So if you
look carefully at this stain or these two
stains, this image of blood I just want to
first of all explain to you how we really
examine blood or the normal way in which the
histologists or hematologists examine blood.
What we do is we take a little drop of blood.
We put it on a glass slide, and then we spread
it out of the slide and let it dry. Air dry.
We then stain that blood smear with various dyes.
We put a cover slip on the slide and then
we can examine it under the microscope. So
when you look at these two images here of
blood showing certain blood cell types what
you are looking at is the whole cell.
You're not looking at a section through the cells
like you do when you look at other tissues.
And for that reason, sometimes the cells look
a little bit blurred because you are actually
looking sometimes at different depth of foci.
And also it is sometimes difficult to actually
identify blood cell type because sometimes
you use the shape of the nucleus as the characteristic
feature to help identify a different blood
cell type and depending on the orientation
of the cell on the slide, it is very difficult
sometimes to see those characteristics.
So it is not unusual to look at those blood cells
and not know what it is. Have a look at the
red blood cell. You can see there that they
have a ring of dense eosinophilic stain, which
represents the hemoglobin and there is that
central clearer or lighter area of the red
blood cell that represents the biconcave disc
shape of the red blood cell.
Well let us look at stains. Stains, different stains
are used to identify components of the blood
cells particularly the white blood cells,
the granulocytes that I am going to talk about
now in more detail. We use methylene blue
or azure dyes to stain the bluey tinge you
see when you look at blood cells. They are
basic dyes and we use ASN or ASN like dyes
as acid dyes or acidic dyes. And they stain
the granules in these granulocytes and different
stains will show up these granules in different
colours and I was asked to distinguish the
different granulocytes that I am going to
describe. A basic dye will stain the nucleus.
It has an affinity for the DNA and acids within
the nucleus. Similarly an ASN dye or an acid
dye has an affinity for a basic type component
in the cell or basal cell in this base component
of the chemical nature of some of the components
of the cell. And using these dyes then we
can stain granules as being either eosinophilic
or red as you see in this slide or sometimes
you can use them to show the base dyes. You
can use them to show a bluey tinge in some
granules. The azure dyes are shown here. So
those staining criteria are important to identify
the different granulocytes. On the bottom
left of the slide are listed the most common
granulocytes we are going to come across in
blood, the neutrophil, the eosinophil and