Blood: Red and White Blood Cells

00:01 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.

00:22 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.

01:54 It maintains the shape of it, the stability of that shape and the flexibility.

02:02 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.

02:31 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.

03:49 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.

04:22 We put it on a glass slide, and then we spread it out of the slide and let it dry. Air dry.

04:30 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.

04:51 You're not looking at a section through the cells like you do when you look at other tissues.

04:56 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.

05:29 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.

05:57 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.

06:52 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 the basophil.