Let's just define a few terms when we
look at the cell.
Here is a diagram on the right-hand side typical of a
mammalian cell or a eukaryote.
First of all, the term protoplasm. This refers to
the nucleus and the cytoplasm,
both labeled 1 on the image you see in front of you. Then you have on the outside,
the cell membrane, labeled 2.The cell membrane
is a very, very important structure.
It is the barrier between the very stable internal environment of the cell and the external environment.
It allows transfer of materials across the cell membrane. Oxygen, nutrients, waste products, etc.
can pass in and out of the cell through the cell membrane through a very detailed
set of transport processes, and this system whereby there is transfer across the cell wall
in the mammalian cell is referred to in
Physiology as an open system.
The cell has a nucleus, and that nucleus has a nuclear envelope around it or a nuclear membrane.
Within the nucleus is the nucleoplasm that is a series of very fine scaffolding fibers as well as some fluid.
It contains also chromatin, which really are just strands of DNA, and rather obvious in this image
is that semi-spherical structure you see colored in blue.
That is the nucleolus. It's the typical structure found in mostly all nuclei in the mammalian cell population.
The cytoplasm consists of the ectoplasm and endoplasm.
Ectoplasm is just that very fine piece of cytoplasm
immediately underneath the cell membrane.
It doesn't contain any organelles. All it does is contain very fine actin filaments,
and those actin filaments help to support
the very delicate cell membrane.
The endoplasm is that part of the cytoplasm that contains all the organelles, those structures
I mentioned earlier that are membrane-bound
and that serve specific functions in the cell.
The endoplasm also includes what we call
Cytoplasmic inclusions are structures that may not be in all cells. They're inclusions that might be peculiar
to individual cell populations, and we'll see those when I describe these in more detail in a later lecture.
And of course, there is the cytosol or the cell sap, cell fluid. And lastly, I just want to briefly mention
the cytoskeleton, again, consisting of microtubules, intermediate filaments, and microfilaments
and again, let me just repeat that the cytoskeleton is involved with stabilizing the position of organelles,
supporting those organelles, even
moving them around where necessary,
and also supporting the cell membrane.
Now, this is a picture of your skin. This is the first time you've seen a histological section.
It shows you the detail of what your skin
looks like under a microscope.
on the bottom left part of the slide, you can see some very bright pink flaky material. That's keratin.
If you run your finger across the back of your hand
like I am here, you can scrape off that keratin.
That keratin is really the dead products of cells
that precede keratinization that form
the keratin in the surface layer of cells, and that keratin is lost continuously in our lives.
That keratin helps to waterproof our body. Underneath that keratin, you can see layers of cells.
Mostly, you just see circular pale-staining nuclei of the cells, and then further into the slide
towards the right-hand side, a much lighter region,
that's the dermis of your skin.
That is supporting connective tissue.
Without going through all the details—and we don't want to do that in this initial lecture. You don't need to know
the details of all this skin here—but what I want you to understand is you can see detail in this slide.
You can see details of the histology of what your
skin looks like. You can see that detail
because you use a tool in histology called a microscope, and a microscope does two things.
It magnifies or zooms in a slide of your tissue such as skin and it also provides you detail of what's in that slide.
And first of all, you need to cut a very thin
section of your skin to be able to magnify it
and also to see the detail. Here is a nice
picture of the earth and the moon,
and you can see in that picture some of the continents.
Lights are on in many of the cities in those continents. You can't see the details of those lights.
You can't even see sometimes the difference
between lights in one city and another.
And if I blow up or magnify that picture,
you're still not going to see any more detail.
Magnification doesn't provide any more detail of what you see unless your optical system also improves
what we call resolution or what we call
finding the detail.
If we zoom in on our world and get closer,
we can see more detail.
We start to see buildings and cities.
We start to see in this lovely city
where I'm giving these lectures in histology, Leipzig in Germany, you can start to see the streets and cars.
And if we zoom in more, if we increase the magnification and have the oculus system to see detail,
you start to see writing, the clock on the Town Hall, again, in this lovely city of Leipzig.
So what I really mean is for you to look at all the histological sections you're going to look at
in your histology course, you need to use a microscope that is going to magnify what is in the section
and it's going to provide detail. It has the resolving power to distinguish objects that are very, very close together
and our eyes can only distinguish objects that are about 0.2 mm apart.
If I look at my skin, I can't see any objects that are
closer than 0.2 mm or 200 µm apart.
The light microscope enables you to look at detail as you see in this section
and you can see objects that are as close as 0.2 µm apart. Again, that's what I mean
by greater resolving power using a microscope.