In this lecture, I'm going to talk about epithelium.
Epithelium is one of the four basic tissues of the body.
The other three are connective tissues, muscle and nerve.
Epithelium is very important to understand because it's located in most organs of the body.
And if you can identify the different sorts of epithelium,
and you know the different functions of each of these epitheliums.
Then it's very important and very easy for you to understand,
then the structure of organs and being able to identify different organs.
At the end of this lecture, I would like you to understand the following:
Firstly, that epithelial cells are orientated in certain ways.
They're also classified or named differently depending on how they appear.
And also, in some instances their functions.
They have certain surface specializations
that have a very important role in some parts of the body.
Epithelial cells are very tightly held together by junctional complexes.
And I'll explain the different types of junctional complexes.
Epithelial are also very thoughtly anchored to underlying connective tissue.
Let me just summarize what the main functions of epithelia are.
And then we'll look at the structures of the epithelia that serve these particular functions.
Epithelia cover body surfaces. A skin is an example.
Skin is the external covering of the body. It's a very specialized epithelium.
And I'll talk about skin especially in another lecture.
Epithelia lines the body cavities, such as the thoracic cavity, the pleural cavity, and abdominal cavities.
It also aligns tubes. Some of those tubes are external to the body, such as the respiratory passages,
the gastrointestinal tract. And some tubes are internal, such as blood vessels.
Epithelia also forms secretory tissues or glands
and also the ducts or conduits that carry the secretory product of these glands to the surface.
And they're also in special instances receptors.
And we'll learn about those in more detail when we look at the ear,
and the tongue, and olfactory epithelium in the nasal cavity, and also the eye.
It's very important first of all to understand what the characteristics of epithelia are.
It has three major characteristics that really identify epithelia.
Firstly, each of the epithelial cells has an apex
or a surface that's adjacent to the lumen, which is often a hollow tube.
Here, you see a section through a collecting duct in the kidney.
You don't need to understand the details of the kidney at this stage,
but just have a look at this image, have a look at the sections through this tube.
Identify the lumen, and identify the epithelial cells.
They stain light pink, some you can see have a nice round nucleus.
In other instance you can't see the nucleus
because the section just hasn't pass through, that part of the cell.
But these epithelia all have the surface that opens into the lumen
which is the clear area in the center.
Epithelia also have lateral border, and that lateral border, has very important functions,
and that's where junctional complex has occur to hold these epithelial cells very closely together.
All epithelia sit on a basement membrane.
And therefore are anchored to underlying connective tissue.
We call that underlying connective tissue, lamina propria.
And I'll be talking about lamina propria a number of times in this lecture and also in other lectures.