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