Epithelium: Introduction

00:01 In this lecture, I'm going to talk about epithelium.

00:05 Epithelium is one of the four basic tissues of the body.

00:09 The other three are connective tissues, muscle and nerve.

00:14 Epithelium is very important to understand because it's located in most organs of the body.

00:21 And if you can identify the different sorts of epithelium, and you know the different functions of each of these epitheliums.

00:30 Then it's very important and very easy for you to understand, then the structure of organs and being able to identify different organs.

00:40 At the end of this lecture, I would like you to understand the following: Firstly, that epithelial cells are orientated in certain ways.

00:50 They're also classified or named differently depending on how they appear.

00:56 And also, in some instances their functions.

00:59 They have certain surface specializations that have a very important role in some parts of the body.

01:08 Epithelial cells are very tightly held together by junctional complexes.

01:14 And I'll explain the different types of junctional complexes.

01:18 Epithelial are also very thoughtly anchored to underlying connective tissue.

01:25 Let me just summarize what the main functions of epithelia are.

01:31 And then we'll look at the structures of the epithelia that serve these particular functions.

01:39 Epithelia cover body surfaces. A skin is an example.

01:44 Skin is the external covering of the body. It's a very specialized epithelium.

01:50 And I'll talk about skin especially in another lecture.

01:54 Epithelia lines the body cavities, such as the thoracic cavity, the pleural cavity, and abdominal cavities.

02:04 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.

02:20 Epithelia also forms secretory tissues or glands and also the ducts or conduits that carry the secretory product of these glands to the surface.

02:32 And they're also in special instances receptors.

02:35 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.

02:47 It's very important first of all to understand what the characteristics of epithelia are.

02:53 It has three major characteristics that really identify epithelia.

03:00 Firstly, each of the epithelial cells has an apex or a surface that's adjacent to the lumen, which is often a hollow tube.

03:11 Here, you see a section through a collecting duct in the kidney.

03:16 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.

03:24 Identify the lumen, and identify the epithelial cells.

03:29 They stain light pink, some you can see have a nice round nucleus.

03:35 In other instance you can't see the nucleus because the section just hasn't pass through, that part of the cell.

03:42 But these epithelia all have the surface that opens into the lumen which is the clear area in the center.

03:51 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.

04:05 All epithelia sit on a basement membrane.

04:11 And therefore are anchored to underlying connective tissue.

04:16 We call that underlying connective tissue, lamina propria.

04:20 And I'll be talking about lamina propria a number of times in this lecture and also in other lectures.