Epithelium: Introduction

by Geoffrey Meyer, PhD

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    00:01 In this lecture, I am 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.

    00:15 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 is 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 are also classified or named differently, depending on how they appear and also in some instances, their functions. I 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 will explain the different types of junctional complexes. Epithelia are also very tightly anchored to underlying connective tissue. Let me just summarize what the main functions of epithelia are, and then we will look at the structures of the epithelia that serve these particular functions. Epithelia cover body surfaces. Our skin is an example. Skin is the external covering of the body. It is a very specialized epithelium and I will talk about skin specially in another lecture.

    01:55 Epithelia lines the body cavities such as the thoracic cavity, the pleural cavity, and the abdominal cavities. It also lines 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 are also in special instances receptors, and we will 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 is very important, first of all, to understand what the characteristics of the epithelium are. It has three major characteristics that really identify epithelia. Firstly, each of the epithelial cells has an apex or surface that is adjacent to the lumen, which is often a hollow tube. Here you see a section through a collecting duct in the kidney. You do not need to understand the details of the kidney of 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.

    03:36 In other instance, you cannot see the nucleus because the section just has not passed through that part of the cell. But these epithelia all have a surface that opens into the lumen, which is that clear area in the center. Epithelia also have a lateral border and that lateral border has very important functions and that is where junctional complexes 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 will be talking about lamina propria a number of times in this lecture and also in other lectures.

    About the Lecture

    The lecture Epithelium: Introduction by Geoffrey Meyer, PhD is from the course Connective Tissue.

    Included Quiz Questions

    1. They are anchored to underlying connective tissue by the lamina propria.
    2. They have a surface adjacent to a lumen or free space.
    3. They are held together by junctional complexes.
    4. They all have an apical segment (an "apex").
    5. They all have a lateral border.

    Author of lecture Epithelium: Introduction

     Geoffrey Meyer, PhD

    Geoffrey Meyer, PhD

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