Anatomy 9-1

Anatomy and Physiology, Grades 11 and 12

Module #2: Histology, The Study of Tissues

Lecture 2 of 2  —  Simple Epithelial Tissue

Text pages 34 to 36, Figures 2.1, 2.2, and 2.3  |  40 Minutes  |  Mr. Gibbs

At a Glance

• 0:00 to 0:04  Review the naming system

• 0:04 to 0:13  Simple squamous epithelium, Figure 2.1

• 0:13 to 0:22  Simple cuboidal epithelium, Figure 2.2

• 0:22 to 0:34  Simple columnar epithelium, Figure 2.3

• 0:34 to 0:39  The beauty of histology

• 0:39 to 0:40  Close and announcement

Materials: whiteboard, textbook open to Figures 2.1, 2.2, and 2.3. Keep yesterday’s classification grid on the board.

The whole lecture runs on one idea, and the book states it explicitly at the end: cell size determines how much cellular machinery fits inside, and that determines how complex a task the tissue can do. Squamous does simple work, cuboidal does more, columnar does the most. Build toward that rather than presenting three unrelated tissues.

1. Review the Naming System

4 minutes. Cold call. They should be able to rebuild this from yesterday.

• What are the two things we look at to classify epithelial tissue? Number of layers and shape of the cells.

• One layer is called what? Simple. Several layers? Stratified.

• Flat cells are called what? Squamous. Cube shaped? Cuboidal. Tall like a column? Columnar.

• What are the two surfaces of epithelial tissue called, and what is the glue between the basal surface and the tissue below?

• One more, since it is the concept most likely to have slipped: what does avascular mean, and how do epithelial cells get oxygen and nutrients?

2. Simple Squamous Epithelium

9 minutes. Figure 2.1, page 34.

• Name it from the grid first: one layer, so simple. Flat, squatty cells, so squamous. Simple squamous epithelium.

• Now ask the book’s two questions, and let the class answer both: does this epithelium look like something that is going to offer a lot of protection? No. Does it look like there can be a lot of cellular machinery in there? No.

• Draw the conclusion the book draws: simple squamous epithelium cannot be used for protection or complex tasks. However, in certain applications it is perfect.

Where it is found, and what it does

• Two locations from the book: our blood vessels are lined with simple squamous epithelium, and the tiny air sacs of the lungs are also made of simple squamous epithelium.

• The function, stated plainly: the function of simple squamous epithelial tissue is TO ALLOW DIFFUSION. The tissue offers just a minimal barrier through which diffusion can occur.

• Use the book’s lung example: in our lungs, oxygen moves into the blood vessels strictly by diffusion, through this very delicate simple squamous epithelium. Carbon dioxide diffuses the other way.

• Land the structure to function point in the book’s words: the tissue does not offer much of a barrier, but that is okay. The thinner the tissue, the more effective the diffusion. Simple squamous epithelial tissue is perfectly suited for its function.

Connect back to Module 1 here if you have thirty seconds. They studied simple diffusion during the transport lecture. This is that same process, and this tissue is the anatomy that makes it possible.

3. Simple Cuboidal Epithelium

9 minutes. Figure 2.2, page 35.

• Have them compare the two figures directly, as the book instructs: notice the difference between these cells and the ones drawn in Figure 2.1. The cells are not squatty. They are shaped more like cubes.

• Name it from the grid: the tissue is still only one cell layer thick, so it is still simple epithelial tissue, but the cells are cubic. Thus, this is a SIMPLE CUBOIDAL EPITHELIUM.

• Now the reason the shape matters, and this is the heart of the lecture: since the cells are thicker in this kind of tissue, there is more room for cellular machinery like mitochondria, Golgi apparatuses, endoplasmic reticulum, and so on.

BOOK LANGUAGE:  cellular machinery. The book uses this phrase repeatedly. Use it rather than substituting "organelles," because the phrase is what carries the argument in the closing section.

• The resulting function: simple cuboidal epithelium allows for diffusion, BUT it is also used for absorption and secretion.

• The book’s example: our kidneys are absorbing certain substances and secreting others constantly, in order to clean the blood. The tissue found in the kidneys is mostly simple cuboidal epithelium.

• Ask the connecting question: why can this tissue absorb and secrete when simple squamous cannot? Because absorption and secretion take machinery, and there is now room for it. Get that answer from a student before you move on.

4. Simple Columnar Epithelium

12 minutes. Figure 2.3, page 36. This section has the most in it.

• Name it from the grid again: even though the cells are very tall, the tissue is still only one layer thick. Those tall cells are shaped like columns. Thus, this is a SIMPLE COLUMNAR EPITHELIUM.

• Extend the machinery argument one more step: since the cells are so much taller, there is room for even more cellular machinery. As a result, this kind of tissue can perform more complex secretion and absorption tasks than simple cuboidal epithelium.

Goblet cells

• Point out that Figure 2.3 has something new in it: there is a new type of cell in this tissue. These cells are called GOBLET CELLS, and their main job is to produce mucus. Have them find the goblet cell and the mucus in the goblet cell on the figure.

Where it is found, and the stomach problem

• The location: the lining of the stomach and intestines comes to mind right away.

• Pose the problem the book poses: the stomach is very, very acidic because of the acid it secretes. That acid is necessary for the digestion of food. Nevertheless, stomach acid would immediately kill the epithelial tissue if it were not protected.

• Then the solution: the mucus protects the epithelial lining from being damaged by the acid. The mucus secreted by the goblet cells forms a nice coating over the top, protecting the stomach.

• And the comparison the book adds: in the small intestine, the protection of the mucus is not as critical, because the small intestine is not as acidic as the stomach.

This is the best example in the section. The stomach has to make acid strong enough to digest food, and it is lined with living tissue that the acid would destroy. The goblet cells are the answer. Ask the class how a stomach avoids digesting itself before you give it to them.

Cilia

• Note what the figure does not show: in some parts of the body, the simple columnar tissue has CILIA as well. The cilia are not pictured in the figure, but they are sometimes there nevertheless.

• The book’s example: when we study human reproduction, we will learn that the female egg is moved from the ovary to the uterus via the fallopian tube. The simple columnar epithelium in the fallopian tube has cilia, and the mucus covering the epithelium is moved by the beating of those cilia. The egg is moved along with it.

• Call back to Module 1: they already met cilia during the organelle review. Same structure, and here is a tissue built around them.

5. The Beauty of Histology

5 minutes. The book flags this section by name. Do not cut it.

• State the book’s claim: before we move on to stratified epithelial tissue, you need to understand the beauty of histology. When we look at tissue, analyzing the type of tissue helps us determine its FUNCTION.

• Walk the three, in order, as the argument the book builds:

◦ In SQUAMOUS tissue, the cells are not big enough to provide much protection. They also cannot hold much cellular machinery. Thus, squamous cells can perform only simple tasks, such as providing a thin barrier for diffusion.

◦ CUBOIDAL cells are larger and can therefore hold more cellular machinery. This increase in cellular machinery allows the cells to do more complex tasks, such as active transport.

◦ Finally, the tall cells of COLUMNAR tissue can perform the most complex tasks, because their increased size allows for more cellular machinery.

• Land it in the book’s words: in the end, you can look at tissue on the microscopic level and see the kind of task that the tissue must do.

• Then draw the whole grid together on the board: three shapes, three levels of task complexity, and one reason underneath all of it. Have a student state the reason in one sentence.

The book calls this an incredible testament to something, and the sentence continues onto the next page, which I do not have. Read that closing line straight from your copy so the wording is the book’s and not mine.

6. Close

1 minute.

• Preview the next section: so far every tissue has been one layer thick. Next we take on STRATIFIED epithelial tissue, and that is where the avascular problem from yesterday finally pays off. Ask them to think about what happens to cells in a thick tissue that end up far away from the blood supply.

ANNOUNCEMENT.  Remind them the histology slides are set up in the dining room during first period all this week. Tell them again that anyone is welcome to come look, and give the specifics: whether they need permission to be in there, whether the scopes are already focused, and what is to be left alone. Say it even though you said it yesterday.

• Assign the reading. Dismiss by procedure.

Objectives

• Students will classify simple squamous, simple cuboidal, and simple columnar epithelium using number of layers and cell shape.

• Students will state the function of simple squamous epithelium and give two locations where it is found.

• Students will explain why simple cuboidal epithelium can perform absorption and secretion when simple squamous cannot.

• Students will identify goblet cells and explain how mucus protects the stomach lining from its own acid.

• Students will explain how cell size determines the amount of cellular machinery and therefore the complexity of the task a tissue can perform.