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A&P 1 Histology Labs #3 -

Understanding What You Are Looking At Under The Scope Lab Exercises

Have someone in your group read the following out loud, while the others read along:

In this "Lab Exercise", we will be looking at how to look at tissues under the microscope. We do not expect you to be an expert with microscopes by the end of this "Walk-About". But, we hope to give you a better understanding of what you are seeing on a slide! You will not be tested on your ability to focus or otherwise use a microscope. PLEASE NOTE: Your group will be needing a microscope at the workstation. All of the steps in this guide are designed to be done at the workstation. DO NOT use a microscope that is already set up in the room, being used as a demo. Instead, get a new one from the microscope storage, get out a power cord, plug the cord into the microscope, and use the microscope at your station! The Steps found in this "Lab Exercise Guide" SHOULD be done in the order they are found. Please do all the questions within a step before moving on to another step! Remember that this is trying to give you a better understanding of what you are seeing in the microscope. If you do not understand the main point of a question, please discuss it with your instructor!

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Step 1. The Airplane Ride: Learning how to look at slides.

Have someone in your group read the following out loud, while the others read along:

Opening Paragraph (we'll be referring to this later) Before we begin identifying tissues, let us look at some common problems that students often have when looking at slides for the first time. This will be worth the effort, as it will save us lots of time later! There are 3 common problems students first have:

1. Not understanding how differently the same objects look at different powers. 2. Not understanding what is a "cell" is on a slide. 3. Not understanding what an "artifact" is on a slide.

If everyone in the group feels comfortable with these 3 concepts, we can skip this STEP and move on to the histology identification labs. Well...are we going to do this step? If yes...keep reading! If not, go on to the histology identification labs! The next few pages have a lot of reading to be done. Keep moving at a good pace, so you'll have time to look at some tissue slides. Check the time: you'd like to have more than an hour to proceed with tissues. You can come back to this later if need be! Continue Reading: First of all, let's think about what we are doing. Looking through a microscope is like looking out the window of an airplane.....things look very different depending on whether we are close to them or far away.

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Continue Reading:

In an airplane, that depends on whether or not you have taken off....houses look really different "close to the ground" , say, a couple f hundred feet, from what they do at 10,000 feet! Look at the image below, which shows you this simple fact:

In a microscope, the distance is always the same, but how detailed things look depends on the POWER. Think of going higher in power as going LOWER in an airplane: things are closer, and you see more detail. Look at IMAGE "A" below, and discuss what is being shown:

This is like "going up in an airplane", right? Things get farther away. You see less detail but you see more of them.

Image "A"

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See the point we are making? You see CELLS really well at high power, but TISSUES (collections of cells) at lower powers!

When we look at tissues in lab, we will usually do this in reverse: start at low power, and work our way up to higher power. Now look at IMAGE" B" below, and discuss what it is showing you.

This is like "landing in an airplane", right? The cells get closer and more detailed as we move in!

Image "B"

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#6 Continue Reading: Now it is time to look at the slide labeled "Small Intestines: Duodenum, Jejunum, Ileum"

Recall ... The slide should look something like this:

Hold the slide up to the light in the ceiling, and take a look. Can you see that this is 3 sections of different parts of the digestive tube? Can everyone in your group see, on all 3 slices:

Lumen Epithelial lining

Serosal Covering

Now, we are going to put it in the microscope, and zoom in to get a closer look.

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Continue Reading:

Make sure your scope is on low power (40x). Now, look in the eyepiece. It doesn't matter which of the 3 organs you have in view.....it should look something like this:

Or

Note: The rest of this STEP should be done while looking at the microscope, NOT looking at these images. The photos in this document do not have enough resolution to show you what you need to see!! Make sure you can see something like this in your scope!

Whole tube Part of the tube

In microscope

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#9 Continue Reading: ID the lumen on you slide in the microscope, using the image below. The dark area next to the lumen is the "mucosae"...it is an epithelial tissue layer:

Q1. Look at the area on your slide that is similar to the boxed-in area in the photo above. Can you see cells, with nuclei? Can you detect cell shape? Please pick from the following:

YES NO Not Sure

Pick a part of the tube to zoom in on. In this guide, we will choose this area:

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Q2. When we go to a higher power (100X), it can you see cells? Nuclei? Please pick from the following 4 choices:

YES NO Not Sure Better than before

Q3. To answer this, use the image below. Which of these is indicating a cell (more or less)? A B C None of them

Continue Reading: On your microscope, zoom into the region that is similar to the region marked "B" on the photo above. Go to the next page.

A

B

C

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Continue Reading: If we go to 400X, it will be like doing this zoom-in:

And you will see something like this in the eyepiece:

At 400X, we can clearly determine the nuclei of individual cell, as well as get an idea of their shape. In the above image, there are 2 main types of cells: elongated ones, and small, round ones.

Q4. Can you trace the outline of some of the cells on the image? How about a nucleus?

A guide is found on the next page, but you should try before looking!

Zoom in Zoom in

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On all of them, the nuclei are "roundish", dark structures. The nuclei help your eye see where the cell is! First, look at the lumen. Then find both sets of nuclei. Then, determine what a "cell" is!

Now, go back to the first question in this step. Do you see that most of you should have chosen "not sure"?

The truth is...most of you had no idea what I meant when I asked if you could see a cell, or nuclei, or cell shape. But once your brain can ID them, you can usually see them right away!

Q5. Now put your microscope BACK onto low power. Can you now identify:

1. some Nuclei? 2. "What is a cell?" 3. Some "Cell shape?"

--------------------------------------------------------------------------------------------------- You have finished the exercises you should do in lab before looking at "Epithelial Tissues". If you have time, you can do the section 2 which discusses "Artifacts". Otherwise, you can do that part later. ---------------------------------------------------------------------------------------------------

Lumen

nuclei

nuclei

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Step 2. Artifacts Remember, we said there are 3 common problems:

1. Not understanding how differently the same objects look at different powers. 2. Not understanding what is a "cell" on a slide. 3. Not understanding what an "artifact" is on a slide.

We've discussed #1 & #2. But...what is an artifact? Here is a text book's definition: "An artifact is an artificial feature introduced into a section because of the way it was prepared."

Q6. One common artifact is the presence of air bubbles in the mounting medium. How do you think an air bubble would look? On the image below, which might represent an air bubble? Place a "bubble" on all that apply! Q7. Some tissues shrink during preparation. Tissues that are in contact during life may therefore be separated by a gap in the section you are viewing. On the image below, which might represent separating tissues? Place a "shrink" on all that apply! Q8. Another common problem that occurs is when students focus on the slide itself, or an area of the slide that doesn't have tissues. Or perhaps the student focuses on some sort of debris on the slide (smudges, cracks in the glass, ect.). Which of the images below represent this scenario? Place a "debris" on all that apply!

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An air bubble

Debris in the lumen

A tear in the tissue (find at least 4)

That does it for our lesson on using the microscope, and looking at tissue slides. Your group should now move on to "Epithelial Tissue ID".