A&P 1 Histology Lab Week 1

Pre-lab Guide – Putting Tissues In Context

This is an exercise I do with students in class to teach about

landmarks

Have someone from your group go to the slide tray marked “esophagus” and bring back a slide

There is a document with a summary online!

Last column!

#1

There are 2 versions of the “Squamous Tissue In-Lab Guide: One for people who know how to use a scope, and another for inexperienced people. This In-lab guide starts with “Step 1. ID Stratified Squamous Tissues, and learn some important lessons about microscopes, pointers, and tissue slides.” Do in order. If we run out of a slide in the tray, ask me, because other slides will have the same tissue. It helps to have someone in your group who has had a class where they learned to use a scope. I do not test you on your ability to use one! Believe it or not, I encourage students to look into a microscope with just one eye, placing your left eye on the right eyepiece, or vice a versa. It makes focusing MUCH easier! I know, I know…other science teachers tell you to keep both eyes open, but that is silly unless you are going to become a scientist. I keep one eye closed! The truth is … they usually do, too! Another thing … if you wear glasses, take them off. If you do not, you will not put your eye against the lens, leaving a gap so you won’t scratch your glasses. You will always struggle with focusing. And that eyepiece is a much better lens than your glasses, so you will make up for it when you focus!

Lastly: Remember what I told you about the different ways squamosal can look.

#2 The Pre-lab notes have info you need from the videos.

Tissues, Tissue layers and Cells “working together” What is the difference between “tissues” & “tissue layers”? 1. Tissues – collection of cells, doing a job. - 4 basic tissue types, each w/ subtypes:

* Epithelial- lining a cavity or surface, covering & secretion.

* Connective - support & attachment.

* Muscle - movement (locomotion & pump).

* Nervous - e- transmission for info & control of other tissues.

2. Tissue layers – important word is layers

- The term 'Visceral organs' is not an exact term. It usually refers to the abdominopelvic and thoracic organs involved in Digestion, Reproduction, Respiration, Excretion.

Each visceral organ is made up of

combinations of 2 or more of these,

arranged in tissue layers:

Typical Visceral Organ: What they do:

(NOTE: not all have these layers; this is just a starting point)

- The organ will move a substance through the lumen of the tube, and typically do one of 2 things (or

both):

a. Absorb substances from the lumen

into the tissues.

b. Secrete something into the lumen.

c. Also, the organ needs to provide protection, especially from harmful agents within the lumen,

and support and connect the organ to the body wall.

- Each tissue layer will have one or more tissue type. Tissue layers have specific functions. Here is a

pattern we are often going to see:

1. Mucosa: lines the cavity (lumen), and does all the absorbing & secreting in and out of

the lumen. Protects deep tissues from harmful things in the lumen.

Bacteria, viruses, abrasive materials, toxins

2. Submucosa: connects the mucosa to underlying tissues, contains glands for secreting

into the lumen, and blood vessels for supplying blood flow (see later).

3. Muscularis externa: move substances through the tube (e.g.: peristalsis). 2 layers:

longitudinal and circular.

4. Serosa: Give an outer "shell" to the organ, connect the tube to surrounding structures,

and (often) surround the organ in a protective fluid-filled bag.

However, our slides are often “pieces of the organ”

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Epithelial tissues line open areas. They secrete, absorb and protect.

They have 2 surfaces: - apical surface – next to lumen. May have brush border (microvillae) or cilia - basal (basilar) surface – next to deep tissues. Basement membrane attaches the mucosa to the deep tissues.

Notice there is usually fat & connective tissues surrounding the organ

In your visceral organs, we will see them in the mucosa (among other places, like the serosa).

Serosa

This leads to their “characteristics”:

The cells attach to each other, forming a sheet – nothing can “slip by them”. They can be 1 layer of cells, or “more than one” (“stratified” = “layered”).

1 layer = absorption or secretion. More than 1 = protection. Note the word “diffusion”. More in class.

They are associated with mucus, and other protective substances. Can’t have “stratified” in the gut, because we also must do absorption & secretion.

The apical surface is either going to be adapted for absorption/secretion (villi, brush border with microvilli), or protection (stratified or goblet cells and glands underneath).

They are named after their cell shapes, of which there are 3:

1. Squamous = flat. Simple squamous = diffusion surface, such as needed in the lungs. Stratified squamous = protection against things inside the lumen, like bacteria, etc.

Anywhere near outside world. Skin, cheek

2. Cuboidal = “square”. Both types = secretion = Glands” = “glandular epithelium”. “Rings of cells”.

3. Columnar = “long”. Absorbing cells. May also see Goblet cells.

Simple “Pseudostratified” = usually ciliated

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Before we begin: Why you hate microscopes: Our brains are easily confused. And cannot always see what is right in front of our faces. When we go to higher magnification, it is as though we are looking out a window as a plane lands.

Trouble is…we start at scanning power, when we should start at high power!

You must get to high power so your brain can recognize features. Then, even at low power, you brain can recognize landmarks. See the bridge in the first photo? On microscopes, we want to get to high power quickly! Do not “study it” on your way there! We will show your brain what it needs to see on high power. We will show it a pattern. Then we show it again at lower powers, and it will still see it!

Once your brain sees a pattern…it can’t stop seeing it! It will see it again, later…even if it looks a little different! This is NOT the Lion King: But I bet you CAN’T NOT SEE IT!

Low Power (Scanning power)

Medium Power

High Power

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The following is found in the “In-lab guide”, so you can skip it when you get to this:

Have someone from your group go to the slide tray marked “esophagus” and bring back a slide

Look at the accompanying image. You see a thin slice of an esophagus, without stain. Notice that you cannot see much in the way of layers or structures. So we stain them. The staining is different shades, depending on the fat and protein content of the cells and tissues. Staining the slice lets your brain see things much more clearly. Sometimes you will see the whole organ on the slide, especially if it from a mouse or other small animal. If it is from a larger animal, like a human, they will only give you a small piece (see box on image) Sometimes, if it is an older slide, the stain evaporates, as seen in the image. You should make sure you get the “darkest” slide available in the slide tray! Usually, when I have you look at a slide, I will start by having you simply holding it up to the light and orienting yourself. That way, you know what you are looking at!

We always need to ID the

lumen, mucosa, and submucosa!

But first: A word on our “purple stain”: Look at your esophagus slide, placing it on a piece of white paper, or holding it up to the light. So what do we expect on the slide? Depends if we are mostly protecting, or absorbing/secreting, or diffusing: “Thick shell” Thin lining with goblet cells and glands in submucosa Thin lining with nothing else

Slides have more than 1 tissue. Put things in their place on a slide!

Next to “white”. Highly variable, or thick shell. Dark staining = lots of protein. Note the other side of the organ with serosa and connective tissues

Webscope: Esophagus slide

Webscope: Small Intestines slide

We always need to ID the

lumen, mucosa, and submucosa!

H&E stain: This is a standard histology stain. "H&E" stand for hematoxylin and eosin. Hematoxylin and eosin stain is used for routine tissue preparation frequently. This is the most often used combination in the histology lab for general purpose staining. Hematoxylin binds to acidic structures, staining them blue to purple. It will bind and stain nucleic acids. Therefore, the nucleus stains dark blue. Eosin is an acid dye. It will bind to and stains alkaline structures (or negatively charged structures), such as amino groups on proteins. It stains them reddish-pink. More protein = darker red/pink Cytoplasm, connective tissue, colloid, all stain lighter pink to pink/orange/red with eosin. With an H&E stain, mucus and other watery solutions will stain a light blue color…almost white.

In the lumen, there is often “nothing”, so it will be white. So will the “outside” of the organ!

Look at your esophagus slide, placing it on a piece of white paper, or holding it up to the light. So what do we expect on the slide? Depends if we are mostly protecting, or absorbing/secreting, or diffusing: “Thick shell” Thin lining with goblet cells and glands in submucosa Thin lining with nothing else

Slides have more than 1 tissue. Put things in their place on a slide! Next to “white”. Highly variable, or thick shell. Dark staining = lots of protein. Note the other side of the organ with serosa and connective tissues

Just if we have time……the camouflage game is next. Otherwise, go to the first “In-lab guide” and go through microscope use

Webscope: Esophagus slide

Webscope: Small Intestines slide

#3

Just if we have time…… Camouflage goes away once your brain understands what it is seeing. What are you looking at? What is the difference between the two images?

OK…let me educate your brain…….

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This is called a Ghillie suit, made out of cheap material like burlap. Snipers like it because it is so effective, especially in a “laying down” position:

Notice the outline in the grass of the sniper, and the peculiar look on the head, due to the “hat”.

OK, now what are you seeing? Let’s look again (scroll down):

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What’s the difference? In the second one, we zoomed in on the sniper!

Camouflage works because it confuses your brain.

If we stop confusing your brain, and tell it where to look, it stops working

(the camouflage, that is)!

How many snipers are in the first photo? Sometimes zooming in with a microscope helps!

If time: Go to Anil Seth’s YouTube talk on audio

camouflage

NOW do you see why we use

microscopes?

Zoom in