# 3.1: Examining epithelial tissue under the microscope (2023)

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## Information

Epithelial tissue serves two main functions in the body.

1. It providesliningsfor external and internal surfaces that face harsh environments. The outer layer of the skin is epithelial tissue, as are the innermost layers of the digestive tract, the respiratory tract, and blood vessels.
2. It formsglandsthat secrete materials onto epithelial surfaces or into the blood. Sweat glands, salivary glands, mammary glands, adrenal glands, and pituitary glands are examples of glands made of epithelial tissue.

Epithelial tissue is often classified according to numbers of layers of cells present, and by the shape of the cells. See Figure 3.1.

Asimple epitheliumis only one layer of cells thick. Astratified epitheliumis more than one layer of cells thick. Apseudostratified epitheliumis really a specialized form of a simple epithelium in which there appears at first glance to be more than one layer of epithelial cells, but a closer inspection reveals that each cell in the layer actually extends to the basolateral surface of the epithelium.

There are three basic shapes used to classify epithelial cells. Asquamousepithelial cell looks flat under a microscope. Acuboidalepithelial cell looks close to a square.

Acolumnarepithelial cell looks like a column or a tall rectangle. A few epithelial layers are constructed from cells that are said to have a transitional shape.Transitionalepithelial cells are epithelial cells specialized to change shape if they are stretched laterally. They can transition from columnar- and cuboidal-looking shapes in their unstretched state to more squamous-looking shapes in their stretched state.

When classifying a stratified epithelial sheet, the sheet is named for the shape of the cells in its most superficial layers. So, a stratified squamous epithelium only necessarily has squamous-shaped cells in its highest layers and might have a different-shaped cell in its lower layers.

Under a microscope, epithelial cells are readily distinguished by the following features:

• The cells will usually be one of the three basic cell shapes – squamous, cuboidal, or columnar.
• The cells will be closely attached to one another, in either a single layer or in multiple layers, and usually will not have room for extracellular material between the attached cells.

The epithelial layer on one side will face an empty space (or, in some organs, it will face a secreted substance like mucus) and on the other side will usually be attached to connective tissue proper.

Usually, a slide will have a section of tissue cut out of a larger organ. Slides with epithelial tissues usually have some of the underlying tissue found beneath the epithelial tissue with them.

(Video) Identifying Epithelium | Review and Practice Questions

A layer of epithelial cells always serves as an outer layer for some structure, but, when looking at a tissue preparation on a slide, do not assume that just because you have found one end of the tissue sample you are automatically looking at epithelial tissue. Look for the cell characteristics listed above to be sure you are on the epithelial side of a tissue slice.

In Figure $$\PageIndex{2}$$, only one edge of the tissue slice has epithelial cells. In Figure $$\PageIndex{2}$$A that edge is indicated with an arrow, but when looking at a specimen under a microscope, you have to figure out for yourself where the edge with the epithelial cells is.

In the tissue slice in Figure $$\PageIndex{2}$$, there are three edges that are not epithelial cells. If you just mindlessly started viewing the first edge you find, you have a good chance of looking as something other than the epithelial cells in the preparation. Be sure what you are looking at has the three visual characteristics of epithelial tissue:

• The cells will usually be one of the three basic cell shapes – squamous, cuboidal, or columnar.
• The cells will be closely attached to one another, in either a single layer or in multiple layers, and usually will not have room for extracellular material between the attached cells.
• The epithelial layer on one side will face an empty space (or, in some organs, it will face a secreted substance like mucus) and on the other side will usually be attached to connective tissue proper.

In the following figures are some more epithelial layers. Note that whether the epithelial layer of the specimen is on the top, bottom, right, or left of the slice varies with how the specimen slice was positioned on the slide. In every case, you have to find which edge has the epithelial layer.

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## Setting up a microscope

Lab 1 Exercise 1

1. Plug in the microscope & turn on light source.

2. Pick up microscope by carrying arm, position it so it is accessible to your seat, with open side of the stage facing you

3. Rotate the objectives so that the lowest power objective (smallest in size) clicks into place.

4. Look at the slide with your naked eye and find the location of the specimen.

5. Clip the slide into place with the stage clips. The cover slip on the slide must face up. Find the stage controls and make sure that, when they are turned, the slide moves smoothly left and right or up and down, depending on the knob.

6.Use the stage controls to move the slide so that the light source is shining directly on to the specimen to be magnified.

7.Find the coarse and fine focus knobs. Watching the stage and objective, use the coarse focus knob to bring the low power objective as close to the slide as it will go.

8.Put your eye to the eyepiece (or eyepieces, if the microscope is binocular) and rotate the coarse focus knob in the lowering direction until some aspect of the specimen comes into focus.

9.Move your hand to the fine focus knob and get the specimen into perfect focus for your eyes.Do NOT touch the coarse focus knob again.

(Video) Epithelial Tissue Identification Video

10. Use the stage control knobs to move you specimen to close to the exact center of your field of view

11.Move to the next highest power objective (do not skip the individual objectives) and use only the fine focus to get your image into perfect focus for your eyes.

12.If you need further magnification, move to the next highest power objective and use only the fine focus to get your image into perfect focus for your eyes.

13.Do not use the 100x objective (if you have one) in this course. It must be used with immersion oil and we won’t have students doing that.

(Video) Epithelial Tissue Review & Practice

Lab 3 Exercise $$\PageIndex{1}$$

Simple columnar

Simple cuboidal

Simple squamous

Stratified squamous

Pseudostratified columnar

(Video) Epithelial Tissue Practice quiz

Transitional

1. Obtain a slide of one of the tissues listed below from the slide box at your table.
2. Follow the checklist above to set up your slide for viewing.
3. View the slide on the objective which provides the best view. Find the representative object.
4. In the circle below the name, draw a representative sample of the tissue, taking care to correctly and clearly draw their true shape in the slide. If it is a stratified epithelium draw all the layers. Draw your structures proportionately to their size in your microscope’s field of view.
5. Fill in the blanks next to your drawing.

### A) Prophase

Repeat this for each of the tissue types seen below.

## References

A&P Labs.Authored by: Ross Whitwam.Provided by: Mississippi University for Women.Located at:http://www.muw.edu/.License:CC BY-SA: Attribution-ShareAlike

Figure $$\PageIndex{1}$$. The different ways sheets of epithelial cells are categorized.. Provided by: OpenStax College. Located at: https://commons.wikimedia.org/wiki/F...sue_CellsN.jpg. License: CC BY- SA: Attribution-ShareAlike

Figure $$\PageIndex{2}$$. A slice of a trachea. A. Magnified 1.8x. The arrow indicates which edge in this slice contains the epithelial cells B. Magnified 20x. The arrow indicates an individual columnar epithelial cell.. Authored by: Kent Christensen, Ph.D., J. Matthew Velkey, Ph.D., Lloyd M. Stoolman, M.D., Laura Hessler, and Diedra Mosley-Brower. Provided by: University of Michigan Histology and Virtual Microscopy Learning Resources. Located at: http://141.214.65.171/Histology/Basic%20Tissues/Epithelium%20and%20CT/020_HISTO_20X.svs/view.apml. License: CC BY-NC-SA: Attribution-NonCommercial-ShareAlike

Figure $$\PageIndex{3L}$$. A slice of the colon, 20x.. Authored by: Kent Christensen, Ph.D., J. Matthew Velkey, Ph.D., Lloyd M. Stoolman, M.D., Laura Hessler, and Diedra Mosley-Brower. Provided by: University of Michigan Histology and Virtual Microscopy Learning Resources. Located at:http://141.214.65.171/Histology/Basic%20Tissues/Epithelium%20and%20CT/176_HISTO_20X.svs/view.apml. License: CC BY-NC-SA: Attribution-NonCommercial-ShareAlike

(Video) Epithelial Tissue Histology Explained for Beginners | Corporis

Figure $$\PageIndex{3R}$$. A slice of the esophagus, 10x.. Authored by: Kent Christensen, Ph.D., J. Matthew Velkey, Ph.D., Lloyd M. Stoolman, M.D., Laura Hessler, and Diedra Mosley-Brower. Provided by: University of Michigan Histology and Virtual Microscopy Learning Resources. Located at: http://141.214.65.171/Histology/Basic%20Tissues/Epithelium%20and%20CT/153_HISTO_20X.svs/view.apml. License: CC BY-NC-SA: Attribution-NonCommercial-ShareAlike

Figure $$\PageIndex{4}$$ A slice of the stomach, 20x.. Authored by: Kent Christensen, Ph.D., J. Matthew Velkey, Ph.D., Lloyd M. Stoolman, M.D., Laura Hessler, and Diedra Mosley-Brower. Provided by: University of Michigan Histology and Virtual Microscopy Learning Resources. Located at: http://141.214.65.171/Histology/Basic%20Tissues/Epithelium%20and%20CT/160_HISTO_40X.svs/view.apml. License: CC BY-NC-SA: Attribution-NonCommercial-ShareAlike

Figure $$\PageIndex{5}$$. A slice of the urinary bladder, 10x.. Authored by: Kent Christensen, Ph.D., J. Matthew Velkey, Ph.D., Lloyd M. Stoolman, M.D., Laura Hessler, and Diedra Mosley-Brower. Provided by: University of Michigan Histology and Virtual Microscopy Learning Resources. Located at: http://141.214.65.171/Histology/Urinary%20System/212_HISTO_40X.svs/view.apml. License: CC BY- NC-SA: Attribution-NonCommercial-ShareAlike

## FAQs

### What is the best way to identify epithelial tissues in histology? ›

Light microscopy (LM) is typically used to visualize stained epithelial cells. LM can be used to determine the morphology of the epithelium present in the tissue specimen. Columnar epithelial cells tend to be rectangular, cuboidal cells appear square, and squamous cells are long and flat.

What are the 4 layers of epithelial tissue? ›

Simple epithelial tissues are generally classified by the shape of their cells. The four major classes of simple epithelium are: 1) simple squamous; 2) simple cuboidal; 3) simple columnar; and 4) pseudostratified.

What steps would you take to determine what type of epithelial tissue you are examining? ›

What steps would you take to determine what type of epithelial tissue you are examining? First, find the free or exposed surface. Next, determine the shape of the cells (squamous, columnar, or cuboidal). Finally, determine the number of layers (one—simple; many—stratified).

How do you observe epithelial tissue under microscope? ›

A squamous epithelial cell looks flat under a microscope. A cuboidal epithelial cell looks close to a square. A columnar epithelial cell looks like a column or a tall rectangle. A few epithelial layers are constructed from cells that are said to have a transitional shape.

What features can you use to identify epithelial tissue? ›

Epithelial tissues are identified by both the number of layers and the shape of the cells in the upper layers. There are eight basic types of epithelium: six of them are identified based on both the number of cells and their shape; two of them are named by the type of cell (squamous) found in them.

What are the general identifying features of epithelial tissue? ›

Tightly packed cells and form a continuous sheet. Tissue is vascular i.e. without blood vessels. All epithelium is usually separated from the underlying tissue by an extracellular fibrous basement membrane.

What is one way you can identify a tissue as epithelium? ›

All epithelial tissues have these common characteristics:

They form sheets of tightly bound cells or roll into tubes. Epithelial cells lie on the basement membrane. Epithelial cells have two different “sides”—apical and basolateral. The apical side always faces out of the body (outside or into a lumen).

What are the two ways epithelial tissues are identified? ›

Epithelial tissue can also vary based on how the cells are arranged. The descriptors, or adjectives, for the way the cells are arranged, include: Simple: A simple epithelium means that there's only one layer of cells. Stratified: A stratified epithelium is made up of more than one layer of cells.

How is tissue prepared for microscopic examination? ›

Production of stained tissue sections for examination by light microscopy is a step-wise process which begins with preservation of tissue (fixation), then dehydration and clearing of the tissue, and finally impregnation with wax (processing).

Which are functions of epithelial tissue? ›

Epithelial tissues are widespread throughout the body. They form the covering of all body surfaces, line body cavities and hollow organs, and are the major tissue in glands. They perform a variety of functions that include protection, secretion, absorption, excretion, filtration, diffusion, and sensory reception.

### What is the structure of epithelial tissue? ›

Epithelial tissue is formed from a tightly fitted continuous layer of cells. One surface of the epithelial tissue is exposed to either the external environment or the body fluid. The other surface is attached to tissue by a membrane, which consists of fibres and polysaccharides secreted by epithelial cells.

What is the function of epithelium tissue? ›

Epithelial tissue, commonly referred to as epithelium, is made up of compactly packed cells with very little intercellular matrix. The primary function of the epithelium is to line the outer and inner surfaces of the body.

What is epithelial cells in microscopic examination? ›

Epithelial cells are a type of cell that covers the inside and outside of the surfaces of your body. They are found on your skin, blood vessels, and organs, including your urinary tract.

What are the three steps in preparing tissues for observation under a microscope? ›

Fixation stabilizes and preserves the tissue. Embedding converts the tissue into a solid form which can be sliced ("sectioned"). Sectioning (slicing) provides the very thin specimens needed for microscopy. Staining provides visual contrast and may facilitate identification of specific tissue components.

What are the materials required to observe epithelial tissue? ›

Requirement: Live material/concerned tissue, beakers, glass slides, coverslips, watch glasses, dropping bottle, dropper, required stain, glycerine, NaCl solution (0.9% w/v), needle, forceps, brush, toothpick, water, wash-bottle, dissecting tray, microscope.

What type of microscope is used to view tissues? ›

The transmission electron microscope is used to view thin specimens (tissue sections, molecules, etc) through which electrons can pass generating a projection image. The TEM is analogous in many ways to the conventional (compound) light microscope.

What features would you use to distinguish between epithelial tissue and connective tissue? ›

Epithelial tissue is avascular with no blood supply. Connective tissue is vascular and thus are rich in blood vessels, except for cartilages and tendons. Epithelial tissue also doesn't have nerve supplies. Connective tissue is innervated except for cartilage.

How can you distinguish connective tissue from muscle tissue from epithelial tissue? ›

Muscle tissues are classified as striated (skeletal), unstriated (smooth), and cardiac.
...
Theory:
Epithelial tissueConnective tissue
They perform various functions that include protection, secretion, absorption, respiration and excretion.It is responsible for supporting and connecting organs and tissues.
6 more rows

Which function of epithelial tissues distinguishes them from connective tissues? ›

In nearly all epithelia, cells are attached to one another and thus evenly spaced, in distinct contrast with connective tissue cells which are scattered and not attached.

What separates epithelial and connective tissues? ›

Basement membrane: every epithelium lies on a basement membrane that separates the epithelial cells from the underlying connective tissue.

### What are at least 3 distinguishing characteristics of epithelial tissue? ›

All epithelial tissues have these common characteristics:

They form sheets of tightly bound cells or roll into tubes. Epithelial cells lie on the basement membrane. Epithelial cells have two different “sides”—apical and basolateral. The apical side always faces out of the body (outside or into a lumen).

What is the function of epithelial tissue? ›

Protection: Epithelial tissue protects several aspects of your body. For example, your skin is made up of epithelial tissue and protects the tissues deeper in your body, such as blood vessels, muscle and internal organs.

What is epithelial tissue Short answer? ›

Epithelial tissues are widespread throughout the body. They form the covering of all body surfaces, line body cavities and hollow organs, and are the major tissue in glands. They perform a variety of functions that include protection, secretion, absorption, excretion, filtration, diffusion, and sensory reception.

Where are epithelial tissues found in the body? ›

Where is epithelial tissue found? Surface epithelial tissue is found throughout the body covering all surfaces both inside and outside of the body. Each cell type is prominent in specific locations. Single-layered epithelial tissue is often found along the linings of organs.

What is epithelial tissue characterized by? ›

Epithelial cells are typically characterized by unequal distribution of organelles and membrane-bound proteins between their apical and basal surfaces. Structures found on some epithelial cells are an adaptation to specific functions.

How is epithelial tissue formed? ›

Epithelial cells are derived from each of the three embryonic layers: ectoderm, mesoderm, and endoderm. Ectoderm develops into the epithelial lining of the skin, nose, mouth, and anus. Mesoderm creates endothelium, composed of epithelial cells that line vessels and lymphatics.

What is the origin of epithelial tissue? ›

In fact, epithelial tissue can be derived from either the ectoderm or endoderm. The epithelial tissue derived from the endoderm includes the epithelial lining of the digestive tract, except at the open ends, and the epithelial lining of all hollow structures formed as outpockets in the digestive tract.

What is the structure of epithelial cells? ›

Epithelial cells are held together by tight junctions, adhering junction and desmosomes and attach to a specialized form of extracellular matrix called the basement membrane. Epithelial cells are polarized with an apical surface facing the lumen or external environment and a basal surface facing the basement membrane.

What organelles are found in epithelial cells? ›

Epithelial cells have six organelles in each cell, with specialized cells having additional organelles. The six common organelles are the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and ribosomes.

How many types of epithelial tissue are there? ›

Epithelial tissue in the body is of two types.

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