Lab 2 and Lab 3 - Classification and Identification of Tissues
Exercise 6
Introduction to Histology
This exercise uses information in Exercise 6A in your lab manual. The study of tissues is
called histology. Tissues are defined as groups of cells that are similar in structure and
perform a common or related function. There are four basic adult tissue types: epithelial,
connective, muscle and nervous tissue. Tissue structure is closely related to tissue
function, and because of that, we will continue to look at histology throughout both
semesters of the course. In this exercise we will identify several types of epithelial,
connective and muscle tissues. Nervous tissue will be studied along with other aspects of
the nervous system, and more detail on other tissues will be studied later on as well.
This exercise is designed to help you practice looking at tissue slides and recognizing
important visible characteristics of different tissue types. Identification here is based on
things that can be seen with the microscope. It is important to remember that while
there are other important tissue characteristics that cannot be seen easily with the
microscope, they will not be useful in this exercise.
One important characteristic of epithelial tissue is polarity. This means that there is an
apical or free surface exposed to a cavity or the exterior, and a basal surface attached to
underlying glycoproteins called the basal lamina. The basal lamina and an underlying
layer of the protein collagen form the basement membrane which reinforces the
epithelium and marks its boundary. (See page 68 for more on special characteristics of
epithelium.) Epithelia tissue covers surfaces and lines cavities. It is often supported by
underlying connective tissue.
Here is an example of epithelium lining a cavity or tubule (Atlas Plate 3).
Apical Surface
Lumen of Tubule
Here is an example of epithelium covering a surface with underlying connective tissue.
(Atlas Plate 6)
Lumen
Apical Surface
Underlying Connective Tissue
Connective tissue characteristics are described on page 74. For identification purposes,
most connective tissues have a large amount of extracellular matrix, non-living material
that separates the cells of the tissue. Adipose is an exception as it has a sparse matrix,
but it shares other connective tissue characteristics.
Here is an example of cells and extracellular matrix. (Atlas Plate11)
Cell Nuclei
Extracellular Matrix
Many connective tissue cells are hard to see. The nucleus picks up dark stain but the
plasma membrane cannot be distinguished with the light microscope. See Figure 4.8 in
the text for a drawing of some cell shapes. Bone slides do not contain actual cells. You
will see empty lacunae, where bone cells (osteocytes) are usually found, surrounding a
large central canal.
Muscle cells contain myofilaments made of the proteins actin and myosin. In some
muscle tissue types the myofilaments are organized and give the cells a striped or striated
appearance. Smooth muscle is not organized in the same way and often looks similar to a
type of connective tissue called dense regular connective tissue. It is important to
remember that the myofilaments are inside the muscle cells, while the matrix fibers are
outside the connective tissue cells.
In this lab you will be provided with prepared slides that contain each of the tissue types
listed below. It is your responsibility to be able to locate and identify the tissues correctly
on the slides. It can be a bit tricky at first as some slides have more than one tissue type
on them. As you practice and become better at tissue recognition, you will find yourself
identifying several different tissue types on some of the slides.
One way to help you begin to recognize different tissues on prepared slides and in figures
is to prepare a dichotomous key. This key will lead you through a series of questions,
and at the end will identify the tissue for you. In order to make the key, you need to do
some background work at home. Once you have prepared the key you can use it to work
on identifying tissue unknowns. You may also bring it to the lab practical to help with
tissue identification.
Activity Sheet - Pre Lab
 Getting Started - Before You Come to Lab.
Here is a list of tissue types you are responsible for in this exercise. Pictures and
descriptions of these tissues can be found in Exercise 6A in the lab manual .
Note: Use only these tissue types in the assignment.
simple squamous epithelium
dense regular connective tissue
simple cuboidal epithelium
dense irregular connective tissue
simple columnar epithelium
hyaline cartilage
pseudostratified columnar epithelium
bone
stratified cuboidal epithelium
skeletal muscle
stratified squamous epithelium
cardiac muscle
areolar connective tissue
smooth muscle
adipose tissue
1. Read through the sections on epithelial, connective and muscle tissue in Exercise 6A and
note the general characteristics of epithelial tissue, connective tissue, and muscle tissue.
2. Cut out the attached color pictures of tissues, attach each to an index card, and label them on
the back, using the figures in the lab manual for reference.
3. Make a list of the assigned tissues that have an apical surface (have a free edge). These are
all epithelial tissues. There should be 6 when you have finished. List the 6 types of
epithelial tissue here. Separate these cards from the group.
Types of Epithelial Tissue
_____________________________________
_____________________________________
_____________________________________
_____________________________________
_____________________________________
_____________________________________
4. Epithelial tissue cells have three different shapes - squamous, or flat, cuboidal and
columnar. Most epithelia have either one layer and are called simple, or more than one layer
and are called stratified. (Figure 6A.1) Thus, most epithelia have a two-part name. For
example, simple squamous means one layer of flat cells, stratified cuboidal means several
layers of cube-shaped cells. There are exceptions. Sometimes an epithelium looks stratified,
but is actually one layer of cells. The term for this is pseudostratified.
List the 4 epithelia from your list above that have one layer of cells, and indicate the cell
shape. Put their picture cards together in one pile. Be careful, one is tricky!
_____________________________________ ____________________
cell shape
______________________________________ ___________________
cell shape
______________________________________ ___________________
cell shape
____________________________________ _____________________
cell shape
List the 2 epithelia with more than one layer of cells, and indicate the cell shape at the apical
surface. These cards will be in a separate pile.
____________________________________ _____________________
cell shape at apical surface
____________________________________ _____________________
cell shape at apical surface
5. Now look at the nine remaining cards with pictures of the tissues. Make a list of the assigned
tissues that have a large amount of extracellular matrix. These are all examples of
connective tissue. If the description mentions fibroblasts, gel-like matrix, firm matrix, hard
calcified matrix, collagen, elastin, or fibers other than muscle fibers, the tissue has a matrix.
Read the descriptions carefully. There should be 5 when you have finished (all examples
of connective tissue). Be careful, there is a connective tissue example that does not fit here.
Sort these out into a group.
_____________________________________
_____________________________________
_____________________________________
_____________________________________
_____________________________________
6. List the tissues named above that have visible fibers in the matrix. The word visible is
important here. Separate these three cards from the group of connective tissue figures, and
write the tissue types here.
_____________________________________
_____________________________________
_____________________________________
Look carefully at the 3 tissues with visible fibers in the matrix. Distinguish among the three
tissue types, based on fiber arrangement. (How do they look different to you?)
Tissue____________________________Fibers_______________________________
Tissue____________________________Fibers_______________________________
Tissue____________________________Fibers_______________________________
7. Which tissue named in the list in 5. has a matrix described as amorphous? Separate it out.
__________________________________
8. Which tissue named in 5. has a matrix with a pattern organized around central canals (routes
for blood vessels)? Separate it out.
___________________________________
9. Which tissue has a sparse matrix and many large cells? This tissue should not be in the
group of 5 slides you sorted out in 5. _________________________
10. The remaining three tissue types all have myofilaments (strands of muscle protein) inside
the cell. Look carefully at these three tissues. Distinguish among the three muscle types based on
things you can observe. This should include things like number of nuclei per cell, striations,
branching cells, intercalated discs.
Cardiac Muscle
Observations_____________________________________________________
Skeletal Muscle
Observations_____________________________________________________
Smooth Muscle
Observations_____________________________________________________
You have now begun to sort out the tissues based on things that can be seen under the
microscope. These are features that will be useful to you as you use the microscope to
identify tissues on prepared slides.
DO NOT COME TO LAB UNPREPARED. IT WILL SET YOU BACK AND
MAKE THE ASSIGNMENT MUCH MORE DIFFICULT.
Activity Sheet - in Lab
Using the information you have added to the activity sheet, develop a dichotomous
key in flowchart format to use in lab.
1. Short exercise on how to make a dichotomous key. We will do this as a group.
2. Prepare a draft of a dichotomous key. The rules are simple.
a. The question asked can have only yes or no as an answer.
b. The question should separate out one or several of the tissues from the whole
group.
c. Continue asking questions until each tissue type is standing alone at the end of the
flow chart.
d. Start with the question "Is there an apical surface?" The answer is either yes
(epithelial tissue) or no (all other tissue types).
Ask the question and draw a line for Yes and a line for No
Sort out the pictures of epithelial tissue on your cards, and continue to ask questions
until each type of epithelium is alone at the end of a branch of the flow chart. Use the
characteristics you described in the first part of the exercise that you did at
home.
Is there an apical surface?
(6)
Yes
Is it simple?
Yes
No
No
(9)
e. Return to the original question and begin asking questions to sort out the
remaining tissues. Use the work you have done on the worksheet to direct
your questions. You have actually already done much of the sorting. Once you
get started the sorting should be easy if you have done the worksheet correctly.
Use your cards with the pictures of the tissues to do the sort first. Remember that
you are sorting based on what you can see and not necessarily according to
general tissue type. For epithelial tissue it is best to use cell shape and number of
layers (parts 3 and 4 in the pre-lab assignment). For connective tissue with
abundant matrix, look at the choices you made in parts 5 through 8 in the pre-lab
assignment. Look at your choices in 9 and 10 of the pre-lab assignment to
complete the chart.
f. The questions do not have to be technical in every case. You are basing your
decisions on what the tissue looks like under the microscope. Students in the past
have referred to "owl eyes", "tree rings", "bubbles" etc. in their questions.
g. You are finished when all 15 tissue types have been sorted out and are alone at the
end of a branch of the flow chart or key.
3. Once you have finished the key, look at the prepared slides and make sure that the key
is useful to you. I will collect the first draft of the key at the end of the lab. It must
eventually fit neatly onto 8 1/2" x 11" paper. I will return the key with comments
before the next lab. I will also give you the number of your tissue unknown for the
next part of the project.
When studying anatomy and histology, it is important to develop good observational
skills. This takes practice, and may be easier for some of you than others at first. It is
also important to develop the habit of logical and sequential thinking. Developing and
using a dichotomous key for tissue identification will help you enhance these skills.
Your skills will be tested by identifying several unknown tissues.
Using A Key to Identify Unknown Tissues
1. If your key was not correct when you turned it in earlier, reconstruct it so that it is
useful. Please note that the final key is a part of the tissue identification grade. The key
should allow you to identify15 tissue types.
2. I will assign a slide to you when I return your key to you with comments.
Record the number of your assigned slide here. _________ These slides are in a
pinkish gray box in the lab. Each slide contains four or more tissue types.
Your assigned a slide contains a section of an organ. The identification of the
organ is not important at this time. Each slide has four or more different
tissue types on it. Please do not remove the slide or the box from these rooms,
as other students may be using the same slide.
Using your key, identify on the assigned slide three different tissue types
from the 15 you have sorted on the key. In your report clearly describe how
you used your key to come to your conclusions about the tissue types. Use the
provided sheets for your report.
For each tissue type, the report should include:
a. The name of the tissue and its description (from the lab manual).
b. A colored pathway through the attached key from the first question to the
tissue type. If you do not have colored pencils, see me as I have many!
c. A pencil drawing of what you observed. Color is preferred, but not
required. The figure should be labeled, indicating characteristics of the
tissue you described. Use a ruler to construct leader lines, and print the
labels.
For epithelial tissue, label nuclei, epithelial cells (including cell
shape), underlying connective tissue, apical surface and basal
surface.
For connective tissue, label cells or cell nuclei, matrix, fibers (if
applicable), lacunae (if applicable).
For muscle tissue, label nuclei, striations (if applicable), intercalated
discs (if applicable), branched cells (if applicable).
Turn in the dichotomous key on 8 1/2" x 11" paper, along with the three tissue
identification sheets and the grading sheet. Be sure to include your name on
each sheet. The key and tissue identification are worth 5% of your grade in
this class. The grading sheet is attached at the end so that you can make sure
that you are doing the project correctly and have included everything that is
required.
Tissue Identification Sheet 1
Name __________________________
Unknown Tissue Slide # __________
Tissue Type 1 _____________________________
Pathway to this decision marked clearly in color on the attached key.
Tissue Description (from the lab manual):
Labeled drawing of what you observed (in pencil or colored pencil). I must be able to
recognize the tissue from your drawing. Do not copy figures in the text.
For epithelial tissue, label nuclei, epithelial cells (including cell shape),
underlying connective tissue, apical surface and basal surface.
For connective tissue, label cells or cell nuclei, matrix, fibers (if applicable),
lacunae (if applicable).
For muscle tissue, label nuclei, striations (if applicable), intercalated discs (if
applicable), branched cells (if applicable).
Tissue Identification Sheet 2
Name __________________________
Unknown Tissue Slide # __________
Tissue Type 2 _____________________________
Pathway to this decision drawn in a different color on the attached key.
Tissue Description (from the lab manual):
Labeled drawing of what you observed (in pencil or colored pencil). I must be able to
recognize the tissue from your drawing. Do not copy figures in the text.
For epithelial tissue, label nuclei, epithelial cells (including cell shape),
underlying connective tissue, apical surface and basal surface.
For connective tissue, label cells or cell nuclei, matrix, fibers (if applicable),
lacunae (if applicable).
For muscle tissue, label nuclei, striations (if applicable), intercalated discs (if
applicable), branched cells (if applicable).
Tissue Identification Sheet 3
Name __________________________
Unknown Tissue Slide # __________
Tissue Type 3 _____________________________
Pathway to this decision drawn in a third color on the attached key.
Tissue Description (from the lab manual):
Labeled drawing of what you observed (in pencil or colored pencil). I must be able to
recognize the tissue from your drawing. Do not copy figures in the text.
For epithelial tissue, label nuclei, epithelial cells (including cell shape),
underlying connective tissue, apical surface and basal surface.
For connective tissue, label cells or cell nuclei, matrix, fibers (if applicable),
lacunae (if applicable).
For muscle tissue, label nuclei, striations (if applicable), intercalated discs (if
applicable), branched cells (if applicable).
Grading Sheet
Dichotomous Key and Unknown Tissue Identification
_____Key (55 points)
Questions on the key correctly sort the tissues into groups of one (45)
The map arrangement is orderly and neat (10)
_____Tissue Unknown (45 points)
Tissue Unknown 1
Tissue identification is correct (6)
Tissue is described (2)
Tissue is described, neatly drawn and correctly labeled (5)
Logical path through attached key is used (2)
Tissue Unknown 2
Tissue identification is correct (6)
Tissue is described (2)
Tissue is described, neatly drawn and correctly labeled (5)
Logical path through attached key is used (2)
Tissue Unknown 3
Tissue identification is correct (6)
Tissue is described (2)
Tissue is described, neatly drawn and correctly labeled (5)
Logical path through attached key is used (2)
_____Total Grade