Download The “Micro” and “Macro” of Tissues

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The “Micro” and “Macro” of Tissues
Elaine S. Chapman, PhD
Professor of Biology
Illinois College
Jacksonville, IL 62650
(217) 245-3446
[email protected]
The concept of tissue is sometimes difficult to understand
for introductory anatomy and physiology students. While they
may work to identify tissue types under the microscope, students
often are unable to make the connection between these tissues
and the structure of organs. For instance, students may initially
think that a skeletal muscle consists entirely of muscle tissue.
I have tried to design a lab which fills that gap between microscopic anatomy of the tissues and gross anatomy of an organ.
During the previous lab period students learn to use the microscope and to distinguish the various tissue types under the microscope. In this lab, students work in pairs to examine the gross
anatomy of a fresh chicken thigh or leg, purchased at a local grocery store. It is always surprising to me that many students ask to
wear gloves, despite the fact that the chicken is fresh and could
just have easily become their lunch. This lab is very inexpensive,
easy to set up and enjoyable for the students.
Instructions for dissection of the chicken leg/thigh:
Identify the skin on the surface of the leg. The outermost
layer of the skin is the epidermis; remember that feathers, like
hair, are epidermal derivatives. The epidermis is a good example
of stratified squamous epithelium.
Carefully skin the chicken leg. The deeper layer of the skin
is the dermis, which is an excellent example of dense, irregular
connective tissue. The membranous material which may cling to
your hands as you work with the chicken skin is loose connective
(areolar) tissue. On most chicken legs you should be able to identify another subcategory of connective tissue. Adipose tissue is
found in the subcutaneous layer (also called the hypodermis), and
often around the muscles.
Now examine the muscle. Note that there is a tough membrane, the deep fascia, enclosing each muscle and separating
muscle groups; this is another example of dense, irregular connective tissue. Examine the muscle closely; you should be able to
identify the stringy groups of muscle fibers called fascicles. Then
follow a muscle to its attachment to a bone. The tendon which
attaches the muscle to the bone is composed of dense, regular
connective tissue. Remember that bone is also a subcategory of
connective tissue. Depending on the cut of the tissue, you may be
able to identify ligaments; these connect bone to bone and are also
composed of dense, regular connective tissue. Also, depending on
the cut, you may be able to find the menisci in the knee; these are
composed of fibrocartilage, just as they are in your knees. If you
have a chicken thigh, you may be able to differentiate the hamstring muscles from the anterior thigh muscles. If you have a chicken
leg, the gastrocnemius and soleus muscles are clearly evident as
they connect to the Achilles’ tendon. Recall that cartilage is a subcategory of connective tissue; more cartilage (articular cartilage)
can be identified on the chicken leg at the ends of the femur or
tibia. Note the whiteness and translucent appearance of the cartilage and the menisci; this should remind you that cartilage is avascular (it lacks blood vessels).
As you try to separate the muscles, look for blood vessels and
nerves. Arteries and veins are composed of an epithelial lining,
some connective tissue, and smooth muscle. The blood inside the
vessel is also a type of connective tissue. Arteries have a much
thicker smooth muscle layer and more elastic fibers than the accompanying veins. If a specimen is large enough, it is easy to feel
the difference between an artery and a vein by rolling the vessel
between your fingers; the artery will feel much more “springy,”
while the vein will readily collapse. A nerve will appear as a whitish cord-like structure running generally parallel to the vessels. If
you have a chicken thigh, you should be able to identify the sciatic
nerve, the largest nerve in the body.
After removing all the tissues from the bone, wrap it in a piece
of aluminum foil and weigh it. Then bake the foil-wrapped bone in
a 400 °F oven for at least 30 minutes. Then let it cool and weigh it
again; the difference is the weight of the water lost during baking.
Then do the calculation: weight of water lost / the weight of
the fresh bone x 100 = % of bone weight composed of water. (I
recommend that the bones be baked longer (5-6 hours) which yields
better results, and then weighed the next lab period).
On the tissues lab practical, I require that my students be able
to identify the various tissue types under the microscope as described in the tissues lab as well as on a chicken leg/thigh.
HAPS-EDucator - Fall 2005 - page 17