Download Fetal Pig Dissection

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Fetal Pig Dissection
INTRODUCTION
(Introduction developed by Dr. Mark Stanback at Davidson College)
In the following laboratory exercise, you will examine in some detail the external
and internal anatomy of a fetal pig (Sus scrofa). As the pig is a mammal, many aspects of
its structural and functional organization are identical with those of other mammals,
including humans. Thus, a study of the fetal pig is in a very real sense, a study of
humans.
The fetuses you will use in the following weeks were salvaged from pregnant
sows being slaughtered for food. They are not raised specifically for dissection
purposes. The fetuses are removed from the sow and embalmed with a preservative,
which is injected through the umbilicus. Following this, the arterial and venous systems
are injected under pressure with latex, a rubber-like compound. Arteries (red) are
injected through the umbilicus; veins (blue) are injected through one of the jugular veins
at the base of the throat.
With the possible exception of the abdominal cavity, organs rarely appear as they
are presented in a diagram. If the purpose of this exercise were simply to have you
memorize diagrams (or computer screens), we would do only that and bypass the
expense, time, and controversy of dissecting! Dissection is a powerful teaching method
especially for concrete thinkers and visual learners. Only by dissecting can you really
appreciate the structural and functional role of the many membranes, mesenteries, and
connective tissues that will impede your progress every step of the way. Only by
dissecting can you really appreciate the relationship between an organ's texture, location,
and function. I do not take the life (or death) of your pig specimen lightly – this is why I
demand that you take your dissection seriously and utilize your pig to the fullest extent
possible.
During these exercises, keep several points in mind. First, be aware that "to
dissect" does not mean "to cut up," but rather primarily "to expose to view." Actual
cutting should be kept to a minimum. Tissues are picked and teased apart with needle
probes, forceps, and blunt probes in order to trace the pathways of blood vessels, nerves,
muscles, and other structures. Never cut or move more than is necessary to expose a
given part. Second, pay particular attention to the spatial relationships of organs, glands,
and other structures as you expose them. Realize that their positions are not
random. Third, we encourage you to engage in collaborative discussions with your
classmates and compare dissections.
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Additional instructions:
1. Answer all of the questions in this packet. You will be graded on completeness and
correctness of your answers. Note that many questions are meant for you to answer AT
HOME. Spend your time in class on the dissection and describing what you see.
2. Do NOT cut or remove any organs unless you are instructed to do so.
3. At the end of the class, you are responsible for cleaning up your dissecting
instruments, the lab area and for storing your pig properly.
You must respect the pigs. We are dissecting them to learn from them.
Failure to abide by this will result in your being asked to leave the lab and
you will receive a zero on that day’s work.
You have 3 major resources to help you with the dissection:
1. Dissection Manual (DM) – these are in the 3-ringed binders and give a lot of
information in the text.
2. The Concise Fetal Pig – this is a single (double-sided) page of labeled
photographs. Use this to help identify structures in your fetal pig. This is
especially useful when you are attempting to identify organs and your instructor is
unavailable.
3. Visual Guide to Fetal Pig – this 5 page color guide has drawings in addition to
photographs. Like the “Concise Fetal Pig,” this is a great resource to help you
navigate the inside of the fetal pig’s body.
1. Use pages 3-4 in the dissection manual (DM) to label the following picture of a fetal
pig. You must label: ventral, dorsal, anterior, and posterior.
2. Read pages 9-10 in the DM and answer the following questions
a. What are two major differences between the male and female pigs?
(hint: it has nothing to do with the tail)
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b. Determine the sex of your specimen:
c. Now examine a specimen of the opposite sex. Do both sexes have mammary papillae?
d. How many pairs of mammary papillae does your specimen have?
e. Do both sexes of humans have mammary papillae?
You must now tie down your pig so that it will not move or slip around in the dissection
tray. Your instructor will show you how to do this.
Page 61 of the DM has a diagram outlining the first incisions you will be making. Follow
the order suggested as you progress through the dissection!
The Abdominal Cavity (cuts 1-4)
Locate the following organs and describe their appearance (a sketch may be helpful). In
some cases you may want to note the location as well.
Organ
Diaphragm
Liver
Gall bladder
Stomach
Small intestine
Large intestine
Pancreas
Spleen
Appearance/Location
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The following questions can be answered AT HOME. Please use complete sentences
and site any sources that you use. Use your own words. Quotation marks MUST be used
in cases that are difficult to rephrase.
 What type of tissue is the diaphragm composed of?
 What is the function of the diaphragm? Describe how it works.
 What is the digestive function of the liver?
 What is the function of the gall bladder?
 What is an endocrine gland? How does the pancreas function as an endocrine
gland?
 What is an exocrine gland? How does the pancreas function as an exocrine gland?
 What is the function of the spleen?
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Dissection of the abdominal organs (in class)
Find the place where the stomach joins the esophagus and where it joins the duodenum
(the beginning section of the small intestine). The cardiac and pyloric sphincters are
located here. Make cuts at these locations to remove the stomach. Carefully cut open the
stomach and rinse with water.
1. What did you find in the stomach?
2. Describe the appearance of the stomach’s interior/lining. Why does it look like
this?
Remove a small portion of the small intestine. Carefully cut it open and rinse with water.
3. Describe the contents of the small intestine.
4. Describe the appearance of the small intestine’s inner lining. How does this
contrast with the stomach?
Carefully cut open a piece of the large intestine and rinse it with water.
5. Describe the contents of the large intestine.
6. Describe its internal appearance. Is this similar to or different from the stomach
and small intestine?
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AT HOME
 Why is there no digested food in the stomach?
 What is the greenish substance called sometimes found in the stomach? What is it
composed of?
 What is the significance of microscopic structures known as villi found in the
small intestine?
Excretory and Reproductive Systems (in class)
Locate the following organs. Describe their appearance (a sketch may be helpful) and
location in the pig’s body.
Pages 105-110 in the Dissecting Manual will be helpful here.
Organ
Kidney
Bladder
Appearance/Location
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Remove one of the kidneys and cut it so that it resembles figure 32.5 in your textbook.
(Alternatively – see drawing of kidneys in the “Visual Guide”). Identify all of the parts of
the kidney.
AT HOME
 What is the main function of the excretory system?
 Through what blood vessel does blood enter the kidney?
 Through what blood vessel does blood exit the kidney?
 What is the function of the ureters?
 What is the function of the renal pelvis?
 Locate the urinary bladder. What is its function?
The Thoracic Cavity (in class, cuts 5 and 6)
Make incisions 5 and 6 (see p. 61 in DM) to open the thoracic cavity. It may be helpful
to carefully cut the diaphragm where it meets the rib cage. Pages 68-70 may help you
with this section.
Respiratory System
1. Examine and describe the lungs.
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Circulatory System
Locate the membranous sac that encloses the heart. Remove it to expose the heart.
Locate and describe the structures below. You will need to gently remove surrounding
tissues to clearly see the different blood vessels.
Organ/Structure
Appearance/location
Thymus gland
Heart
Coronary arteries and veins
Posterior and anterior vena cavae
Pulmonary artery
Pulmonary veins
Aorta
Left/right ventricles
Left/right atria
Tip: Use the laminated “Visual Guide” and/or a textbook to help you locate and identify
the structures of the heart.
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Removal of heart
Before you remove the heart, be sure to familiarize yourself with the heart’s orientation
in the pig’s body. Carefully cut all of the major vessels that are connected to the heart
(do not cut them too close to the main chambers of the heart). Be careful not to damage
the surrounding tissues. I will assist you in cutting open the heart so that you can view
the internal anatomy. Use the sheets provided to develop a good understanding of the
different components of the heart.
Ask your instructor to quiz your knowledge of the heart components at this point.
Dissection of Neck Region (extension of cut 5)
Extend cut 5 toward the chin of the fetal pig. Identify and describe the following
structures.
Organ/structure
Appearance/location
Trachea
Larynx
Esophagus
External and internal jugular veins
Carotid arteries
Cut open the larynx and observe the vocal folds.
1. How does the structure of the trachea differ from the structure of the esophagus?
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AT HOME
 What is the name of the sac that encloses the heart?
 What is the function of the thymus gland?
 What is the function of the coronary arteries and veins?
 What is the function of the anterior and posterior vena cavae?
 Why are the names superior and inferior vena cavae in humans?
 The aorta has many branches. What areas of the body do these branches supply?
 What type of tissue is the esophagus made from?
 What type of tissue holds open the trachea?
 Why do the trachea and esophagus differ in structure? What is the function of
each?
 What is the function of the external and internal jugular veins?
 What is the function of the carotid arteries?