RAT DISSECTION
Important
Your mark on the dissection (practical and written report) will count for the structure and function
unit as well as the culminating assignment for your final exam. This assignment will be worth 10%
of your final exam, the remaining 20% will come from the written component of the exam.
You will be required to submit a lab report individually about your findings during the dissection.
Email submissions are NOT allowed.
DUE DATE: TBA_____________________________________
Your report will include the following:
Introduction (~half a page)
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State the purpose of the lab
Explain why rats were chosen for this lab and how the specimens were prepared for
dissection. (research answers for questions you are unsure of; use credible sources; cite all
sources using APA)
Materials
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Create a list of all materials used throughout the dissection
Observations & Technique
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Identify specified structures (written in bold in dissection manual) to teacher and use careful
dissection technique (evaluated as a group during dissection)
Include all diagrams you are instructed to draw throughout the dissection in lab report.
All diagrams will be properly labeled with figure numbers and titles and will be included as an
appendix at the end of the report.
All diagrams must be hand drawn and completed in class.
Discussion:
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Include written observations from the questions posed in the dissection outline. (see
‘dissection summary’ also)
Extension Questions
1. In the rat, Rattus norvegicus, the albino colouring of the white rat is recessive to dark colouring in
the brown rat. These traits are controlled by a single allele (A or a).
Consider a cross between a pure bred albino lab rat and a heterozygous wildtype brown rat of the
same species. Answer the following questions:
a)
b)
c)
d)
Use a Punnett square to show the cross between the two rats.
Indicate the genotype and phenotype ratios of the F1 generation.
Construct a Punnett square to show a cross using two offspring from the F1 generation.
Indicate the genotype and phenotype ratios of the F2 generation.
2. Which digestive structure is much larger in the rat than the human? This structure has a
different name in humans; what is it called? Suggest an explanation for this difference.
3. (We will cover this next week) Classify the albino lab rat for all seven categories of taxonomy
(kingdom through to species). At which level do rats differ from humans? Provide the name of
another species that shares the same genus as the rats used in this dissection (provide both the
common and scientific name).
4. Rats are known to be notorious for spreading deadly diseases.
a) Name the common disease(s) associated with rats.
b) What role does the rat play in spreading/communicating these diseases?
5. Rats have many characteristics that have given them a survival advantage in a variety of
locations.
a) The rat has an unusually long tail. How does the long tail help rats in their struggle for
survival?
b) Describe 2 other features of rats that might give them a selective advantage and explain
how these features are beneficial.
Conclusion
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
Summarize the results of your lab; include sources of error and any unexpected or unusual
results.
The rat is used to observe the human organ systems studied in class. Do you think the rat is a
good model for human anatomy? Why or why not? Discuss any differences between the rat
and human.
RAT DISSECTION
The term dissection means “exposing to view” or “separating into parts for examination”; IT DOES NOT MEAN
“cutting up”. In this lab you will take the role of a scientist rather than a butcher. To get the most out of this
lab, read the following instructions carefully.
The rat you will be dissecting is an albino lab rat (Rattus norvegicus). The rat has been selected because of its
convenient size, because it is easy to dissect, it is readily available, and because its internal body structures are
very similar to ours. The blood vessels of the rats have been injected with coloured latex to make them more
visible; red in the arteries and blue in the veins.
1. Equipment:
Preserved rat
Disposable gloves
Dissection tray
Dissecting tools (probe, large and small scissors, forceps, scalpel, pins)
Knowing the function of the dissecting tools will help in your dissection:
Large scissors: Used to cut through bone or tough tissue.
Small scissors: Used to make delicate, precise cuts.
Probe: Used to lift or push aside tissues so that underlying structures can be seen. Don’t be afraid to use
your fingers as probes.
Forceps: Used to hold and lift tissues. Use them to lift tissue so that underlying parts will not be destroyed.
Pins: Used to pin back tissues such as skin so that underlying structures can be more visible.
Scalpel: Used to make precise cuts through tissue. It is easy to cut too deep using the scalpel; it is
recommended that scissors are used unless otherwise instructed.
2. Helpful Tips:
a) Work in groups of 3. One person can read the instructions and make sure all steps are completed. The
second person can do the dissection. The third person can write down the observations and answer
the questions. (group members may rotate jobs each day)
b) Rinse your rat with water on the first day. This will help to get rid of some of the smell which you may
find bothersome.
c) Follow all instructions carefully, one step at a time.
d) DO NOT CUT anything unless instructed to do so.
e) Answer all questions and give diagrams proper labels and titles
f) At the end of each class, place any removed organs back into the proper cavity of the rat, close the skin
flaps and seal the rat tightly in a plastic bag with group members names on it.
g) At the end of each class, CLEAN ALL DISSECTING EQUIPMENT. It is important to dry tools thoroughly
because they will rust. Dissecting trays must be thoroughly washed but may stand to dry. Make sure
your LAB BENCH IS CLEAN AND DRY.
3. Terms to Know: The following terms make it easier to describe the position of various structures in the
rat.
Abdominal: Lower part of the body below the diaphragm
Thoracic: Within the chest, above the diaphragm
Cranial: Toward the head
Caudal: Toward the hind end
Dorsal: Toward the back surface
Ventral: Toward the belly
Lateral: Toward the sides (left or right)
Medial: Toward the middle
Part A: The External View
1. The body of the rat can be divided into the head, trunk, and tail. The trunk consists of the thorax (chest
cavity) and the abdomen (cavity below the ribs).
2. What is the sex of your rat? _____________________________
Both males and females have separate urogenital and anal openings.
Males: The urogenital structures consist of the penis and the scrotum, containing the testes.
Females: The urinary and genital opening are separate. The urethral opening is cranial to the vaginal
opening. The anal opening is caudal to the vaginal opening.
3. Lay the rat on its side in the tray and draw a labeled diagram. Include the applicable structures listed above
in bold. Also, indicate the cranial, caudal, dorsal and ventral sides. Use a blank paper and include a label and
title.
Part B: The Digestive System
1. Use the scissors to cut both sides of the mouth so that the lower jaw can be pulled back enough to see the
back of the oral cavity.
2. Identify the hard palate (the hard, ridged rook of the mouth). Also look for the soft palate (the roof of the
mouth caudal to the hard palate). The pharynx is the general area at the back of the mouth.
3. Look at the teeth. Describe their shape, location, and their function.
___________________________________________________________________________________________________________________________
___________________________________________________________________________________________________________________________
4. Observe the tongue. What are the two functions of the tongue? _________________________________________________
___________________________________________________________________________________________________________________________
5. Pull the jaws apart until the opening of the trachea and the opening of the esophagus can be seen. You
may have to do more cutting. Which tube is dorsal and which tube is ventral?
Dorsal: __________________________
Ventral: _____________________________
The epiglottis is a small piece of cartilage located near the trachea. What is the function of the epiglottis?
_______________________________________________________________________________________________________________________
6. With the ventral side of the rat facing up, make a series of cuts as shown on the diagram below.
a. Using scissors, make a cut just under the ribs.
Cut through the skin and muscle layer, but do
NOT cut too deep. Don’t damage the organs in
the abdomen. Use the forceps to lift the abdominal
wall while cutting
b. cut the abdominal wall along the midline down to anus.
c. Make two cuts close to the hind legs so that the sides of
the abdominal wall may be pulled back to view the
contents of the abdominal cavity
9. Rinse the abdominal cavity under water under running water. Let the cavity drain before proceeding.
10. Look for the diaphragm that is a dome-shaped muscle at the anterior end of the abdominal cavity. It
separates the abdominal cavity from the chest cavity (thorax).
11. Identify the liver, the large brown organ at the anterior end of the abdominal cavity.
How many lobes does it have? ____________________
What is the function of the liver as it relates to digestion? ____________________________________________
12. Find the stomach which is located under the liver on the left side of the rat. What are the functions of the
stomach? ___________________________________________________________________________________
See if you can find the esophagus which is attached to the top part of the stomach. It may be difficult.
13. Find the spleen, a long, smooth, reddish-brown gland that covers much of the stomach.
14. Find the duodenum, the first part of the small intestine leaving the stomach. You should be able to see
the pancreas, a lumpy looking, whitish, leaf-shaped organ lying next to the duodenum and under the
stomach.
What is the function of the pancreas? ____________________________________________________________
15. Observe the small intestine. Examine the mesentery, the thin layer of tissue which holds the small
intestine together.
What are the TWO functions of the small intestine? _________________________________________________
What makes up a large part of the mesentery? _____________________________________________________
16. Identify the large intestine. It appears coiled. What is its function?
___________________________________________________________________________________________
17. Find the rectum, the straight, posterior end of the large intestine. It leads to the anus that opens to the
outside. Locate the caecum, the ‘dead-end’ pouch that branches off where the small and large intestine
meet.
18. Draw a LABELLED DIAGRAM of the INTACT DIGESTIVE SYSTEM of the rat. Be sure to include the
mouth. Show only the organs that are visible to you. Use a blank paper and include a label and title.
19. Carefully remove the liver without cutting any major blood vessels.
20. Attempt to locate the gall bladder. What do you notice? ___________________________________________
21. Carefully unravel the digestive tract with your fingers (scissors may be used to trim away any excess
tissue). This may take some time. Be patient.
22. STOP! Have the teacher come and evaluate your dissection.
23. Remove the digestive tract from the stomach (where it meets the esophagus) down to the posterior end of
the large intestine – Keep the tract intact. Indicate the length of the stomach, small intestine, and large
intestine.
Length of stomach __________ Length of small intestine ___________ Length of large intestine ___________
24. Cut open the following structures and describe their inner surface.
Stomach: ____________________________________________________
Small Intestine: _______________________________________________
Large Intestine: _______________________________________________
Part C: The Respiratory System
1. With the rat on the dissecting tray,
ventral side up, make a cut though
the ribs to the chin as shown on the
diagram to the right. Avoid
damaging underlying organs by
cutting too deep. Pull the arms of
the rat back in order to expose as
much of the chest cavity as possible.
2. Carefully cut through the tissue of the neck to locate the trachea and the larynx. The trachea is
a tube with rings around it and the larynx is an enlarged bulge at the cranial end of the trachea.
a) What are the rings of the trachea made of? ______________________________________________
b) What is the purpose of these rings? ____________________________________________________
c) Which opening in the mouth leads to the larynx? _________________________________________
d) What is the function of the larynx? ____________________________________________________
3. The trachea leads down to the lungs.
a) What organ is surrounded by the lungs? ________________________________________________
b) The lungs are divided into lobes. How many lobes are there in each lung?
Left _______________________________
Right ______________________
c) What is the function of the lungs? _____________________________________________________
d) Where in the lungs does this function take place? ________________________________________
4. Lying posterior to the lungs is a smooth sheet of muscle (diaphragm). Describe its shape.
___________________________________________________________________________________
What is the function of the diaphragm? ___________________________________________________
5. STOP! Have the teacher come and evaluate your dissection.
6. Draw a LABELLED DIAGRAM of the RESPIRATORY SYSTEM of the rat. Label the parts observed in steps
2-4 above. Use blank paper and include a label and a title.
Part D: The Circulatory System
1. Leaving the heart and blood vessels intact, remove lungs and trachea. Try not to damage the heart. Use a
probe and gently lift up the lungs and begin to trim away connective tissue. Please be very careful of the blood
vessels and arteries and try to leave as many intact (attached to the heart) as possible.
2. Locate the heart and remove the pericardium, a thin membrane covering the heart. Without cutting into
the heart, identify the 4 major compartments of the heart: the right atrium, the left atrium, the right
ventricle, and the left ventricle.
3. Remove any fat or connective tissue around the heart or nearby blood vessels. Carefully cut away the
tissue of the neck and chest anterior to the heart to expose the major blood vessels. Most of the blood vessels
will be visible since the veins are injected with blue latex and the arteries with red latex.
4. Identify the following blood vessels and state their function.
aorta: _____________________________________________________________________________
vena cava (inferior and superior): ______________________________________________________
pulmonary arteries: _________________________________________________________________
pulmonary veins: ____________________________________________________________________
coronary artery: ____________________________________________________________________
5. Remove any remaining tissue surrounding the heart. Leave as many blood vessels attached as possible.
6. Draw a LABELLED DIAGRAM of the VENTRAL VIEW OF THE HEART and the blood vessels described
above. Label the parts observed in steps 2-4 above. Use blank paper and include a label and a title.
7. STOP! Have the teacher come and evaluate your dissection.
8. Leaving stems of the blood vessels intact, extract the heart from the thoracic cavity
9. Get the scalpel and cut through the wall on each side of the heart to see the VENTRAL LONGITUDINAL
SECTION; cut the heart parallel to the ventral surface of the rat, through the middle of the heart. Identify the 4
chambers of the heart. Which chamber has the most muscular walls and why?
__________________________________________________________________________________________________________________________
__________________________________________________________________________________________________________________________
10. Draw a LABELLED DIAGRAM of the CROSS-SECTION VIEW OF THE HEART and the blood vessels,
described above, which are visible. Use blank paper and include a label and a title.
Group Dissection Evaluation
Digestive System
Quality of Dissection
Structures to Identify:
 Pharynx
 Soft palate
 Hard palate
 Esophagus
 Liver
 Stomach
 Small intestine
 Mesentery
 Large intestine
 Caecum
 Pancreas
 Rectum
 Anus
/5
Respiratory System
Quality of Dissection
Structure to Identify
 Trachea
 Larynx
 Lungs
 Diaphragm
/5
Circulatory System
Quality of Dissection
/5
Structures to Identify
 Heart and Attached Blood Vessels
o Aorta
o Vena Cava
o Pulmonary Arteries
o Pulmonary Veins
o Coronary Artery
Dissection Summary
____________________________________________________________________________________________________________________________
Question to Answer Throughout dissection:
Part A – External
1. What is the sex of your rat?
Part B – Digestive
2. Describe their shape location and function of the teeth.
3. What are the 2 functions of the tongue?
4. The trachea and esophagus can be observed in the pharynx. Which tube is dorsal and which is
ventral?
5. What is the function of the epiglottis?
6. How many lobes does the liver have?
7. What is the role of the liver in digestion?
8. What are the functions of the stomach?
9. What is the function of the pancreas?
10. What are the two functions of the small intestine?
11. What makes up a large part of the mesentery?
12. What is the function of the large intestine?
13. What did you notice about the gall bladder?
14. Length of stomach, small intestine, and large intestine
Part C – Respiratory
15. What are the rings of the trachea made of?
16. What is the purpose of the trachea rings?
17. Which opening in the mouth leads to the larynx?
18. What is the function of the larynx?
19. Which organ is surrounded by the lungs?
20. How many lobes are in each lung?
21. What is the function of the lungs? Where in the lungs does this function take place?
22. Describe the shape of the diaphragm.
23. What is the function of the diaphragm?
Part D - Circulatory
24. State the function of each of the following: aorta, vena cava, pulmonary arteries, pulmonary
veins, coronary arteries,
25. Which heart chamber has the most muscular walls? Explain why?
Diagrams Required:
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External View
Digestive System
Respiratory System
Circulatory System (heart and attached blood vessels: external ventral and cross-section)