Download Rat Dissection

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Rat Dissection Lab
PreAP Biology
Material and diagrams taken and adapted from “An Illustrated Dissection Guide to the Rat” by Allen Kurta, “Rat Dissection Manual” by Bruce D.
Wingerd, “Photo Manual and Dissection Guide of the Rat” by Fred Bohensky, and www.biologycorner.com “Rat Dissection”
I. INTRODUCTION
Background:
The Norway rat, Rattus norvegicus, belongs to the family Muridae, a large group of rodents that includes
the house mouse, gerbil, and hamster. The rat is believed to have originated in Asia and migrated to Europe in the
mid-1550s. During the fourteenth century it is estimated that almost half of the population of continental Europe
was killed as a result of the “Black Death,” or bubonic plague that is carried by rats. Rats are thought to have
migrated to North America in the late 1700s after stowing away on ships. In addition to disease, the rat also wrecks
havoc on farmer’s crops, attacking small animals, etc.
Rats can be beneficial as well. They have allowed for important scientific discoveries in the laboratory
environment in the areas of AIDS, cancer, and brain research. They are a valuable research and diagnostic tool
due to their anatomical and physiological similarities to the human, high reproductive rate, and ease of
maintenance.
Rats and humans belong to Domain Eukarya, Kingdom Animalia, Phylum Chorodata, Subphylum
Vertebrata, and Class Mammalia. The two primary mammalian characteristics that distinguish them from other
vertebrates such as fish, amphibians, birds, and reptiles, is that their skin is covered with hair or fur and they have
milk producing mammary glands in the female to nurse the young. Below is the entire classification of the white
laboratory rat (a variety of the Norway rat) and humans.
White Rat
Human
Domain—Eukarya
Domain—Eukarya
Kingdom—Animalia
Kingdom—Animalia
Phylum—Chordata
Phylum—Chordata
Subphylum—Vertebrata
Subphylum—Vertebrata
Class—Mammalia
Class—Mammalia
Order—Rodentia
Order—Primates
Family—Muridae
Family—Homidae
Genus—Rattus
Genus—Homo
Species—norvegicus
Species—sapien
Variety—albinus
As you can see, rats and humans are similar through Class Mammalia, it is at the Order level where they differ. It
is thought that there are probably more species of rodents today than all other mammals combined.
Rats typically begin to breed at 3 months of age and can produce a litter of about 8 young every 21-25
days. The average lab rat’s lifespan is about 36 months, whereas rats in the wild typically live about 12-18 months.
Anatomical Terminology
There are many anatomical terms used when
referring to organisms. The terms used in this laboratory
are for quadrapeds, or four-legged animals like rats,
therefore, not all terms are used for bipeds, or
two-legged animals such as humans.
Directional Terms:
 Cranial/anterior—toward the head
 Caudal/posterior—toward the tail
 Dorsal—toward the backbone
 Ventral—toward the belly
Planes of Sections:
 Transverse (Cross section)—perpendicular
to the long axis of the body
 Sagittal—divides body into right
and left halves
 Frontal—divides the body into
dorsal and ventral parts
II. EXTERNAL STRUCTURES
A. Observing appearance--observe the external structures of your rat.
1. Note the hairy coat that covers the rat and the sensory hairs (whiskers) located on the rat's face,
called vibrissae.
2. The mouth has a large cleft in the upper lip which exposes large front incisors. Rats are gnawing
mammals, and these incisors will continue to grow for as long as the rat lives.
3. Note the eyes with the large pupil and the nictitating membrane found at the inside corner of the
eye. This membrane can be drawn across the eye for protection. The eyelids are similar to those
found in humans.
4. The ears are composed of the external part, the pinna, and the auditory meatus, the ear canal.
5. Examine the tail, the tails of rats do not have hair. Some rodents, like gerbils, have hair on their tails.
6. Locate the anus, which is ventral to the base of the tail.
B. Determining sex
1. Turn your rat onto it’s dorsal side so that the ventral surface is facing you. Determine whether your rat
is male or female.
2. Locate the mammary papillae on the ventral surface of the rat. Check a rat of another sex and
determine whether both sexes have mammary papillae.
3. On female rats, just posterior to the last pair of mammary papillae, you will find the opening to the
urinary tract and behind that the opening to the vagina.
4. On males, you will find the large scrotal sac which contain testes. Just anterior to the scrotal sac is a
bulge of skin surrounding the penis. The end of the penis has a single opening to both the urinary and
reproductive tracts. where both urine and sperm exit.
5. Answer the questions on your lab paper.
III. INTERNAL STRUCTURES
Fig.A
A. ORAL CAVITY
1. Look at box that is Figure A. Using your dissecting
scissors, make the appropriate cuts.
2. Cut carefully so as to not puncture organs as you cut through the
fur, skin, and muscle.
3. Refer to Figures 8 & 9 on the next page. Locate the salivary
glands, which on the sides of the neck, between muscles by.
carefully removing the skin of the neck and face.
4. Find the lymph glands which lie anterior to the salivary glands.
Lymph glands are circular and are pressed against the jaw
muscles.
5. The thyroid gland is a gray or brown swelling on either side of the
trachea. To locate the trachea you will need to carefully cut
through the muscles of the neck. **Do not try to open the jaw as
shown in Figure 9. The trachea is identifiable by its ringed cartilage
which provides support. The esophagus lies underneath the
trachea, though it is easier to locate in the abdominal cavity where it enters the stomach. Use your
dissecting needle to separate the trachea and esophagus.
6. Cut out the organs listed on your Rat Organ sheet and place them in the appropriate boxes.
(trachea, larynx, esophagus, salivary glands, lymph nodes could be an “other”)
7.
B. THORACIC CAVITY
1. Cut through the abdominal wall of the rat following the incision marks in Figure B. Be careful not to
cut to deeply and keep the tip of your scissors pointed upwards. Once you have opened the body
cavity, you may need to rinse it in the sink.
2. Refer to Figures 11, 12, & 13. Locate the diaphragm, which is
a thin layer of muscle that separates the thoracic cavity from the
abdominal cavity.
3. The heart is centrally located in the thoracic cavity. The two
dark colored chambers at the top are the atria (single: atrium),
Figure B
and the bottom chambers are the ventricles. The heart is
covered by a thin membrane called the pericardium.
TRACE THE FLOW OF BLOOD INSIDE THE HEART
A. Blood from the posterior portion of the body enters the right atrium of the heart through
the inferior vena cava.
B. Blood from the anterior parts of the rat enter the heart from the superior vena cava.
C. Blood flows from the right atrium to the right ventricle via the tricuspid valve.
D. Blood is then pumped through the pulmonary semilunar valve and into the left and
right pulmonary arteries - these are the only arteries in the body that carry
deoxygenated blood.
E. Blood then flows through the pulmonary arteries to the lungs where it is oxygenated and
then returns from the lungs to enter the left atrium via four pulmonary veins.
F. Blood goes from the left atrium to the left ventricle via the biscupid (or mitral) valve.
G. Blood is then pumped into the aorta where it is carried to the body.
4. Locate the thymus gland, which lies directly over the upper part of the heart.
5. Locate the lungs on either side. Notice the number of lobes of the right and left lung.
6. Cut out the appropriate organs listed on the Rat Organ sheet and place them in the appropriate
boxes. (lungs, heart, the thymus could be one of your “other” organs)
Figure 12
C. ABDOMINAL CAVITY
Figure 13
1. Look again at Figure 13 & refer to Figure 13.5. The
cavity is covered by a membrane called the
peritoneum.
2. Locate the liver, which is a dark colored organ
suspended just under the diaphragm. There are four
parts to the liver. Rats do not have a gall bladder
which is used for storing bile in other animals.
3. The esophagus pierces the diaphragm and moves
food from the mouth to the stomach. It is distinguished
from the trachea by its lack of cartilage rings.
4. Locate the stomach on the left side just under the
diaphragm.
5. Slit the stomach lengthwise and notice the ridges,
called rugae.
6. The spleen is about the same color as the liver and is
attached to the greater curvature of the stomach. It
looks like a tongue.
7. The pancreas is a brownish, flattened gland found in
the tissue between the stomach and small intestine. It
looks like chewed up gum.
8. The small intestine is a slender coiled tube that receives partially digested food from the
stomach.
9. Use your scissors to cut the
mesentery of the small intestine, but
do not remove it yet from its
attachment to the stomach and
rectum. If you are careful you will be
able to stretch it out and untangle it
so that you can see the relative
lengths of the large and the small
intestine.
10. Locate the colon, which is the large
greenish tube that extends from the
small intestine and leads to the
anus. The colon is also known as
the large intestine.
11. Cut out the appropriate organs
listed on the Rat Organ sheet and
place them in the appropriate
boxes. (liver, stomach, small & large
intestines, spleen, pancreas)
D. UROGENITAL SYSTEM
Figure 13.5
The excretory and reproductive systems of
vertebrates are closely integrated and are
usually studied together as the urogenital
system. However, they do have different
functions: the excretory system removes wastes and the reproductive system produces gametes (sperm &
eggs). The reproductive system also provides an environment for the developing embryo and regulates
hormones related to sexual development. Observe Figures 14 and 15. Follow the procedure below, then
cut out the appropriate organs of the Urogenital System and place on your Rat Organ sheet. (urinary
bladder, kidneys, reproductive organs)
EXCRETORY ORGANS
1. The primary organs of the excretory system are the kidneys. These organs are large bean shaped
structures located toward the back of the abdominal cavity on either side of the spine.
2. Locate the delicate ureters that attach to the kidney and lead to the bladder. Wiggle the kidneys to
help locate these tiny tubes.
3. The urethra carries urine from the bladder to the opening to the outside of the body.
4. The small yellowish glands embedded in the fat atop the kidneys are the adrenal glands.
THE REPRODUCTIVE ORGANS OF THE MALE RAT
1. The major reproductive organs of the male rat are the testes (singular: testis) which are located in
the scrotal sac. Cut through the sac carefully to reveal the testis. On the surface of the testis is a
coiled tube called the epididymus, which collects and stores sperm cells. The tubular vas
deferens moves sperm from the epididymus to the urethra, which carries sperm though the penis
and out the body.
2. The lumpy brown glands located to the left and right of the urinary bladder are the seminal
vesicles. The gland below the bladder is the prostate gland and it is partially wrapped around the
penis.
THE REPRODUCTIVE ORGANS OF THE FEMALE RAT
1. The short gray tube lying dorsal to the urinary bladder is the vagina. The vagina divides into two
uterine horns that extend toward the kidneys. This duplex uterus is common in some animals and
will accomodate multiple embryos (a litter). In contrast, a simple uterus, like the kind found in
humans has a single chamber for the development of a single embryo.
2. At the tips of the uterine horns are small lumpy glands called ovaries, which are connected to the
uterine horns via oviducts. Oviducts are extremely tiny and may be difficult to find without a
dissecting scope.
IV. CLEAN UP
 Raise your hand when your group is finished with the lab. Your teacher will check your
work.
 Follow your teacher’s instructions to clean up the lab. Make sure that all rat parts are
thrown in the trash and your dissection equipment is washed with soap and water and
DRIED well. Wash your hands with soap and water and clean your table with disinfectant
spray and dry it.