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Welcome to the Rat Lab!
I know you have all be anxiously awaiting this wonderful lab! Here are some things to know
about the changes in this lab.
 First of all there is an addendum that needs to be handed out to students. I wasn’t satisfied
with the urogenital or the circulation parts so I added some more info.
 Also before you begin, make sure to spend a few minutes going over some basic anatomy
terms like frontal plane, medial, lateral, ventral, etc. If you have questions just ask!
 The students need to get all sections signed before they move onto the next one! We need to
make sure they have actually did the dissections and laid all the parts out to get as much as they
possibly can out of the rat. We don’t want their deaths to be in vain!
 I have generated a list of questions to ask students before you sign their papers. Each section
has their own set. You don’t need to ask all of them to each student, just as long as they know
what they’re talking about. These questions will not be the write up rather they will aid in their
knowledge of anatomy to assist them in their write up.
 This lab will take the entire time. When students ask in the beginning of lab, just let them
know that they will get out in 2 hours and 50 minutes. I want them to learn as much as
possible so it should take awhile to go through everything in detail.
Questions to ask before you sign out students:
Digestive(c) How do you tell the difference between the trachea and the esophagus? The trachea is a striated
structure located on top of the esophagus, which is smoother.
(d) If you were designing an organism why might you have one opening which leads to two separate
compartments? Answers will vary. They may not design it this way. Anything is acceptable as long as
they’re thinking.
(e) What did you notice about the inside of the stomach? Very rough with many folds. What function
might account for this anatomy? The stomach needs to digest all the foods we eat. Therefore, the low
pH leads to high rate of turnover in the stomach, which accounts for the roughness. The many folds
increase the thickness of the stomach wall so you don’t degrade through it. Ulcers occur when the
stomach lining gets too thin.
(f) What was the length of the small and large intestine? Varies. How do you think the length relates to
function? The small intestine is much longer so it can absorb many more nutrients. Practically all
absorption of nutrients takes place in the small intestine. You also see a lot of folds to increase the
surface area to increase absorption. The large intestine is much shorter than the small. The large
intestine does not need to absorb much more than water. The function is to form feces from the things
the small intestine could not use. You really don’t want all the rejects hanging out in your bowels that
long so it is shorter to allow the absorption of water and then it leaves the body.
Uro-genital1) What is the difference between the length of the urethra between the sexes? The female
urethra is much shorter than the males. In the male you have three sections: membranous
urethra- middle portion, spongy- extends through the length of the penis allowing the urine to
leave through the urogenital orifice.
2) Why are the kidneys behind the dorsal wall? For protection. The organism needs to protect
the kidneys so don’t want them to get tangled up in the peritoneal cavity. If an animal was to
suffer a blow to the stomach the kidneys will not be damaged if they are in the retroperitoneal
cavity.
3) How does the lining of the uterus differ from the lining of the stomach? Why is this so? The
uterus is much smoother than the stomach was. The uterus needs to be protective and gentle to
any developing embryo. You do not need low pH so it doesn’t need to be that thick and rough.
4) How did the reproductive tract of the opposite sex function? Make sure they have checked out
another rat and they have switched explanations.
Heart1) Find both the Atria and both ventricles. How do you tell the left from the right chambers? The
right chambers will be on the rat’s right side. Make sure they know where the septum that
divides the two.
2) What functional difference accounts for the difference in anatomy between the left and right
ventricle? The left ventricle has to pump blood to the entire body so it must be much thicker
because it has more work to do. The right just pumps blood into the lungs.
3) What is the difference between arteries and veins? Arteries carry blood away from the heart.
Veins carry blood to the heart. Why isn’t the pulmonary vein what people typically think of
when they think of veins? The pulmonary vein returns oxygenated blood from the lungs to the
heart. People typically think the difference between veins and arteries is in how much O2 they
contain. Not so!
2. Uro-genital system
a) After removing the intestines, you will see one of the two kidneys embedded in the dorsal body wall.
From these, ureters lead to the urinary bladder. The ureters are small white tubes and are often difficult to
find. The urinary bladder empties to the outside through the urethra. Be sure you can locate the urethral
opening on both male and female rats. After examining the tubes, return back to kidneys. Carefully
remove one of the two. Make a frontal planar cut so you can see the inside of the organ. Locate the
following features:
Hilus: depression near the center of the medial border. The renal artery and vein, lymphatic
vessels, and nerves enter and exit through here.
Pelvis: located in the center of each kidney, the pelvis contains cuplike extensions called calyces.
These collect newly formed urine and channel it out of the kidney.
Cortex: The outer region of each kidney. Renal corpuscles, which function in blood filtration, are
found here.
Medulla: The inner region of the kidney
b) The reproductive system of the female rat is relatively simple. In the female, the prominent uterine
horns pass dorsally to the bladder and ureters. Where the horns join, dorsal to the urethra, is the vagina,
which opens to the exterior through the vaginal opening. On the exterior, the anus is just ventral to the tail,
the vaginal opening is ventral to the anus, and the urethral opening is ventral to the vagina. At the anterior
end of each uterine horn is a short, convoluted oviduct, which opens into a transparent pocket around the
small, round ovary. Often the ovary is hard to find. Feel the fat at the end of the uterus for a small, hard,
round body. Some female rates may be pregnant and have small embryos in the uterine horns. Cut
longitudinally along the uterine horns. If your rat was pregnant, you may observe embryos. How does the
interior surface of the uterus differ from the interior surface of the stomach? Why might you expect to
find a difference in the two tissues?
c) The male reproductive system is more complicated than that of the female. Locate the male’s scrotum.
Cut longitudinally through just the skin to locate the testes. Separate the skin from the testes and continue
the cut up to the abdominal cavity. Notice the epididymis lying around each testes. Find the vas deferens
that leads from each testes to the urethra. You will probably have to cut through some muscles in the
pelvic area to locate some of these structures; be careful as you cut. Two sets of glands are located on
either side of the bladder, the smaller, round more posterior ones are the prostate glands. The larger pair of
glands is the seminal vesicles, which are actually two separate glands – the vesicular glands and the
coagulating glands. Follow the urethra as it goes through the penis. In males the bladder and the testes
both empty to the outside through the urethra.
Q1. The kidneys are found lying in between the mesenteries and the dorsal body wall. However, the
remaining organs of the urinary tract, the ureters and the urinary bladder, are found inside the peritoneum
(the coelom, or body cavity). What does this tell you about the developmental origins of these structures?
(Hint: see Chapter 47)
Q2. Find a group that has dissected an animal of the opposite sex from your own. Explain to them the
reproductive tract of your animal. How do the reproductive tracts of the two animals differ?
Uro-genitary tract T.A. Signature______________________________
3. Circulatory System
The circulatory system consists of three basic components. The heart is a pump that imparts pressure to
the blood to establish the pressure gradient needed for blood to flow to the tissues. The blood vessels
serves as the passageways through which blood is directed and distributed from the heart to all parts of the
body and then returned back to the heart. The blood serves as the transport medium within which
materials being transported are dissolved or suspended.
(a) Return to the heart in the thoracic cavity. The heart lies in the posterior center of the thoracic cavity
and is surrounded by membranes that together make up the pericardial cavity. The heart consists of 4
chambers: the right atrium, the left atrium, the right ventricle and the left ventricle. In general, the atria are
receiving chambers, while the ventricles are discharging chambers. The major mass of the heart, which
you see immediately upon opening the cavity, is in the ventricles.
(b) Circulation from the body to lungs: blood returns to the heart from the systemic circulation through the
systemic veins. These veins, which enter the heart from the anterior part of the body, are the vena cava.
Blood entering the right atrium is pumped through the tricuspid valve into the right ventricle. Blood leaves
the right ventricle through the pulmonary semilunar valve into the pulmonary artery, which goes to the
lungs. This is the only time in which an artery will carry deoxygenated blood. Once the blood travels
through the lungs, it becomes oxygenated.
(c) Circulation from lungs to heart to body: oxygenated blood returns to the heart through the pulmonary
vein. Most people are confused by the name, but the pulmonary vein is actually a vein. Why all the
confusion? The oxygenated blood enters the heart through the left atrium and then the blood passes
through the bicuspid valve into the left ventricle. The heavy walled ventricle pumps blood though the
aortic semilunar valve into the aorta. The aorta delivers oxygenated blood to the body through the body's
major arteries.
(d) Other feature of the heart: besides the main chambers of the heart, there are many other features in the
heart that should be noticed. Notice that the heart is divided by a muscular partition (the septum). This
separation is very important because the right half of the heart is receiving and pumping low-oxygenated
blood while the left side of the heart receives and pumps high-oxygenated blood. Be sure to notice the
three types of tissues that make up the heart. The endocardium is a thin layer of endothelium and is a
unique type of epithelial tissue that lines the entire circulatory system. The myocardium is composed of
cardiac muscle and makes up the bulk of the heart wall. The epicardium is the thin external membrane
covering the heart.
For your dissection, carefully remove the heart from the thoracic cavity and lay it on the lab bench. Make
a planar cut so you can see the four chambers. Find both atria and both ventricles. Locate the septum
dividing the heart into left and right portions. This muscular partition separates the low O2 blood from the
blood with high O2 content. Notice the wall of the ventricle is much thicker than the wall of the right
ventricle. What functional difference accounts for the difference in anatomy?
Q1. How do nutrients from the digestive system find their way to the kidneys?
Q2. What is the difference between arteries and veins?
Circulatory System T.A. Signature______________________________
Ten -point Write-up
Individual Exercise; Due ????
A. Animal Use
1. Rats provide an excellent model for many human processes that cannot ethically be explored. For
example, the mechanisms of many neurobiological processes are similar between the two animals. Do you
think it's OK to use rats for experiments in which knowledge is gained that might possibly benefit
humans? What might be some alternative ways to gain the same knowledge without using live animals for
experimentation?
B. The Dissection
1. What do rats eat? Follow a bolus of rat food from its mouth to its anus. At each step of the journey,
comment on the digestive processes that are occurring (physiology) and the morphological features of
each organ (brain, mouth, esophagus, stomach, small intestine, large intestine, rectum) that are involved in
digestion.
2. What feature of the kidneys allows mammals to be well adapted to a terrestrial environment? Why is
this such an important advancement in evolution?
3. Choose one aspect from each of the female and male reproductive systems and describe its function
and importance.
4. Make a schematic diagram of the circulatory system. Label the following: Right Ventricle, Pulmonary
arteries, capillary beds (in lungs), Left Atrium, Left Ventricle, Aorta, Capillary beds (head and arms, as
well as abdominal organs and legs), Anterior Vena Cava, posterior Vena Cava, and Right Atrium. Be sure
to include the oxygen content at each step.
C. Learning Goals
1. Now that you have successfully completed the dissection of the rat, how do you think this lab is
important to you? In your study of biology? In your understanding of the material of this class?