PRAC 7 – INTERNAL STRUCTURE OF A RAT
Caitlin Bowie 10A
BACKGROUND INFORMATION:
Rodents are the largest group of mammals, making up about 40% of the total mammalian population. Rat
dissections are commonly used in schools to teach students about parts of a typical mammal’s body
systems and organs. The rat’s body structure and organ systems are relatively similar to humans. This
similarity provides an interesting look into mammalian anatomy and allows us to make some connections
between humans and other mammals.
Rat’s digestive system is for the most part the same as ours. After the food is ingested though the mouth
it goes into the stomach where contractions finish the process of physical breakdown then the acid in the
stomach start the chemical breakdown of the food. Next the small intestine has the job of taking in
nutrients from the ingested food. At the end of the small intestine is another organ called the caecum
which is responsible for the rat's ability to breakdown cellulose from plant materials. After most of the
food is absorbed by the small intestine and the caecum, the rest of the food travels to the large intestine,
where the remaining water from waste material is removed by the large intestine and prepares the solid
faecal matter for removal from the body into the rectum and out of the anus.
AIM:
For this experiment, the purpose was to examine and identify the internal structures of a typical mammal
and to become familiar with the appearance of their internal organs and also to relate the structure of
these organs to their functions.
METHOD:
Please see attached prac sheet.
MATERIALS:
The materials we used in the rat dissection included: apron, gloves, newspaper, rat, pins, dissection
board, probe, forceps, scissors and scalpel.
DIAGRAM OF MATERIALS:
DIAGRAM OF RESULTS:
Teeth
Ribcage
Liver
Heart
Stomach
Pancreas
Large Intestine
Small Intestine
Anus
SAFETY:
To ensure the experiment was safe we had some safety procedures to follow for everyone in the
room and also for the people who would be involved in cleaning up further afterwards. We had to
wear gloves and an apron, avoid direct contact with the rat with your hands, mouth, eyes etc, always
cut away from yourself and others, know what to do and who to tell if you cut yourself, be extremely
careful when using the instruments, when finished wrap the rat inside of the newspaper and dispose
of as directed, put the pins and dissection board on the tray in the correct place also put all
instruments sharp-side down in the bleach solution.
PRE-EXPERIMENT REFLECTION:
1) In the rat dissection I am looking forward to...?
I am looking forward to seeing the internal structure of the rat and how their body and organs are
structured compared to a human body.
2) Rat dissections are useful to us in Science because...?
Rat dissections are useful to us in science because their body and organs are constructed similarly to
a human’s body because we are both mammals. Rats are also inexpensive and easy to buy in bulk for
school experiments such as this.
3) In the dissection I expect to see...?
I expect to see the organs and internal structure and anatomy of the rat such as the stomach, liver
and intestines.
DISCUSSION QUESTIONS:
1) What is the function of the small intestine?
The main function of the small intestine is to absorb the nutrients and minerals from ingested food.
90% of the digestion and absorption of food occurs in the small intestines, the other 10% taking
place in the stomach and large intestine. The small intestine is made up of the duodenum, jejunum,
and ileum.
2) Rats have a large liver compared to many other animals. Explain what they use their liver for.
The liver is the largest internal organ in the body. Rats eat a large variety of materials for food from
leather to fruit and insects. As they can eat and digest just about anything and so their liver needs
to cope with whatever harmful products may be in them they need a large liver to process all
of this.
3) Humans and rats have similar digestive systems. Why do humans have a gallbladder but rats do
not?
As humans and rats are both mammals, we have many similar organs systems and body structures that
work the same way. In humans our gallbladder is located just under our liver; however rats do not have
this organ because they simply do not need one and given their eating habits and foods they eat,
digestion occurs faster when less organs are involved. The gallbladder is a pouch that stores bile. This is a
fluid made by the liver that is released during digestion to help break down fatty foods. In rats the bile
flows directly from the liver through the bile duct straight into the small intestine.
4) What are villi? What do they do?
Villi are finger-like bumps that line the small intestine and help absorb food more efficiently in the
body. Villi increase the surface area of the intestinal walls. Villi are also covered with microvilli. The
purpose of both structures is to increase the small intestine’s surface area so that nutrient
absorption is enhanced. The increase in surface area is how villi aid the digestive system because
they increase the rate of absorption and digestion happens at a faster rate.
5) How do the stomach, gallbladder and stomach relate to each other?
The stomach, gallbladder and pancreas are three of the most important digestive organs in the human
body. The stomach, gallbladder and pancreas work together as a team to perform the majority of the
digestion of food in our bodies. The stomach, gallbladder and pancreas all function together as storage
organs of the digestive system. The stomach stores food that has been ingested. Although the gallbladder
and pancreas have no food passing through them they act as storage organs by storing the chemicals
necessary for the chemical digestion of foods. The gallbladder stores bile produced by the liver and the
pancreas stores pancreatic juice so that it is ready to digest food at all times.
6) How could you determine if a rat is a herbivore, omnivore or carnivore?
As rats are scavengers, they eat a diverse range of foods such as plant material, small insects, garbage,
fruits and seeds. Rats have two pairs of large teeth at the front of their mouths. One pair of teeth is found
on the top jaw and the other pair on the bottom jaw. These gnawing teeth allow rats to bite through hard
seeds and other tough objects that rats commonly eat. They also have the digestive track that makes it
easier to eat and digest meat.
7) What would happen if villi were not present?
Villi increase the surface area for the absorption of nutrients in the small intestine and if they were not
present then less nutrients would be absorbed and be able to get in the blood stream which carries the
supplements to the rest of the body, causing the person to eventually become underweight and
undernourished.
8) Rats are mammals, why do you think we are dissecting rats while learning about the human body
systems?
As we are both mammals, the rat’s body structure and organ systems are relatively similar to humans.
This similarity provides us with the opportunity to make some connections between humans and other
mammals. Their body and organs are constructed similarly to a human’s body and so many schools
dissect rats so that we can learn about the main body systems. Rats are used because they are
inexpensive, easy to buy in bulk and can be related to many other animals.
9) What is the function of the pancreas?
The pancreas is an organ located in the abdomen behind the stomach and is surrounded by other organs
including the small intestine and liver. It plays an essential role in converting the food we eat into fuel for
our body. The pancreas has two main functions. The first is to make digestive enzymes which help us to
digest food. These enzymes help to make proteins, fats and carbohydrates smaller which help the
intestines absorb these nutrients. The second function is to make hormones which regulate our
metabolism.
10) Based on what you know, what would happen to the digestive system without enzymes?
Enzymes are what our body uses to break down food items so we can benefit from them. Without
enzymes no food would get broken down or absorbed into the bloodstream. The bloodstream is what
carries the nutrients to every cell in the body and the nutrients are the only thing that keeps the cells
alive. Without enzymes, no metabolic activity will occur in our bodies. A body that does not efficiently
metabolize the necessary nutrients cannot maintain a healthy body.
RELECTIVE QUESTIONS:
1) During the dissection I discovered...?
I discovered that there was a thin membrane separating the skin from the internal organs. This
membrane is also called connective tissue.
2) The rat dissection was/wasn’t what I expected because...?
The dissection wasn’t what I expected because when we dissected a rat in previous years, it seemed
very unorganised and I didn’t really understand the dissection and the different parts of the rat. This
time, the dissection was different because the rats didn’t smell as much because we were more
careful not to puncture the stomach and small intestines and the group was more methodical in the
opening up of the rat and was more respectful towards it.
OBSERVATIONS AND ANALYSIS:
The results showed that a rat’s internal anatomy is very similar to that of a human with only a few
slight differences. We noticed that rats have no gallbladder which a human does; this is because
they simply have no need for one. Also the rat’s liver has more lobes compared to a human’s liver
because it has so many functions such as cleaning your blood by removing toxins, producing bile,
makes proteins & enzymes for the majority of chemical reactions in the body and fights infections in
the body.
The findings in this experiment were to be expected. The aim of this experiment was to examine and
identify the internal structures of a typical mammal and to become familiar with the appearance of
their internal organs and also to relate the structure of these organs to their functions and our group
achieved this goal. During this experiment we observed organs in the digestive system such as the
stomach, pancreas, liver, small intestine and large intestine.
CONCLUSION:
Throughout this experiment we had no specific difficulties as a group. When dissecting the rat, the
group had a little bit of trouble trying not to cut the stomach or intestines or the rat would start to
smell. The experiment could only be improved by discussing beforehand other body systems and
identifying them when we dissected the rat so that we could understand more about the rat and
how it works.
In this experiment the patterns and trends between a human’s digestive system and a rat’s digestive
system was evident. They were similar because we are both mammals and so have many of the
same features and functions. We saw how by dissecting a rat we could better understand more
about their body and ours at the same time.
In future investigations I would like to learn about different animal’s body systems and see how they
compare to our own and why they differ.