1. Write a response to the question, “Why are we dissecting in science class?”
We are dissecting so that we can get a 3-D idea of how the body systems are put together and how
a mammal’s organs appear on the inside.
2. Why dissect a rat and not a different thing?
Humans are mammals and so are the rats. So in order to be familiar with mammalian anatomy, a
rat is a good animal to look at.
3. ANSWERS VARY
4. How can you differentiate between a male and female rat from the external features?
Externally, males have a scrotum females do not. Females have external nipples and males do not
have any nipples.
5. What external clue is there for the approximate number of “babies” that a female rat could
produce?
The number of nipples that they have. Mammals feed their babies through milk produced in the
nipples and therefore the more nipples they have, the more babies they could feel.
6. Locate the trachea and the esophagus. Describe several ways in which you could tell them apart.
The trachea is lined with cartilage, leads to the lungs, and is located ventrally to the esophagus
when the rat is on its back. The esophagus is a smooth muscle with no cartilage, leads to the
stomach and is dorsal to the trachea when the rat is on its back.
7. Cut the trachea about halfway down its length. Now insert the glass pipette with attached bulb
into the part of the trachea still leading to the lungs. What things do you observe when you
squeeze the bulb?
You can see the lungs inflate and look more like the sac-like organ that they are.
8. Although the alveoli of the lungs are too small to be seen with a microscope, what is their
function?
They are very thin-walled and allow oxygen and carbon dioxide gases to diffuse across the
membrane both into and out of cells.
9. Locate the diaphragm. What is its function?
The diaphragm is the muscle that contracts and relaxes when we are breathing. It changes the
volume of the thoracic cavity and allows air to rush in when it is pulled down and contracted and
allows air to be pushed back out when it in relaxed.
10. How many chambers are there in the rat’s heart? Name them:
The rat’s heart has 4 chambers. The right and left atria and the right and left ventricles.
11. Locate one or more of the parotid, mandibular, and sublinqual glands. By their location and the
fact that they are part of the digestive system, what must their function be?
They secrete digestive enzymes to help break down food.
12. Locate the trachea and the esophagus. Describe several ways in which you could tell them apart.
The trachea is lined with cartilage, leads to the lungs, and is located ventrally to the esophagus
when the rat is on its back. The esophagus is a smooth muscle with no cartilage, leads to the
stomach and is dorsal to the trachea when the rat is on its back.
13. Where in the digestive system does mechanical digestion occur?
In the mouth, stomach.
14. Cut along the length of the stomach and describe its interior:
The stomach is folded and very muscular.
15. What are the general functions of the cardiac and pyloric sphincters?
The cardiac sphincter is a tight muscle that separates the esophagus and the stomach. It functions
to keep food down once it’s in the esophagus. The pyloric sphincter is located between the
stomach and the small intestine and functions to control the speed as which partially digested food
moves into the intestine.
16. ANSWERS VARY
17. Besides the glands in the walls of the duodenum, what accessory organ releases numerous
digestive enzymes in to the digestive system at that site?
Pancreas
18. What does the liver secrete to aid in the process of digestion and what is the function of that
secretion?
The liver secretes bile
19. What sac in humans stores the liver’s secretion?
Gall bladder
20. Why must the rat be able to get along without that sac?
Rats do not have a high fat diet and so they do not need to have large stores of bile to digest their
fat. They do, however, have a caecum. This organ helps them digest the fiber that they eat in their
diet.
21. Cut the membrane (mesentery) that keeps the intestines in place. Determine the approximate
length of the small intestine, which ends at the caecum.
The small intestine is about 2 to 2.5 feet long in the rat.
22. Why is the small intestine sooooooooo long?
This is where most digestion and absorption of nutrients occurs. Therefore the longer the
intestine, the more absorption can occur.
23. What is the function of the caecum?
To aid in the digestion of fiber and to move chime through the digestive system.
24. Chemical digestion occurs at three points along the digestive track. Name those three points and
what type(s) of foods are being chemically digested at each one.
In the mouth starch is partially digested
In the stomach proteins are digested
In the small intestine the rest of the food (but not fiber) is digested
25. What is the function(s) of the large intestine (colon)?
The colon reabsorbs water and absorbs certain vitamins and minerals.
26. Locate a kidney. Trace the pathway of the urine through the following structures of the excretory
system. Describe the function of each:
a)
b)
c)
d)
Kidneys: Filter the blood of water, salts, etc...
Ureters: Connect the kidneys to the urinary bladder.
Urinary bladder: Holds the urine until enough collects and it is excreted.
Urethra: The tube that connects the urinary bladder to the external body.
27. Male: Cut open one of the scrotal sacs so that you can see the testis and epididymis. What is the
function(s) of each of those two structures?
The Epididymis functions as a storage site for maturing sperm cells. The testicle acts as the gland
that produces male sex hormones and also produces sperm.
28. Female: Locate the uterus and the two ovaries attached to it. Cut open the uterus to check for
embryos. Notice its large “V” shape; why is it such a different shape from a human’s pear-shaped
uterus? (Hint: Think about your answer to #5.)
Rats have multiple babies in each of their births. Therefore, this V-shape allows for more surface
area in which to carry the babies as they are developing.
29. What is the function of the cerebrum?
Memory and thinking occur here.
30. What is the function of the cerebellum?
Controls balance and muscle coordination.
31. Where is the medulla oblongata located, and what is its function?
In the brain stem and it controls respiration, heart rate and regulation of the diameter of blood
vessels.