Experiment Regarding Virtual Fetal Pig Dissection

A virtual dissection reveals the gross anatomy of a fetal pig.

Introduction

Fetal pigs are excellent specimens for anatomical study because they have many structures in common with humans. Pigs are mammals, warm blooded animals that maintain their body temperature, are covered with hair, and feed their young from mammary glands. Pigs, like humans, develop in a placenta. The unborn pigs are attached to the placenta with umbilical cords.

Most of the anatomical structures in pigs and humans are analogous. The differences are primarily due to the structural distinctions between two-and four-legged animals. In addition, the human liver has four lobes while the pig liver has five. Unlike humans, the first part of the large intestine in the pig is coiled. At the point of attachment of the small and large intestines, pigs have a cecum, a blind pouch that helps in digestion. Humans have a remnant of the cecum, the appendix. In female pigs, the uterus is bicornate, meaning that it has two cavities instead of one central cavity as in humans.

Although most of the blood vessels in the thoracic cavity are the same, there are a few differences. In fetal pigs, the brachiocephalic artery divides into the right subclavian and the bicarotid trunk, which subdivides into the left and right carotid arteries (see Figure 1). Humans lack a bicarotid trunk; the left carotid comes directly from the aorta, while the right carotid branches off the brachiocephalic artery. Most other structures in the abdominal and thoracic cavities are the same. In this experiment, you will examine the external and internal structures of a preserved fetal pig through a virtual dissection. Figure 2 shows the fetal pig and some of its external structures.

Figure 1

Figure 2

Time Required

55 minutes

Materials

• computer
• access to the Internet
• science notebook

Please review and follow the safety guidelines at the beginning of this volume.

Procedure

1. Go to the Web site http://www.whitman.edu/biology/vpd/.

2. Click on “Virtual Fetal Pig Dissection.”

3. Under “Study Guides,” select “Anatomical References.”

4. Select each of the five tabs, one at a time, and review the information provided. Answer Analysis questions 1 through 4.

5. In your science notebook, draw a picture of a fetal pig and label these regions:

a. anterior

b. posterior

c. dorsal

d. ventral

6. On the same drawing, show the saggittal, transverse, and frontal planes.

7. Under “Study Guides,” select “Sexing Your Pig.” Answer Analysis questions 5 and 6.

8. Under “Study Guides,” select “Digestive System.” Answer Analysis questions 7 through 25.

9. Under “Study Guides,” select “Excretory System.” Answer Analysis questions 26 through 30.

10. Under “Study Guides,” select “Circulatory System.” Answer Analysis questions 31 through 40.

11. Under “Study Guides,” select “Reproductive System.” Answer Analysis questions 41 and 42. Safety Note

12. Under “Study Guides,” select “Respiratory System.” Answer Analysis question 43.

13. Under “Study Guides,” select “Nervous System.” Answer Analysis questions 44 through 46.

14. Complete each of the “Quizzes” on the Web site.

Analysis

1. The cranial region is (anterior/posterior) to the pectoral region.

2. In a (sagittal/transverse/frontal) section, an imaginary plane is passed through the pig separating it into equal left and right halves.

3. The fetal pig’s spine is (medial/lateral) to its shoulders.

4. Using the spine as a point of reference, the fetal pig’s toes are (proximal/distal) to its foreleg.

5. How can you distinguish a male and female pig?

6. Where does the urogenital tract open in a male pig?

7. What is the function of the paired nares?

8. Taste buds in the _________________ are located along the tongue. Describe the appearance of the tongue.

9. Describe the location of one of the salivary glands.

10. Describe the differences in the hard and soft palates.

11. What are unerupted teeth?

12. The _____________________ is the junction of the passageway of the _________________ (along which food travels to the stomach) and the _________________ (along which air travels to the lungs).

13. When the pig swallows, the _______________ prevents food from entering the lungs.

14. What is the large, dark brown structure in the upper quadrant of the pig’s abdomen?

15. How can you locate the stomach?

16. What is the approximate length of the small intestine?

17. What is the function of the small intestine?

18. How does the large intestine differ in appearance from the small intestine?

19. Where is the gallbladder? What is its function?

20. What is the function of the pyloric sphincter?

21. What are rugae in the stomach?

22. Where is the spleen in relation to the stomach?

23. What is the function of the rectum?

24. What is the function of the pancreas?

25. What are the functions of the mesenteries?

26. What is the function of the excretory system?

27. Where are the kidneys located?

28. What are the functions of the kidneys?

29. Unfiltered blood enters the kidneys through _________________.

Filtered blood leaves the kidneys through __________________.

30. Urine travels from the kidneys through _____________ to the bladder. The ____________ is a tube that carries urine from the bladder to the exterior.

31. What membranous structure covers the heart?

32. What two organs are adjacent to the heart?

33. Where is the thymus gland located? What is its function?

34. Where is the coronary artery? What is its function?

35. How do the atria differ from the ventricles in color and size?

36. Describe the path of the aorta as it leaves the heart.

37. In an adult pig, which ventricle is thicker, the left or right? Why?

38. Which chamber of the heart receives deoxygenated blood from the body?

39. Which chamber receives oxygen rich blood from the lungs?

40. Where are heart valves located? What is their function?

41. Describe the position and appearance of ovaries, oviducts, and uterus in the female pig.

42. Describe the position and appearance of the testicles and epididymae of the male pig.

43. Describe the path of air from the nares to the lungs.

44. What membranes cover the brain?

45. Name three structures that can be seen on the ventral surface of the brain.

46. Where is the thalamus? What is its function?

Virtual dissections have many advantages. These exercises provide excellent experiences for those who do not want to participate in actual dissections. Alternately, a virtual dissection can be used to preview work that will be done during an actual dissection. Dissection, the process of taking apart and observing a once-living thing to see how it works, is valued in the study of anatomical structures.

Both actual and virtual dissections help connect the abstract concepts of biology and anatomy to real structures. Pigs are especially useful because their organ systems are very similar to those of humans. As a result, they are the animals of choice in most human anatomy classes. Pigs are also important dissection specimens in comparative anatomy classes in which students compare the structures of different animals including fish, sharks, amphibians, and reptiles.

Fetal pigs used in virtual and actual dissections are a by-product of the meat industry. When pregnant sows are slaughtered for food, their developing fetuses are removed and saved for classroom study. The fetal pigs are prepared by injection with preserving fluid. In addition, preparation may include injection of colored latex into the circulatory system. Red latex is used in the arterial system and blue in the venous system.

Connections

Dissection of humans is most often reserved for students studying medicine and graduate students in various fields of biomedical research. Human cadavers used in dissection come from individuals who donated their bodies to science. Bodies are prepared by removing the blood and replacing it with embalming fluid.

The body is also immersed in embalming fluid for several months. The primary chemicals in embalming are formaldehyde and phenol. In high concentrations, these are carcinogens, so they are used in low concentrations to prepare the bodies. In many cases, the bodies are cremated after dissection, then the ashes returned to the families.