Fetal Pig Dissection Materials Preserved Fetal Pig Cotton String Dissection tray Dissection pins Disposable Gloves Paper towels Dissection scissors Label pins Lab apron Re-sealable bag Dissection probe Metric Ruler Introduction Mammals are warm-blooded vertebrates that feed their young milk from mammary glands and have hair or fur on their bodies. The largest single group of mammals is the placental mammals. Placental mammals develop inside their mother, where they are connected to her by a placenta, a large organ filled with blood vessels. These blood vessels allow the mother s blood to supply the fetus with nutrients and oxygen while removing wastes and carbon dioxide. Humans are placental mammals and so are most domesticated animals; such as dogs, cats, horses and cows. The fetal pig is an excellent organism to study because it is relatively small, easy to acquire, and exhibits all mammalian characteristics as well as special fetal structures. A. Preparing the Fetal Pig 1. Obtain disposable gloves, lab apron, dissecting tray and dissecting equipment, and a fetal pig. 2. With safety glasses and gloves on, remove the pig from the pail and lay on a dissecting tray. 3. Review the directional terms for the pig in Figure 1. Note the differences between fourlegged animals and humans. Anterior is toward the head end of the pig. Posterior is toward the tail end of the pig. Dorsal is toward the back surface. Ventral is toward the belly surface. 4. Place your pig ventral surface up on the dissecting tray. 5. Measure the length of your fetal pig (from snout to rump) in cm. 6. Determine the gender of your pig. Males have a urogenital opening (opening for the penis) that is posterior to the umbilical cord. The scrotum (small bulges) is anterior to the anus. Females also have a urogenital opening located anterior to the anus. The opening is enclosed by small folds called labia that form a projection called the genital papilla. 7. Locate the mammary papillae. These are nipples on the abdomen. They are present in both male and female pigs. 8. Label the re-sealable bag with the names of your group members and the gender of your pig. FIGURE 1 Directional Terminology for the Fetal Pig Dorsal Posterior Anterior Ventral
B. Preparing for dissection 1. You will be dissecting and observing the internal organ systems by system. Do not remove any organ before you are directed to do so. Take care not to damage any structures when locating and dissecting other structures. Also, remember that no system functions alone. Be aware of how each system relates to others. 2. Secure the pig for dissection using two pieces of cotton string. Tie one piece of string securely around one wrist of your pig. Take the string under the dissecting pan and tie it to the other wrist. Repeat this procedure with the ankles. Tighten the strings to keep the legs apart. 3. Study the diagrams carefully to help you locate all the structures printed in italics. Throughout this investigation italic type will indicate major structures that need to be located and labeled on your diagram and inside the pig. 4. Begin the dissection of the abdominal cavity by making cuts with your scalpel as shown in Figure 2. Cut through the skin and muscle tissue, but be aware of the depth of your scalpel, so as not to injure the underlying organs. Use scissors to cut through the thoracic cavity, gently cut through the bones of the rib cage so as not to damage the heart and lungs. 5. After making these cuts, pin back the flaps of skin and tissue to expose the thoracic and abdominal cavities. 6. Follow the large vein at the base of the umbilical cord. Cut the vein so that the flap of skin with the umbilical cord can be turned back. 7. After each structure has been located and observed, label it in the diagram and use the indicated number to label it inside your pig. FIGURE 2 Directions for making incisions FIGURE 3 Endocrine Organs
C. The Endocrine System 1. There are two main endocrine organs in the thoracic cavity, the thyroid gland and the thymus. The thyroid gland is an oval gland lying over the trachea posterior to the larynx. The thymus is a glandular looking with small lobules and is posterior to the larynx on top of the thyroid gland on the trachea, and extending to partially cover the heart. Because the pig is fetal, the thymus gland will be quite large with two definite lobes. 2. There are three main endocrine organs in the abdominal cavity: the pancreas, adrenal glands, and female gonads. Locate the diaphragm that separates the thoracic and abdominopelvic cavities. Reflect the stomach and look beneath it for the glandular-looking pancreas. It is located close to the curve in the first part of the small intestine and extends to the left toward the spleen. Label the pancreas when labeling the digestive organs. 3. The bean-shaped adrenal glands are located near the anterior part of the kidneys. Both the kidneys and adrenal glands are located behind the peritoneum. Label the adrenal glands when labeling the kidney 4. Have the instructor check the labeling of the thyroid gland and the thymus. D. The Respiratory and Circulatory Systems 1. Beginning at the top of the stomach, trace the esophagus as it passes through the diaphragm and under the heart. At the anterior end of the esophagus on the ventral side is the trachea. Notice the rings of cartilage that surround the trachea. These rings give the trachea the appearance of a vacuum cleaner hose. Trace the trachea to the point at which it branches to each lung. 2. Continue the dissection of the neck anteriorly to find an enlarged area of cartilage. This is the larynx, often called the voice box. At the beginning of the trachea is the epiglottis, which is a flap that covers the respiratory tract during ingestion. FIGURE 5 Circulatory and Respiratory Organs FIGURE 6 The Heart
3. Using Diagrams 5 and 6, locate and label the lungs and the heart, which is enclosed in the pericardium. 4. Have the instructor check the labeling of the respiratory organs and the heart. 5. Remove the pericardium from the heart. Using Figure 6, locate the following structures on the ventral side of the heart; right atrium, right ventricle, left atrium, left ventricle, coronary artery. 6. Turn the heart onto the dorsal side without removing it. Locate the two major veins that bring blood back to the heart; the superior vena cava and the inferior vena cava. Locate the right and left pulmonary veins. This is the pair that brings blood back to the heart from the lungs. Both of these empty into the left atrium. 7. Carefully dissect around the heart, picking away the connective tissue between the blood vessels. Locate the pulmonary artery, on the ventral side of the heart, as it leaves the right atrium. The aorta, the largest and most important artery, can be found just beneath the pulmonary artery as it leaves the left ventricle. E. Digestive System 1. Find the large, three-lobed liver at the anterior end of the abdominal cavity. Under the liver is the stomach, a large pouch-like organ with two parts. The large, anterior end is the cardiac stomach and the smaller end is the pyloric stomach. The part where the stomach and the small intestine meet is called the pyloric sphincter. 2. Posterior to the sphincter is the small intestine. Follow it to where it enlarges to become the large intestine or colon. The difference is that the large intestine is slightly larger in diameter and has a small, blind pouch called the caecum. The caecum ends in the appendix in humans and in the pig. FIGURE 4 Digestive Organs 3. Closely observe the membranous, net-like tissue that can be found over the intestines. This is the messentery. The large intestine continues and enlarges, forming the rectum. The point at which the rectum opens to the outside of the body is the anus. Relocate the liver. Lift it up and trace the stomach anteriorly to the esophagus. 4. Observe the dome-shaped muscular wall at the most anterior end of the abdominal cavity just above the liver. This is the diaphragm. 5. Embeddded in the underside of the right central lobe of the liver is the greenish gall bladder. Locate it and then find and trace the bile duct, a small tube-like structures that is attached to the gall bladder. Directly below the gall bladder, on the underside of the stomach you will find a granular-looking organ, the pancreas. Both the gall bladder and pancreas release enzymes through a duct into the small intestine to aid in digestion. Attached to the left edge of the stomach is a reddish smooth organ, this is the spleen.
6. Have the instructor check the labeling of the digestive organs. 7. Carefully remove the organs of the digestive cavity and measure the entire length of the digestive tract. F. The Urogenital System 1. Since the organs of the digestive system have been removed, the organs of the excretory and reproductive systems will now be exposed. The kidneys are the pair of dark, bean-shaped organs lying on the dorsal wall, behind the peritoneum. The kidneys are supplied with blood by the renal arteries. The renal veins take blood away from the kidneys. They are located just below the renal arteries. Remove these blood vessels very carefully. 2. Coming from the posterior end of the kidney is the ureter. This is the tube that drains urine from the kidney into the urinary bladder for storage. Trace the ureter to the bladder. Cut through the cartilage of the pelvic girdle with scissors. Spread the legs and pelvic girdle as far apart as possible. Locate the urethra, which comes from the urinary bladder to the urogenital opening, through which urine is eliminated from the body. 3. The female gonads, the ovaries and are small, oval organs located posterior to the kidneys. 4. The male gonads, the testes, are located outside of the abdominopelvic cavity in the scrotum. Because these pigs are fetal, the scrotum and testes have not descended much and are merely small bulges. Open the scrotum to view the testes. 5. Have the instructor check the labeling of the urogenital organs. FIGURE 7 Male Urogenital Organs FIGURE 8 Female Urogenital Organs G. Post Dissection 1. Make sure that the instructor has checked all the labeled organs of your pig and that you have correctly labeled all the diagrams.
2. Remove all the pins and place the fetal pig, the cotton string and all portions removed into the re-sealable bag. 3. Place the re-sealable bag in the container indicated by the instructor. 4. Thoroughly wash and dry all dissection equipment. 5. Clean your table with disinfectant and wash your hands thoroughly before leaving the lab Student Student Fetal Pig Dissection 1. The fetal pig assigned to you measures cm ( mm) in length. 2. What is the sex of your dissection pig? 3. How many papillae are there on your pig? 4. What is the function of the papillae? 5. To where does the large vein at the base of the umbilical cord go? 6. What is the function of the thyroid gland? 7. What is the function of the cartilage rings in the trachea? 8. What could happen if the epiglottis failed to cover the respiratory tract during ingestion? 9. To what system does the diaphragm belong? 10. What are the four chambers of the heart? 11. What is the function of the coronary artery? 12. What structure connects the stomach to the mouth? 13. What is the function of the stomach? 14. To what other system, besides the digestive system, does the pancreas belong? 15. What is the function of the mesentery? 16. At what structure does the digestive tract open to the outside? 17. The digestive tract of the fetal pig assigned to you measures cm ( m) in length. 18. What are the functions of the kidneys? 19. What is the function of the urinary bladder? 20. What is the function of the testes /ovaries? Place the numbered pins according to the body parts below. Shaded Boxes for Teacher Use Only # Body Parts Labeled Correctly Pts. Possible Pts. Earned 1 Thymus 4 2 Thyroid 4 3 Heart 4 4 Lung 4 5 Larynx 4 6 Diaphragm 4 7 Liver 4 8 Gall Bladder 4 9 Stomach 4 10 Spleen 4 11 Pancreas 4
12 Small Intestine 4 13 Large Intestine 4 14 Kidney 4 15 Adrenal glands 4 16 Urinary Bladder 4 17 Urethra 4 18. Male Testes / Female Ovaries 4 Label the diagrams below Internal Organs The Heart L 16 1 A K 15 2 B J C I 14 3 D H 13 12 11 11 10 9 1. 2. 3. 4. 5. 6. 7. 8 4 5 6 7 E A. B. C. D. E. F. G. H. I. J. K. L. G F
8. 9. 10. 11. 12. 13. 14. 15. 16.