Fetal Pig DissectionBackground:

Pigs are placental mammals (just like humans) and exhibit very similar characteristics to us. These pigs are obtained from slaughterhouses that produce pork. Pregnant sows are harvested for their meat so the fetal pigs are taken for education and research. Basically, it is a recycling of material that would otherwise go to waste. The anatomy of a fetal pig is very similar to human anatomy, so it is one of the best alternative specimens to study.

For this dissection you will work in groups of three. One person will give instructions, one will cut, and one will hand dissection instruments to the person who is cutting. Please rotate these jobs so that everyone has a chance to dissect.

As you conduct the investigation, you will remove all of the organs from the body cavity. This gives you a better view of all the organs in each system and how space is conserved through the folding and placement of the organs within the body cavity. At multiple points during the dissection you will be required to identify structures for your teacher. Points will be earned based on your ability to identify structures, behavior and involvement in the dissection.

Procedures:

A. External Anatomy 1. Each group should obtain a dissecting

tray, a fetal pig, dissecting equipment (scalpel, scissors, probe, forceps), and personal equipment (goggles, gloves, and lab coat).

2. Cut the fetal pig bag near the top and carefully drain all the preservative fluid into the sink. Run the water for a few seconds to wash all the fluid down the drain.

3. Measure the length of the pig from the tip of the nose to the base of the tail along the dorsal side using string. String works better than a ruler since it bends and follows the curvature of the body. Next, measure the string with a metric rule to determine the pig’s length. The age of your fetal pig from conception can estimated from overall length. See the table below.

Length of Specimen Approximate Age in Days From Fertilization4 cm 56 days20 cm 75 days25 cm 100 days30 cm 105 days35 cm 111 days40 cm 115 days (full term)

4. Carefully examine the external features of your pig beginning with the head. Pay attention to the amount and color of hair, birth marks, and other unique markings.

5. Examine the ventral (front) side and note any unusual markings. Note the number and location of mammary papillae (teats). Observe the end of the umbilical chord and identify the umbilical chord vein, artery, and allantoic duct. The allantoic duct is connected to the fetus’ bladder and is used for removing metabolic wastes. These structures may be easier to view if you cut off a small portion of the chord.

6. Determine the gender of your pig by using Figure 1. If your pig is male you will see the urogenital opening posterior to the umbilical chord. It serves as a passageway for urine and semen. Depending on the age you may or may not see scrotal sacs. The penis is not visible but you can feel it by pressing the skin between the urogenital opening and the scrotal sacs. The males’ mammary papillae will never develop but in females they will develop into teats during pregnancy. If you pig is female, you will see the spike-like genital papillae under the tail. This releases metabolic wastes and is the opening to the reproductive system. Be sure to observe another group’s pig of the opposite gender. Call your teacher over and identify the gender of your pig.

B. Incisions for Internal Anatomy1. Place the pig in the dissecting tray on its back ***Remember: when observing structures from the ventral

side, left and right will be reversed. 2. Tie a piece of string around the “wrist” of one of its front legs. Run the cord under

the width of the dissecting tray and tie it around the wrist of the other front leg. Pull the cord fairly tight so that the legs are spread apart. Secure the hind legs in the same manner. (See Figure 2 below)

Figure 2. Positioning the pig on the dissecting tray.

3. Figure 3 shows where your incisions should be made. In making incisions use only the tip of the dissection scissors to cut through the skin. This will decrease the chance of damaging the internal organs. Be particularly careful in the incision over the chest area. Begin the incision on line 1. Then make the incision shown by line 2 and continue to follow the numbering when you make the cut. See Figure 3 below for examples and the diagram.

Figure 3: Use the dissecting scissors and the numbering tofollow for your first incisions.

The ends of the diaphragm, the muscle that separates the abdominal and chest cavities, are attached to the body wall right around incision 3.

4. Gently pull apart the flaps of the body wall along the long incisions between the front and hind legs (Incisions 2 and 3). Do not lift the flap with the umbilical cord. As you separate the flaps under the front legs, use your scissors or scalpel to carefully cut the ends of the diaphragm at the body wall so that the flap can be pinned down. Pin the flaps down under the front legs and above the hind legs. You should have four pins total (two pins on each side).

5. Carefully pull up the flap with the umbilical cord very slightly. You will see the umbilical vein extending from the inside of the umbilical cord up through the liver, toward the head. In order to pull up this flap, use your scissors to cut the umbilical vein. Do not cut off the flap. After cutting the vein, just leave the flap extending backward between the hind legs of the pig.

C. The Abdomen – Digestive System1. A membrane called the peritoneum covers the organs of the abdominal cavity. When

you pulled apart the flaps of the body wall to expose the abdominal cavity, some of the peritoneum may have been pulled off. If not, carefully slit the peritoneum and then use your forceps to pull it off the organs of the abdomen. (note: some specimens may not have a fully developed peritoneum)

2. Use a dry paper towel and wipe out/soak up any extra fluid in the abdominal cavity.3. The red-brown liver fills much of the upper part of the abdomen of the pig, while the

intestines fill the lower part. See Figure 4. The other organs of the abdomen can be seen by moving aside the liver and intestines.

Figure 4: The Abdomen

4. Examine the liver, both the upper and lower surfaces. Locate the gall bladder on the undersurface. Very carefully use your forceps to remove the peritoneum covering the gall bladder.

5. When you have finished examining the liver, remove it. Identify the stomach. The long flattened, organ that lies along the outer curve of the stomach is the pancreas.

6. Find the junction of the stomach and the esophagus, cut to separate. Find where the stomach joins the small intestine, cut to separate. Remove the stomach from the body. Cut open the stomach, beginning where it joined the esophagus and extending to where it joined the small intestine. Rinse out the stomach under running water and examine its inner surface. The folds in the stomach are called rugae.

7. Examine the small intestine, beginning at its junction with the stomach. Spread apart some of the coils of the intestine in place. Blood vessels and nerves also run through this midsection. Find the junction of the small and large intestines.

8. Pull up the intestines and cut the large intestine, leaving a short section showing. Cut off a 1” section of the small intestine. Insert the scissors into one end and make a lengthwise cut. Open the small intestine. Notice the velvety texture of the lining. This is due to the presence of villi, tiny structures that increase the surface area for absorption.

9. Call your teacher over and identify the following structures: liver, gallbladder, stomach, pancreas, spleen, large intestine, small intestine.

D: The Abdomen – Urogenital System1. The large artery and vein that run along the midline of the dorsal surface of the

abdomen (under where the intestines were located) are the abdominal aorta and the inferior vena cava. Identify the abdominal aorta and the inferior vena cava. (note: the arteries are dyed red and the veins are dyed blue)

2. Locate the kidneys, which are large, bean-shaped organs found against the dorsal body wall on either side of the abdomen. The kidneys are outside the peritoneum, so that membrane will probably cover them.

3. Using your forceps, gently pull the peritoneum away from one kidney. Be particularly careful if your pig is a female because the small ovary is just below the kidney. Leave the kidney on the other side of the body intact.

Pancreas

4. On the side where the kidney is exposed, identify the ureter, a large white tube that carries urine to the bladder.

5. Trace the ureter from the kidney to the bladder, which is found in the flap of tissue containing the umbilical cord. Do not remove any structures that may be in the way. Just move them aside where necessary. Identify the urethra, which carries urine from the bladder to the outside of the body.

6. Use a sharp scalpel to cut through the kidney lengthwise midway between the front and the back. Remove the front half of the kidney. You should be able to see three distinct regions- the renal pelvis (funnel like structure exiting the kidney) the medulla (dark tissue in the center), and the cortex (tissue in the outer rim). The cortex and medulla contain nephrons which filter the blood.

7. Before starting your study of the reproductive system, you will have to open the pelvic region of the pig. Use your scalpel to make an incision, slightly to one side of the midline, through the flap containing the umbilical cord, toward the anus. Pull back the skin, and then carefully cut through the muscle and cartilage of the pelvis.

In the female pig, the small, kidney-shaped ovaries are found just below the kidneys.

Unlike the kidneys, however, the ovaries are inside the peritoneum. Eggs released from the ovaries enter the oviducts, which are twisting tubes that carry the eggs to the uterus. The uterus, which is small in the fetal pig, is found along the midline of the body. Extending from the uterus is the vagina. The vagina and the urethra share a single opening (the urogenital opening) to the outside of the body, anterior to the anus.

8. Call your teacher over and identify the following structures: Kidney, ureter, bladder

E: The Chest Cavity – Heart and LungsThe chest cavity contains the heart and lungs and a different membrane covers each organ. The pleural membrane covers the chest wall and lungs while the heart is covered by the pericardium.

1. Gently pull apart the body wall of the chest along the incision made previously. Pin down the two flaps. See Figure 10. Carefully remove any of the pleural membrane that has not been pulled away with the body wall. Note how the diaphragm forms a muscular floor for the chest cavity. Figure 8

2. Examine the lungs. Compare the number of lobes of the left and right lung.

Figure 10:Lungs and Diaphragm

3. Cut the lungs out and examine the heart, which is enclosed by the pericardium. See Figure 11. The anterior end of the heart is partly covered by the thymus gland, try to see if you can identify it.

4. Cut away the pericardium.5. Identify the right/left atrium and right/left ventricles

Figure 11:Fetal PigHeart

6. Lift up the bottom of the heart and identify the inferior and superior vena cava which enter the right atrium. Identify the pulmonary artery leaving the right ventricle. This large artery divides to form the two pulmonary arteries to the lungs a short distance after leaving the heart. Try to trace these vessels. Put the heart back in place and identify the aorta, which comes from the left ventricle.

7. You will now remove the heart very carefully. Use scissors to very carefully cut the blood vessels around the heart. Do not cut them at the surface of the heart; cut at a short distance away. Leave enough of the vessels so that you can study their positions and relationships.

8. Carefully cut through the heart to expose the chambers. Your cut should divide the heart into anterior and posterior sections. Cut as if you were cutting between the left and right sides of the heart. Examine the different chambers of the heart and the relative thicknesses.

9. With the heart removed, identify the trachea by its cartilage ring structure. Find where it divides into two bronchi and enters the lungs. Identify the esophagus, which is dorsal to the trachea.

10. Call your teacher over and identify the following structures: atria, ventricles, aorta, , lungs, diaphragm, trachea, esophagus

After the dissection:Discard all excess animal parts in the designated garbage bag. Only place animal parts in this bag. Clean and dry your lab utensils (scalpel, probe, scissors, etc.) and lab tray. Spray your work area with cleaner and wipe it down with paper towels. Your work station should be as clean as it was when you started. Used paper towels should be discarded in the bag with the animal parts. *Note: it is the job of ALL group members to clean the utensils and work area. Do not leave your work area until it is cleaned. Failure to help clean your work area will result in loss of credit for the dissection.AFTER you have finished cleaning your work area and utensils, you may remove your gloves. All dirty gloves should be discarded in the bag with the animal parts.Remove goggles, place them in the goggle cabinet. Remove lab aprons/coats. Lab aprons/coats should be hung up. Wash your hands thoroughly!!! You should wash your hands vigorously for at least 30-60 seconds.