Fetal Pig Lab

John F. Kennedy Catholic High School

Fetal Pig Lab

A.P. Biology Final Exam Project

Jonathan Mullen

5/4/2011

Study in detail the external and internal anatomy of a fetal pig. Note that the pig is a mammal. Many aspects of its structural and functional organization are identical with those of other mammals, including humans. Thus, a study of the fetal pig is in a very real sense, a study of humans.

Jonathan Mullen Fetal Pig Lab Final Exam Project 2011

Abstract / Background:

Study in detail the external and internal anatomy of a fetal pig. Note that the pig is a mammal therefore, many aspects of its structural and functional organization are identical with those of other mammals, including humans. Thus, a study of the fetal pig is in a very real sense, a study of humansThe fetuses used in the following weeks were salvaged from pregnant sows being slaughtered for food. They are not raised specifically for dissection purposes. The fetuses are removed from the sow and embalmed with a preservative, which is injected through the umbilicus. Following this, the arterial and venous systems are injected under pressure with latex, a rubber-like compound. Arteries (red) are injected through the umbilicus; veins (blue) are injected through one of the jugular veins at the base of the throat.With the possible exception of the abdominal cavity, organs rarely appear as they are presented in a diagram.

During these exercises, keep several points in mind. First, be aware that "to dissect" does not mean "to cut up," but rather primarily "to expose to view." Actual cutting should be kept to a minimum. Tissues are picked and teased apart with needle probes, forceps, and blunt probes in order to trace the pathways of blood vessels, nerves, muscles, and other structures. Never cut or move more than is necessary to expose a given part. Second, pay particular attention to the spatial relationships of organs, glands, and other structures as you expose them. Realize that their positions are not random. Third, you are encouraged to engage in collaborative discussions with your classmates and compare dissections.

Objectives:

Identify important external structures of the fetal pig.Identify major structures associated with a fetal pig’s digestive, respiratory, circulatory, urogenital, and nervous systems.Compare the functions of certain organs in a fetal mammal with those of an adult mammal.

Safety Precaution: Wear your lab apron and goggles at all times

Materials:

Materials RequiredTools Chemicals

Beaker (For Rinsing) WaterProbe

ScapelSizzors

Dissection PanMarker

Paper TowelsTwine

1 Pair Latex GlovesPlastic Bag (For Disposal)


Procedure:External Anatomy

1. Obtain a fetal pig and rinse off the excess preservative by holding it under running water. Lay the pig on its side in the dissecting pan and locate:

*dorsal: toward the back of the body *ventral: toward the underside of the body *anterior (cranial): toward the head end of the body *posterior (caudal): toward the tail end of the body lateral: to the side of the body median: toward the center of the body right and left: the pig's right and left. proximal or basal: closer to the trunk distal: farther from the trunk superficial: lying closer to the body surface deep: lying under or below head: (cranial) region neck: (cervical) region trunk region: (thoracic region) tail: (caudal) region (abdomoninal region)

Figure 1: Fetal Pig External Anatomy

*The terms anterior and posterior are sometimes used synonymously with ventral and dorsal, respectively, for humans.

2. A fetal pig has not been born yet, but its approximate age since conception can be estimated by measuring its length. Measure your pig's length from the tip of its snout to the base of its tail and record this on your hand-in. (See Table 1)

Table 1: Pig Length based on Time from Conception

Time from Conception

Pig Length in mm


21 days 11 mm35 days 17 mm49 days 28 mm56 days 40 mm

100 days 220 mm114 days (birth) 300 mm

3. Examine the pig's head.(See Figure 2) Locate the eyelids and the external ears or pinnae. Find the external nostrils

Figure 2: Fetal Pig Head

4. Study the pig's appendages and examine the pig's toes. Notice how the number of toes is reduced in your pig. The middle two digits form hooves.

5. Locate the umbilical cord. With scissors, cut across the cord about 1 cm from the body (See figure 3). Examine the 3 openings in the umbilical cord. The largest is the umbilical vein, which carries blood from the placenta to the fetus. The two smaller openings are the umbilical arteries, which carry blood from the fetus to the placenta.

Figure 3: Fetal Pig "Umbilical Area"


6. Lift the pig's tail to find the anus. Study the ventral surface of the pig and note the tiny bumps called mammary papillary. These are present in both sexes. In the female these structures connect to the mammary glands.

7. Determine the sex of your pig by locating the urogenital opening through which liquid wastes and reproductive cells pass. In the male, the opening is on the ventral surface of the pig just posterior to the umbilical cord. In the female, the opening is ventral to the anus.

8. Carefully lay the pig on one side in your dissecting pan and cut away the skin from the side of the face and upper neck to expose the masseter muscle that works the jaw, lymph nodes, and salivary glands.

9. With scissors, make a 3-cm incision in each corner of the pig's mouth. Your incision should extend posteriorly through the jaw.

10. Spread the jaws open and examine the tongue.

11. Observe the palate on the roof of the mouth. The anterior part of the palate is the hard palate, while the posterior part is the soft palate. The hard palate has ridges, and separates the oral cavities from the nasal cavities. The soft palate is soft because there is no bone underneath.

12. Locate the epiglottis, a cone-shaped structure at the back of the mouth. This is the flap that covers the glottis during swallowing. Above the epiglottis, find the round opening of the nasopharynx. This cavity carries air from the nostrils to the trachea.

13. Dorsal to the glottis, find the opening to the esophagus. Examine the tongue and note tiny projections called sensory papillae.

14. Examine the teeth of the pig. Canine teeth are longer for tearing food, while incisors are shorter and used for biting. Pigs will eat both plants and other animals.

Internal Anatomy

Figure 4) Upper and Lower Jaw


Internal Anatomy

1. Examine the diaphragm, a sheet of muscle that stretches across the abdominal cavity and separates it from the thoracic cavity where the lungs are located. The fetal pig does not use the diaphragm because gas exchange occurs through the umbilical cord. The diaphragm in adult pigs moves up and down changing air pressure in the chest cavity causing air to move into and out of the lungs.

2. In the thoracic cavity, carefully separate the pericardium (or sac) surrounding the heart and the diaphragm from the body wall.

3. Locate the two, spongy lungs that surround the heart. The tissue that covers and protects the lungs is called pleura. The fetus has not used the lungs so they have never contained air.

Figure 5) Lungs

4. Find the trachea, a large air tube that lies anterior to the lungs. The trachea is easy to identify because of the cartilaginous rings that help keep it form collapsing as the animal inhales and exhales.

5. Notice that the trachea branches into each lung. These two tubes are called bronchial tubes. Inside the lungs these branch into smaller bronchioles that end with a grape-like cluster of air sacs or alveoli where oxygen and carbon dioxide are exchanged with capillaries.

6. At the top, anterior end of the trachea, find the hard, light-colored larynx or voice box. This organ contains the vocal cords that enable the animal to produce sound.


Figure 6) Trachea, Bronchial Tubes, and Vocal Cords

7. Locate the heart, which is covered by a thin tissue called the pericardium. Remove this membrane to study the heart.

8. Pigs, like all mammals, have four-chambered hearts. The right side of the heart pumps blood to the lungs, while the left side of the heart pumps blood to all other parts of the body. Locate the right and left sides of the heart.

9. Each side of the heart has an upper and a lower chamber. Upper chambers are called atria and receive blood, while lower chambers are called ventricles and pump blood out of the heart. Locate the right and left atria and ventricle.

10. Notice that the surface of the heart is covered with blood vessels. These are part of the coronary circulation, a set of arteries and veins whose only job is to nourish the heart tissue. Blockage in these vessels causes heart attacks.

11. Anterior to the heart, locate another large vein that enters the right atrium. This vein, the anterior vena cava, brings blood to the right atrium from the anterior part of the body.

12. Now lift the heart to view its dorsal surface. Observe the posterior vena cava that carries blood from the posterior part of the body and empties it into the right atrium.

13. Find the pulmonary artery, which leaves the right ventricle. After birth, this vessel carries blood to the lungs. However, in a fetus, a shunt called the ductus arteriosus allows fetal blood to bypass the lungs and go directly to the aorta, the largest artery of the body.

14. Locate the pulmonary veins that enter the left atrium. After birth, these vessels carry oxygenated blood from the lungs to the heart.

15. Identify the aorta, a large artery that transports blood from the left ventricle. Many arteries that carry blood throughout the body branch off of the aorta.

16. Remove the heart by severing the blood vessels attached to it.


17. Hold the dorsal and ventral surfaces of the heart with your thumb and forefinger and rest the ventricles on your dissecting tray. With a scalpel, cut the heart into dorsal and ventral halves.

Figure 7) Fetal Pig Heart

18. Remove any material inside the heart and expose the walls of the atria and the ventricles.

19. Study the internal features of these chambers and note where vessels leave or enter each chamber. Locate the valves between each atrium and ventricle. These structures prevent blood from flowing backward in the heart

Urogenital System

1. Remove the digestive organs to study the excretory and reproductive organs that make up the urogenital system.

Figure 8) Overview of the Heart


2. Locate the large, bean-shaped kidneys lying against the dorsal body wall. Notice that they are covered by the peritoneum. Kidneys filter wastes from blood.

3. Find the ureters, tubes that extend from the kidneys to the bag-like urinary bladder. The bladder lies between the umbilical arteries and temporarily stores liquid wastes filtered from the blood.

4. Lift the urinary bladder to find the urethra, the tube, which carries urine out of the body. Follow the urethra to the urogenital opening on the outside of the pig's body.

5. Make an incision from the caudal side of the umbilical cord to the anus. Be careful to not cut too deep and damage the internal organs.

Male System

1. In the male pig, locate the two scrotal sacs at the posterior end of the pig. If the pig is in the later stages of development, you will find a testis in each sac. If the pig is in an early stage of development, the oval-shaped testes will be in the abdominal cavity. These testes have not yet descended into the scrotal sacs.

2. On each testis, find the coiled epididymis. Sperm cells produced in the testis pass through the epididymis and into a tube called the vas deferens. This tube crosses over a ureter and enters the urethra.

3. Follow the urethra to the penis, a muscular tube lying just below the skin posterior to the umbilical cord. In mammals, the penis is the organ that transfers sperm.

Female System

1. In the female pig, find the two bean-shaped ovaries at the posterior end of the abdominal cavity. Observe the coiled Fallopian tube attached to each ovary, which carries eggs from the ovary.

Figure 9) Male Sex Organ found in Fetal Pig


2. Follow the Fallopian tube to the uterus, which is dorsal to the urinary bladder and the urethra. 3. Trace the uterus to a muscular tube called the vagina. The vagina will appear as a continuation

of the uterus. Sperm from the male are deposited into this organ during mating. The vagina and the urethra open into a common area called the urogenital sinus. This cavity opens to the outside at the urogenital opening.

Results / Discussion

Upon receiving the fetal pig and conducting the external observations (part 1 of the lab) it was evident that the sex of the pig was a male. This was proven by locating the penis, the scrotum, as well as the urogenital opening. (See Figure 11)

Figure 11) External area of a male

Once the sex was determined, the fetal pig was washed and marked for dissection. After comparing the markings on the lab sheet to the markings made on the fetal pig, a probe was inserted into the umbilical area so that the scissors would be able to cut at the appropriate depth.

Once the flesh was cut and moved aside for internal observations we were able to locate various organs including but not limited to: The lungs, The Heart, The pancreas, The Liver, Large intestine, Small intestine, Esophagus, Larynx, thyroid, ect…

Figure 10) Female Sex Organs


The inside of the fetal pig was rinsed and once permission was given for organ removal we started to remove the digestive system. It was decided that in order to prevent internal damage, the esophagus would be cut from the stomach, and the liver would be the first organ to be removed.

Through the use of a scalpel, the liver was removed, followed by the stomach, the small intestine, than the large intestine. (Note that the large intestine was removed from the anal cavity during this process.) Once removed the parts were separated, and labeled on a paper towel.

Figure 12) Fetal Pig Digestion System

Because of the various liquids that occupied the cavity in the fetal pig, it was determined that it would be best to flush internal area of the fetal pig with water. Through careful maneuvering this was a success. Because the digestive system had been removed, the lungs were removed next, as they were the easiest “access.” This was done by cutting various nerves and a membrane which attached the lungs to the diaphragm. Once removed from the fetal pig these too were placed and labeled on a paper towel.

Figure 13) the Respitory System


The heart was removed next, which required nothing more than cutting the arteries and veins extending from it. Once removed, the heart was observed, the different sections were identified, and the organ was placed on the paper towel.

Figure 14) PARTS OF THE HEART

We then focused on the throat area where we identified all the organs and began with removing each individual part. After several minutes of precise separation the esophagus, larynx, trachea, bronchus, and thyroid were removed, and placed on the labeled paper towel.

Figure 15) Internal throat area of the fetal pig

At this point, we observed the sex organs of the female from a neighboring group, then went on to complete the pre lab assignment.


Figure 16) Female reproductive system

Upon completion of the pre lab, we determined that there was enough time and we continued on to trace out the nervous system of the fetal pig, which included the eyes, the eye sockets, the ear canal, the ear drum, and most importantly the brain. Due to the thickness of the skull, we attempted to pry it; however this caused damage to the left lobe to the brain, so we made our observations based on the right lobe. (Figure 17 shows an intact brain of a fetal pig)

Sources:

Lim, J. (2007, August 3). Fetal pig dissection lab. Retrieved from http://www.ccsf.edu/Resources/Faculty/jllim/documents/FetalPigDissectionLab.pdf

Pig_lab.pdf. (2001). Informally published manuscript, Department of Science, Seattle Central Schools, Seattle, Washington. Retrieved from http://www.seattlecentral.edu/faculty/adavis/241_OCLWINTER/Lab_HAndouts/PigLab_Draft.pdf

Gregory Ph.D., M.J. (n.d.). Fetal Pig Dissection. Clinton community college. Retrieved May 07, 2011, from http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20102/bio%20102%20laboratory/fetal%20pig/fetal%20pig.htm

http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20102/bio%20102%20laboratory/fetal%20pig/fetal%20pig.htm

http://faculty.clintoncc.suny.edu/faculty/michael.gregory/files/bio%20102/bio%20102%20laboratory/fetal%20pig/fetal%20pig.htm

http://www.seattlecentral.edu/faculty/adavis/241_OCLWINTER/Lab_HAndouts/PigLab_Draft.pdf

http://www.seattlecentral.edu/faculty/adavis/241_OCLWINTER/Lab_HAndouts/PigLab_Draft.pdf

http://www.ccsf.edu/Resources/Faculty/jllim/documents/FetalPigDissectionLab.pdf

Documents

Fetal Pig Lab