Fetal Pig Dissection
Pig dissections visually show students the various systems inside a pig, connected with our own bodies. Although the size of a fetal pig is smaller than a human body, the organization of major organs and their functions are still the same. They are similar to humans by the fact they have skin, are omnivores, and as a fetus, receive nutrients from their mother by an umbilical cord. It’s easier to compare human organ systems to a pig, than let’s say a frog. Dissection engages students in “observational and kinaesthetic learning that instills a recognition, an appreciation for the three dimensional structure of the animal body, the interconnections between organs and organ systems, and the uniqueness of biological material” (1). Students get to examine the heart, which is the major organ in the circulatory system that pumps oxygenated blood around the body, and deoxygenated blood to the lungs. The small intestine gets examined as well, which is the major organ in the digestive system that not only digests the foods, but absorb nutrients from it as well. These systems control the basic functions of life and without one, all cannot perform. This can majorly benefit students who are going into any science, health, nursing, or math program. Not only is it an educational experience, but hands-on as well.
Purpose: To dissect a fetal pig and examine the structures and arrangements of the digestive, respiratory, and circulatory systems.
Hypothesis: My prediction of the fetal pig was that it would be very large, bright pink, with very bloody organs. The case of this dissection was the complete opposite. I thought it would be easy to reference all of the part of the systems, but for some things, it was very difficult (ex. identifying the pancreas and spleen). I also guessed that the inside would be filled with veins, which was accurate. The heart was smaller than I had estimated, and extremely tough.
Equipment & Materials: See pg. 510-513 of Nelson Biology 11 Textbook
Procedure: See pg. 511-513
When we received the pig, it was much smaller than expected. Instead of having a predicted pink tint, it’s skin had a pale, yellow colour. Since it is a mammal, during its development, it does have little white hairs on its body, but more consistently on its face. The lips around the mouth are developed, as well as the tongue, which is a more prominent yellow tint. The tongue appeared to be sticking out, very marked up on its edges, slightly curled. The nostrils were small, and oval shaped on the nose. For the ears, they had a “flexible outer flap called the pinna” (2). This helps sound travel to the middle of the ear. The colour of the ear is more pink than any other place on the body. The eyes are closed, with both an upper and a lower lid. For the feet, the hooves were just beginning to form, very soft, but curled at the end, consisting of a dark yellow, almost orange tint. There are a paired row of nipples on the ventral surface of its abdomen. This is the same for both males and females. The gender for this pig was immediately recognized. This fetal pig was female, for it had a urogenital opening “immediately ventral below the tail and anus.” (3). The genital papilla is marked, which presence helps to easily determine the sex of the pig.
When cutting down the medial line, preserving fluid spilled out of the open cut, resembling water. The skin was thicker around the chest cavity, and thinner as we proceeded down. Pinkish/red blood spilled out of it’s chest and stomach cavity. The organs and muscle all consisted of a dull grey/brown tint. There were many veins in the neck, with soft layers of skin. We cut down to the umbilical cord, which protruded out of the abdomen. It is the fetus’ way of getting oxygen, nourishment, and nutrients needed to grow. It is attached to the mother’s placenta, which receives oxygenated blood from the heart and the small intestines and delivers it to the fetus. The fetal pig also uses the umbilical cord to dispose of any wastes left in his/her body.
Once the mouth had been opened, the most dominant feature of the oral cavity (besides the tongue) is the hard palate, which makes up the anterior part of the roof in the mouth. It feels very stiff, since it is made of bone, and a rigid texture. Horizontal lines from either end as well. This hard palate seperates the oral cavity from the nasal cavities. Posterior to this is the soft palate, which is the same pale pink tint, without the horizontal ridges. It’s a smooth continuation of the mucous membrane, and contains no bone, hence the name ‘soft’. 8 teeth are visible, all very small. The incisors are found at the front of the mouth, and the cheek teeth are located at the back. The pharynx is located at the base of the tongue, and leads to the esophagus and trachea. Both of these were visible as well, very long, and tube-like. Once we opened the mouth far enough, the small flap of the epiglottis was visible, controlling the entrance of the wind pipe. The larynx was very hard, sticking out, like there was ball inside of it, attached to the trachea.
The first examined digestive system structure was the liver. The liver was a very large organ, and grey-brown colour. 2 sections were noticeable, with 3 lobes, distal and ventral to the stomach. It resembled a thick, broken mushroom cap in a way. The gall bladder was dorsal to the liver, underneath the 1st lobe posterior to the heart, slightly left to the medial line. We had to lift it up to get a full view. It’s small, tear-shaped, with a slight green-tint. The stomach is a round ball, that is very tender, and loose with liquid. Like a balloon filled with water. It’s a muscular organ attached to the esophagus, in which chemical and mechanical digestion take place. When food enters the stomach, it is churned with acids and enzymes. From the stomach, there is the duodenum, which is C-shaped, and is the beginning portion of the small intestine. The small intestine is a pale yellow colour, resembling soft, scrunched up noodles. The pancreas is a large, whitish, irregular shaped gland below the stomach. It makes a variety of enzymes that travel to the small intestine. It’s filled with veins, and bumpy, like it contains fish eggs. Veins from the liver to the intestine are thin, pink, and connect in the stomach and the liver. They thicken significantly in the liver. The spleen, resembling a tongue, is a wide, thin, flat flap running along the stomach. It is located above the small and large intestine. One note to be made is that on the 2nd day of the dissection, whenever needles were punctured, there were red circles (like bruises).
After cutting open the stomach, it seemed to deflate, spilling chunky, thick liquid with a green glob. The inner lining itself is very veiny, tough and a red colour. After stretching out the small intestine, it came to a measurement of 3.5m. We proceeded to lift the liver and intestines to view the blood vessels that all travelled outwards from the centre, attaching from the same point. The umbilical arteries seemed to look like thick, slimy noodles, with its origin being the liver.
Once being exposed to the heart, the outer appearance consisted of spilling prominent pink coloured liquid, and an oval shape. To touch, it was very tough (being that it is a muscle). The coronary artery was the thickest blood vessel on the heart, with both the right and the left atrium visible. The heart is attached to everything, and is secured by the lungs, which are attached to the trachea. Covering the heart was a thin, tough membrane called the pericardium. The most noticeable artery on the heart was the aorta, which curved to the left and passed along the dorsal side of the thoracic and abdominal wall. The second largest artery was the pulmonary artery, which stemmed from the anterior portion of the right ventricle, and divided into the left and right pulmonary arteries. There were also very thick tissues holding the heart, and it was extremely hard to cut, being one of the toughest muscles. Inside of the heart were many holes, and an area of space to the left of the heart, at the top.
The trachea is a tube that extends from the neck down to the chest. It was a white shade, and lined with cartilage. At the anterior end of it was the larynx, which contained the vocal cords. When you touch the trachea it feels hollow, and hard, but not as hard as bone. It was also extremely bumpy, in-cased in bone to support it, and hold it in place. The lungs, which are located on either side of the heart, are very tender to touch, resembling a butterfly without the heart in place. Both of them were very squishy, tough, with no spaces, and are filled with veins. They are made of tiny air sacs called alveoli (which we’ve learned is where gas exchange occurs.) The lungs were held together by connective tissue (which is visible, and many lobes are at the top, near the medial line. The diaphragm was also visible, and is a “sheet of muscle and connective tissue that helps in breathing” (4).
The top of the pig’s mouth has a ridged roof known as the hard palate, which separate’s the nasal cavity from the mouth, contains several horizontal lines running from either end. The soft palate has more flesh, posterior from the hard palate. There are 8 teeth visible, very small, and quite sharp. The incisors are used for cutting food, and located near the front, and the cheek teeth which are used for grinding the food, are at the back. The tongue is sticking out, rough at the edges, and a pale, yellow tint. The epiglottis is a visible flap at the back of the oral cavity, at the top of the trachea. The function of this tissue is to seal off the windpipe to prevent food from falling in. It closes during swallowing. The food eventually makes it way to the small intestine, which decomposes left over material through micro-organisms and bacteria. Then, the large intestine absorbs water, minerals, and salt missed in the small intestine. The ratio of the length of the small intestine to the large intestine is 1:5, which is the same as humans. In humans, the small intestine is about 6 meters (20 feet), and the large intestine is 1.5 meters (5 feet) long. For a pig, the small intestine is 6-8 feet, and its large is 1-3 feet.
The trachea of a fetal pig is a tube-like structure with smooth, soft tissue, of the respiratory tract that connects the larynx with the bronchi. It’s located in the chest cavity and the neck, anterior to the lungs. It is otherwise known as the windpipe, for it allows air to be transported down into the lungs, where it is cycled into the bloodstream. The rings of cartilage help keep the trachea open for the passage of air so they don’t collapse. This rigid structure of the trachea allows it to remain flexible, yet prevents it from closing. If it wasn’t rigid, then the tube would close and stick together, causing the animal loss of breath. The lungs themselves were very tender to touch, resembling the shape of a butterfly (with the heart cavity). There were no spaces, and filled with veins. They felt quite spongy, because there are millions of alveoli in the lungs. These alveoli are made so that the maximum surface area can take in oxygen for deoxygenated blood. Since there are little spaces between the alveoli, it leaves the lungs feeling spongy, instead of solid.
The left ventricle of the heart is the most muscular. This is because the left ventricle must be strong enough to pump at a very high pressure throughout the body. The right ventricle only needs to pump the blood to the nearby lungs. The lungs are mm away from the heart. But let’s say the feet, on a fetal pig, are so many cm away from the heart. The arteries in the heart carry blood away from the heart, and the veins carry blood toward the heart. There were no colour difference between the two. The veins should’ve been blue, and the arteries red. For our fetal pig, both were red. But the arteries were slightly larger in size compared to the veins. Personally, I found examining the heart the most interesting part. I chose not to touch it, but it was very amazing just looking at it, and splitting it open. In kinesiology, we always examined diagrams of the heart, so to open it up and see it face-to-face was very surreal. I could identify the aorta, the right atrium, the left atrium, the ventricle, and the arteries. The most surprising thing was the digestive system. I couldn’t believe how long the small intestine could stretch to be. It was able to fit and function in such a small space. It leaves me curious to what the heart and intestines inside a human look like (Grey’s Anatomy only shows so much). The most disturbing thing to look at for me was the pig’s face. It looked asleep, not dead (if it weren’t for the smell and body tint giving it away). I would rather see the pig alive and running around, rather than dissecting it. I’m a vegan, so it’s even harder for me to look at the body of a dead animal that millions of people eat. The only difficulty we really had was finding the esophagus. But this was only due to not opening the mouth further. Other than that, all major organs and tissues were easily identified. There were no difficulties faced, but we learned along the way how to cut the skin properly using the body, and maneuvering organs that were distal to view the ones that were more proximal.
Pigs are very complex mammals with many similarities in structure with humans. The pig dissection was a great learning experience that allowed students to distinguish the many organs and organs systems in the pig’s body that can be compared to the human body. All the necessary parts were visible, but the discolouration of the organs were quite surprising. This could be because of the time the pig spent preserved. The size of the heart was smaller than expected as well. It was small, but very muscular due to the constant pumping of blood. In future experiments, it would be interesting to try an online/virtual dissection, perhaps a human brain instead of a pig. This experiment overall though allowed us to learn, hands-on, about the many systems of the body. It presented the organization of the pig’s organs, and their positions