In this lab you will familiarize yourself with the Urinary and Reproductive systems first and then dissect a fetal pig to locate the organs you have been learning about since lab 10.
• Use the models in the lab to locate the structures listed in Part A of the Lab Report.
• Have your instructor verify that you have correctly identified each of these listed structures.
• Use the models in the lab to locate the structures listed in Part B of the Lab Report.
• Have your instructor verify that you have correctly identified each of these listed structures.
Safety and Hygiene
1. Do not place your hands near your mouth or eyes while handling preserved specimens. Although the preservative used is non-toxic to the skin, it may cause minor skin irritations. If the preservative gets on your skin, wash immediately with soap and water.
2. If the preservative gets in your eyes, rinse thoroughly with the safety eyewash.
3. Wear lab gloves and goggles the entire time the fetal pigs are out. Even if you don't plan to touch the pig during the group dissection you need to have your gloves and goggles on.
Obtain a Fetal Pig
• Once your group has obtained a fetal pig from your instructor remove it from the plastic bag (save the bag for later).
• Rinse off the excess preservative by holding it under running water.
• Lay the pig on its side in the dissecting pan.
• Determine the sex of your pig using the images and descriptions of the male and female fetal pigs in the lab manual.
• Note that in both male and female pigs there is one urogenital opening and one anal opening.
• The urogenital opening is a common opening for both the urinary system and reproductive system.
• Record the sex of your pig in the Lab Report.
• Examine the pig's head. Locate the external ears or pinnae. Find the external nostrils or nares. The chin has small hairs called vibrissae. Note the sensory papillae on the tongue.
• Locate the umbilical cord. Examine the 3 openings in the umbilical cord. The largest is the umbilical vein, which carries oxygenated blood from the placenta to the fetus. The two small openings are the umbilical arteries, which carry blood away from the fetus to the placenta.
• Lift the pig's tail to find the anus and scrotum (in males) or female genital papilla (in females) (see Figure 10.1 in the Lab Manual for help identifying these structures).
• Study the ventral surface of the pig and note the tiny bumps called mammary papillae. These are present in both sexes. In females these are the structures that connect to the mammary glands.
• Also locate the following external features: elbow, wrist, knee, and ankle (see Figure 10.2 in the Lab Manual for help identifying these structures).
• Carefully lay the pig on sone 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.
• Try to locate the lymph nodes and salivary glands.
• Locate the structures listed in Part C.1 in the Lab Report.
The Oral Cavity
• Before opening the body cavity of the pig you will be looking at the oral cavity.
• The first steps of digestion, mechanical (chewing) and chemical (enzymatic) digestion, begins in the mouth.
• As food is chewed, saliva and enzymes are mixed with the food to start the digestive process. The area behind the teeth is the oral cavity.
1. Notice that the pig has teeth inside its mouth. Be careful as these are very sharp. Varieties of teeth depend on what the organism eats. Are all the pig's teeth the same or different? How do they compare to your teeth?
2. Use scissors to cut from one corner of the mouth toward the ear. Do the same to the other side. You will cut until the lower jaw opens and reveals the epiglottis, a cartilaginous structure that covers the glottis, thereby closing off the trachea when swallowing. You may have to convince the jaw to open by placing one thumb on the roof of the pig's mouth and the other thumb on its tongue and then pulling apart until you can see the epiglottis.
3. Just behind the epiglottis is the glottis. Father toward the back of the pharynx (throat) is the opening to the esophagus.
4. The ridged, upper portion of the mouth is the hard palate. Farther back, toward the pharynx, is the soft palate. If you use your own mouth and tongue you can feel your hard and soft palate.
5. The pharynx is an area where food and air combine. Toward the back of the soft palate is an opening called the nasopharynx. This opening leads to the nasal cavity.
6. Look toward the cut area at the back of the upper jaw. You should see a salivary gland on each side. It is somewhat rounded at the end, fairly large, and somewhat lobed.
• Locate the structures listed in Part C.2 in your Lab Report.
Digestive System
Before you make any additional cuts, it is necessary to secure your fetal pig in the dissection tray.
1. Place your pig in the dissection tray, ventral surface facing up. Tie one end of string to the right front limb distal to the elbow. Bring the string under the tray and back up on the left side. Tie the other end of the string distal to the left elbow. The wrists should be spread apart and under some tension. Do the same for the back limbs, tying the string just above the ankles. The legs should also be spread apart and under some tension.
2. With the scalpel, make a shallow incision below the rib cage and cut towards the tail end to 1 cm anterior (before) the umbilical cord. Refer to the diagram on Page 3 of the Ward's Science Fetal Pig Visual Dissection Guide for help making the proper cuts.
3. If you pig is female, make a complete circular cut around the umbilical cord. Continue from the cord on the midline to the anal region.
4. If your pig is male, make two incisions, one on each side of the midline to avoid cutting the penis, which lies beneath. These two incisions continue to the anal region from the arc around the cord.
5. Make a lateral incision from the umbilical cord to the groin on each side.
6. Use the diagram on Page 3 of the Ward's Science Fetal Pig Visual Dissection Guide to continue cutting open the abdominal cavity of your pig. At this point you may want to give your pig another rinse with water. Occasionally the abdominal cavity will be filled with preservative, latex, or fluid. The latex sometimes fills the cavity when blood vessels burst during the injection process. The largest organ in the abdominal cavity is the liver. The liver lies just beneath the diaphragm. It is brownish-red in color, contains 4 lobes, and has many important functions in the body. In addition to producing bile, the liver also converts an excess of glucose into glycogen (stored glucose), breaks down red blood cells, makes plasm proteins and produces many hormones that regulate metabolic functions of the body. These are only a few of its many functions.
7. Lift up the right central lobe of the liver and look for a small sac-like organ called the gallbladder. The main function of the gall bladder is to store the bile produced by the liver. Bile functions in the emulsification of fat droplets. Occasionally the cholesterol in bile will accumulate into lumps to form gallstones.
8. The gall bladder looks like it is fused to the liver, but it isn't. Use your dull probe to tease it away from the liver tissue. You will notice that the gallbladder is connected to the liver by a duct. This is called the cystic duct. The cystic duct and the hepatic duct from the liver form the common bile duct. The bile produced by the liver can go directly into the digestive tract via this duct. That is why you can survive without your gallbladder.
9. Just below the liver on the pigs left side will be the stomach. You will be able to see where the esophagus penetrates the diaphragm and connects to the upper part of the stomach. There are two muscular rings that regulate the passage of food into and out of the stomach. Use your fingers to feel these two rings. The upper muscular ring is the cardiac sphincter (so named because it is located close to the heart). It regulates the passage of food from the esophagus into the stomach. More importantly, the cardiac sphincter helps keep food in your stomach as it undergoes a wavelike motion called peristalsis. If the cardiac sphincter fails, the acidic chyme in the stomach flows back into the esophagus causing a burning sensation we call heartburn! Don't worry about your heart it is not burning, but your esophagus is! The muscular ring at the lower end of the stomach is the pyloric sphincter. It regulates the passage of food from the stomach into the small intestines.
10. Along the greater curvature of the stomach, you will see an organ that is very flat and elongated. It is attached to the greater curvature by the peritoneum. This is the spleen. The spleen has three main functions: it removed and destroys old or dead red blood cells, it stores and synthesizes antibodies, and it removes antibody tagged bacteria from circulation.
11. Use your fingers or a dull probe to lift up the stomach and spleen. You should be able to see an elongated, granular organ called the pancreas. You may need to remove some of the peritoneum (tissue that holds organs in the abdominal cavity in place) in order to get a clear view of the pancreas.
12. The pancreas is connected to the upper part of the small intestine (duodenum) by a duct (the pancreatic duct) near the junction of the pyloric sphincter.
13. The pancreas functions as both an endocrine and an exocrine gland. As an exocrine gland it produces many digestive juices, such as lipases that break down fat droplets, sodium bicarbonate that neutralizes the stomach's contents (chyme) as the chyme enters the small intestine, trypsin that digests proteins, and maltase that digests maltose. As an endocrine gland it produces various hormones such as insulin, glucagon and somatostatin.
14. Connected to the pyloric sphincter of the stomach is the small intestine. The small intestine is divided into three regions: the duodenum, the jejunum and the ileum. The junctions from one section into another cannot be easily distinguished. The majority of food digestion occurs in the jejunum and ileum. The small intestine is a very long organ, typically five times the height of the individual.
15. At the end of the small intestines, there is valve between the ileum and the cecum (first part of the colon) called the ileocecal valve. Mutualistic bacteria inhabit the colon and produce vitamin K, which is absorbed and utilized. In humans the cecum has a small fingerlike projection coming from it. This is the appendix. In herbivores, the cecum is very large and contains bacteria, which produce enzymes to break down cellulose. In omnivores and carnivores, the cecum is reduced to what to what you see in the pig. The appendix is one of the first observable differences between the human and pig digestive systems as pigs lack an appendix. The diameter of the colon (aka -large intestine) is another difference. In humans, the colon is larger in diameter than the small intestine (thus the name large intestine), whereas in the pig, it is not.
16. At the end of the colon is the rectum. The rectum opens to the outside of the body by way of a muscular ring called the anal sphincter, leading to the anus. Be very careful and do not cut open the rectum. It does contain feces that can be very messy.
• Locate the structures listed in Part C.3 of the Lab Report.
The Neck Region
Use the diagram on page 3 of the Ward's Science Fetal Pig Visual Dissection Guide to expose the organs in the neck and thoracic cavity. Take care when opening the thoracic cavity. There are blood vessels that lead from the heart to the arms. You want to leave these vessels undamaged.
1. Once you have opened the rib cage, you will see that the thoracic cavity is subdivided in two. The lungs are surrounded by a membrane called the pleural membrane, and the heart is surrounded by the pericardium.
2. Locate the trachea in the neck region. The trachea is held open by a series of hard cartilage rings that keep it from collapsing.
3. Follow the trachea down to the thoracic cavity and note that it divides into two major branches, the bronchi. The bronchi further divide into bronchioles and the bronchioles terminate in alveoli. You will not be able to see the bronchioles and alveoli, they are both located inside the lungs and the alveoli are microscopic.
4. Look at the two lungs and notice they are not symmetrical. They have a different number of lobes.
5. Below the heart and lungs is the diaphragm. Put your fingers into the pig's abdomen above the liver and feel the area where the diaphragm meets the body wall.
Locate the structures listed in Part C.4 and C.5 of the Lab Report.
The Thoracic Cavity:
1. The veins that carry blood from the head and arm regions are symmetrical. The internal and external jugular veins take blood from each side of the head and join together as the veins get closer to the heart.
2. Refer to page 9 in the Ward's Science Fetal Pig Visual Dissection Guide to identify the veins and arteries in the thoracic region. Pay particular attention to the subscapular and subclavian veins that take blood from the arms and return it to the heart. The area at which these two veins combine is called the brachiocephalic vein. The name is a description of the two combined areas. The term brachial refers to the arm region and the term cephalic refers to the head region; therefore, the brachiocephalic vein carries blood from the arms and head region to the heart.
3. The brachiocephalic vein leads directly into the anterior (in humans -superior) vena cava, which carries deoxygenated blood to the right atrium of the heart.
4. In order to see the brachiocephalic vein, you will need to open the rib cage. Use scissors to cut through the sternum and gently pry the cavity open.
5. Once you have the rib cage open you will be able to see the entire thoracic cavity, which contains the heart and lungs. The lungs are not yet functional as these are fetal pigs, meaning they had yet to be born. All oxygen and waste products must come from and to the mother through the placenta and umbilical cord.
Circulatory System Structures in Thoracic Cavity
1. Find the heart in the thoracic cavity and remove the thymus gland and the pericardial sac, assuming it is still intact. Notice the two flaps that cover the op of the heart. These are called auricles. They cover the atria, the upper two heart chambers.
2. You should be able to distinguish the cardiac veins and arteries that lie on the surface of the heart. These vessels supply the heart muscle with oxygen and remove waste products like carbon dioxide. The blood flowing through the heart passes though. The heart is muscle and like any organ, it requires oxygen for respiration.
3. The circulatory system is divided into two circuits, one that involves the blood flowing to and from the lungs (pulmonary circuit), and another that involves blood flowing throughout the remainder of the body (systemic circuit).
4. While looking at the heart, look at the large vessel that leaves the heart and curves away to the pig's left side. This is the pulmonary trunk which splits to form the left and right pulmonary arteries which carry deoxygenated blood (blood without oxygen) from the heart to the lungs.
5. Students have often been misled to believe that veins, or blue blood vessels, always carry deoxygenated blood. This is NOT true for the pulmonary circuit. Rather than trying to learn things by color, learn that arteries always move blood away from the heart, and veins move blood towards the heart.
6. If you lift up the pulmonary trunk, you will see the aorta, the largest artery in the body. Trace the aorta as it descends into the abdominal cavity. Here it is called the dorsal aorta.
7. The path of blood in the fetal pig is different from an adult. While in the womb, the pulmonary circuit is bypassed at two locations. The first bypass is through a connection called the ductus arteriosus that connects the pulmonary trunk and aorta. In the adult this bypass closes and becomes the ligamentum arteriosum. The second bypass is between the right and left atria. There is a small opening called the foramen ovale. As with the ductus arteriosus, the foramen ovale closes after birth, becoming the fossa ovalis.
Locate the structures listed in Part C.6 of the Lab Report.
Systemic Circulation- Posterior to the Heart.
1. Go back to the heart and look at the posterior extension of the aorta. As mentioned earlier, the posterior extension is called the dorsal aorta and it follows along the dorsal side of the pig.
2. If you move aside the liver and stomach, you will be able to see the dorsal aorta as it continues from the heart into the abdominal cavity. At the area around the stomach and live you will see a branch coming off the dorsal aorta, leading to the stomach, liver and spleen. This is the celiac artery, and it delivers oxygen to the stomach, liver and spleen.
3. Continue posterior along the dorsal aorta and located the anterior mesenteric artery. This artery branched to the pancreas and duodenum.
4. Posterior to the anterior mesenteric artery are the renal arteries. They are short blood vessels that lead into each kidney.
5. The last part of the dorsal aorta ends in branches. Two branches are the external iliac arteries. One branch goes into each hind limb. The center part the the branch leads to the sacral artery, which leads towards the tail. This artery becomes the caudal artery when it enters the tail.
6. Another branch leads to the intestinal iliac arteries, which lies just anterior to the sacral artery. The internal iliac artery branches, and two branches enlarge to form the two umbilical arteries. One umbilical artery lies along each side of the allantoic bladder.
7. Blood vessels of the posterior venous system are names similarly to the arterial system, and in fact the veins lie right alongside the arteries. Where you see the renal artery, you will also see the renal vein. Where you see the external iliac arteries, you will see the external iliac veins. This makes learning the blood vessels much easier.
8. The hepatic portal system is a network of vessels that collects blood from the organs and accessory organs of the digestive tract, in the abdominal region and carries it to the liver by way of the hepatic portal vein. Portal veins collect blood form the capillary bed of one organ to the capillary bed of another organ.
9. Just as the dorsal aorta runs posterior along the dorsal side of the pig, the posterior vena cava does the same for the venous system. It is easiest to see the posterior vena cava near the level of the kidneys. The renal veins and arteries are short and connect to either the posterior vena cava or dorsal aorta.
10. The first blood vessel to branch off the aortic arch is the brachiocephalic artery. The brachiocephalic artery branches to form the carotid trunk and the right subclavian artery. The carotid trunk branches to form the two carotid arteries in the neck region. Trace these blood vessels so that you will be able to identify them.
11. The right subclavian artery leads to the right forearm. This blood vessel changes names as the location changes, much like a street having one name in one part of town but changing names in another town. As the right subclavian artery approaches the shoulder region it becomes the right axillary artery. When it enters the upper forelimb, it becomes the right brachial artery.
12. The second vessel to branch off the aortic arch is the left subclavian artery. The left subclavian artery changes name in the same manner as the right. The blood vessel goes from being the left subclavian artery to the left axillary artery to the left brachial artery.
13. The major vessels to enter the heart are the anterior and posterior vena cava (in humans they are called the superior and inferior vena cava). Both of these blood vessels deliver blood to the right atrium.
14. The brachiocephalic vein branches off the anterior vena cava. There are vessels that branch off the brachiocephalic vein. The pattern forms a "V". One side of the "V" branches to form the right and left subclavian vein, which becomes the right or left axillary vein, which becomes the right or left brachial vein as they move into the upper forelimb.
15. At the top of the "V" there are two additional branches on each side. These form the internal and external jugular veins.
16. Trace the path of blood through an adult heart, starting with the posterior and anterior vena cava.
Identify the structures listed in Part C.7 of the Lab Report.
1. Lift the mass of small intestine to find the two large, kidney bean-shaped organs. These are the kidneys and they are attached to the dorsal wall of the pig by a membrane called the peritoneum. You need to remove the peritoneum to see the kidneys.
2. There are three structures attached to each kidney: the red renal artery, the blue renal vein and the cream-colored tube called the ureter.
3. The ureter delivers urine from the kidney to the allantoic bladder. Underneath the bladder, you may be able to see the urethra.
4. In the fetal pig the allantoic bladder leads to a small opening in the umbilical cord called the allantoic duct. After the fetus is born, the duct collapses and the allantoic bladder becomes the urinary bladder.
5. Clear away the membrane covering one of the kidneys. Attempt to locate the adrenal gland on its medial, anterior side. The small narrow strip of glandular tissue mat be difficult to find.
6. Cut the ureter, the renal vein and renal artery. carefully remove the kidney. Place on a paper towel and slice in ventral and dorsal halves with a longitudinal cut.
7. Observe the structures inside the kidney with a hand lens.
Locate the structures listed in Part C.8 in the Lab Report.
Female Reproductive System
1. Earlier you determined the gender of your pig. The female pig has a prominence called the genital papilla on the outside of the body, near the anal opening. All external female genitalia are referred to as the vulva. The vulva includes the genital papilla, the labia, the clitoris, and the opening of the urogenital sinus.
2. The urogenital sinus does not exist in the adult pig. As the fetus develops, the urethra and vagina each form their own external opening.
3. Anterior to the urogenital sinus is the thick-walled, muscular vagina. You may need to cut into the urogenital sinus to see it. The vagina is continuous with the uterus. The pig has what is referred to as a bicornuate uterus, which means that the uterus branches off into two uterine horns, in which the fetuses develop. In humans a bicornuate uterus is called a "heart-shaped" uterus and is an abnormality. Pigs give birth to multiple litters that develop in the uterine horns.
4. The ovaries are located at the distal end of the uterine horns, posterior to the kidneys. They are small, pale-yellow, kidney-bean shaped organs. Each ovary will produce eggs that will mature inside the ovary and rupture from the surface to enter the very short oviducts and uterine horns. In addition, the ovaries produce the female sex hormones estrogen and progesterone.
5. The ovaries, oviducts and uterine horns are supported by a thin layer of connective tissue called the broad ligament. There is a. additional ligament that supports the ovary, called the round ligament. If you look closely, you will see where these two ligaments cross. The broad ligament develops from the dorsal body wall and the round ligament arises from the lateral wall.
If you have a female pig locate the structures listed in Part C.9 of the Lab Report.
Male Reproductive System
1. Locate the scrotum and make a midline incision through the scrotal tissue and underlying muscle. Look for the two bulb-shaped structures that are covered with a thin membrane called the tunica vaginalis, which is an outgrowth of the abdominal wall. The bulbous organs are the testes, the structures that produce sperm and testosterone.
2. Open the tunica vaginalis and look at the testicle. It is a very smooth oval organ. There is a coiled mass of tubes sitting along one side of the testis. This structure is the epididymis and its function is to provide a place for the maturation and storage of sperm. At the end of the tunica vaginalis you will see a tough white cord on the inside of the sac. This is the gubernaculum, which functions in pulling the testes posteriorly into the scrotal sac.
3. If you follow the epididymis back towards the pig's body cavity you will see a thin tube. This is the spermatic cord and consists of the vas deferens, and the spermatic vein, artery and nerve. It is the vas deferens that is severed when a vasectomy is performed.
4. If you gently pull on the spermatic cord you will be able to see where it goes through an opening called the inguinal canal. The inguinal canal is an actual opening in the abdominal wall through which the testes descend towards the scrotum. If part of the intestines drop though this canal it is referred to as an inguinal hernia.
5. In order to find the penis you will need to make an incision through the muscle between the hind legs, until the hind legs lie flat (splayed open). Continue to remove muscle tissue and cut through the pubis bone until the urethra is uncovered. Next, cut through he connective tissue that attaches the urethra and the rectum.
6. On the dorsal surface of the urethra you may see a pair of very small glands called the seminal vesicles. Look for the area where the vas deferens enters the urethra. Depending on your surgical skills, these may be difficult to locate. The seminal vesicles one of three accessory glands that aid in the production of semen. The seminal vesicles contribute a thick sugary, alkaline fluid to the semen.
7. Between the bases of the seminal vesicles is the prostate gland. This gland adds a milky alkaline fluid that increases sperm motility. This gland may become enlarged in the adult human male.
8. Lastly, there are two elongated glands that lie on either side where the penis and urethra meet. These are the bulbourethral (Cowper's) glands and they contribute a lubricating fluid that is full of mucus to the semen.
9. The products of the three accessory glands along with the sperm make up semen. If a man has a vasectomy, he will still produce sperm and semen. The sperm will be stopped at the cut in the vas deferens and will be absorbed by the body. Only the products of the three accessory glands will be ejaculated.
If you have a male pig locate the structure in Part C.10 of the Lab Report.
Clean you work area and properly return your Fetal pig
1. Lab gloves and paper towels go in the regular trash. Discarded pieces of pig go into the red plastic biohazard bag located in the laboratory room.
2. At the end of the lab put your pig back in the plastic bag and tie the bag closed.
3. Place the bagged pig in the storage tub in the front of the lab.
4. Rinse the dissecting tray and stack it neatly by the sink.
5. Wipe up your station clean.
6. Clean and return your dissecting tools.
Non-majors College Biology Lab Manual © 2021 by Marie McGovern Ph.D. is licensed under CC BY-NC 4.0