NU Biology Blood Vessels Carrying Blood Coronary Arteries Questions

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p. 1 of 12 FETAL PIG DISSECTION LAB (2-WEEK ACTIVITY)

Goals:

• Identify internal structures on multiple pigs of various sizes and both sexes.

• Understand the role of each structure in important functions such as digestion and reproduction. • Identify major arteries and veins. Understand the flow of blood through the heart. Review before you begin:

• Path of food through the digestive tract and the role of each structure along that path. • Role of additional structures (e.g. liver, gall bladder, and pancreas) in digestion.

• Arteries deliver O2 and nutrients to tissues; veins remove CO2 and wastes from tissues.

• The path of blood through the heart. Additional resources: A wide variety of color photos of dissected pigs are available on the web for studying. For example, www.biologycorner.com/pig/review.html provides several links.

Introduction

A dissection allows a unique opportunity to investigate biology on the level of an entire organism. You will see the connections and relationships between parts of the body that is not possible by looking at pictures or hearing a lecture. As you do the dissection, think about how the smaller scales of biology (e.g. molecules) connect to larger scales (e.g. organs) to make an organism function. For example, each of the organs you will identify in the digestive system contributes to the breaking down of food into the major molecules of life. Some of those molecules are then burned to create energy, using oxygen provided by the lungs. The heart, arteries, and veins move those molecules and oxygen to tissues throughout the body. Another reason for conducting a dissection is that no two organisms (from a sexually reproducing species) are the same. Whether due to differences in genetics or the surrounding environment, every member of a species will be slightly different. You will see those differences on the outside– the pigs will be different colors and sexes. You will also see those differences on the inside– organs in different pigs will be different sizes and in slightly different places. This variation is natural and important, because variation is what allows a species to adapt to changing conditions. Rules for dissection: • We are using the pigs for a serious educational purpose- treat them with the respect you would give to a living organism. • Wear safety goggles and gloves, to prevent the chemical preservative from getting on your skin or in your eyes. • Do not remove anything used in the dissection or any parts of the pig from the room. • Read all instructions before cutting anything. • Do only the dissection listed in this handout or as instructed by your instructor. • Do not cut anything off of the pig without permission from your instructor. • Pig parts must go in biohazard, but all general garbage should stay out of the biohazard bin. Before you begin, rinse the outside of your pig. Cut a slit in the bag and pour out any liquid. Then fill the bag with tap water to rinse the pig within the bag. Repeat several times, so that you rinse the outside of the pig really well. After you cut open the pig, you will also rinse the inside of the pig with tap water. Pig dissection p. 2 of 12 EXTERNAL EXAMINATION Start by examining the pig from the outside. (In Figure 1, note that the leg on your left is labeled as the “right” forelimb. This is not a mistake- we talk about the organs and body parts as if we were the ones lying in the dissecting pan.) While your pig may not look like a human, all of the important parts are there. It has 2 front and 2 hind legs (your arms and legs). The head, eyes, mouth, nose and ears are a different shape than yours, but serve the same purpose. Since this is a fetal pig, it has an umbilical cord just as a human fetus would. As you will see, the similarities continue under the skin as well. See the cut on the pig’s neck, which has been made to inject the pig’s circulatory system with colored latex. When you open the pig, you will see that the veins have been filled with blue latex and the arteries with red latex, to allow easier identification. Sometimes the latex breaks out of a blood vessel or fills an organ, so you may see large amounts of colored latex in different parts of your pig. INITIAL INCISIONS First, tie the pig onto a dissection pan by putting the pig on its back and tying a string to one front leg. Run the string underneath the pan and up the other side. Pull the front legs apart and tie the free end of the string to the other front leg. Repeat for the rear legs. Once your pig is secured, you will make incisions to access the internal organs. Each cut should be deep enough to cut through the skin and underlying muscles, but not so deep as to cut the organs. If you have doubts about how far in to cut, be cautious– you can always cut a little deeper later. Your first three incisions will open the chest, or thoracic cavity (see Fig. 1). Use a scalpel to open incision 1, which starts just under the tuft of hair on the chin and runs down the chest until a point just below a line drawn from one armpit to the other. (Stop here to avoid cutting the diaphragm.) Incisions 2 and 3 cut across the pig’s chest as shown. Use a scalpel to cut all the way from shoulder to shoulder for incision 2. Use scissors to cut from armpit to armpit for incision 3. The next four incisions will open the abdominal cavity and are easier to make with scissors. To start incision 4, poke the point of the scissors through the skin and muscle. Complete incision 4 by cutting down to just above the umbilical cord and cutting up to just below the diaphragm. (Look through the hole in the abdomen to see the diaphragm– it will be a layer of muscle that walls off the abdominal cavity from the thoracic cavity). For incision 5, cut around the umbilical cord by cutting from the bottom of incision 4 around one side of the umbilical cord and down most of the way to the tail. Do the same on the other side of the umbilical cord. For incisions 6 & 7, make sideways cuts as in Fig. 1. Pig dissection p. 3 of 12 ABDOMINAL CAVITY To get into the abdominal cavity, slowly lift up the flap of skin that holds the umbilical cord. Notice the umbilical vein, which looks like a blue thread, running from the umbilical cord into the abdomen. Cut this vein halfway between the flap of skin and the abdominal organs. Now you can lift the flap away from the abdomen. Also open the two flaps made by incisions 6 and 7. (If the strings holding your pig in the dissection pan have become loose, then retie them. You should also clean out the pig by taking it to the sink and running water over the abdominal organs.) Liver and gallbladder The most obvious organ in the abdominal cavity is the liver. It is the large brown organ at the top of the abdomen that should extend from one side of the pig to the other. The liver has a wide range of functions. It breaks down toxins and disposes of worn-out red blood cells. It maintains blood glucose levels by either storing excess glucose as glycogen or breaking down glycogen to release glucose. The liver also produces bile that is used by the digestive system to emulsify fats. Excess bile is stored in the gallbladder. Lift up the liver. The gallbladder is a small, bulbous mass (it may be greenish colored) attached to the underside of the liver. Spleen The spleen is a long, thin organ on the pig’s left side (remember, this will be on the right as you look at the pig). It wraps around and may be attached to another large organ– the stomach. As part of the immune system, the spleen stores white blood cells and filters bacteria from blood that may cause infection. The many capillaries that fill the spleen make it delicate and prone to bleeding. If damaged, the spleen will be removed, but a person must then take care to avoid infection by receiving immunizations and taking antibiotics. DIGESTIVE SYSTEM Pig dissection p. 4 of 12 Most of the rest of the abdominal cavity is filled by organs of the digestive system. Lift up the liver to see the stomach, a large organ on the pig’s left side. Look carefully above the stomach to see the esophagus, the tube running up from the stomach, through the diaphragm, and up into the mouth. The esophagus moves food to the stomach. Stomach Use the scalpel and make a cut along the outer edge of the stomach (the “greater curvature” in Fig. 3). Notice that the inside of the stomach is ridged, which helps its muscular walls grind food and also allows the stomach to expand after a large meal. Breakdown of food is also accomplished by hydrochloric acid and hydrolytic enzymes in the stomach. Still looking at the stomach from the inside, at the rightmost part of the stomach (the left side as you look at it), you should be able to find a small hole. This is the pyloric sphincter. A ring of muscles surrounds this hole and controls when food moves from the stomach into the next organ, the small intestine. Pancreas Before examining the small intestine, lift up the stomach. Underneath should be a granular looking gland, the pancreas. It produces pancreatic juice that contains digestive enzymes as well as sodium bicarbonate– an antacid that neutralizes the hydrochloric acid from the stomach. The pancreas also produces insulin and glucagon– two hormones that control the levels of glucose in the blood. Pig dissection p. 5 of 12 Small intestine The pyloric sphincter empties from the stomach into the first part of the small intestine – the duodenum. The duodenum is a mixing place. When the partially digested food comes out of the stomach, it combines with the pancreatic juice and bile. If you look closely, you should be able to find a tube or “duct” that leads into the duodenum from the pancreas and that connects to another duct coming from the liver and gallbladder (the common bile duct). From the duodenum, material moves into the remainder of the small intestine (the jejunum). As food travels through the small intestine (30 feet in length in humans), digestive enzymes complete the process of digestion. The resulting nutrients are absorbed through the lining of the small intestine. The lining has multiple layers of folds called villi that provide a huge surface area for nutrient absorption. Take a section of the small intestine and spread it out. Connecting the loops of the intestine is the mesentery– connective tissue with a series of blood vessels running through it. The blood vessels in the mesentery collect the nutrients from the small intestine and deliver them to the liver for processing. Large intestine If you follow the twisting loops of the small intestine, you will eventually reach the large intestine, where the tube becomes wider. The spot where the two intestines meet is the cecum and is where the appendix would be in humans. In pigs, the cecum helps digest very fibrous material, so it may be very large compared with the small intestine or even the rest of the large intestine. If the cecum on your pig does not appear very different from the rest of the intestines, then check other pigs. By the time material reaches the large intestine, almost all digestion and nutrient absorption is done. The function of the large intestine (also called the colon) is to absorb water from remaining undigested material. The pig’s colon looks very different from yours (one of the few big differences)- it is in a spiral on the pig’s left side. In humans, the colon runs in three fairly straight segments: up, over, then down, with no spiral. The large intestine finally straightens out at the rectum, where feces are stored before exiting the body. URINARY SYSTEM The urinary system processes waste from the cells and removes it from the body. You can easily find three parts: kidneys, ureter, and urinary bladder. Kidneys Lift up the intestines and look at the body wall underneath. Stuck into the back wall of the abdominal cavity are two “bean” shaped organs- the kidneys. You may need to cut through a thin membrane in order to see them clearly. Blood enters the kidneys through the renal arteries. The kidneys filter waste from the blood and concentrate that waste as urine. Because the kidneys are concentrating waste, they use active transport and therefore a good deal of energy. Water and valuable nutrients are retained in the blood, which leaves the kidneys through the renal veins. Urine leaves the kidneys through the ureter. Ureter and urinary bladder The urine is moved through a duct called the ureter that exits the kidney in the middle of the smaller inner curve. The ureter carries urine to the urinary bladder where it is stored for later release. You can trace the ureters from the kidneys down toward the tail. In your pig, the urinary bladder is attached to the flap of skin you cut around the umbilical cord. Pig dissection p. 6 of 12 REPRODUCTIVE SYSTEM Male and female pigs will be in your class. Be able to identify the reproductive structures in both sexes. Male Look for two small loops that go up and over the umbilical veins at the bottom of the abdominal cavity (see Fig. 4). These are the ductus deferens, or vas deferens, that bring sperm from the testes to the penis. The penis is hidden in the flap of skin connected to the bladder. To find the testes, you will need to cut down between the tail and the leg and remove the membranes in which each testis and epididymis is enclosed. The sperm are produced in the testes, but mature in the epididymides. Female The female reproductive organs are still very small at this point in development. The uterine horns, which are more prominent in animals than in humans, are where the uterus and fallopian tubes meet (see Fig. 5). At the end of each horn is an oval-shaped ovary. Eggs are produced in the ovaries. Embryos implant and develop in the uterus in humans. In pigs, which have multiple embryos, the embryos implant and develop in the uterine horns. THORACIC CAVITY To expose the organs of the thoracic cavity, peel back the skin flaps created by incisions 3 and 4, which will give you a view of the rib cage. Using your scissors, clip down the center of the rib cage, cutting it into two halves. Be careful not to cut the organs underneath. Pull the ribcage to the side exposing the organs. To make this easier, you may need to clip a few ribs on the side– if you are having trouble, ask your instructor for help. The thoracic cavity is filled by two organs– the heart in the center, and surrounding it the lungs. The bottom of the thoracic cavity is defined by the diaphragm. This layer of muscle helps to enlarge the thoracic cavity every time you breathe in, to aid in breathing by allowing the lungs to fill with more air. Lungs On each side of the heart you will see one of the pig’s lungs. This pig is only a fetus, so it never breathed air and its lungs were never inflated. Therefore, they will seem small and dense. If you could follow the trachea from the neck into the lungs, you would see that it branches over and over again each time making more but smaller passages. Eventually, the passages end in tiny sacs called alveoli. It is here that oxygen is diffused into the blood, and carbon dioxide diffuses out of the blood to be exhaled. A close examination shows that the pig’s right lung is larger (with three “lobes”) than its left (with two lobes). This is because the heart and major blood vessels take up some of the room on the pig’s left side. Pig dissection p. 7 of 12 NECK REGION Beginning at the top of incision 1, carefully pull back the skin and cut through the neck muscle. As you cut, use a blunt probe to pull the tissue to the sides of the incision. After pulling most of the muscle to the side, find 5 structures of interest (Fig. 6). The larynx (voice box) is the large white structure at the top of your incision. On both sides of the larynx should be a pair of long soft thymus glands. T-cells (white blood cells that fight infection) mature in the thymus. The thyroid gland is a small, round lump just below the larynx. The thyroid produces hormones that increase oxygen consumption and metabolic rate in all cells of the body. Extending down from the larynx is the trachea or windpipe. Run your finger over the trachea and notice that it has rigid rings of cartilage that keep the airway open. Sitting directly under the trachea is the esophagus- a thin, pale white tube. This muscular tube brings food from the mouth to the stomach. PREPARE FOR THE PRACTICAL QUIZ Find each of these structures on multiple pigs and know the function of each structure. STRUCTURE Diaphragm Ductus (vas) deferens Epididymis Esophagus Gallbladder Kidneys Large Intestine Larynx Liver Lungs Ovaries Pancreas Rectum Small Intestine Spleen Stomach Testis Thymus Thyroid Trachea Urinary Bladder Uterine horns I can identify it in multiple pigs (Yes/No) Describe the function (important role in the pig) Pig dissection p. 8 of 12 FETAL PIG DISSECTION WEEK 2 Read the instructions to find arteries and veins and to understand the flow of blood through the heart. A list of the structures that you will find today is below. Heart (distinguish atria & ventricles) Coronary arteries Pulmonary trunk Ductus arteriosis Aorta and aortic arch Superior (anterior) vena cava Inferior (posterior) vena cava Carotid arteries Jugular veins Renal arteries and veins Iliac arteries and veins Umbilical arteries Heart The heart is slightly to the left of the center of the thoracic cavity. Its job is to move blood throughout the body. Cut off the membrane (called the pericardium) that surrounds the heart to see its details. Just like your heart, the pig’s heart has 4 chambers. The two atria are the small dark flaps of muscle on the top of the heart. The rest of the heart is made of two chambers fused together- the ventricles. Your pig’s heart is structurally different from yours because it is a fetus and is not using its lungs. At this point in the pig’s (and human’s) development, a mechanism is in place to allow blood flow to bypass the lungs. At its top left, see a large vessel coming out of the upper portion of the heart and wrapping over the top. This is the pulmonary trunk, which splits into the pulmonary arteries that deliver blood to the lungs. In the fetus, the ductus arteriosus vessel connects the pulmonary trunk to the aorta to bypass the lungs. Before birth, the ductus arteriosis vessel shrinks and eventually vanishes. The aorta is the large artery coming from the left ventricle and out of the top left of the heart. Rotate the heart to the pig’s right see it clearly. Follow the aorta as it arches (the aortic arch) and then descends under the lungs down to the diaphragm. Look at the front of the heart for the coronary arteries and veins, which run diagonally across the surface. The heart’s muscle cells get their oxygen from blood delivered by the coronary arteries. In a heart attack, a blockage in a branch of a coronary artery causes heart muscle cells to die due to lack of oxygen. Put pins in structures as indicated below and answer the following questions: Find the two atria and the two ventricles on the pig heart. Put a pin on the pig’s right atrium. Which chambers are larger: the atria or the ventricles? Find coronary arteries (stained red) on the outside of the pig’s heart and put a pin in it. What happens if a branch of a coronary artery becomes blocked? Find the pulmonary trunk on the pig’s heart and put a pin in it. The pulmonary trunk carries blood from the …………………………………….(chamber of the heart) to the Pig dissection p. 9 of 12 What is the function of the ductus arteriosus? Explain why this vessel shrinks and eventually vanishes before birth. The aorta, which carries blood away from the left ventricle, extends up and then arches at the top of the heart. Put a pin on the aortic arch of the pig. Why do you think that it is so large? (Hint: think about the purpose of the left ventricle.) BEFORE CONTINUING, WRITE DOWN THE NUMBER OF THE PIN PLACED IN EACH STRUCTURE AND ASK YOUR INSTRUCTOR TO CHECK THAT YOUR PINS WERE PLACED CORRECTLY. Structure Pin # Right atrium Coronary artery Pulmonary trunk Aortic arch Circulatory system All body cells require oxygen and nutrients, so the vessels of the circulatory system extend throughout the body. Arteries, stained red in your pig, carry blood away from the heart and to the organs. Veins are stained blue and return blood from the organs back to the heart. The arteries and veins are usually named for the body parts they serve (see Fig. 8). Entering the heart from the back right is the body’s largest vein, the vena cava. It is divided into two parts. The superior (or anterior) vena cava brings blood from the head and arms to the heart while the inferior (or posterior) vena cava returns the blood from the rest of the body. If you follow the superior vena cava up, it will quickly branch into a number of smaller veins while the inferior travels as a single large vein under the lungs and through the diaphragm. Pig dissection p. 10 of 12 In the neck, you can see the carotid arteries that supply blood to the brain and the jugular veins that drain blood from the brain. There are actually two of each (an external and an internal) on each side of the neck. To find them, use the blunt probe to push the neck muscles apart. A cut carotid artery would result in faster death, but the jugular veins are more likely to be damaged because they are closer to the skin. In the abdomen, the vena cava and the aorta extend from the heart and then through the diaphragm and down the middle of the cavity in the back. The renal arteries and veins branch off of each and go to the kidneys. At the bottom of the abdomen, the aorta splits into 4 arteries– 2 umbilical arteries and 2 iliac arteries. (The iliac arteries further split and form the femoral arteries, which are often punctured in crime dramas causing people die from blood loss.) The vena cava splits into a pair of iliac veins running down each leg. Put pins in structures as indicated below and answer the following questions: Find the vena cava, which enters the right atrium of the heart from the back. The superior (anterior) vena cava drains blood from the top of the body. The inferior (posterior) vena cava drains blood from the bottom of the body. Put a pin in either the superior or inferior vena cava. right. Into which chamber of the heart does the vena cava deliver blood? Does the blood have oxygen at this point? Use a blunt probe to push the neck muscles apart so that you can see the carotid arteries and the jugular veins in the neck. Put a pin in either the carotid artery or jugular vein. (Ask your instructor for help if necessary!) Which delivers blood to the brain and which drains blood from the brain? Which contains oxygen, and which contains carbon dioxide? Put a pin in either the a renal artery or a renal vein, which deliver blood to and drain blood from the Follow the aorta to the bottom of the abdomen, where it splits into 2 umbilical arteries and 2 iliac arteries. Choose one and put a pin in it. BEFORE CONTINUING, WRITE DOWN THE NAME OF EACH STRUCTURE IN WHICH YOU PUT A PIN AND THE PIN #. ASK YOUR INSTRUCTOR TO CHECK THAT YOUR PINS WERE PLACED CORRECTLY. Structure (write the name) Pin # Pig dissection p. 11 of 12 Flow of blood through the heart Before your pig’s heart (and your heart) pumps blood to the body, the blood has to pick up oxygen from the lungs. Using one of the plastic models of the heart in the classroom, follow the path of blood through the heart. Label the diagram below and fill in the blanks to demonstrate your understanding. Label on the diagram: right atrium left atrium right ventricle left ventricle anterior (superior) vena cava posterior (inferior) vena cava aortic arch lungs (right and left) Fill in each blank with a term from above to describe the flow of blood through the heart. a) Deoxygenated blood from the body returns to the heart via two blood vessels: ……………………………………………………and……………………………………………………… b) These blood vessels empty into the chamber of the heart called the………………………………… c) The blood then goes to the ……………………., from where it is pumped through the pulmonary trunk to the…………………………………………. d) Blood returns to the …………………………………….. of the heart. Does the blood now contain oxygen? e) Blood then enters the …………………………..…., from where it leaves the heart through a blood vessel called the………………………………… to be delivered to the body. Pig dissection p. 12 of 12 PIG WEEK 2 WRITE-UP ASSIGNMENT 1. The blood vessels that carry blood to the heart are called________________. Name one such vessel observed on your pig (see Fig. 8) and describe from where in the body this vessel obtains blood. 2. The blood vessels that carry blood away from the heart are called_______________. Name one such vessel observed on your pig (see Fig. 8) and describe to where in the body this vessel delivers blood. 3. What occurs when a coronary artery is blocked, and why? Hint: Read this handout. 4. Compare the right and left atria of the heart. From where does each atrium receive blood? Why does one atrium have deoxygenated blood, while the other atrium has oxygenated blood? 5. Compare the right and left ventricles of the heart. To where does each ventricle deliver blood? Which is larger (with the thickest muscles), and why? Hint: Think about the distance that the blood needs to travel after it leaves each ventricle. 6. What is the function of the ductus arteriosus? Is this vessel needed after birth? Explain why or why not.

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