1. Sheep Heart Dissection
Welcome to Sheep Heart Dissection. This powerpoint was created to be downloaded and used with your students. Please feel free to edit to meet the needs of your students. To fully participate in this professional development, it would be ideal for you to have a sheep heart and all the dissection equipment necessary for you to perform the sheep heart dissection along with me.

2. Objectives By the end of this lesson, students will be able to:
Demonstrate proper dissection safety techniques
Identify the right and left sides of the heart
Identify the parts of the heart: auricles, superior vena cava, pulmonary vein, aorta, left ventricle, pulmonary artery, bicuspid and tricuspid valve.
Measure the diameter of the aorta, pulmonary trunk, left atrium, left ventricle and right ventricle.
Compare and contrast the structure of a sheep heart to a human heart
Read this slide as written.

3. External Anatomy
Identify the right and left sides of the heart. On one side of the heart you will see a diagonal line of blood vessels that divide the heart.
The half that includes all of the apex (pointed end) of the heart is the left side.
Confirm this by squeezing each half of the heart. The left half will feel much firmer and more muscular than the right side.
Identify the right side of the heart from the left by using two references: the diagonal line of blood vessels that run on the surface of the heart and the apex. The diagonal line provides a reference point that can be used to divide the heart into two sides. Additionally, the apex or pointed end of the heart will aide in identifying the halves as well. The half of the heart that includes all of the apex is the left side. One way to confirm that you have correctly identified the right and left side is to squeeze each half. The left half will feel much firmer and more muscular than the right. This is an example of how structure is related to function, which is one of the big ideas of science. The left side of the heart firmer and more muscular (therefore stronger) than the right because it has to pump blood to the whole body while the right side only pumps blood to the lungs.
Right Side
Left Side
Apex

4. External Anatomy
Turn the heart so that the right side is on your right, as if it were in your body. This will mean that you are now looking at the back or posterior surface of the heart.
Examine the flaps of darker tissue on the top of the heart.
These ear-like flaps are called auricles.
Auricle
Now turn the heart so that the right side is on your right just as if it were in your body. Examine the flaps of darker tissue on the top of the heart. These earlike flaps are called auricles. Interestingly, this is the same name given to the external portion of your ear. The auricles of the heart are wrinkled portions of each atrium that protrude externally to form a pouch. This structure is sometimes referred to as the atrial appendage. The auricles function as a reservoir for the atria. The term atria is plural for atrium an refers to both the right and left atrium collectively.

5. External Anatomy
Find the large opening at the top of the heart next to the right auricle.
This is the opening to the superior vena cava.
Stick a probe down the vessel. You should feel it open into the right atrium.
Superior Vena Cava
Before we go on to identifying the major vessels of the heart, let’s compare and contrast the three types of blood vessels. A blood vessel is a hollow tube that carries blood in animals (including humans) around the body’s system allowing for proper oxygenation of tissues including muscles and nerves. Arteries, veins and capillaries are all different kinds of blood vessels.
Arteries are blood vessels that carry blood away from the heart. The aorta, right and left pulmonary arteries are examples. Arteries are the higher pressure part of the circulatory system as they are getting blood from the heart and sending it out to other parts of the body. Arteries are fairly large, elastic and muscular. These vessels are three layers thick as they have to withstand the high pressure of blood being pumped off the heart. These are the strongest of the three types of vessels. Veins are blood vessels that carry blood back to the heart from the body. Veins carry deoxygenated blood back to the heart, although this is not the case with the pulmonary vein which carries oxygenated blood. Veins are just tubes that collapse when not filled with blood. Like arteries, veins have three layers but are not as thick or tough since they do not transfer blood at such a high pressure as the arteries. Both veins and arteries are most easily defined by the direction of blood flow rather than by oxygen content although oxygen supply is generally high for arteries and low for veins, but not always. Remember, arteries move blood away from t he heart, while veins move blood toward the heart. Capillaries function to facilitate the exchange of various things between blood and tissue. They act as a middleman receiving blood from the arteries rich in oxygen, exchanging it for carbon dioxide from surrounding tissue and then dumping the waste rich blood out to the veins in order to get it back to the heart for cleansing and recirculation. Capillaries are very thin and fragile. What’s interesting is that veins run parallel to the arteries throughout the body, with capillaries forming a web-like network between them. So, in summary, arteries carry blood away from the heart, capillaries connect the arteries to veins and the veins carry the blood back to the heart.
Now, place your heart in its original position with the left atrium and ventricle in your right hand. Locate the large opening at the top of the heart next to the right auricle. This opening is the superior vena cava. Stick a probe down the vessel and you should feel it open into the right atrium. I have also had students just place their finger into the superior vena cava to explore. The superior vena cava brings blood from the top half of the body to the right atrium. Is this vessel an artery or a vein? (USE WAIT TIME) If you said vein, you would be correct. What reasoning did you use for your answer? (USE WAIT TIME) If you said veins move blood toward the heart, then your rationale would be correct.
Auricle

6. External Anatomy
Superior Vena Cava
A little down and to the left of the superior vena cava, there is another blood vessel opening.
Insert your probe into this. It should also lead to the right atrium. This is the inferior vena cava.
Inferior Vena Cava
Locate the inferior vena cava. This vessel can be found a little lower and to the left of the superior vena cava. The inferior vena cava brings blood to the heart from the lower part of the body.
Inferior Vena Cava

7. External Anatomy Now look at the left side of the heart.
Inferior Vena Cava
Now look at the left side of the heart.
You can also see another blood vessel next to the left auricle. This is the pulmonary vein.
Superior Vena Cava
While observing the inferior vena cava, you should have also noticed another blood vessel next to the left auricle. This is the pulmonary vein. The pulmonary vein brings blood from the lungs into the left atrium.
Pulmonary Vein

8. External Anatomy
Sticking straight up from the center of the heart is the largest blood vessel you will see. This is the aorta. The aorta takes oxygenated blood from the left ventricle to the rest of the body.
Aorta
The aorta takes oxygenated blood from the left ventricle to the rest of the body. There is a right and left ventricle referred to collectively as ventricles. The ventricles are the lower chambers of the heart. The aorta branches into more than one artery right after it leaves the heart, so it may have more than one opening on your heart specimen. Look carefully at the openings and you should be able to see that they are connected to each other. Is the aorta an artery or a vein? (USE WAIT TIME) If you said it is an artery, you are correct.
Left Ventricle

9. External Anatomy
Behind and to the left of the aorta there is another large vessel. This is the pulmonary artery.
Answer the questions on your lab WS: External Anatomy.
You should also check all structures with teacher before making ANY incisions.
Pulmonary Artery
Just behind and to the left of the aorta there is another large vessel. This vessel is called the pulmonary artery. The pulmonary artery takes blood from the right ventricle to the lungs.

10. Incision 1
Insert your dissecting scissors or scalpel into the superior vena cava and make an incision down through the wall of the right atrium and ventricle, as shown by the dotted line in the picture.
Chordae Tendonae
Papillary Muscle
Now that we have observed the heart externally, let’s begin to look at its internal structure. Insert your dissecting scissors or scalpel into the superior vena cava and make an incision down through the wall of the right atrium and ventricle as shown by the line in the picture. Pull the two sides apart and look for three flaps of membrane. These membranes form the tricuspid valve between the right atrium and the right ventricle. The tricuspid valve was named so because it has three cusps or flaps. This valve allows blood to enter the ventricle from the atrium, but prevents backflow of blood from the ventricle into the atrium. Chordae Tendinae or “heartstrings” are the tendons that connect the papillary muscles to the membranes of the valve. The valve acts much like a door that opens in only one direction. The tricuspid valve is one of two atrioventricular valves also called AV. The right AV is called the tricuspid valve.
Tricuspid Valve

11. Pulmonary Semilunar Valve
Incision 2
Insert your probe into the pulmonary artery and see it come through the right ventricle. Make an incision down through this artery.
Pulmonary Semilunar Valve
Pulmonary Artery
Insert your probe into the pulmonary artery and see it come through to the right ventricle. Make an incision down through this artery and look inside it for three small membranous pockets. These form the pulmonary semilunar valve, which prevents blood from blowing back into the right ventricle. In summary, the flow of blood through the right side of the heart works like this: deoxygenated blood returns from the body to the heart trhough the superior and inferior vena cava and enters the right atrium. Blood from the right atrium enters the right ventricle through the one-way tricuspid valve. Blood exits the right ventricle through the pulmonary trunk and is prevented from returning to the right ventricle by the pulmonary semilunar valve. Blood is then sent to each lung via the right and left pulmonary arteries that branch from the pulmonary trunk.

12. Observe and Measure Observe the right half of the heart.
Identify the following:
Tricuspid valve
Pulmonary semilunar valve
Papillary muscles
Chordae Tendonae
Measure the following:
Diameter of the right atrium and ventricle
Wall thickness of the right atrium and ventricle
Diameter of the aorta and pulmonary trunk
Now that you have opened the right atrium and ventricle, take a moment to observe the tricuspid valve, pulmonary semilunar valve, papillary muscles and chordae tendinae. Measure both the diameter and wall thickness of the right atrium and right ventricle in centimeters and record on your Dissection Data Sheet. Additionally, measure the diameter of both the aorta and pulmonary trunk and record on your Dissection Data Sheet.

13. Observe
Try to find the three layers of the heart wall: endocardium, myocardium and epicardium
You may need to use the dissecting needle to lift the endocardium or epicardium

14. Incision 3
Insert your dissecting scissors or scalpel into the left auricle at the base of the aorta and make an incision down through the wall of the left atrium and ventricle as shown by the line.
Chordae Tendinae
Bicuspid Valve
Now let’s investigate the left half of the heart. Insert your dissecting scissors or scalpel into the left auricle at the base of the aorta and make an incision down through the wall of the left atrium and ventricle as shown by the line. Locate the mitral valve (or the bicuspid valve) between the left atrium and ventricle. This will have two flaps of membrane connected to papillary muscles by the chordae tendinae just like the tricuspid valve. The mitral valve is the other atrioventricular valve that prevents blood from flowing back into the atrium from the ventricle.
Papillary Muscle

15. Incision 4
Insert a probe into the aorta and observe where it connects to the left ventricle. Make an incision up through the aorta.
The final incision will be through the aorta. Insert a probe into the aorta and observe where it connects to the left ventricle. Make an incision up through the aorta and examine the inside carefully for three small membranous pockets. These form the aortic semilunar valve, which prevents blood from flowing back into the left ventricle.

16. Observation Observe the left side of the heart.
Identify the following:
Mitral or Bicuspid valve
Aortic Semilunar valve
Papillary muscles
Chordae tendonae
Measure the following:
Diameter of the left atrium and ventricle
Wall thickness of the left atrium and ventricle.
Now that you have opened the left atrium and ventricle, take a moment to observe the bicuspid or mitral valve, aortic semilunar valve, papillary muscles and chordae tendinae. Measure both the diameter and wall thickness of the left atrium and left ventricle in centimeters and record on your Dissection Data Sheet.

17. Clean Up
Place all dissecting specimens and parts into approved container provided by the instructor.
Wash dissecting equipment and trays in dilute bleach solution provided by the instructor.
Dry equipment thoroughly to prevent rusting.
Clean table tops with dilute bleach solution provided by the instructor.
Wash hands thoroughly before leaving the classroom.
At the end of the lab, make sure all equipment has been returned. Dissection specimens should be disposed of in a double bag. You can use two large ziplock baggies for this placing one inside another and zipping both before throwing in the garbage. Instruments should be washed in a 10% bleach solution and dried thoroughly to prevent rusting.
Make sure everyone has stopped the activity when it is time to clean up. See that work surfaces are washed with soap or bleach disinfectant and dried completely. This is a great habit to instill even if it doesn’t seem necessary. Make clean up a responsibility for the students, but have them use a mild detergent or a 10% bleach solution. Do not allow students to leave the room for appointments or pullout programs unless they first clean up their work areas. Better yet, don’t allow anyone to leave the room until all equipment has been returned, workspaces cleaned and hands washed.

18. Resources
Color Me Heart Heart House Heart Dissection Lab Heart Anatomy labelinterior/label.shtml
The next two slides provide some additional resources for your investigation should you be interested in pursuing more information or activities that relate to the sheep heart. All of these sites are excellent resources. Thank you for participating in sheep heart dissection.

19. Resources
Heart Lessons Animations/Interactives Heart Diagram Color Heart Diagram