Sheep Heart Dissection Procedure: 1. Line dissection tray with paper towels. Rinse the sheep heart in water. Pat dry with paper towels. 2. Locate the pericardium. Look for a tough, thick membrane at the top of the heart. 3. Observe the epicardium. Using a sharp probe, pull a little of this serous membrane away from the myocardium. How does it differ from the pericardium? 4. Examine the external surface of the heart. Notice the accumulation of adipose tissue, which in many cases marks the separation of the chambers and the location of the coronary arteries. Carefully scrape away some of the fat with a scalpel to expose the coronary blood vessels. 5. Identify the base and apex of the heart, and then identify the two wrinkled auricles, earlike flaps of tissue projecting from the atrial chambers. The balance of the heart muscle is ventricular tissue. To identify the left ventricle, compress the ventricular chambers on each side of the longitudinal fissures carrying the coronary blood vessels. The side that feels thicker and more solid is the left ventricle. The right ventricle is much thinner and feels somewhat flabby when compressed. Hold the heart in its anatomical position, with the anterior surface uppermost. In this position, the left ventricle composes the entire apex and the left side of the heart. Identify the base and apex of the heart.* 6. Find the superior and inferior vena cava. They will be the large vessels entering the right atrium. Place your blunt probe into the superior vena cava, and through the inferior vena cava. * 7. Make a cut through the superior vena cava toward the apex of the heart. You will be cutting into the right atrium. After you cut through the atrium, remove your scissors and insert your gloved finger into the right ventricle. This will help you visualize where your cut will be made. Continue cutting along the lateral edge of the heart until you can fully open the right ventricle. 8. Visualize the right atrium, tricuspid valve, right ventricle, chordae tendineae and papillary muscles. 9. Examine the layers of the heart wall: epicardium, myocardium, and endocardium. 10. Place your blunt probe in the tract that lies behind the tricuspid valve and exits through the pulmonary valve. * 11. Use your scissors to make a cut, following the path of your blunt probe. 12. Open your incision and visualize the pulmonary valve and pulmonary artery. 13. Turn your attention to the left side of the heart. Place one blade of the scissors into the auricle of the left atrium. Make one scissor-length cut, remove scissors and place a gloved finger into the heart. Palpate the depth of the left ventricle. 14. Continue cutting toward the apex of the heart along the lateral side. Open and examine the left atrium. Use your blunt probe to search for the openings of the four pulmonary veins on the posterior side of the left atrium. 15. Examine the bicuspid valve, chordae tendineae, papillary muscles, and left ventricle. 16. Compare the thickness of the left ventricular wall to the right ventricular wall. 17. Place one finger in the left ventricle and one finger in the right ventricle. Palpate the interventricular septum. 18. Starting at the left ventricle, place your blunt probe up through the aorta. Your probe should exit the heart at the base.* 19. Using your scissors, cut along the path of your probe. 20. Visualize the aortic valve and aorta. 21. Look for a small opening that leads to the coronary arteries just distal to the aortic valve. Insert your blunt probe into the opening. You may be able to trace it to a coronary vessel. 22. Discard your specimen as directed by your instructor. 23. Clean your instruments and tray. DRY ALL TOOLS AND TRAY! Sheep Dissection Lab Name:___________________________ Period:________ Date:______________ 1. Compare and contrast the structure of the tricuspid valve with that of the pulmonary valve. 2. Which valves have chordae tendineae? What is the purpose of chordae tendineae? 3. What is the significance of the difference in thickness between the walls of the ventricles? Which is thicker and why? 4. Compare the thickness of the wall of the superior and inferior vena cava and the aorta. Which is thicker and why? 5. What function do the coronary blood vessels perform? 6. List in order the major blood vessels, chambers and valves which a drop of blood must pass in traveling from vena cava to the aorta.