LAB 12-1 HEART DISSECTION GROSS ANATOMY OF THE HEART

Transcription

1 LAB 12-1 HEART DISSECTION GROSS ANATOMY OF THE HEART Because mammals are warm-blooded and generally very active animals, they require high metabolic rates. One major requirement of a high metabolism is the need for oxygen and nutrients to reach body cells in sufficient quantities to satisfy their needs. Metabolic waste needs to be carried away quickly for disposal so that they don t interfere with the cells operation. These functions are carried out by the circulatory system which in turn is driven by the heart. The heart is a four-chambered organ that is shaped roughly like an inverted pear, slightly larger than a clenched fist. Its weight ranges from 230 to 280 grams in females and 280 to 340 grams in males. The heart and its surrounding pericardial cavity are located within the mediastinum, a centrally located area within the thoracic cavity. Anterior View Posterior View Examining the Gross Anatomy of the Human Heart Preserved sheep hearts are the most commonly dissected of the mammalian hearts. This is due to their low cost and ready availability. Sheep hearts usually come from the packing houses with the major vessels trimmed very close to the heart itself. This is normal and although not ideal from a dissecting standpoint, they are still very easy to work with.

2 Preserved hearts come in two ways: with the pericardium and without. The pericardium is a membranous sac that envelopes the heart. It protects the heart and separates it from the rest of the thoracic cavity. It is attached to the heart where the large vessels emerge. 1. Identify the pericardial sac if it is present. This structure includes the fibrous pericardium and parietal pericardium. The fibrous pericardium is a thick outer layer of fibrous connective tissue and fat that encloses the heart. With a pair of scissors, cut along the pericardial sac for a short distance (about 2.5. cm) and fold it back to expose its inner surface. The thin, shiny layer along this surface is the parietal pericardium. 2. By making a cut in the pericardial sac, you have exposed the outside surface of the heart wall. Notice that the heart wall is covered by a thin, translucent membrane. With forceps, lift a portion of this membrane off the heart s surface. This is the visceral pericardium. The space between the parietal pericardium and the visceral pericardium is the pericardial cavity. Identify the space by placing a probe into it. External Anatomy of the Heart 1. Carefully remove the pericardial sac to expose the entire heart. This can be accomplished by continuing your initial cut toward the base of the heart and detaching the pericardial sac s attachments to the great vessels. The whitish lumpy tissue on the outer surface of the heart is fat tissue. The bulk of the heart tissue is the reddish- brown heart muscle, the myocardium. The chambers of the heart are lined with a tissue called the endothelium. The endothelium also lines the blood vessels of the body. 2. Hold the sheep heart so that the anterior surface is facing you. At the inferior tip of the left ventricle, identify the apex of the heart. Identify the pulmonary trunk and the aorta. From an anterior view, the pulmonary trunk is anterior to the aorta.

3 3. Observe the major sulci that travel along the surface of the heart. They can be best identified by the large amount of fat that is located along their paths. a. The atrioventricular groove travels around the heart s circumference and separates the atria from the ventricles. b. The anterior interventricular sulcus travels between the left and right ventricles on the anterior surface. c. The posterior interventricular sulcus travels between the left and right ventricles on the posterior surface. 4. The atria on the sheep heart are quite small and are comparable to the auricles on the human heart. Often, during commercial preparation of the heart, these chambers are partially removed, leaving the internal structures exposed. Therefore, the superior and inferior venae cavae leading into the right atrium and the pulmonary veins leading into the left atrium are usually absent. Identify the base of the heart by locating what remains of the atrial walls. 5. Since fat deposits are found along the major grooves on the heart s surface, in order to identify the blood vessels that travel along the grooves, it is necessary to remove this fat. With forceps, carefully strip away the fat from a small section along one of the grooves to verify the presence of blood vessels. a. Anteriorly, locate the left coronary artery behind the pulmonary trunk and the anterior interventricular artery which descends toward the apex along the anterior interventricular sulcus. b. The right coronary artery travels to the right along the atrioventricular groove. It curves around the right side and continues onto the posterior surface. c. The great cardiac vein ascends along the anterior interventricular groove, running alongside the ant. interventricular artery and empties into the coronary sinus. 6. Hold the sheep heart so that the posterior surface is facing you. Along the atrioventricular groove, carefully remove the fat to reveal a thin-walled, dilated blood vessel that empties into the right atrium and drains most of the venus blood from the heart wall. This vessel is the coronary sinus. a. Posteriorly, locate the posterior interventricular artery which descends toward the apex along the posterior interventricular groove. b. The middle cardiac vein ascends along the posterior interventricular groove, running alongside the post. interventricular artery and empties into the coronary sinus.

4 Anterior View Posterior View Internal Anatomy of the Heart 1. Expose the interior of the right atrium and ventricle in the following manner. a. Insert the blunt end of a pair of large scissors into the superior vena cava. If the superior vena cava is not present, insert the scissors into the opening where the blood vessel drains into the right atrium. b. Cut along the lateral margin of the right atrium. c. Continue to cut along the lateral margin of the right ventricle to the apex. Be sure to cut through the entire thickness of the ventricular wall but avoid damaging internal structures. 2. Expose the interior of the left atrium and left ventricle in the following manner. a. Using a scalpel or a knife, make a small incision in the lateral wall of the left atrium. b. Insert the blunt end of a large scissors into the incision and cut along the lateral margin of the left atrium. c. Continue to cut along the lateral margin of the left ventricle to the apex. 3. Identify the interatrial septum that separates the left and right atria. Locate the atrioventricular orifices that lead to the ventricles.

5 4. Identify the interventricular septum that divides the two ventricles. Notice how the inferior portion is thick and muscular, and the superior portion is thin and membranous. 5. Beginning at the apex, cut through the interventricular septum with a large scissor. Continue cutting through the interatrial septum until you have completed a coronal section of the heart. 6. In the coronal section, identify the following structures. a. The atrioventricular (AV) valves are located between the atria and the ventricles. The tricuspid valve, with three cusps, is on the right side and the bicuspid valve, with two cusps, is on the left. For each valve, observe that the cusps are connected to the papillary muscles by the chordae tendinae. b. The trabeculae carneae are muscular elevations along the walls of both ventricles. Notice that they are found predominantly in the inferior portions of these chambers. c. The superior portions of the ventricles are narrow, smooth corridors that lead to the great arteries. 7. From the cut margins of the aorta and pulmonary trunk, cut along the walls of these blood vessels toward the ventricles until you reach the semilunar valves. Observe that each valve is composed of three half moon-shaped cusps. 8. Along the wall of the aorta, just superior to the aortic semilunar valve, use a blunt probe to find the openings to the right and left coronary arteries.

6 Name: Period: Date: HEART DISSECTION LAB REPORT I. Purpose II. Analysis 1. What is the mediastinum? 2. What are the atria? 3. What are the ventricles? 4. What is the primary function of the pulmonary circulation? 5. What is the primary function of the systemic circulation? 6. What are the three tissue layers that comprise the heart wall? 7. Where is the bicuspid valve located? 8. Where is the tricuspid valve located? 9. Where is the pulmonary semilunar valve located? 10. Where is the aortic semilunar valve located? 11. What is the function of the chordae tendinae? 12. The major bulk of the heart wall is composed of cardiac muscle tissue, called 13. A groove that separates the atria and the ventricles on the external surface of the heart is the

7 In the following diagram, of the anterior view of the heart, identify each numbered structure by writing its name and labeling with the color that is indicated: 1. = yellow 2. = yellow stripes 3. = red 4. = red stripes 5. = blue 6. = purple = orange 8. = pink 9. = blue 10. = blue stripes 11. = brown 12. = brown stripes 13. = green

8 In the following diagram, identify the labeled structures III. Conclusion