Download Cardiovascular System-Sheep Heart Dissection

Cardiovascular System-Sheep Heart Dissection
Background
The human heart is the muscular pump of the cardiovascular system. The rhythmic contractions of the cardiac
cycle produce the pressure responsible for arterial circulation, which delivers blood and oxygen to body
tissues. The pump is composed of four (4) hollow chambers. The two right-side chambers relate to the lungs
and are responsible for the pulmonary circulation. Deoxygenated blood from the body enters the right atrium
and is pumped to the lungs, under relatively low pressure, by the right ventricle. The two left-side chambers
relate to the rest of the body and are responsible for systemic circulation. Oxygenated blood returns, from the
lungs, to the left atrium and is pumped to the body tissues by the left ventricle, under rather high pressure.
The cardiac valves regulate this one-way flow of blood. The bi- and tricuspid valves prevent backflow between
atria and ventricles, while the pulmonary valve prevents reflux between the right ventricle and pulmonary
artery and the aortic valve between the left ventricle and aorta.
The human heart displays the four-chambered structure which is typical of birds and mammals, and
serves to effectively separate oxygenated and deoxygenated blood. This separation ensures that body cells of
these endothermic organisms will receive a maximal amount of oxygen with each cardiac cycle. The large
oxygen requirement is necessary to produce the energy needed by warm-blooded organisms. These structural
similarities allow us to use a non-human, mammalian heart– from a young cow– to directly study the anatomy
of the human heart.
Focus Questions
• What are the structural similarities shared by all mammalian hearts?
• What are the structural differences between arterial and venous connections to the mammalian heart?
• What are the structural differences between right and left sides of the mammalian heart?
• What are the structural differences between atria and ventricles of the mammalian heart?
• What are the structural differences between mammalian heart valves?
Procedure
Part A. External Anatomy
1. Obtain a dissecting tray, rubber gloves for the dissector and a sheep heart.
2. Place the heart in a dissecting tray with the ventral side up. Study/observe closely the blood vessels which
enter and leave the heart. Use your finger or a blunt probe to follow the vessels into their respective heart
chambers. Use that information to identify the following: right atrium, left atrium, right ventricle, left
ventricle, aorta, vena cava (inferior and superior), pulmonary artery and pulmonary vein.
3. Locate all of the coronary arteries and follow, as much as is possible, the path of cardiac circulation.
Data Collection
Drawing. Make a detailed, scaled and labeled drawing of the external view of the heart. Label the
following structures: right atrium, left atrium, right ventricle, left ventricle, aorta, vena cava (inferior
and superior), pulmonary artery and pulmonary vein.
Measurements. Conduct the following measurements: aortic diameter (mm); thickness of aortic wall
(mm); vena cava diameter (mm); thickness of vena cava wall (mm). Record these measurements in your
data table.
Written Descriptions. Record a set a written observations on the following 'great vessels' of the heart:
aorta; vena cava (inferior and superior); pulmonary artery and pulmonary vein. Focus on the
differences between arteries and veins, as well as the specific connections between vessels and heart
chambers. Feel free to support your written observations with appropriate, labeled diagrams.
Part B. Internal Anatomy
1. Locate the superior vena cava. Open the right atrium by inserting a scissors blade into the superior vena
cava and cutting downward through the atrial wall. Observe the structure of the atrial wall.
2. Locate and observe the tricuspid valve. Note how the flaps of the valve open in response to pressure from
the atrium and close in response to pressure from the ventricle.
3. Open the right ventricle by cutting downward through the tricuspid valve and the right ventricular wall
until you reach the apex of the heart. Observe the structure of the ventricular wall.
4. Locate and observe the chordae tendinae and the papillary muscles.
5. Locate the pulmonary artery and observe the pulmonary valve. Pour a small amount of water
into the pulmonary artery to observe how the valve closes in response to pressure from the artery.
5. Repeat this procedure on the left side of the heart.
6. Return the heart, any leftover pieces and your rubber gloves to the storage bag for disposal. Wash and dry
your dissecting equipment. Thoroughly wash your hands.
Data Collection
Drawing. Make a detailed, scaled and labeled drawing of the internal view of one side of the heart.
Label as many chambers, valves and vessels as possible, including the chordae tendinae and the
papillary muscles
Measurements. Conduct the following measurements: thickness of right atria wall (mm); thickness of left
atria wall (mm); thickness of right ventricle wall (mm); thickness of left ventricle wall (mm). Record
these measurements in your data table.
Written Descriptions. Record a set a written observations on the following heart valves: tricuspid valve,
bicuspid valve, aortic semilunar valve and pulmonary semilunar valve. Focus on the differences
between the valves, as well as the specific connections between valves, vessels and heart chambers. Feel
free to support your written observations with appropriate, labeled diagrams.