Download 6.2 heart dissection

ACTIVITY 3: Heart Dissection
Because the pig/ sheep/ cow heart is very similar to the human heart, it is an excellent model for learning about
the structure and function of the human heart. In fact, pig hears are so similar to human hearts that
malfunctioning aortic valves in humans often can be replaced with aortic valves from pigs.
Materials:
Preserved sheep heart
Dissecting pan
Dissecting kit
Small water bottle
Wooden craft sticks
Purpose: To review the structural characteristics of the human heart and to examine the major features of a
mammalian heart.
Procedure:
CAUTION: scalpels are sharp! Use extreme care.
1. Put on disposable gloves and obtain a preserved heart.
2. Rinse it in water thoroughly to remove as much of the preservative as possible. Also run water into the
larger blood vessels to force any blood clots out of the heart chambers.
3. Place the heart in a dissecting tray with its ventral (front) surface up. Locate the visceral pericardium,
which appears as a thin, transparent layer on the surface of the heart. Use a scalpel to remove a
portion of this layer and expose the myocardium beneath. Also note the abundance of fat along the
paths of various blood vessels. This adipose tissue occurs in the loose connective tissue that underlies
the visceral pericardium.
Identify and label the following: right atrium, right ventricle, left atrium, left ventricle, coronary arteries
4. Squeeze both ventricles.
Which wall seems thicker and less pliable? Why is this so?
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5. Observe the two large, thick vessels at the top section of the heart. Insert a blunt end of a probe into
each vessel to determine into which chamber it opens. The aorta is the vessel that arises from the left
ventricle and the pulmonary artery has its origins in the right ventricle.
Which vessel is thicker? Why is this so?
6. Examine the blood vessels that are attached to the surface of the heart. These are part of the coronary
circulation, which provides oxygen and nutrients to the cells of the heart.
What results if there is blockage in these vessels?
7. On the outer surface of the heart are masses of heart, globular material. This substance is fat.
What is the color of this material?
8. Examine the dorsal (back) surface of the heart.
a) Locate the stumps of two relatively thin-walled blood vessels that enter the right atrium.
Demonstrate this connection by passing a slender probe through them. The upper vessel is the
superior vena cava, and the lower one is the inferior vena cava.
b) Locate the left atrium and the pulmonary veins feeding into it.
Label the superior vena cava, the inferior vena cava, the pulmonary veins, the aorta and the
pulmonary artery on the diagram below.
Make a rough sketch of what you predict the interior of the pig heart to look like. Label the four
chambers and draw arrows to indicate the direction blood travels through the chambers.
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9. Open the right atrium. To do this, follow these steps:
a) Insert a blade of the scissors into the superior vena cava and cut downward through the atrial wall
Cut here:
b) Open the chamber and locate the superior and inferior vena cava.
c) Locate the atrioventricular valve and examine its cusps.
How many cusps does this valve have?
d) You should see cords of connective tissue attached to the valve. This tissue ensures the valve only
opens in one direction.
What is the name of these cords?
e) Using a water bottle, run some water through the tricuspid valve to fill the chamber of the right
ventricle.
f)
Gently squeeze the ventricles and watch the cusps of the valve as the water moves up against
them.
Describe the action of the valve when you squeezed the water-filled right ventricle.
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10. Open the right ventricle as follows:
a) Continue cutting downward through the valve and the right ventricular wall until you reach the apex
of the heart.
Cut here:
How do the walls of the atria compare with the walls of the ventricles and why are they different?
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b) Find the opening to the pulmonary artery. This is where blood would exit the right ventricle and go
to the lungs.
c) Follow the pulmonary trunk until you have exposed the pulmonary semi-lunar valve.
How many cusps does this valve have?
11. Open the left side of the heart. To do this, follow these steps:
a) Insert the blade of the scissors through the wall of the left atrium and cut downward to the apex of
the heart. Since the left ventricle wall is very thick, it will probably take several cuts to cut through
the chamber.
Cut here:
b) Open the left atrium
openings of the
and locate the
pulmonary veins.
c) Pass a slender probe
and locate the stump of its vessel.
through each opening
d) Examine the left atrioventricular valve and its cusps. Locate and observe the cords of connective
tissue attached to the left AV valve.
How many cusps does this valve have?
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12. Locate the aorta, which leads away from the left ventricle:
Compare the thickness of the aortic wall with that of the pulmonary artery.
13. Use scissors to cut along the length of the aorta to expose the aortic valve at its base.
How many cusps does this valve have?
14. Insert labeled wooden
the
a) Aorta
b) Pulmonary artery(s)
c) Pulmonary vein(s)
d) Superior vena cava
e) Inferior vena cava
craft sticks into
Stamp for labels: _____________
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Heart
functioning
(10)
15. Now you will model the first steps of a surgical valve replacement by removing the aortic valve from the
pig.
a) Place your fingers on the aorta and feel where it leads to the top of the left ventricle. Cut through
the base of the aorta so that the aortic valve remains attached to the heart.
b) Note the ring of cartilage that surrounds the aortic valve. This cartilage supports the aortic valve
against the tremendous force of blood pushed from the left ventricle. Remove the valve by using
your scalpel to cut around the outside ring of cartilage.
c) Stamp for removal of the aortic valve: ____________
d) Hold the valve under gently running water. Observe the difference when you try to pour water
through the valve in the wrong directions.
Describe the action of the valve:
16. Discard the specimen as directed. Clean up stamp: _____________
Label the diagram of the human heart below.
1__________________________________
2. _________________________________
3. _________________________________
4. _________________________________
5. _________________________________
6. _________________________________
7. _________________________________
8. _________________________________
9. _________________________________
10. ________________________________
11. ________________________________
12. ________________________________
13. ________________________________
14. ________________________________
15. ________________________________
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