For most mammals, the heart is an extremely important organ in their bodies. Acting as a pump, the heart can control the blood by alternating the contractions of muscles and their relaxations. Because of this pumping action, the blood can be kept flowing throughout the bodies.
Like other mammals, the pig’s heart has a complex structure. The heart is made up of three layers, the epicardium, mycardium and endocardium (Pathguy, 2005). It is also divided into four main chambers. They are the right atrium and right ventricle, the left atrium as well as the left ventricle (Lane, 2010b). On both sides, the upper chambers are known as the atria, and the ventricles are lower. Since the left ventricle needs to pump the oxygenated blood throughout the body, it has thicker muscle. The left ventricle wall is thicker than other chambers’ (Lane, 2010b). It is three times the thickness of the right ventricle¼ˆSkillstat, 2005¼‰. The right and left sides of the heart are separated by a muscle called septum. The septum is made up of two regions; the interatrial septum and the interventrial septum (Buddyproject, 2000).
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In the heart, there are a series of valves used to control the blood flow direction. On each side, a special valve separates the atrium and the ventricle. The valve between the right atrium and the right ventricle is called the tricuspid valve. This valve allows blood to enter the right ventricle from the right atrium. And it can also prevent the backflow of blood (Lane, 2010b). Having similar functions, the valve on the left side is the bicuspid valve (Lane, 2010a).
Double circulation in mammal consists of the pulmonary circuit and the systemic circuit (Pickering, 2000). These two circuits are separated. Deoxygenated blood from the body can be received and pumped to the lungs by the right side of the heart (Losos, Mason & Singer, 2008). This is the pulmonary circuit. The systemic cycle is that the left side of the heart carries oxygenated blood and pumps it to the tissues and organs. This double circulation is also achieved by the arteries and veins in the heart (Losos, Mason &Singer, 2008). The superior vena cava and the inferior vena cava can return deoxygenated blood from the tissues to the right atrium. To oxygenate the blood, pulmonary artery can deliver the deoxygenated blood from the right ventricle to the lungs¼ˆNHLBI, nd). Oxygenated blood can enter the left atrium via the pulmonary veins. Aorta is principal vessel. It can take oxygenated blood to the body from the left ventricle¼Œfollowed by the systemic circulation (NHLBI, nd).
Methods & Observations:
The apparatus in the experiment included a fresh pig heart, container, a dissecting pan, forceps and a scalpel, as well as several pairs of gloves.
Procedures of examining the external structure (Lane, 2010a)
1. A heart was washed and placed in a dissecting pan.
a. The heart appeared sanguineous colour. Its size was a little larger than human fist. In the upper part, there were some substances appearing cream colour.
2. Using the forceps, part of the pericardium was removed.
The pericardium membrane covering the heart was thin and hard to be removed.
3. The heart was turned so that the front or ventral side was facing the observers. Four chambers were located.
c. In Figure 1, the half including the apex was the left side of the heart. A groove was on the front of the heart and divided the heart into two sides. The coronary artery can be found in the groove. The positions of four chambers, the aorta and the pulmonary artery were located. There were era-shaped extensions (labeled 1 & 2) on both sides.
4. The heart was turned over. Other main blood vessels, including the pulmonary veins, the superior vena cava and the inferior vena cava were located.
d. As Figure 2 shows, pulmonary veins were inferior to the pulmonary artery. Two vessels joining together were located as the superior vena cava and the inferior vena cava.
Procedures of examining the internal anatomy (Lane, 2010a)
1. The heart was cut deep enough to go through the side of the pulmonary artery until the wall of the right ventricle.
2. Dried blood inside the chambers was rinsed out the heart.
3. The right atrium was located.
4. Other main structures in the right side, including the inferior vena cava, the superior vena cave and the tricuspid valve were located.
a. As Figure 3 shows, the top of chamber was the right atrium. The tricuspid valve separated the right atrium and right ventricle. The muscle on the right side is located as septum.
5. The heart was cut continually from the outside of the left atrium downward into the left ventricle.
b. With a thicker wall, it was harder to cut on the side.
6. The heart was pushed open. Dried blood was rinsed out with water.
7. Main structures on the left side, including the bicuspid valve and the left ventricle were examined.
8. The heart was cut across the left ventricle toward the aorta and then cut to expose the valve.
9. The three flaps or leaflets on the tricuspid valve were counted and observed.
C. The bicuspid valve was thick. The aortic valve was between the left ventricle and the aorta (see Figure 4). It had three flaps and a half-moon shape.
Results:
Figure 1 shows the external structure (anterior view) of the heart.
Figure 2 shows the external structure (posterior view) of the heart.
Figure 3 shows the internal structure of the right side in the heart.
Figure 4 shows the internal structure of the left side in the heart.
All these diagrams are attached at the end of this report. Some functions of the labeled structures are also noted on the right sides of those diagrams.
Discussion:
The heart in a dissecting pan can be imagined that the heart is in the body of a person facing the observers. The left side of the heart is on the right side of the dissecting. This makes the observers easier to be confused when examining the heart’s structures.
Those cream substances in the upper part of the heart can be deduced as fat around the muscle pump. The left side of the heart has more muscular and firmer than the right one. This provides the left side with enough energy to pump blood to the whole body.
It is hard to identify the positions of the inferior and superior vena cava correctly. The superior vena cava returns blood to the right atrium from the upper part of tissues, while the inferior vena cava carries blood from the lower tissues (NHLBI, nd). Therefore, it is more reasonable that the inferior vena cava is below the superior vena cava instead of connecting to each other (As shown in Figure 2).
In this experiment, the semi-lunar entering to the pulmonary veins has not been found. The ear-shaped extensions (labeled 1&2 in Figure 1) may not belong to the structure of the heart. But based on their positions, it is possible that they are the extensions of the right atrium and the left atrium.
Conclusion:
The heart is a pump muscle. It can pump oxygenated blood and carry nutrients to the tissues throughout the body. A pig’s heart has four chambers, the left and right ventricle and the left and right atrium. A series of main vessels are responsible for the pulmonary and systemic systems, such as the aorta, the pulmonary artery and pulmonary veins, as well as the inferior and superior vena cava. The vales between atria and ventricles act as barriers to prevent blood backflow. Each simple structure of the heart is contributed to providing blood for the survival of the tissues in the bodies.
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