The purpose of this practical is to understand the function and structure of the heart by dissecting a pig's heart and drawing labeled diagrams of the external and internal structures.
"A good heart is better than all the heads in the world", once said Edward Bulwer-Lytton, an English novelist and politician (Famous Quotes and Authors, 2010). Indeed, kindness as a moral quality is pivotal to the enhancement of civilization. Meanwhile, the heart is extremely crucial for human physically. The function and structure of the heart will be described.
Note that all mammals share similar heart function and structure. Therefore, the function and structure of a human heart can be understood by analysing a pig's heart.
For mammalian, the heart plays a key role in physiological regulation of the body. According to Polar Electro (2010), the heart is a pump that generates and pushes out blood in circulatory system. The circulatory system, which consists of cardiovascular system and lymphatic system, is responsible for blood and nutrition transport to all the tissues in the body (Lane, 2010b). The heart accomplishes the transportation of blood by continual contracting to pump blood to the entire body (Lane, 2010b). This is the most important function of the heart.
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The mammalian heart has a unique structure. As stated by Integrative Biology (2010), the heart is an organ that looks like an up-side down pear. There are four chambers in the heart, the left and right atria on the top, and the left and right ventricles on the bottom (Lane, 2010a). The inside of these chambers are hollow, filling with blood. The left half of the heart (the right atrium and ventricle) is responsible for transporting deoxygenated blood from the body to the lungs while the right half of the heart (the left atrium and ventricle) is in charge of generating oxygenated blood to the entire body (MamasHealth, 2010). The two halves are separated by a solid septum, which is a thick wall that prevents blood to flow between left and right sides of the heart. The heart goes through systole and diastole to pump blood. During systole, in which the heart contracts, a three-leaflet valve between the right ventricle and atrium named tricuspid valve that controls blood flowing from the right atrium into the right ventricle will close up (Lane, 2010a). Whereas in diastole, namely the relaxation of the heart, this valve will open up and allow blood to get through. Between the left atrium and the left ventricle there is also a valve that controls blood flow - bicuspid valve, which consists of two leaflets. This valve dominates blood from the left atrium flow into the left ventricle during systole and diastole.
The process of blood transportation is as follows. It is stated by Pickering (2000) that a vein named superior vena cava brings deoxygenated, or used, blood from the body to the right atrium. The blood then goes into the right ventricle through tricuspid valve. As blood pressure increasing, the tricuspid valve closes up, resulting in filled right ventricle with deoxygenated blood (Pickering, 2000). Pickering (2000) further states that deoxygenated blood will then go into pulmonary artery which carries used blood from the right ventricle to the lungs for reoxygenation. The oxygenated blood comes back to the heart from the lungs through pulmonary veins, and then goes into the right atrium (Pickering, 2000). Via bicuspid valve, the oxygenated blood gets into the left ventricle which forces blood into the whole body via aortic valve (Pickering, 2000). Via articles, veins and capillaries, the blood reaches every corner in the body.
Methods & Observation
Materials needed in this experiment: a fresh pig heart, forceps, scalpels, scissors, dissecting pan, gloves.
The experiment was conducted following these steps modified from Lane (2010a). Observation of the heart was noted below the procedure.
A fresh pig heart was placed in a dissecting pan.
The heart had smooth lining and it was palm-size big. It felt like a heavy shell but rather soft. The pig's heart was dripping with blood and appeared blood red. There were fats covering the upper part of the heart, making it appear yellow white. Few grooves went across the heart on the surface with white fats nearby.
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The front side of the heart was found by recognizing a groove (coronary artery) that extended from the right side of the broad end of the heart diagonally to a point above and to the left of the apex.
On the front side, there were two apparent tubes extending from the heart that were believed to be aorta and pulmonary artery. Also, on both side of the top of the heart, there was a huge purple muscular piece that looked similar to a mushroom. On the back side, there were two big tubes (the ones that could be seen from the front side) and three holes that seemed to be entrances or exits of vessels (pulmonary vein and superior vena cava) (See Figure 1 and Figure 2).
The pericardium was removed, the muscle texture can be observed clearly.
The pulmonary artery was cut through. The cutting continued until the wall of the right ventricle was cut through. The cutting line was above and paralleled to the groove of the coronary artery.
The heart was pushed open at the cut with fingers. Any dried blood inside the chambers was rinsed out. The cutting continued following the chamber line to the back of the heart.
The right atrium and ventricle were seen with thin muscular wall cut open. After most dried blood being rinsed out, the tricuspid valve was seen clearly (See Figure 3).
The left atrium was cut open from the outside by scissors. The cutting went downward into the left ventricle toward the apex to the septum at the center groove. The dried blood inside the chambers was rinsed out. The left ventricle towards the aorta was cut open, the valve was exposed.
The left ventricle was exposed. It had much thicker muscular wall than the right ventricle had. The bicuspid valve was clearly seen. After the aorta was cut through from the atrium, the aortic valve was exposed. There were chordae tendinae liking to papillary muscle (See Figure 4).
Several problems encountered during dissection and drawing of results.
A considerable amount of time was spent on finding the frond side of the heart. The groove was not as apparent as expected. Also, only having short tubes or holes on the heart rather than intact tubes makes the finding of vessels difficult. Hence, the superior vena cava was not surely found during this experiment (further explanation will be given later). The aortic arch was not found as well.
Not all pericardium of the heart was removed since it would take a long time to get rid of all the surface membrane when there was a time limit for the experiment. Although this did not seem to have apparent detrimental influence on the result of this experiment, it may help to understand how the muscle texture is arranged for the heart to function in highest efficiency.
There were two vessels on the heart that seem to be at the position of superior vena cava and they were all linked to the right atrium. However, superior vena cava is supposed to be only one vessel going into the right atrium. These tubes can also be mistaken because they looked similar to two branches of pulmonary artery going to the two lungs. However, pulmonary artery was found already. It remains unclear whether they are branches of the superior vena cava.
There were two huge mushroom-like muscular pieces on each side on the top of the heart. They were connected to the atria on each side respectively. After examination, it seemed that the muscle piece connected to the right atrium was also linked to the supposed superior vena cava. These two muscular pieces might be some extra muscle of the pig but some model pictures of the heart suggest that they might be parts of the atria.
The finding of different organs in the heart was not smooth due to incomprehensive understanding of the heart structure. Although the practical handout was read thoroughly and some research about the heart structure and function was done before the practical, when it came to the real dissection, some organs seemed much harder to find. A thorough understanding of the practical should be had before the experiment, including some theory and the exact location of items.
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The pear-like mammalian heart functions as a pump to generate deoxygenated blood and push oxygenated blood into the body as part of the circulatory system. How the heart functions is strongly linked to its structure. The left and right atria and ventricles are the four chambers in the heart. There are tricuspid valve and bicuspid valve between the atria and ventricles on each side to control blood flow during diastole and systole. Deoxygenated blood flows into the right atrium and ventricle from superior vena cava and goes into pulmonary artery to meet the lungs for reoxygenation. Oxygenated blood flows back to the heart from the lungs and goes into the left atrium and ventricle to be pumped into the aorta, which takes blood to the entire body.