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To dissect and observe a sheeps heart in order to understand the anatomy of the human heart, to distinguish between the left and the right side of the heart and the structures of the ventricles and the atriums and to recognise the blood flow through the different types of blood vessels in the heart and its purpose.
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The heart is a major organ located in the thoracic cavity in mediastinum with the functions of pumping oxygenated blood around body. It consist of special muscles known as the cardiac muscles which are referred to as myogenic due its ability to stimulate its own contractions using electrical impulses created by the Sino atrial node (SAN also known as the pacemaker), atrioventricular node and the purkinje fibres hence any stimulus from the nervous system. The heart muscle is very resistance to fatigue. (Tharp et al, 2009).
Cardiovascular disease is the disease associated with the heart these include angina, heart attack, cardiomyopathy, heart failure, heart valve disease and stroke. It is important that we learn the anatomy of the heart as every year the in number of cases with cardiovascular diseases increases dramatically in undeveloped countries as well as developed countries. There are a number of factors that can increase the risk of cardiovascular diseases such as age, i.e. the older you are the more chances of developing cardiovascular disease increases, Sex, men are more prone to cardiovascular disease than women at a young age, smoking, high blood pressure, obesity, high blood cholesterol, stress, and ethnic background. (Kannal and McGee, 1979)
In order to prevent such diseases of the heart it is essential to maintain a healthier life style by controlling the diet and doing reasonable amount of exercise and reduce the number of risk factors as much as possible. By conducting a dissection of the sheep’s heart the anatomy of the human heart can be explained this can be used in the medical industry to gain a better understanding of the heart in order to help treat cardiovascular diseases. Sheep’s heart is cheaper and easily available and because it has similar anatomy to that of a human’s heart it is even more convenient to observe it.
Materials: Dissecting scissors, scalpel, probe, sheep’s heart, dissecting tray
Before the heart was incised using the hands, the four chambers of the heart was felt to determine their sizes and the internal arrangements. A probe used to represent blood was inserted through the aorta and its pathway was detected as it leads into the left ventricle. Using the scalpel the heart was carefully incised from the aorta down the walls of the left ventricles and up the walls of the right ventricles. Open up the heart to inspect the internal anatomy.
Using a probe the heart was followed from the right atrium into the right ventricles through three thin flaps attached to white string like structures known as the chordae tendinae this was identified as the tricuspid valve. Likewise on the left side of the heart there were two thin flaps recognised as the bicuspid valve. From the left ventricles the probe was used to follow the flow of blood along the aorta where another set of thin half-moon shaped structures were spotted and identified as the aortic semi lunar valve. Similarly from the right ventricles the probe was used to follow the flow of blood along the pulmonary artery through the pulmonary semi lunar valve which was also seen.
Figure 1 shows the external anatomy of the heart. Superior end of the heart in known as the base and the pointed end are called the apex. The right and the left coronary arteries and veins can be seen these blood vessels supply the heart with oxygenated and nutrient filled blood. The blood vessels are also surrounded by fat tissue known as adipose.
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Figure 1: External view of the heart.
Figure 2: Deep cut view of the right side of the heart.
Figure 2 the right side of the heart can be seen. The chordae tendinae and the tricuspid valve are also visible along with the papillary muscle as labelled. Major blood vessels such as the vena cava (the large opening near the right auricle) can also be seen. The pulmonary artery and the pulmonary semi lunar valve are also noticeable. The Sino atrial node, atrioventricular node and the purkinje fibres however are not observable.
Figure 3: Drawn and labelled superficial image of the left side of the heart.
During the dissection of the heart the left and the right side of the heart can be identified as the left side of the heart has thicker ventricles than the right side. This is due to the fact that the left ventricle has to pump oxygenated blood around the whole body therefore the walls of the left ventricle must be able to exert high pressure to overcome the systemic circulation, whereas the right ventricle only has to pump deoxygenated blood to the lungs. The size of the walls of the atriums are less muscular than that of the ventricles this is due to the fact the atriums only pump blood down to the ventricles therefore they do not need to generate high pressure. (Hill and Laizzo, 2009)
The bicuspid and tricuspid also known as the atrioventricular valves are also visible along with the pulmonary and aortic semilunar valves. The bicuspid and tricuspid valves are connected to string like structures called the chordae tendinease which is connected to a lump of muscle on the sides of the walls of the ventricles. The opening and closing action of the valves are controlled by the contraction and relaxation of the papillary muscle. For example when the blood flows through the bicuspid valve also known as the mitral valve into the left ventricles the papillary muscles relax decreasing the tension in the chordae tendinease allowing the bicuspid valve to open. Once the right atrium finishes contracting fully and the left ventricle is filled with blood the left ventricle contracts and pumps the blood up through to the aortic semilunar valve. Due to gravity there is a tendency for the blood to back in to the ventricles because the structures of the semilunar valves and the atrioventricular valves are umbrella like it prevents the back flow of blood and ensures that the blood flows in one direction only. (Wilcox et al, 2004)
When comparing the sheep’s heart with that of a human it can be seen that they are both very similar in anatomy mainly due to the reason that they both have the same functions and purpose. This is expected as they are both mammals both the hearts contains similar features such as four chambers left and right atrium and ventricles and the circulatory pathway of the blood. The only obvious difference is the difference in size of both hearts. (Hill and Laizzo, 2009)
Although the overall dissection was successful there are a few limitations that also need to be taken into consideration. The dissection of the heart was not accurate by means of when the left and the right side of the hearts were cut the delicate structures inside were also cut accidently, this made it difficult to locate some parts within the heart. This could also be due to the fact that the heart is not symmetrical so it is hard to incise accurately. One way this dissection could be improved is getting a step by step demonstration on the heart dissection.
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