Like human hearts, a sheep’s heart contains two atria and two ventricles. These four chambers work together to pump deoxygenated blood to the lungs and oxygenated blood to the rest of the body; this allows blood to circulate the body in a regular manner. The important reason for carrying out this experiment is to examine and understand the structural features of the heart which will help us appreciate how the heart operates. It is vital that location of both and exterior and interior vessels and chambers are clear before any dissection takes place. It is important to note that when looking at the heart it’s like looking at a mirror reflection, hence the right side of dissection is actually the left side of the heart and vice versa. From the anterior view the location of all four chambers (two upper atria and two lover ventricles) should be noted, the left and right side of the heart should be separated by a line of fat and vessels called the interventricular sulcus.
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The heart muscle, unlike the rest of the body’s muscle, is unique to its function. It requires no energy (ATP ƒ ADP) in order to pump. Cardiac muscle has the characteristic automaticity, what this means is that the heart is under no influence of hormones of neurons for it to beat, the cells themselves have their own beating power. The heart’s cells are part of a system known as the heart’s conducting system. Special cells within the heart (part of the SA and AV nodes) are responsible for the heart beat, however if circumstances in the body change and the heart is required to pump more or less blood to the body then the autonomic nervous system plays a role via special nerves called the sympathetic and parasympathetic nerves.
The heart circulates blood around the body, it is nothing but two pumps joined in a single organ.
The left ventricular wall (left myocardium) is thinker than that of the right ventricular wall (right myocardium), this is due to the reason that the right side of the heart only pumps blood (deoxygenated) to the lungs, whereas the left side pumps blood (oxygenated) to the entire body.
Materials and methods:
Preserved sheep heart
Dissecting pan
Surgical scalpel
Surgical scissors
Dissection:
The aim is to obtain a frontal section through the left and right side of the heart. During the dissection I had to be very cautious not to cut any valves of vessels that would result in negative results.
I first located the interventricular sulcus; from there I identified the right ventricle and the left ventricle. The right side of the heart was to the left of the sulcus, after identifying the superior vena cava I then made an incision using the scissors through the vena cava till the top of the atrium. At this point using a scalpel would be easier, I therefore continued the incision using the scalpel through the wall of the right atrium down to the bottom of the right ventricle. The right side is now split into two part, I pulled these two apart and immediately identified the tricuspid valve that separated the atrium from the ventricle. The presence of the tricuspid valve indicated and confirmed that the incision was made through the right side of the heart.
Moving on to the left side of the heart, I located the pulmonary artery and using the scalpel I made an incision through it down to the bottom of the left ventricle. The semi-lunar valve of the pulmonary vein was present, as was the bicuspid valve that separates the left atrium from the left ventricle.
My final incision was made through the aorta; this incision was done to observe the aortic semi-lunar valve.
Several pictures were taken for the results section.
Results:
Anterior (stern-costal) surface view
Vena cava
Pulmonary artery
Right atrium
Right ventricle
Interventricular sulcus
Pulmonary vein
Aorta
Left atrium
Left ventricle
Heart apex
The left and the right sides of the heart are divided by a line called the interventricular sulcus.
Right side of the heart:
The picture on the right shows the tricuspid valve clearer than the one below it.
Tricuspid valve
Tendons
Papillary muscles
Right ventricle
The below picture has been provided as the one above does not show ALL the right side of the heart.
Tendons
Wall of right ventricle (thinner than that of left ventricle)
Vena cava
Right atrium
Tricuspid valve
Semi-lunar valve
From the picture above we can tell that the right ventricular wall is thinner than the left ventricular wall. The reason for this is due to how the heart works and how it circulates blood and to where (see introduction section on page 1). We can compare this picture to the one below, where the left ventricular wall is obviously thicker.
Left side of the heart:
Aorta
Pulmonary vein (cut)
Left atrium
Bicuspid valve
Tendons
Papillary muscles
Left ventricle (thick)
Superior view of heart:
Right atrium
Vena cava
Pulmonary vein
Cardiac skeleton
Aorta
Left atrium
Pulmonary artery
Conclusion:
The dissection was a relative success, all the chambers, vessels and valves were identified. After intense analysis of the interior of the heart , the heart has two sides, the right side of the heart received deoxygenated blood via the vena cava from the superior and inferior sides of the body. This deoxygenated blood travels through the vena cava into the right atrium, down the tricuspid valve into the right ventricle. When the ventricles contract the deoxygenated blood in the right ventricle is pumped through the pulmonary artery passing the semi-lunar valve. This deoxygenated blood then travels to the capillaries of the lungs where they exchange waste products such as carbon dioxide for oxygen. The blood is not oxygen-rich therefore oxygenated. The oxygenated blood then travels from the capillaries of the lungs to the pulmonary vein which leads to the left atrium of the heart, once the oxygenated blood is in the left atrium it is pushed (atrium systole) through the bicuspid valves into the left ventricle when it is then further pumped (ventricular systole) though the aortic semi-lunar valves into the aorta where it is distributed to the rest of the body where oxygen is required.
A lab and gloves was worn to prevent biological contamination, after the dissection the gloves were put into biological waste bins and hands were washed with antibacterial after taking off the labcoats.
Evaluation:
More dissection practice would bring more accurate results, although I have dissected a sheep’s heart more than a few times. Different sizes of hearts would have portrayed the different sizes of valves and vessels; it would bring more attention to how the heart evolves. As this practical involved sharing a single sheep’s heart between three students, room for error was encountered. Different cuts and incisions wanted to be made, however the results came out accurate.
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