The heart is one of the most important parts of the body. It is responsible for pumping of blood to other parts of the body.
The mammalian heart has four chambers, and the type of blood circulation is double loop circulation. There are two ventricles and two atria, which are completely separated. In the double loop blood circulation, oxygen-poor blood does not get into contact with oxygen-rich blood. Oxygenated blood is handled by the left side of the heart while the right-hand side of the heart receives and pumps deoxygenated blood to the lungs.
Double circulation ensures that there is no mixing of blood, maintains blood pressure, and ensures that delivery of oxygen throughout the body is enhanced for cellular respiration. Mammals require a lot of oxygen as opposed to other vertebrates, since being endotherms; they need to keep the body warm from heat released by metabolic processes.
We undertook a procedure of dissection in order to identify various parts of the heart. We also took several pictures as we moved on with the procedure. We used fresh pig’s heart.
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Objective of the dissection
The objective of this dissection is to be able to observe and identify parts of the heart. These include blood vessels, major chambers, and valves. We also aim to describe how blood, both oxygenated and deoxygenated, flows in and out of the heart. We will also explain functions of various parts of the heart.
First, we had to separate the heart from the rest of the body. After placing the heart on the dissecting pan, we were able to locate thin membrane covering the heart. This thin membrane is referred to as the pericardium or pericardial sac. The pericardium is double-layered and is responsible for anchoring the heart. It has two tissue layers, the visceral pericardium and the parietal pericardium. The parietal pericardium covers the parietal sac on the inside, while the visceral pericardium covers the heart’s surface. However, the two tissues are continuous with each other, especially at the entry points and exit points of the blood vessels. The pericardial cavity is found where there is a gap between the parietal pericardium and visceral pericardium. The pericardial cavity is filled with a fluid, the function of which is to reduce friction between the layers. This is the friction that would be experienced as the heart pumps.
Directly below the pericardium there is the heart’s muscle. This muscle is known as the myocardium. Due to the heavy work of the ventricles, most of the myocardium is found in the lower chambers of the heart. These chambers are known as the ventricles. The upper chambers of the heart do not have very thick myocardium.
The heart was covered by fat tissue, but nonetheless it was not very difficult to find out how the heart is oriented. Several features helped us distinguish the front and the back of the heart. First, extending to the top of the heart is the large pulmonary trunk. The pulmonary trunk enters the heart at an angle. Secondly, the top of the atria is covered by flaps of the auricles. Finally, we were able to distinguish the front from the back since the back is more flat. The front side is entirely curved.
With our fingers we were able to feel the top of the heart and locate several blood vessels. These include the aorta, pulmonary trunk, superior vena cava, and the pulmonary vein. The aorta is located behind the pulmonary artery, near the right atria. It is curved to form the aortic arch. The function of the aorta is to supply blood to the upper body. The pulmonary artery branches from the right ventricle. Its function is to carry blood to the lungs, where it will be oxygenated. The pulmonary vein returns blood from the lungs to the heart, specifically to the right atrium. The superior vena cava carries deoxygenated blood from the upper part of the body back to the heart.
After locating all the major vessels, we then proceeded to cut through the heart down the wall of the right ventricle, and push open at the cut so as to view various chambers as well as valves.
We were able to locate the right atrium, which is a receiving chamber. It has noticeably thin muscular walls. The right atrium receives deoxygenated blood from the body via the superior vena cava and inferior vena cava. Through the tricuspid valve it then pushes blood to the right ventricle. The tricuspid valve has three leaflets. It also has long fibres of connective tissue, called chordae tendinae. The right ventricle is just below the right atrium. Its function is to force deoxygenated blood to the lungs, through the pulmonary artery, via the pulmonary valve. When the ventricles contract, pressure in the right ventricle forces the tricuspid valve to close.
We were also able to feel the inner part of the right ventricle. It had smooth lining and thick muscular wall. On the inner wall, there is also a network of muscular cords that are irregular. The right ventricle on its right side has a thick muscular wall called septum. This wall separates the left and the right ventricle.
We also cut the heart from the left atrium down to the left ventricle and pushed it open to reveal the inner parts. Only the left ventricle extends to the apex of the heart. Between the left atrium and the left ventricle we noticed the mitral (bicuspid) valve. This valve controls the flow of blood to the left atrium and left ventricle.
The left atrium collects oxygenated blood from the lungs. The blood is supplied by the pulmonary vein. As the left atrium contracts, blood is forced through the mitral valve into the left ventricle. The left ventricle has a function of pumping oxygenated blood throughout the body. On closely examining the left ventricle we found out that just like the right ventricle, it has a network of muscular cords. However, its wall is thicker than that of the right ventricle. This is because it has more work of pumping blood for a longer distance as opposed to the right ventricle which pumps blood only to the lungs.
We also cut the left ventricle towards the aorta to reveal the aortic valve. The valve is made up of three flaps. These flaps are half-moon in shape. As the ventricles contract, the valve opens to allow blood to flow into the aorta, from where it is supplied to the rest of the body. As the ventricles relax, the aortic valve closes to prevent blood from flowing back into the heart.
On the wall of the aorta we noticed a hole (called coronary sinus) which leads to the important vessel called the coronary artery. The coronary artery is responsible for supplying blood to the heart muscles. This is because heart muscles need to be constantly nourished with oxygen.
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