The aim of this practical is to dissect accurately a fresh pigs heart, observe it and give the result of drawing and labeling the external and internal structures of this heart.
In mammal body, heart is a muscle organ that functions in controlling blood circulation. According to American Heart Association (???), it locates slightly left of the breastbone in human body and weights approximately one pound. Heart functions in circulating blood throughout the body by contraction and relaxation. The pumping blood takes away wastes from body and gets refreshed by lung with oxygen (American Heart Association, ???). During this process, a healthy heart beats around 70 per minutes and pumps about 4.7 liters of blood every minutes, or 1800 gallons every day (American Heart Association, ???).
Human, like other mammals, has a heart with four chambers that as rooms pump and receive blood. The muscle of the heart is called myocardium, which is mostly located in the chambers (Lane, 2010) .Losos, Mason and Singer (2008) introduced that two separated atria are the upper ones while two separated ventricles located at the bottom. They also stated that the right atrium (which is on the left side towards you) receives the deoxygenated blood from the body throughout superior vena cava (will be introduced later). The other atrium, left atrium, has the similar functional that collecting blood. Cherry and Fenton (2007) stated that oxygenated blood by lung enters this chamber through pulmonary vein. The ventricles at the bottom contracts to pump the waste-rich or the deoxygenated blood to the lung and to the rest of the body (Losos, Mason and Singer, 2008). Furthermore, Cherry and Fenton (2007) suggested, once the ventricles are filled by blood from upper chambers, they begin to contract, producing pressure that allow the blood to flow into vessels and out of the heart. Right ventricle pumps to the lung through pulmonary artery and left one pump the blood delivered from the left atrium to the body through aorta (Losos, Mason and Singer, 2008). According to Cherry and Fenton (2007), the contraction and relaxation of the two lower ventricles is caused by electrical activation.
The oxygenated and deoxygenated blood is carried by several vessels connecting to the heart: aorta, pulmonary artery, pulmonary veins, inferior vena cava and superior vena cava. Artery and vena connecting to the heart play different role in controlling blood. According to Losos, Mason and Singer (2008), the two vessels at top, pulmonary arteries, are linked to the right ventricle and has branches vessels that towards right and left. The linkage is responsible for the delivery of oxygen-depleted blood proceeding to the lung where carbon dioxide and oxygen will exchange. Another artery is the aorta which is the largest vessel (Cherry and Fenton, 2007). As Cherry and Fenton (2007) said, it is the centre combining body and the heart, and conveyed the oxygen-rich blood from left ventricle under great pressure. The two arteries are located at the top of a heart. In addition, veins are the vessels that collect the blood back from either the lung or the body. Farr (2002) suggested the superior and the interior vena cava are the largest veins in the heart that carry deoxygenated blood from the body, entering the right atrium. The superior is near the top and the interior is a little beneath the superior. Pulmonary vein, locating at top side, is the only vessel that transfer oxygenated blood and back to left atrium (Cherry and Fenton, 2007). These vessels are the entrances to the heart for blood flowing.
In heart’s circle, valves are used to prevent blood from flowing back and ensure the correct direction. According to Cardiovascular Consultants (2006), there is a one-way valve called tricuspid valve. It separates right atrium from right ventricle. When right is filled with blood from body, the valve opens to allow the blood into right ventricle. It closes to avoid flow-back to right atrium when the ventricle contracts. After this contraction, the pumping of blood to pulmonary artery ensues via another valve called pulmonary valve and located within the artery (Cardiovascular Consultants, 2006). Similarly, the one-way valve attached to left ventricle’s wall and exists between left atrium and left ventricle is called mitral valve or bicuspid, preventing blood backwards to left atrium when left ventricle pumps (Farr, 2002). He also said aortic valve is the valve which controls blood in the aorta. In addition, it is reported (Cardiovascular Consultants, 2006) that, a tissue called chordae tendineae connects to the papillary muscle, linking to tricuspid valve and mitral valve to control the valves open and close.
Method and Observation
These materials were provided:
Fresh pig heart
Container for heart
External structure examination
1. A pig heart was placed in a dissecting pan.
2. The heart was placed in the position that front side was toward people, the major blood vessels were on the top and a tip called apex was down. The front side was recognized by a groove that extended diagonally.
3. Four Chambers: left atrium, left ventricle, right atrium and right ventricle were located in the heart. These blood vessels were located as well: coronary artery, pulmonary artery, and aorta, pulmonary veins and interior and superior vena cava. Figure 1 is the hand draw diagram of front heart.
4. The heart was turned around. Figure 2 the is the hand draw diagram of back heart.
The side of pulmonary artery was cut continually down to the wall of right ventricle, using scissors. The cutting line was parallel to the groove.
The dried blood inside the internal structure was rinsed out. Using my fingers, these internal structures were examined and located: right atrium, the place where interior and superior vena cava enters this chamber, pulmonary artery, the valve between them was located and noticed whether a tissue called chordae tendinae and papillary muscle existed. Figure 3 is the hand draw diagram of left side heart.
3. The thickness of the right ventricle and its smooth lining were felt by fingers.
Using scissors, the left atrium downward into left ventricle was cut and continued to the apex. The dried blood was rinsed out again.
In left chamber structures, left atrium, pulmonary veins, semi-lunar valves, bicuspid and left ventricle were examined. The thickness of ventricular wall was noticed. And the thickness of left ventricle is greater than others
Finally left ventricle was cut across toward the aorta to examine the valves further. Figure 4 is the hand draw diagram of right side heart.
During the heart dissection and examination, there were several errors leading missing some structures. While observing the external structure, the material on the left top which had a ‘cap’ shape was wrongly recognized as one of the vena cava vessel, as it had an entrance towards internal structure. After research, it is probably the right atrium. Although the pulmonary artery was recognized exactly, the pulmonary valve was not found in the expected position. This might be caused by the cutting of pulmonary artery so that the valve was likely to be destroyed. Alternatively, the valve may not exist originally or already be cut in advanced. The same problem or mistake existed in the location of aortic valve with similar reasons.
To avoid this sort of problems, any steps of dissection should be cautiously handled. Before cutting, it is necessary to familial with the structure of the place which is to be cut, preventing getting rid of the key structure.
In conclusion, mammal’s heart has similar structure that contains four chambers to collect and pump blood for gas and nutrition exchange. The deoxygenated blood from the body returns through interior and superior vena cava to right atrium and then to the right ventricle by allowance of tricuspid valve. The right ventricle contracts to pump the blood, which then flow back through pulmonary vein, to the lung. Through aorta, the oxygenated blood is conveyed to the rest of the body from the heart.