The Workings and Structure of the Heart


Introduction


For homeostasis to remain balanced throughout the body millions of respiring cells need to discard carbon dioxide and waste products and also replenish with oxygen and nutrients. For this transaction to occur a complex transportation network called the cardiovascular system initiates. The cardiovascular system consists of the heart, arteries and veins.


The heart is a double pumping organ which is the driving force of the cardiovascular system, although only weighing approximately three hundred grams the heart is powerful enough to beat over seventy times a minute pumping blood around the body. The heart is located on the left hand side of the diaphragm lying within the mediastinum in the thoracic cavity. Resembling a pyramid on an oblique angle the heart is hollow and composed of three layers, myocardium, endocardium and pericardium. Myocardium formulates the majority of the heart; this is composed of specialised cardiac muscle occurring only in the heart. Endocardium is a smooth delicate membrane, which lines the interior surface of the heart chambers and valves, and the pericardium; which is a connective tissue, this acts as a protective barrier, the fibrous pericardium fuses with arteries which pass through it to form attachments which help to anchor the heart to its surrounding structures The interior of the heart is divided into two sides the right and left, nearly mirror image of each other a few differences can be recorded (see conclusion).


Figure 1


As figure 1 shows there is a complex network of arteries and veins which branch into the heart. It is through these arteries and veins that blood is transported throughout the body. The arteries carry oxygenated blood from the heart to tissues and cells throughout the body whereas the veins carry deoxygenated blood received to the heart.


As the heart is attached only by soft tissue it can change position in the diaphragm while it contracts and relaxes (diastole and systole) as in figure 2 and 3.



Figure 2 Figure 3


For a better understanding of the structure and workings of the heart a heart dissection was performed, below are the conclusions gathered from the experiment.


Conclusions



o Distinguish between the dorsal and ventral sides of the heart. (The ventral side is more rounded than the dorsal side, and the thick walled arteries arise from this side).
Note:


The right and left atria (auricles) and right and left ventricles,


Pulmonary artery and aorta arising from right and left ventricles,


Anterior and posterior vena cava opening into right atrium,


Coronary vessels in the heart wall,


Ø Figure 4 shows the ventral side of the heart clearly showing the pulmonary artery and aorta, the left and right atria and ventricles and the coronary vessels of the heart wall.


Figure 4



o Clamp posterior vena cava, then run water through anterior vena cava, from the water runs through the pulmonary artery, this is the route of the pulmonary circulation which receives deoxygenated blood from the systemic circulation and transported to the lungs to be oxygenated.
Now run water through the pulmonary vein, which vessel does the water emerge?


Ø The water runs through the aorta, this is the route of the systemic circulation, the systemic circulation takes oxygenated blood away from the heart to oxygenise respiring cells throughout the body.


Figure 5


Ø Figure 5 shows the systemic circulation in red and the pulmonary circulation in blue.



o Expose the left ventricle by a longitudinal cut through ventral wall of the ventricle, note your findings. Through the cut in the left ventricle wall the following observations were recorded. (see figure 3)
Ø The left ventricular walls were visible, consisting of thick myocardium (cardiac muscle); the reason for the thickness of the left ventricle is because the left ventricle is responsible for the pumping of blood at high hydrostatic pressure throughout the systemic arterial system.


Ø The bicuspid valve, this valve is used to prevent backflow of blood from the left ventricle to the right atrium.


Ø Chordae tendinae, used to anchor the flaps of the bicuspid valve to the papillary muscle to prevent the valve turning inside out due to pressure.


Ø Papillary muscle, this is part of the myocardium of the ventricle and contains irregular shaped columns called trabeculane carnae.



o Turn the heart upside down and run water into the ventricle through the slit you have cut, note your findings.
Ø The water ran through