The heart is a muscular pump that supports the entire cardiovascular system. It is constantly beating, starting from a few weeks after conception, all the way through life. Although mechanically easy to explain, the heart is controlled by a complex intrinsic bioelectrical circuitry and it is also influenced by the nervous and hormonal systems of the body.
Fig 1.1 Normal Heart. The chambers of the heart and connecting blood vessels are labeled.
The heart is made up of 4 chambers: Two upper "receiving" chambers - the right atrium (RA) and the left atrium (LA), and two lower muscular, "pumping" chambers - the right ventricle (RV) and the left ventricle (LV).
The right atrium is connected to the right ventricle via the tricuspid valve (TV), while the left atrium is connected to the left ventricle via the mitral valve (MV).
The right atrium receives two veins - the superior vena cava (SVC) and the inferior vena cava (IVC).
The left atrium, on the other hand, receives four veins - the four pulmonary veins (Pulm veins).
The right ventricle gives rise to the pulmonary artery (PA) - this is the artery leading to the lungs. The pulmonary valve (PV) guards the entrance of the pulmonary artery.
The left ventricle gives rise to the aorta (Ao) - this is the largest artery in the body and it supplies blood to all parts of the body except the lungs. The aorta is guarded by the aortic valve (AV).
Essentially, the heart works as two pumps connected in series:
Let's follow the course the blood flow through the heart (Fig 1.2 & 1.3). We shall look at the right pump first.
Fig 1.2 Blood flow through the heart.
Fig 1.3 Blood flow through the heart.
Blue blood (deoxygenated blood - blood low in oxygen) flows from the body via the upper and lower body veins (SVC and IVC) to the right upper receiving chamber of the heart (the right atrium, RA). The blood then crosses the tricuspid valve (TV) into the right lower pumping chamber (the right ventricle, RV), which then pumps the blood across the pulmonary valve (PV) into the lung artery (pulmonary artery, PA) which leads to the lungs.
In the lungs, gaseous exchange occurs. Oxygen diffuses into the blood and carbon dioxide diffuses out of the blood. The blood becomes red (oxygenated blood - blood high in oxygen content).
The red blood from the lungs returns to the left upper receiving chamber of the heart (left atrium, LA) via the four pulmonary veins (Pulm Veins). From here, the blood crosses the mitral valve (MV) into the left lower pumping chamber (the left ventricle, LV). The left ventricle then pumps the blood across the aortic valve (AV) into the aorta (Ao), which then carries the red blood to all parts of the body except the lungs.
The heart and circulatory system can also be depicted diagrammatically as in figure 1.4.
Note that in the normal heart, there are no holes or connections between the left and right pump systems. Thus, the blue blood and red blood do not mix.
Fig 1.4 The heart and the circulatory system. Blue arrows indicate the path of deoxygenated blood, red arrows indicate the path of oxygenated blood.
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