The cardiovascular system includes blood vessels and the heart. The heart pumps blood into the blood vessels, and they, in turn, circulate the blood throughout the body. This blood plays an important role in transporting oxygen and nutrients to the tissues and removes carbon dioxide and other waste products from the tissues.
The blood vessels of the circulatory system are the arteries, arterioles, aorta, capillaries, veins, venules, and venae cavae. The muscular heart and the blood vessels produce a series of sequential events that are vital for survival. Here, let’s look more at the function of the heart in our circulatory system.
Functioning of Heart
The human heart is a four-chambered muscular organ that mainly contributes to the pumping of blood all through the circulatory system. It is situated in between two lungs. The heart is made up of four chambers, two ventricles (right and left ventricles) and two atria (right and left atria). The musculature of heart ventricles is thicker than that of atria. Moreover, the force of contraction of the heart depends upon the muscles.
Most animals have a heart as a part of their circulatory system. But it widely differs from the structure and functioning of the human heart. The human circulatory system is a complex structure with a network of blood vessels, blood and heart. This circulatory system has two parts – systemic circulation and pulmonary circulation. Systemic circulation is also known as great circulation. Here, the blood is pumped from the left ventricle, and it passes through a series of blood vessels and finally reaches the tissue. The exchange of materials happens in the tissue, and then the blood enters the venous system (network of veins) and returns to the right atrium of the heart. From the right atrium, blood enters the right ventricle. In the pulmonary or lesser circulation, the blood is pumped from the right ventricles to the lungs through the pulmonary artery.
The ‘LUB’ and ‘DUB’ of the Heart
A sequence of events happens when the heart performs its function. The sequential event comprises the systole (contraction), diastole (relaxation) and the intervening pause. During the systole of each heartbeat, the heart undergoes contraction and pumps the blood via arteries. During diastole, the heart is relaxed, and thus the blood gets filled in the heart. These changes are repeated cyclically during every heartbeat.
Different sounds in the heart are created by mechanical activities that happen during each sequential or cyclic event. These sounds are produced due to –
- Blood flow through the cardiac chambers
- Contraction of cardiac muscles
- Closure of heart valves
Heart sounds can be heard by placing the ear directly over the chest or by using a microphone or stethoscope. These sounds can also be recorded graphically. The heart activities produce four different types of sounds during every cardiac cycle. These heart sounds are of clinical significance.
The first and second sounds are called classical heart sounds and are heard by using the stethoscope. These are the ‘LUB’ (or ‘LUBB’), and the ‘DUB’ (or ‘DUP’) sounds respectively. The third heart sound is a mild sound, and it is not heard by using a stethoscope under normal conditions. But it can be heard by using a microphone. The fourth sound is very inaudible. It becomes audible only under pathological conditions. This sound is studied only by graphic registration, like the phonocardiogram. The study of heart sounds has a significant diagnostic value in clinical practice. The variations in the heart sounds indicate cardiac diseases that involve the heart valves.
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