The cardiovascular system or circulatory system is a system which moves nutrients, gases and wastes between cells, helps fight diseases, and transports blood throughout the body (Circulatory System). The main components of the human cardiovascular system include the heart, blood, and various blood vessels. There are several different circuits contained in the cardiovascular system. One of these systems is the pulmonary circuit, which is a “loop”, in which oxygenated blood travels through the lungs (Circulatory System). The other circuit is the systemic circuit which transports the rest of the blood in a loop through the body. In the cardiovascular system within the heart, there is the cardiac cycle, which is the flow of blood between heartbeats. The cardiovascular system is essential to the human body for blood to be distributed properly.

The first major component of the cardiovascular system is the pulmonary circuit. The pulmonary circuit carries deoxygenated blood away from the heart and returns the blood in an oxygenated form (Pulmonary Circulation). In the heart, there are four chambers, the right and left atria, as well as the right and left ventricles. In pulmonary circulation deoxygenated blood starts in the right side of the heart. The blood is then pumped by the right ventricle of the heart as deoxygenated blood into the pulmonary artery, which is a blood vessel that’s function, is to carry blood away from the right ventricle. From the pulmonary artery, the blood is taken into the capillaries, which are small blood vessels that connect arteries and veins of the lungs (Pulmonary and Systemic Circulation). Upon the deoxygenated blood entering the lungs, oxygen binds to the red blood cells as carbon dioxide diffuses. Once the blood has become oxygenated it travels along the pulmonary vein into the left atrium of the heart. Upon entering the left atrium the blood joins the systemic circuit.

The systemic circuit is far larger than the pulmonary circuit and therefore is of far greater importance to the body (Pulmonary and Systemic Circulation). The main function of the systemic circuit is to carry blood to and away from all the tissues in the body. Due to the fact that this system is much larger, this causes the walls of the left ventricle to be far stronger than the right side of the heart. These thick muscles of the left side of the heart are essential for blood to be distributed throughout the various tissues in the body (Pulmonary and Systemic Circulation). In the systemic circuit oxygenated blood is transported from the left ventricle into the aorta, which is the largest artery in the body. The aorta branches downward to carry blood to the respective parts of the body. However, as blood is carried down the aorta, there are several smaller arteries which branch off the aorta to carry blood to their respective parts of the body. As blood exits the left ventricle, and begins to travel down the aorta, small arteries branch off of the aorta to carry blood to the upper torso as well as the brain. When blood travels to the brain, the arteries branch continuously, eventually becoming capillaries which reach every single cell within the brain. When capillaries reach each cell in the brain this allows for every cell in the body to have a supply of oxygen as well as a way of disposing of carbon dioxide. Once the carbon dioxide is disposed from the cells the blood becomes deoxygenated once again. This deoxygenated blood travels to the heart by going through the various veins of the body. These veins which are returning to the heart eventually all link together to form the Inferior and Superior Vena Cava, which are the two largest veins in the body. The Inferior and Superior Vena Cava pump the deoxygenated blood back into the right atrium, which starts the circulatory process all over again (Cardiovascular System-Basic Structure).

Another essential part of the cardiovascular system is the cardiac cycle. The cardiac cycle is measured on the basis of systole and diastole. Systole is the period in which the heart is busy pumping blood. Diastole is the period in which the heart is resting as well as filling up with blood. In the atria of the heart, systole is stimulated by “electric” nerve impulses, which is created by a section on the wall of the right atrium called the sinoatrial node, or (SA). This process is known as atrial systole. The SA is essential as it sets the tone of the beating of the heart, and is therefore referred to as a pacemaker. After atrial systole occurs, the electric impulse travels through the walls of the atria to the atrioventricular node, or (AV), which is located in the wall between the right atrium and right ventricle. After reaching the AV, the impulse signal is delayed 0.1 seconds in order to ensure that the atria of the heart have finished contracting. After this delay, the impulse travels through special fibres in the heart known as Purkinje fibres. Once the electrical impulse reaches the end of the Purkinje fibres, the impulse spreads through the original cardiac muscle, which then allows for ventricular systole to occur. Overall, the cardiac cycle takes about 0.8 seconds to complete. Around half of this time is spent between atrial and ventricular systole, and the other half is composed of atrial and ventricular diastole.

The second part of the cardiac cycle is also a major component of the cardiovascular system. This part of the cycle explains that the “lub-dup” heart sounds are caused by the closing of the valves in the heart during the cardiac cycle (Cardiac Cycle). The “lub” sounds is caused by the closing of the AV valves and the beginning of ventricular systole (Cardiac Cycle). The “dup” sound is caused by the closing of the pulmonary and aortic valves during ventricular diastole (Cardiac Cycle). These valves of the heart ensure that the blood flow in the heart is maintained at the same rate by opening and closing systematically. The cardiac cycle is one of the major components to the cardiovascular system.

The cardiovascular system has shown that it is one of the vital systems of the human body. It is truly amazing how the cardiovascular system is an intricate group of systems which combine together to form one larger system. The cardiovascular system is extremely complicated and the slightest malfunction can cause serious problems in the body. For example, in the heart if the valves are opening the wrong way, a person can have a heart murmur, which in some cases can prove to be fatal. These systems such as the systemic circuit, pulmonary circuit, and cardiac cycle must always be functioning at a very high rate. The cardiovascular system is a magnificent and exciting system to learn.

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