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how does heart function?
The heart is one of the most important organs in the entire human body. It is really nothing more than a pump, composed of muscle which pumps blood throughout the body, beating approximately 72 times per minute of our lives. The heart pumps the blood, which carries all the vital materials which help our bodies function and removes the waste products that we do not need.
The role of the heart is to pump oxygen-rich blood to every living cell in the body.In order for the heart to deliver oxygenated blood to all cells, blood is pumped through arteries. Veins bring deoxygenated blood cells to the lungs, which then are oxygenated, and then sent back to heart. In this way, a continuous cycle is formed of the heart pumping oxygenated blood and deoxygenated blood out to their designated destinations, and therefore the heart maintains the circulatory system.The pumping of the heart is called the Cardiac Cycle, which occurs about 72 times per minute. This means that each cycle lasts about eight-tenths of a second. During this cycle the entire heart actually rests for about four-tenths of a second.
The walls of the heart are made up of three layers, while the cavity is divided into four parts. There are two upper chambers, called the right and left atria, and two lower chambers, called the right and left ventricles. The Right Atrium, as it is called, receives blood from the upper and lower body through the superior vena cava and the inferior vena cava, respectively, and from the heart muscle itself through the coronary sinus. The right atrium is the larger of the two atria, having very thin walls. The right atrium opens into the right ventricle through the right atrioventicular valve(tricuspid), which only allows the blood to flow from the atria into the ventricle, but not in the reverse direction. The right ventricle pumps the blood to the lungs to be reoxygenated. The left atrium receives blood from the lungs via the four pulmonary veins. It is smaller than the right atrium, but has thicker walls. The valve between the left atrium and the left ventricle, the left atrioventicular valve(bicuspid), is smaller than the tricuspid. It opens into the left ventricle and again is a one way valve. The left ventricle pumps the blood throughout the body. It is the Aorta, the largest artery in the body, which originates from the left ventricle.
 The heartbeat is made up of systole and diastole, which are the two stages of a heartbeat.The heartbeat is made up of systole and diastole, which are the two stages of a heartbeat.
Systole: Stage when the ventricles of heart are contracting resulting in blood being pumped out to the lungs and the rest of the body. Thick, muscular walls of both ventricles contract.
    Pressure rises in both ventricles, causing the bicuspid and tricuspid valves to close. Therefore, blood is forced up the aorta and the pulmonary artery.
    The atria relax during this time. The left atrium receives blood from the pulmonary vein, and the right atrium from the vena cava.
Diastole: Stage when the ventricles of the heart are relaxed and not contracting. During this stage, the atria are filled with blood and pump blood into the ventricles.Thick, muscular walls of both ventricles relax.
    Pressure in both ventricles falls low enough for bicuspid valves to open.
    The atria contract, and blood is forced into the ventricles, expanding them.
    The blood pressure in the aorta is decreased, therefore the semi-lunar valves close.


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