The heart

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Basic heart structure and features

The heart consists of 4 chambers: Right atrium, left atrium, right ventricle and left ventricle. The right side of the heart pumps deoxygenated blood to the lungs through the pulmonary artery. The left side pumps oxygenated blood into the aorta. The left ventricle wall is much thicker than the wall of the right ventricle. This is because a high pressure is needed so it can contract to force blood into the aorta, hence the function of the left side. Coronary arteries are over the heart surface and carry oxygenated blood to the actual heart muscle. The septum separates the ventricles (and your nostrils :D) from each other. Tendinous cords attach valves to the walls of the ventricles and prevent them turning inside out which would allow blood to flow up into the atria. Semilunar valves at the base of the major arteries prevent blood returning to the heart when the ventricles relax.

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Cardiac cycle

The heart is made up of cardiac muscle which is myogenic (starts its own contraction). It has a natural pacemaker located in the wall of the right atrium (the SAN). It's function is to send out electrical impulses to start each heartbeat ). They spread out across the atrial muscle which is the first to contract. There is a disc of tissue between the atria and ventricles that prevents impulses directly reaching the ventricles. Instead, the impulse gets to the atrioventricular node which is located between the atria and ventricles. This is there to prevent the ventricles from contracting too soon by providing a short delay. It sends impulses along special fast conducting muscle cells in the septum called Purkyne tissue to the apex (base)of the heart. This muscle contracts to push blood up to the arteries.

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The ECG

This records electrical activity of the heart and are used when a heart problem is suspected. 

The QRS wave is caused by contraction of the ventricles. The T wave is caused by relaxation of the ventricles. The P wave is caused by excitation of the atria.

Heart attack= Elevation of ST section

Atrial fibrillation= small/hard to make out P wave

Abnormal ventricular hypertrophy= Deep S wave

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Calculations

Stroke volume= volume of blood pumped in one beat

Cardiac output= heart rate x stroke volume

Heart rate= number of beats per minute

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