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Cardiac Cycle

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Cardiac Cycle Organisms require a transport system for several reasons. As the organism gets larger, so the transport system becomes more complex in order to fulfil its requirements. The surface area to volume ratio becomes smaller to the point where a long-distance transport system is required in order to move substances more rapidly. These systems have two primary functions: to link the interior of the organism with the outside world and to link each cell and organ of the organism to each other. Humans are fairly large mammals and so they naturally have a more intricate transport system. The type of system in a human is known as a closed vascular circulatory system. ...read more.


The purpose of the systole is to squeeze the last few drops of blood from the atrium into the ventricle. Then at 0.15 seconds the atria goes into diastole (relax) and the ventricles begin systole so the ventricular pressure increases. Like the atria, when the ventricles contract they also create an electrical potential but this time a relatively large current is recorded on the ECG. This increase is very rapid because a great pressure is required to pump the blood to its destinations. Immediately the pressure in the ventricle exceeds the low pressure in the atrium and so the valve between the two (atrio ventricular valve) is forced shut. When the valve closes a heart sound can be recorded from the vibrations made by the closing of the valve. ...read more.


The transfer of blood through the heart is directed by the heart valves, the opening and closing of which in turn is controlled by the adjustments in blood pressure that happen within the chambers of the heart. Blood flows from an area of high pressure, to an area of low pressure. During the diastole phase the atria and ventricles are relaxed and the atrioventricular valves are open. De-oxygenated blood from the superior and inferior vena cava flows into the right atrium. The open atrioventricular valves allow blood to pass through to the ventricles. The Sinoatrial Node (referred to as the pacemaker of the heart.) contracts triggering the atria to contract. The right atrium empties its contents into the right ventricle. The tricuspid valve prevents the blood from flowing back into the right atrium. ...read more.

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