MEDICAL
HEART AND PERICARDIUM
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Atria relaxes because the AV node fired a signal
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Atria contracts because the AV node fired a signal
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Atria contracts because the SA node fired a signal
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Atria relaxes because the SA node fired a signal
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Detailed explanation-1: -The P wave occurs when both left and right atria are full of blood and the SA node fires. The signal causes both atria to contract and pump blood to the ventricles (lower chambers).
Detailed explanation-2: -The first wave (p wave) represents atrial depolarisation. When the valves between the atria and ventricles open, 70% of the blood in the atria falls through with the aid of gravity, but mainly due to suction caused by the ventricles as they expand.
Detailed explanation-3: -The P wave indicates atrial depolarization. The P wave occurs when the sinus node, also known as the sinoatrial node, creates an action potential that depolarizes the atria. The P wave should be upright in lead II if the action potential is originating from the SA node.
Detailed explanation-4: -If the sinoatrial node fails, in a normal heart, the atrioventricular node (AV node) should take over the pacemaker function. But the spontaneous rate of the atrioventricular node is lower than that of the sinoatrial node. Hence the heart rate will be lower.