Cardiovascular System Test Prep - Test Prep 1. Describe the...

Test Prep
1. Describe the key components of the intrinsic conduction system of the heart and what
role they have in generating the events of the cardiac cycle. Use a typical
electrocardiographic waveform to diagram the activity of the intrinsic conduction system
and where you think the specific events of the cardiac cycle are occurring.
Atrial
depolarization
P
QRS Complex
R
Q
S
Ventricular
depolarization
T
Ventricular
depolarization

The P wave signals the depolarization of the atria before they contract. Therefore, during this
event blood flows passively from the atria into the ventricles. The semilunar valves are closed
and the AV valves are open. After the P wave signal, the atria contract and force the blood to
the ventricle. This is known as mid-to-late diastole.
The QRS complex shows the depolarization of the ventricles. It precedes the contraction of the
ventricles. After the depolarization, the ventricles begin to contract, causing pressure inside to
increase rapidly. As a result, the AV valves are closed and the semilunar valves are open. During
that time, the atria are relaxed causing their chambers to be refilled with blood. This is called
ventricular systole .
The T wave shows the flow of current as the ventricles repolarize. The ventricles relax; the
semilunar valves are closed; the ventricles are completely closed for a while. This is called early
diastole . During this phase, the intraventricular pressure drops. When this pressure is lower
than the pressure in the atria, the AV valves are forced open, causing blood to refill the
ventricles, completing the cycle.