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Part 39: The Cardiac Cycle part A


About what percentage of blood passes into the ventricles before the atrial walls contract?

About 70%

What is the period during which a heart chamber is contracting called?


What is the period during which a heart chamber is relaxing called?


When are the AV valves (tricuspid and mitral valves) closed?

During ventricular contraction

When are the AV valves open?

During ventricular relaxation

When do the pulmonary and arotic valves open?

When the pressure in the ventricles exceeds the pressure in the pulmonary trunk and aorta.

What causes heart sounds?

Vibrations in heart tissues created by changes in blood flow.

When does the first sound of a cardiac cycle occur?

When the AV valves are closing.

When does the 2nd sound of a cardiac cycle occur?

When the semilunar valves are closing.

What is the sound called when blood leaks back through an incompletely closed valve?

A Murmer

Part 39: The Cardiac Cycle part C


What are the fibers of the cardiac conduction system called?

Specialized Cardiac Muscle Tissue

Under normal circumstances, what serves are the pacemaker of the heart?

The SA node (Sinoatrial node)

Where is the AV (atrio ventricular) node located?

in the inferior portion of the interatrial septum

What do the large fibers on the distal side of the AV node makeup?

The AV bundle

What are the fibers that carry cardiac impulses from the interventricular septum into the myocardium called?

Purkinje fibers

What is a recording of electrical changes occuring in the myocardium during the cardic cycle called?

An electrocardiogram

Between cardiac cycles, cardiac muscle fibers remain __?__ with no detectable electrical changes.


What wave corresponds to depolarization of the muscle fibers of the atria?

The P wave

The QRS complex corresponds to de-polarization of the muscle fibers in the__?__.


The T wave corresponds to repolarization of the muscle fibers in the ___?___.


Why is atrial repolarization not observed in an ECG?

Atrial repolarization occurs at the same time as ventricular depolarization. The QRS complex hides atrial repolarization.

What is a rapid heart beat called?


What is a slow heart beat called?


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