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Example Questions
Example Question #11 : Circulatory System
Which of the following causes the S1 heart sound (lub)?
The opening of the tricuspid and mitral (AV) valves
The closing of the tricuspid and mitral (AV) valves
The opening of the aortic and pulmonary valves
The closing of the aortic and pulmonary valves
The closing of the tricuspid and mitral (AV) valves
The S1 heart sound (sometimes referred to as "lub") is caused by the sudden snapping-shut of the tricuspid and mitral valves during systole, when the heart contracts and tension on the chordae tendinae is released. No sound is produced on the opening of these or any other valves in the heart.
Example Question #12 : Circulatory System
The contraction rate is set in what area of the heart?
The sinoatrial node
The Purkinje fibers
The atrioventricular node
The bundle of His
The sinoatrial node
The contraction rate for the heart is set by the cells of the sinoatrial node, also known as the pacemaker cells of the heart. These cells have membranes that are especially permeable to ions, and are able to depolarize on their own at a rate of 70-100 beats per minute. All the other areas listed do have their own spontaneous contractility, but their rates are slower than that of the sinoatrial node. Thus, the sinoatrial node is the pacemaker in a healthy heart.
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