Practice-Heart Part 3 Lecture

According to the Frank-Starling law, a bigger preload will result in __________.

A bigger preload means increased stretch of the ventricular muscle cells and therefore, a stronger contraction.

Increased pressure in the ventricles would close what valve(s)?

AV valves only

Which of the following happens immediately after the P wave?

After the atrial depolarization (P wave), the atria contract, allowing them to empty and causing the ventricles to reach their EDV.

The maximum amount of blood in the ventricles at the end of the ventricular filling phase is called __________.

At the end of atrial systole, each ventricle contains about 120 milliliters of blood, a volume known as the end-diastolic volume (EDV) because it is the ventricular volume at the end of ventricular diastole.

The AV valves close when __________.

During the isovolumetric contraction phase, the pressure in the ventricles rises rapidly as the ventricles begin to contract. This high pressure closes the AV valves.

Ventricular systole begins during the __________ phase of the cardiac cycle.

During the isovolumetric contraction phase, ventricular systole and atrial diastole begin and the AV valves close.

isovolumetric relaxation phase.

During the next phase, the ventricular filling phase, the ventricles are in diastole and atrial systole occurs.

The ventricular ejection phase of the cardiac cycle is labeled __________.

During the ventricular ejection phase, the semilunar valves open and blood is ejected into the aorta and the pulmonary artery. The volume in the ventricles decreases from the end-diastolic volume to the end-systolic volume.

Which of the following can be heard with a stethoscope most easily?

Heart sounds are an extremely helpful diagnostic tool that is not invasive. The first heart sound, often described as a lubb, corresponds to the closing of the atrioventricular valves. The second heart sound is a sharper and crisper dupp that corresponds to the closing of the semilunar valves. Consequently, the two heart sounds mark the beginning and the end of ventricular systole.

Digoxin is a positive inotropic agent derived from the foxglove family of plants. Which of the following is an effect of digoxin?

Increased contractility and SV would lead to a decrease in the ESV.

An increase in sympathetic stimulation of the heart would increase stroke volume by increasing __________.

Increased sympathetic activity increases heart contractility. This causes cardiac fibers to contract more forcefully at all levels of preload. Regardless of end diastolic volume, this mechanism increases stroke volume by reducing end systolic volume.

The beginning of the QRS complex of the electrocardiogram (ECG) immediately precedes which of the following events?

The QRS complex is a recording of ventricular depolarization. This depolarization begins just prior to the ventricular contraction it initiates. As the ventricles contract, the increase in ventricular pressure closes the atrioventricular valves, beginning isovolumetric contraction. As ventricular pressure increases above the corresponding blood vessel, only then do the semilunar valves open, initiating ventricular ejection.

How will the cardiac output change if you double the heart rate but reduce the stroke volume by one-half?

The cardiac output will remain the same, because CO = HR × SV = 2HR × SV/2.

The chambers that have just emptied when the second heart sound is heard are the __________.

The second heart sound is caused by the closing of the semilunar valves, which happens shortly after ventricular systole is over.

The main negative chronotropic effect on the heart is exerted by __________.

The vagus nerve's effect on the SA node slows down heart rate.

How would a decrease in blood volume affect both stroke volume and cardiac output?

a decreased blood volume would decrease the end diastolic volume, thus lowering the stroke volume. Although this would initially lead to a decrease in the cardiac output, heart rate would increase because of increased activity of the sympathetic nervous system in an effort to maintain cardiac output.

How would an increase in the sympathetic nervous system increase stroke volume?

an increase in sympathetic nervous system activity would increase contractility (by increasing available calcium), thus increasing stroke volume. Contractility causes an increase in stroke volume by decreasing end systolic volume; it does not change end diastolic volume

By what mechanism would an increase in venous return increase stroke volume?

an increase in venous return increases the end diastolic volume. The fibers are stretched more, resulting in an increase in the force of contraction (preload, or the Frank-Starling Mechanism).

Isovolumetric relaxation and ventricular filling (two phases of the cardiac cycle) take place during __________.

both occur during ventricular diastole when the ventricles are not actively contracting and ejecting blood.

Hemorrhage would lead to a __________ preload and therefore __________ cardiac output.

decreased; decreased Blood loss will diminish the venous return and therefore decrease the preload. A decreased preload would cause a decrease in the stroke volume and therefore a decrease in the CO.

What causes the aortic semilunar valve to close?

greater pressure in the aorta than in the left ventricle backflow of blood in the aorta (towards the left ventricle) closes the aortic semilunar valve.

Describe the pressures in the atria and ventricles that would cause the opening of the AV valves.

higher pressure in the atria than in the ventricles forces the AV valves to open and blood moves into the ventricles.

Which of the following would increase cardiac output to the greatest extent?

increased heart rate and increased stroke volume

Put the phases of the cardiac cycle in the correct order, starting after ventricular filling.

isovolumetric contraction, ventricular ejection, isovolumetric relaxation

Which of the following is correct about the filling of the ventricles?

most of the ventricular filling is passive; atrial contraction adds just a little more blood.

As part of a blood drive on campus for the American Red Cross, you and your friends have just donated 500 mlml of blood. You are now relaxing at the student lounge, waiting for A&P lab to begin. Unfortunately, even though you are thirsty, you haven't bothered to buy yourself a drink. Other than a little soreness of the skin and tissue around your median cubital vein, you feel fine. How has your 500 mlml decrease in blood volume most likely affected your cardiac output, heart rate, and stroke volume?

no change in cardiac output, increased heart rate, decreased stroke volume Donating blood does not alter resting cardiac output. However, the decreased blood volume does decrease venous return and end diastolic volume. This decreases preload, thereby lowering stroke volume. By itself, decreased stroke volume would decrease cardiac output. But remember, the body still requires a resting blood flow of around 5 L/minL/min. To meet this demand, homeostatic mechanisms quickly restore cardiac output to resting levels. For example, heart rate is increased as parasympathetic influence is removed and sympathetic activity is increased. Even though your blood volume is a bit low, your body has no problem compensating to meet your resting metabolic needs. Running away from a tiger? Now that might be a different story

Which of the following would increase heart rate?

secreted by the adrenal medulla as a result of sympathetic stimulation, these hormones act as part of the sympathetic response, increasing heart rate.

Heart rate (HR):

the number of heart beats per minute

The aortic valve closes when __________.

the pressure in the left ventricle falls below aortic pressure

The aortic valve opens at __________.

the pressure in the ventricle rises above aortic pressure.

End systolic volume (ESV):

the volume of blood in one ventricle after contraction

End diastolic volume (EDV):

the volume of blood in one ventricle before contraction

Stroke volume (SV):

the volume of blood per heart beat pumped out by one ventricle

Venous return (VR):

the volume of blood per minute flowing into one atrium

Cardiac output (CO):

the volume of blood per minute pumped out by one ventricle