Cardiac Cycle and Regulation of Cardiac Output

During exercise, sympathetic input to the heart is increased. Stroke volume is often maintained, or even increased, even though heart rate is also increasing. How is this possible?

All answers are correct.

Abnormalities within the SA node can cause which of the following symptoms?

Bradycardia or tachycardia

Give the mechanistic explanation as to why tetanus does NOT occur in myocardial contractile cells?

Ca2+ entry depolarizes the cell and lengthens the refractory period, which prevents the summation of the tension developed from repeated action potentials

Which of the following is(are) the same for the left and right ventricles?

Cardiac output, heart rate, and stroke volume

Isovolumetric relaxation occurs after the blood has been ejected from the ventricle.

During isovolumetric relaxation the pressure in the ventricle is less than the pressure in the aorta. The second heart sound is heard at the very beginning of isovolumetric relaxation. During isovolumetric relaxation the heart is not undergoing any type of contraction.

Which of the following will increase the force of contraction of the ventricles?

Increasing end diastolic volume

Which of the following may increase heart rate?

Norepinephrine and epinephrine

Stroke volume is measured as the volume of blood in ml ejected by each ventricle per beat.

Stroke volume is dependent on two primary factors, the amount of blood in the heart, as well as the force of contraction that the ventricle produces. During inspiration, venous return decreases and the end diastolic volume decreases, leading to a decrease in stroke volume.

The second heart sound occurs during which aspect of the ECG?

T wave

During the plateau phase of the action potential in cardiac contractile cells __________.

all answers are correct. During the plateau phase of the action potential in cardiac contractile cells sodium channels are inactivated, inward rectifier potassium channels are closed, calcium channels are open, and the membrane potential remains depolarized.

End diastolic volume is influenced directly or indirectly by __________.

all answers are correct. End diastolic volume is influenced directly or indirectly by heart rate, preload, afterload and sympathetic nerve activity.

Stroke volume can be influenced by __________.

all answers are correct. Stroke volume can be altered by preload, afterload, contractility, and sympathetic nerve activity.

During isovolumetric relaxation __________.

all answers are incorrect

Put the following events of the cardiac cycle in the correct order, starting with the ventricular filling phase: a. first heart sound b. P wave of ECG c. ventricular pressure > atrial pressure d. isovolumetric relaxation

b,c,a,d

Ventricular contractility is influenced by __________.

calcium and epinephrine

Starling's law of the heart can be stated as: __________.

if end diastolic volume increases, stroke volume will increase and if venous return decreases, end diastolic volume will decrease and stroke volume will decrease

Which of the following would result in an increase in cardiac output?

increased end diastolic volume

When you begin to exercise, the working tissue will need an increased delivery of blood in order to obtain the oxygen and nutrients necessary for the maintenance of the increased metabolism. Which of the following will occur in order to help enhance the blood flow to the working tissue?

increased heart rate and stroke volume

Sympathetic activity increases ventricular contractility by __________.

increasing the rate of myosin ATPase activity and increasing the flow of calcium into the cytosol

Cardiac output is increased by __________.

increasing venous return and increasing ventricular filling time

The effect of parasympathetic input to the heart is to __________.

open additional potassium channels in pacemaker cells

During isovolumetric contraction __________.

pressure in the ventricles is increasing

The pulmonary semilunar valve opens in response to __________.

right ventricle pressure > pulmonary artery pressure

Starling's law states that __________.

stroke volume increases as end-diastolic volume increases

All of the following increase stroke volume except __________.

the inspiratory phase of respiration

Regarding ventricular volumes __________.

the larger the end diastolic volume, the larger the stroke volume becomes and an increase in the force of ventricular contraction decreases the end systolic volume

The actions of norepinephrine and acetylcholine on pacemaker cells is similar in that both transmitters __________.

utilize G proteins and affect calcium channels