Ch. 20 Cardio
The long plateau phase of the cardiac muscle action potential is due to
calcium channels remaining open.
When threshold is reached at the SA node (an autorhythmic cell), what channels open causing further depolarization of the membrane?
fast calcium
Action potentials generated by the autorhythmic cells spread to the contractile cells through what structures in the membrane?
gap junctions
What causes the aortic semilunar valve to close?
greater pressure in the aorta than in the left ventricle
The arrow indicates the point of transition from the absolute refractory period to the relative refractory period. Which of the follow occurs just before this point?
Cardiac muscle begins to relax.
Cardiac muscle cells and skeletal muscle cells differ in a few ways. Which of the following is not one of them?
Cardiac muscle cells lack transverse tubules.
Which of the following is correct about the filling of the ventricles?
Most blood flows passively into the ventricles through open AV valves.
Depolarization of the atria corresponds to the EKG's
P wave.
What is the function of the structures indicated by the red arrow? (Intercalated discs)
Permit strong connections between adjacent cells Propagate action potentials from cell to cell Transfer force of contraction from cell to cell (Answer: All of the above)
Describe the pressures in the atria and ventricles that would cause the opening of the AV valves.
Pressure in the atria would be greater than the pressure in the ventricles.
The rapid depolarization phase in the ventricular action potential appears in the electrocardiogram as the __________.
QRS complex
Heart valves are in what state during isovolumetric contraction?
The AV valves and semilunar valves are closed.
Which of these is not needed to determine cardiac output?
blood pressure
During the cardiac cycle, the
both QRS complex of the ECG precedes the increase in ventricular pressure and first heart sound coincides with the QRS complex of the ECG.
Heart rate is controlled by __________.
both the right vagus and sympathetic nerves
During the plateau phase of the cardiac action potential, which ion is entering the cardiac muscle cell?
calcium
Which of these responses by the heart will sympathetic stimulation not cause?
increased end-systolic volume
One of the changes that occurs in the pacemaker potential (unstable resting membrane potential) in the SA node (an autorhythmic cell) is a decreased efflux of what ion?
potassium
The papillary muscles function to __________.
prevent the AV valves from reversing into the atria
The normal pacemaker of the heart is located in the
sinoatrial node.
Which of the following factors will decrease cardiac output?
stimulation of the vagus nerve
In order to cause cardiac muscle contraction, the contractile cells must also depolarize. What causes the depolarization of the contractile cells?
the flow of positive ions from adjacent cells
The one-way nature of the left AV valve prevents blood flow from _________.
the left ventricle to the left atrium
Tetanic muscle contractions don't occur in a normal cardiac muscle because
the refractory period lasts until the muscle relaxes.
The decrease in left ventricular pressure at the end of ventricular systole causes __________.
the semilunar valve to close
If the connection between the SA node and AV node becomes blocked,
the ventricles will beat more slowly.
Which of the following most correctly describes end-diastolic volume?
the volume of the ventricle when it is most full
The majority of ventricular filling occurs while the ventricles and atria are in what state(s)?
ventricular and atrial diastole
Isovolumetric relaxation and ventricular filling (two phases of the cardiac cycle) take place during __________.
ventricular diastole
The closing of the left AV valve occurs near the beginning of __________.
ventricular systole
Repolarization of an autorhythmic cell is due to the opening of which channels?
voltage-gated potassium channels
Left ventricular filling occurs __________.
while the AV valve is open
At a heart rate of 60 beats/minute, a cardiac cycle lasts
1 second.
The heart beats approximately ________ times each day.
100,000
What is the correct order for the flow of blood entering from the systemic circulation?
5, 1, 3, 7, 8, 2, 4, 6
The heart pumps approximately ________ liters of blood each day.
8,000
Increased pressure in the ventricles would close what valve(s)?
AV valves only
The __________ valve prevents backward flow of blood into the left ventricle.
aortic
Which of the labeled valves will open during ventricular systole to allow the flow of blood to the lungs?
The semilunar valve labeled B
Which of these statements concerning the cardiac cycle is false?
Ventricular systole begins at the peak of atrial systole.
In cardiac muscle
about 20 percent of the calcium ion required for contraction comes from outside the cell.
End-systolic volume is defined as the:
amount of blood remaining in a ventricle after contraction
The P wave of the electrocardiogram is closely followed by __________.
contraction of both atria
If the force of ventricular contraction increases, what will happen to the end-systolic volume?
decrease
Cardiac output can be increased by all of the following except one. Choose the exception.
decreasing ejection fraction
What is the relaxed state of the ventricle called?
diastole
During ventricular systole the blood pressure __________ and ventricular volume __________.
increases; decreases
Put the phases of the cardiac cycle in the correct order, starting after ventricular filling.
isovolumetric contraction, ventricular ejection, isovolumetric relaxation
Ventricular diastole begins with the closing of the semilunar valves. What phase of the cardiac cycle happens between this event and the later opening of the AV valves?
isovolumetric relaxation
