Chapter 17 BIO 142
The plateau phase of the cardiac action potential is due to __________.
Ca2+ influx
The _______________ represents the time it takes for the depolarization from the SA node to spread through the atria to the ventricles; it includes the AV node delay.
P-R interval
The main pacemaker of the heart is the __________.
SA node
The pace of the heart is set by the pacemaker cells with the fastest rate of spontaneous depolarization. Normally, these are the cells found here, within the wall of the right atrium. This is where depolarizing impulses normally originate.
SA node
According to the Frank-Starling law, a bigger preload will result in __________.
a stronger contraction A bigger preload means increased stretch of the ventricular muscle cells and therefore, a stronger contraction.
Digoxin is a positive inotropic agent derived from the foxglove family of plants. Which of the following is an effect of digoxin?
decreased ESV Increased contractility and SV would lead to a decrease in the ESV.
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.
The electrical impulse is __________ as it passes through the AV node, because the atria need to contract __________ ventricles.
delayed; before
The positive inotropic effect of hormones and sympathetic stimulation cause ____________ contractility
increased
Ventricular systole begins during the __________ phase of the cardiac cycle.
isovolumetric contraction
Blood returning from the lungs enters the __________.
left atrium
The cardiac chamber with the thickest wall is the __________.
left ventricle
The cells that rhythmically and spontaneously generate action potentials in the heart are called __________.
pacemaker cells
The AV valves close when __________.
pressure in the ventricles increases
The vessels that deliver oxygen to the tissues of the body are part of the __________.
systemic circuit
Blood from the systemic circuit returns to the heart via the __________.
vena cavea
During the __________ ___________ 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.
ventricular ejection
