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