Chapter 20 Check Points

Define cardiac output.

Cardiac output is the amount of blood pumped by the left ventricle in one minute.

Joe's end-systolic volume is 40 mL, and his end-diastolic volume is 125 mL. What is Joe's stroke volume?

SV=EDV-ESV, so SV= 125 mL- 40 mL= 85 mL

What effect would an increase in venous return have on the stroke volume?

The venous return fills the heart with blood, stretching the heart muscle. according to the frank-starling principle, the more the heart muscle is stretched, the more forcefully it will contract(to a point). the more forceful the contraction, the more blood the heart will eject with each beat(stroke volume). therefore, increased venous return would increase the stroke volume(if all other factors are constant).

If the cardioinhibitory center of the medulla oblongata were damaged, which part of the autonomic nervous system would be affected, and how would the heart be influenced?

Damage to the cardioinhibitory center of the medulla oblongata, which is part of the parasympathetic division of the autonomic nervous system, would reduce parasympathetic action potentials to the heart. the resulting sympathetic dominance would increase the heart rate.

Is the heart always pumping blood when pressure in the left ventricle is rising? Explain.

No. When pressure in the left ventricle first rises, the heart is contracting but no blood is leaving the heart. during this initial phase of contraction, both the AV valves and the semilunar valves are closed. the increase in pressure is the result of increased tension as the cardiac muscle contracts. When the pressure in the ventricle exceeds the pressure in the aorta, the aortic semilunar valves are forced open, and blood is rapidly ejected from the ventricle.

How does a drug that increases the length of time required for the repolarization of pacemaker cells affect the heart rate?

a drug that increases the length of time required for the repolarization of pacemaker cells would decrease the heart rate, because the pacemaker cells would generate fewer action potentials per minute.

How would an increase in sympathetic stimulation of the heart affect the end-systolic volume?

an increase in sympathetic stimulation of the heart would increase heart rate and force of contraction. the end-systolic volume(ESV) is the amount of blood that remains in a ventricle after a contraction(systole). the more forcefully the heart contracts, the more blood it ejects and the lower the ESV is. therefore, increased sympathetic stimulation should result in a lower ESV.

Define automaticity.

automaticity, or autorhythmicity, is the ability of cardiac muscle tissue to contract without neural or hormonal stimulation

Caffeine has effects on conducting cells and contractile cells that are similar to those of NE. What effect would drinking large amounts of caffeinated drinks have on the heart?

caffeine acts directly on the conducting system and contractile cell of the heart, increasing the rate at which they depolarize. drinking large amounts of caffeinated drinks would increase the heart rate.

What prevents the AV valves from swinging into the atria?

contraction of the papillary muscles(just before the rest of the ventricular myocardium contracts) pulls on the chordae tendineae, which prevent the AV valves from opening back into the atria.

Damage to the semilunar valve of the right ventricle would affect blood flow into which vessel?

damage to the semilunar valve of the right ventricle would affect blood flow to the pulmonary trunk.

If the cells of the SA node did not function, how would the heart rate be affected?

if the cells of the SA node did not function, the heart would still continue to beat, but at a slower rate; the AV node would act as the pacemaker

Why is it important for impulses from the atria to be delayed at the AV node before they pass into the ventricles?

if the impulses from the atria were not delayed at the AV node, they would be conducted through the ventricles so quickly by the bundle branches and Purkinje cells that the ventricles would begin contracting immediately, before the atria had finished their contraction. As a result, the ventricles would not be as full of blood as they could be, and the pumping of the heart would not be as efficient, especially during activity.

What factor could cause an increase in the size of the QRS complex in an electrocardiogram?

one possible cause for an increase in the size of the ORS complex, which indicates a larger-than-normal amount of electrical activity during ventricular depolarization, the magnitude of the electrical event would be greater.

What effect would stimulating the acetylcholine receptors of the heart have on cardiac output?

stimulating the acetylcholine receptors of the heart would slow the heart rate. since cardiac output is the product of stroke volume and heart rate, a reduction in heart rate will lower the cardiac output(assuming that the stroke volume remains the same or doesn't increase).

Why is it a potential problem if the heart beats too rapidly?

the heart pumps in proportion to the amount of blood that enters. a heart that beats too rapidly does not have sufficient time to fill completely between beats. thus, when the heart beats too fast, very little blood leaves the ventricles and enters the circulation so tissues suffer damage from inadequate blood supply.

Why is the left ventricle more muscular than the right ventricle?

the left ventricle is more muscular than the right ventricle because the left ventricle must generate enough force to propel blood throughout the body, except the lungs; whereas the right ventricle must generate only enough force to propel blood a few centimeters to the lungs

List the phases of the cardiac cycle.

the phases of the cardiac cycle are atrial systole, atrial diastole, ventricular systole, and ventricular diastole

Which structure of the heart is known as the cardiac pacemaker or the natural pacemaker?

the sinoatrial(SA) node is known as the cardiac pacemaker or the natural pacemaker.

Provide the technical terms for heart contraction and heart relaxation.

the technical term for contraction is systole, and the other term for relaxation is diastole.