Blood, Heart, and Circulation 449Performing an ECG measurement on herself for a third time,
she sees an area of the strip where a P wave is not followed
by a QRS or T; farther along in the strip, however, a normal
pattern reappears. What do you think these recordings
indicate?- A newborn baby with a patent foramen ovale or a ventricular
septal defect might be cyanotic (blue). Will a two-year-old
with these defects also be cyanotic? Explain your answer. - People with paroxysmal atrial tachycardia (commonly
called “palpitations”) are sometimes given drugs that block
voltage-gated Ca^2 1 channels in the plasma membrane
of myocardial cells in order to slow the beat. By what
mechanism could these drugs help? - The mechanism of excitation-contraction coupling in cardiac
muscle differs from that in skeletal muscle. How might these
differences relate to the differences in the action potentials in
cardiac muscle compared to skeletal muscle? - Explain how homeostasis of the circulating blood platelet
count is maintained. By what mechanism would blood loss
increase the platelet count?
Test Your Quantitative Ability
Refer to figure 13.17 to answer the following questions:- At which pressure value did blood just start to leave the left
ventricle and enter the aorta? - How much blood was ejected by the left ventricle by the
time the second heart sound was produced? - How much blood was in the left ventricle just before the
atrial contraction? - How much blood was added to the left ventricle by
contraction of the left atrium? - What is the change in intraventricular pressure between the
time the first heart sound begins and the time it ends?
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