chapter 12: the cardiovascular system: the heart 12-3 (heart sounds…
chapter 12: the cardiovascular system: the heart 12-3
the period between the start of one heartbeat and the start of the next is a single cardiac cycle.
during contraction, or systole, the chamber squeezes blood into an adjacent chamber or into an aterial trunk.
systole is followed by the second phase- relaxation, or diastole when the chamber fills with blood and prepares for the start of the next cardiac cycle.
fluids tend to move from an area of higher pressure o one of lower pressure.
during the cardiac cycle, the pressure within each chamber rises during systole and falls during diastole
an increase in pressure in one chamber causes the blood to flow to another chamber (or vessel) where the pressure is lower.
the atrioventricular and semilunar valves ensure that blood flows in one direction only during the cardiac cycle.
phases of the cardiac cycle
if the atria and ventricles were to contract simultaneously, blood couldn't leave the atria because the AV valves would be closed
in the normal heart, atrial systole and atrial diastole are slightly out of phase with the ventricular systole and diastole.
the cardiac cycle begins with the atrial systole.
at the start of a cardiac cycle, the ventricles are partially filled with blood.
during atrial systole, the atria contract and the ventricles become completely filled with blood.
as atrial systole ends, atrial diastole and ventricular systole begins
as pressure in the ventricles rise above the those in the atria, the AV valves swing shut
blood can't begin moving into the arterial trunks until ventricular pressure exceed the arterial pressure
at this point, the blood pushes open the semilunar valves and flows into the aorta and pulmonary trunk
this blood flow continues for the duration of ventricular systole, and lasts approximately 270 msec in a resting adult
when ventricular diastole begins, ventricular pressures decline rapidly
as they fall below the pressure of the arterial trunks, the semilunar valves close
ventricular pressures continue to drop; as they fall below atrial pressures, the AV valves open and the blood flows from the atria into the ventricles.
by the time atrial systole marks the start of another cardiac cycle,, the ventricles are roughly 70 percent filled
physicians use an instrument called a stethoscope to listen for four heart sounds
when you listen to your own heart, you hear the familiar "lubb-dupp" that accompanies each heartbeat
the first sound ("lubb") is produced as the AV valves close and the semilunar valves open
it marks the start of ventricular systole and lasts a longer than the second sound
the second heart sound, "dupp", occurs at the beginning of ventricular of ventricular diastole, when the semilunar valves close
third and fourth heart sounds may be audible as well, but they're usually very faint and are seldom detectable in a healthy adults