680
UNIT 4
Maintenance of the Body
18
1
Ventricular filling: mid-to-late diastole.
Pressure in the
heart is low, blood returning from the circulation is flow-
ing passively through the atria and the open AV valves into
the ventricles, and the aortic and pulmonary valves are
closed. More than 80% of ventricular filling occurs during
turn of the cardiac cycle. As shown in
Figure 18.21
, which
outlines what happens in the leF side of the heart, we begin with
the heart in total relaxation: Atria and ventricles are quiet, and
it is mid-to-late diastole.
1
2a
2b
3
120
80
40
0
Electrocardiogram
Left heart
Pressure (mm Hg)
Ventricular
volume (ml)
P
1st
2nd
QRS
P
Heart sounds
120
50
Atrial systole
Dicrotic notch
Left ventricle
Left atrium
EDV
SV
Aorta
Atrioventricular valves
Aortic and pulmonary valves
Open
Open
Closed
Closed
Closed
Open
Phase
ESV
Left atrium
Right atrium
Left ventricle
Right ventricle
Ventricular
filling
Atrial
contraction
Ventricular filling
(mid-to-late diastole)
Ventricular systole
(atria in diastole)
Isovolumetric
contraction phase
Ventricular
ejection phase
Early diastole
Isovolumetric
relaxation
Ventricular
filling
1
1
2a
2b
3
T
Figure 18.21
Summary of events during the cardiac cycle.
An ECG tracing (
top
)
correlated with graphs of pressure and volume changes (
center
) in the left side of the heart.
Pressures are lower in the right side of the heart. Timing of heart sounds is also indicated.
(
Bottom
) Events of phases 1 through 3 of the cardiac cycle. EDV
5
end diastolic volume,
ESV
5
end systolic volume, SV
5
stroke volume.
previous page 714 Human Anatomy and Physiology (9th ed ) 2012 read online next page 716 Human Anatomy and Physiology (9th ed ) 2012 read online Home Toggle text on/off