The various parts of the heart, including
its chambers, valves and arteries are shown in the
figures displayed below.
The diagram on the right shows a longitudinal
(cut from top to bottom) section of the heart. The
flow of blood is represented by arrows. The narration
will describe different phases of the cardiac circulation.
The animation will serve as
a revision or reinforcement of the various stages
or steps of the circulation, with arrows and labels
serving as a reminder of what takes place. You may
click on the stop, rewind and play buttons to control
below represent a heart that is cut along the horizontal
axis. The picture on the left shows the plane along
which the heart is cut. That is, the top of the heart,
including the right and left atria (atria is plural
for atrium), the pulmonary artery and aorta are removed
on the picture on the right (below). It shows the
heart as you would look down at it from the front.
The tricuspid and mitral valves are represented right
and left, respectively (you can see the right and
left ventricles through the two valves). The aortic
and pulmonic valves are shown up and down, respectively,
in the bottom half of the picture. The heart size
increases and decreases during the filling (DIASTOLE,
pronounced die-as-tull-ee) and contraction or emptying
(SYSTOLE, pronounced sis-tull-ee) of the heart chambers.
The animation on the bottom left shows a longitudinal section of the beating heart, together with valve structures that open and shut to let blood pass through the atria, ventricles and the great vessels. The animation on the right shows a cross-sectional view of the heart.
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The mitral and tricuspid valves
open and the aortic and pulmonic valves are shut while
the ventricles fill during diastole. In contrast,
the mitral and tricuspid valves shut while the aortic
and pulmonic valves open during ventricular systole.
This sequence ensures that the ventricles are filled
to capacity before the aortic and pulmonic valves
are opened. At this time, the mitral and tricuspid
valves are shut so that blood does not leak back into
the the two atria. Yes, the heart is an ingenious
device that could have inspired design of the modern
day mechanical pump and integrated valves.
Did you stop and wonder why each side of the heart
has two pumping chambers (atrium and ventricle)? Why
not just have a ventricle to receive blood and then
pump it straight out? The reason is that the atrium
serves as a "booster pump" that increases
the filling of the ventricle. Filling a normal ventricle
to capacity translates to more vigorous contraction
or emptying. You can compare this to a strong spring,
and imagine that the heart muscle is made up of tiny
little "springs" known as ACTIN and MYOSIN.
Within reasonable limits, the more you stretch a spring,
the more vigorously will be its contraction or recoil.
In medical terms, this is known as "Frank-Starling's"