The heart is the pump station of the body and
is responsible for circulating blood throughout the
body. It is about the size of your clenched fist and
sits in the chest cavity between two lungs. Its walls
are made up of muscle that can squeeze or pump blood
out every time that the organ "beats" or
Fresh, oxygen-rich air is brought to the lungs through
the trachea (pronounced tray-kee-ya) or windpipe every
time that you take a breath. The lungs are responsible
for delivering oxygen to the blood, and the heart
circulates the blood to the lungs and different parts
of the body.
The heart is divided into FOUR
chambers or "rooms". You can compare it
to a Duplex apartment that is made up of a right and
a left unit, separated from each other by a partition
wall known as a SEPTUM (pronounced sep-tum).
Each "duplex" is
subdivided into an upper and a lower chamber. The
upper chamber is known as an ATRIUM (pronounced ay-tree-yum)
while the lower chamber is referred to as a VENTRICLE
The right atrium (RA) sits on top of the right ventricle
(RV) on the right side of the heart while the left
atrium (LA) sits atop the left ventricle (LV) on the
The right side
of the heart is responsible for sending blood to the
lungs, where the red blood cells pick up fresh oxygen.
This OXYGENATED blood is then returned to the left
side of the heart. From here the oxygenated blood
is transported to the whole body supplying the fuel
that the body cells need to function. The blood cells
of the body extract or removes oxygen from the blood.
The oxygen-poor blood is returned to the right atrium,
where the journey began. This round trip is known
as the CIRCULATION of blood.
The figure shown above is a section of the heart,
as viewed from the front. It demonstrates the four
chambers. You will also notice that there is an opening
between the right atrium (RA) and the right ventricle
(RV). This is actually a valve known as the TRICUSPID
(pronounced try-cus-pid) valve. It has three flexible
thin parts, known as leaflets, that open and shut.
The figure below shows the mitral and tricuspid valves,
as seen from above, in the open and shut position.
When shut, the edge of the
three leaflets touch each other to close the opening
and prevent blood from leaving the RV and going back
into the RA. Thus, the tricuspid valve serves as a
trapdoor valve that allows blood to move only in one
direction - from RA to RV. Similarly, the MITRAL valve
(pronounced my-trull) allows blood to flow only from
the left atrium to the left ventricle. Unlike the
tricuspid valve, the mitral valve has only two leaflets.
In the top diagram, you will also notice thin thread
like structures attached to the edges of the mitral
and tricuspid valves. These chords or strings are
known as chordae tendineae (do not even try to pronounce
it. However, if you really must, it is chord-ee tend-in-ee).
They connect the edges of the tricuspid and mitral
valves to muscle bands or papillary (pronounced pap-pill-lurry)
muscles. The papillary muscles shorten and lengthen
during different phases of the cardiac cycle and keep
the valve leaflets from flopping back into the atrium.
The chords are designed to control the movement
of the valve leaflets similar to ropes attached to
the sail of a boat. Like ropes, they allow the sail
to bulge outwards in the direction of a wind but prevents
them from helplessly flapping in the breeze. In other
words, they provide the capability of a door jamb
that allows a door to open and shut in a given direction
and NOT beyond a certain point.
When the three leaflets of the tricuspid bulge upwards
during contraction or emptying of the ventricles,
their edges touch each other and close off backward
flow to the right atrium. This important feature allows
blood to flow through the heart in only ONE direction,
and prevents it from leaking backwards when the valve
is shut. The two leaflets of the mitral valve functions
in a similar manner and allows flow of blood from
the left atrium to the left ventricle, but closes
and cuts off backward leakage into the left atrium
when the left ventricle contracts and starts to empty.
Confused? Continue to hang in there. We will clarify
this further in the next few pages. Please note that
the repetition is intentional! Rephrasing and repeating
an explanation often enhances the understanding and
retention of key concepts. Skip areas that are redundant