Let us now follow the circulation
of blood through the heart. As noted earlier, oxygenated
blood is pumped by the left ventricle to all parts
of the body, other than the lungs. The body tissue
removes much of the oxygen for its own need. The blood,
which is now carrying less oxygen, returns to the
heart. Blood from the head, neck and arms return to
the right atrium (RA) via the SVC or SUPERIOR VENA
CAVA. On the other hand, blood from the lower portion
of the body returns to the RA via the IVC or INFERIOR
VENA CAVA (pronounced vee-nah cave-ah).
The RA contracts when filling
is completed. This builds up pressure within that
chamber and pushes the tricuspid valve open. Blood
now rushes from the RA to the right ventricle (RV).
When the RV is filled, the walls begin to contract
and raises pressure within the RV. The increased pressure
shuts the tricuspid valve and pumps blood into the
pulmonary (pronounced pull-mun-narey) artery through
the pulmonic valve (PV, pronounced pull-mon-nick)
which is pushed open by the increased pressure. The
diagram below once again shows the four heart valves
as viewed from the top, standing in front of the heart,
i.e., we are looking down at the two ventricles with
the right atrium and left atrium removed.
The pulmonic valve is made
up of three cusps or flexible cup like structures.
When the pressure in the right ventricle is low (as
is the case during the filling phase of the chamber)
the three cusps are full of blood and their sides
touch each other to close the opening. This prevents
blood from leaking into the pulmonary artery while
the RV is filling.
When the RV contracts to empty, the pressure within
the chamber rises above that of the pulmonary artery.
This forces open the three cusps of PV and blood rushes
through the pulmonary arteries and is sent to the
lungs. Here the red blood cells pick up oxygen
The oxygenated blood from
the lungs now returns to the left atrium (LA) via
four tubes that are known as pulmonary veins. They
empty into the back portion of the LA. When the LA
contracts after it is completely filled. This opens
the mitral valve and forces blood into the left ventricle
When the LV is completely filled, it starts to empty
its contents by contacting the walls. This increases
pressure within the chamber, shuts the mitral valve
and opens the aortic valve (AV, pronounced a-ortic).
The sequence is similar to that described for the
RA, RV and pulmonic valve.
Blood now rushes through the aorta (pronounced a-or-tah).
The aorta is the main "highway" blood vessel
that supplies blood to the head, neck, arms, legs,
kidneys, etc. Thus, blood is brought to each of these
organs and limbs via branches that originate from
the aorta. The cells within each part of the body
pick up oxygen and nutrients from the blood. The oxygen-poor
blood then returns to the RA, via the superior and
inferior vena cava, and the beat goes on!!
The animation above demonstrates
the flow of blood through the heart and lungs, as
explained above. Notice that the mitral and the right
side of the heart works in synchrony with the left,
but that each atria contracts while the ventricle
Less confused? Good! Continue to hang in there as
we further clarify these concepts