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Unit 19: Biology Part 2 Page 51 of 137

down from the right atrium to the atrioventricular valve and the dub
right ventricle, and with another is caused by the closing of the
beat, the blood moves from the semilunar valve.
right ventricle into a blood vessel.
When you exercise, or get
Stop for a moment and see if you frightened, signals are sent to your
can figure out what kind of vessel heart that more blood is going to
the blood enters. You are right if be needed in certain parts of your
you said that it’s an artery. We body. The blood begins to travel
know it’s an artery because it is faster, and your heart rate
taking blood away from the heart. increases.
This particular artery is called the
pulmonary artery. The blood leaves the heart through
the pulmonary artery and enters
The pulmonary artery is special the lungs. In the lungs, the blood
because it is the only artery in the picks up the oxygen it will deliver
body that carries oxygen-poor to the organs of the body. As you

blood. As we learn more about might guess, the blood is now
circulation, let’s see if we can called oxygen-rich.
figure out why this is.

As you might imagine, it is very
important that the blood moves
from the right atrium to the right
ventricle to the pulmonary artery,
and doesn’t flow backwards. To
make sure this happens, the heart
has valves that stop the blood from
flowing the wrong way.

The atrioventricular valves
separate the atria from the
ventricles and the semilunar

valves separate the ventricles
from the arteries that leave the Figure 29 – Blood gets oxygen
heat. The “lub-dub” sound of your in the lungs.
heartbeat is actually the closing of
these two valves. The lub is The oxygen-rich blood leaves the
caused by the closing of the lungs, and returns to the heart in a

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