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Unit 19: Biology Part 2 Page 52 of 137
blood vessel. What type of vessel? from the heart and has thick walls
You’re right if you said it’s a vein, to handle the high pressure on the
because blood always goes back to blood inside of it.
the heart in veins, and you’re also
right if you guessed that this vein
was called the pulmonary vein.
The pulmonary vein is the only
vein that carries oxygen-rich blood.
Once again, let’s save the question
about why this is the case for a
little later. This process of going
from the heart, to the lungs,
getting oxygen, and going back to
the heart is called pulmonary Figure 30 – The aorta carries
circulation. Have you noticed blood from the heart to all
that we are using the word organs of the body.
“pulmonary” a lot? This is because
pulmonary refers to the lungs, and, The aorta branches out into smaller
as you can see, the lungs are very and smaller arteries, until
important in this part of circulation. eventually the blood reaches the
capillary bed of the organ oxygen
Systemic Circulation is being delivered to. The
exchange of oxygen from the blood
The oxygen re-enters the heart in the capillary bed to the organ
and goes into the left atrium. With takes place, and the blood, which
a beat, the blood goes through the is now oxygen poor, leaves the
atrioventricular valve in to the left capillary bed and enters a tiny
ventricle. With another beat, it vein.
goes through the semilunar valve
into an artery. The blood travels back to the heart
through larger and larger veins.
Since this is the first artery to carry Eventually, the blood gets back to
oxygen-rich blood from the heart one of the two largest veins in the
to the other parts of the body, it body, which lead directly back into
gets a special name. It is called the right atrium of the heart. Just
the aorta. Even though it has this like the aorta has a special name
special name, it is just like any because it is the first artery out of
other artery. It carries blood away
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