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Unit 19: Biology Part 2 Page 50 of 137
Circulation is the movement of
blood around the body and is really
divided into two “loops,”
pulmonary and systemic
circulation. The diagram below
provides an overview of circulation.
In the sections below, we will go
Figure 27 – Capillaries are the into much more detail.
smallest of the blood vessels,
and connect arteries and veins.
In spite of their small size,
however, capillaries are the place
where one of the most important
things in our body happens.
Networks of capillaries, called
capillary beds, are the places
where blood gives off oxygen to
the parts of the body, and collects
waste products like carbon dioxide. Figure 28 – The flow of blood
One of the major purposes of the into and out of the heart
cardiovascular system, oxygen
transfer, is happening in these tiny Pulmonary Circulation
vessels. The more active an organ Let’s start our journey by
is, the more capillaries it will need considering blood that has just
to get oxygen and other nutrients returned to the heart from some
from the blood.
organ in the body. Since the blood
gave oxygen to the organ, it now
Circulation
has very little oxygen in it. Blood
Now that we have examined blood, that has very little oxygen is called
blood vessels, and the heart “oxygen-poor,” just like someone
individually, lets take a look at how who has very little money is poor.
everything works together to get
the organs of our body the oxygen As we said earlier, it is atria of the
and nutrients they need, while heart that takes in blood. The
getting rid of the waste products right atrium is the one that takes in
they don’t. oxygen-poor blood. With a beat,
the oxygen-poor blood moves
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