Video Transcript
Complete the table to correctly
compare the structure of the three major blood vessels.
This question provides us with a
partially filled-in table. We’re given the names of the three
types of blood vessels along the top and various features of their structure along
the side. And we’re being asked to fill in
these four blank spaces with the correct information. In order to fill in these lengths,
we’ll review what we know about the structure of the three major types of blood
vessels. And we’ll start by reviewing their
functions, since we know that structure and function are directly related.
Well, these are all types of blood
vessels. So, we know that their primary
function is to carry blood. The function of veins is to carry
blood into the heart. We’re reminded of this because we
can see the word “in” in the word vein. The function of the arteries is to
carry blood away from the heart. And we’re reminded of this because
both artery and away start with “a.” The function of the capillaries is
to carry blood and allow the exchange of materials.
Here we have a diagram that
represents the general route of blood flow through these three types of blood
vessels. Blood from the heart pumps through
the arteries, where eventually it branches off into a network of tiny blood vessels
known as capillaries. Here, materials like oxygen, carbon
dioxide, water, glucose, and many more pass into and out of the bloodstream. The capillaries connect and
eventually join a vein, and the vein carries the blood back to the heart.
In order to answer our question,
I’ve drawn more detailed diagrams of a vein, an artery, and a capillary. And the information we’re looking
for in these diagrams is the size of the lumen or the space that the blood passes
through, the width of the wall of the blood vessel, and whether or not the blood
vessel possesses any valves which are special structures that keep blood flowing in
one direction.
We’ll start by filling in the
missing information for the vein column. We can see that the width of the
wall is thin, and that part is already filled in. The size of the lumen compared to
the other blood vessels is quite large. And we also can see that valves are
present. Because of the size of the lumen of
the vein and their relative distance from the heart, the blood pressure within them
is quite low, which is why some veins possess valves, which keep the blood flowing
in the correct direction and prevent it from flowing backwards.
Next, let’s work on the artery
column. The size of the lumen is relatively
small. And the blood pressure in arteries
is higher than in veins, so they don’t need valves to keep blood flowing in one
direction. Because of the high blood pressure,
arteries also need thick, muscular walls that prevent them from being damaged.
Finally, let’s complete the
capillary column. Capillaries have very thin walls,
only one cell layer thick, which is what allows the easy exchange of materials into
and out of the bloodstream. The size of the lumen is very
small, so small in fact that blood cells pass through in single file. And there are no valves present in
capillaries. The blood within them flows from
the high pressure of the artery to the low pressure of the vein without the need for
these special structures.
And now our table is complete. We filled in that arteries have
thick walls, veins have a large lumen, and that valves are present in veins but not
present in capillaries.
