Video Transcript
Which of the following is a
function of blood? Is it to carry carbon dioxide from
the heart to the bladder? Is it to carry oxygen from the
lungs to tissues around the body? Or is it to carry oxygen from the
digestive system to the heart?
Before we answer this question,
let’s make sure we understand what a function is. A function is a job that something
has to do. So, we need to decide which of
these three things describe a job that the blood has to do in our bodies.
The blood is part of the
circulatory system; this is a group of organs that work together to move blood
around the body. The heart, arteries, and veins are
all part of this system. The heart works like a pump,
pushing blood away in tubes called arteries. And then, the blood returns to the
heart in tubes called veins.
First, the blood is pumped from the
heart to the lungs to collect oxygen from the air we have breathed in. Then, the blood with its cells
containing lots of oxygen travels through the arteries to tissues around the
body. The cells in these tissues take
oxygen from the blood and use it to produce energy. The process of producing energy
from oxygen creates a gas called carbon dioxide. This gas isn’t needed by the body
tissue, and we call it a waste gas. It passes into the blood cells
replacing the oxygen that was just taken.
When the blood has delivered its
oxygen to the tissue and picked up the waste carbon dioxide, it is pumped back to
the heart in the veins. Now, the process starts again. Blood is pumped to the lungs. The waste carbon dioxide in the
blood is passed into the lungs, and we breathe it out. More oxygen is taken from the
lungs, and the blood full of oxygen again is pumped on to tissues around the body,
and so on. The process continues.
One way of looking at it is the
blood does a similar job to a mailman, but instead of delivering letters and
parcels, it does the important job of delivering oxygen to tissues around the
body. At the same time, the blood also
does another job: like trash collectors taking away the waste carbon dioxide and
disposing of it through the lungs where it can be breathed out.
Now, let’s return to our
question. Which of the following is a
function of blood? Well, we know that blood takes
oxygen from the lungs and delivers it to other tissues around the body, so this is
option (B). But let’s quickly check the other
options to make sure we haven’t missed anything.
(A) is to carry carbon dioxide from
the heart to the bladder. Well, after delivering oxygen to
tissues around the body, we said that blood does take away waste carbon dioxide from
them back, but it takes it back to the lungs to be breathed out. So, there may be some of this waste
carbon dioxide in the blood when it reaches the bladder, but it isn’t used by the
bladder, and it isn’t taken specifically from the heart to the bladder. Therefore, this is not a function
of blood.
(C) is to carry oxygen from the
digestive system to the heart. Now, we’ve seen that blood does
carry oxygen around the body. But the oxygen comes from the
lungs, and the heart is pumping the blood full of oxygen away from itself to tissues
around the body. Blood cells don’t carry oxygen from
the digestive system to the heart. So, this is not our answer.
So, which of the following is a
function of blood? It’s to carry oxygen from the lungs
to tissues in the body.
