Video Transcript
The diagram provided shows a cross
section of the human heart. State the correct chambers
indicated by the letters A, B, C, and D.
This question presents a diagram of
the human heart. So let’s review some key facts
about the structure and function of the heart in order to answer it correctly.
The heart is a muscular organ,
which is part of the cardiovascular system. It is responsible for pumping blood
to all of the cells within the body. The blood acts as a major transport
system, and, amongst other things, it carries oxygen and nutrients to the cells and
wastes away. The main components of blood are
red blood cells, plasma, white blood cells, and platelets. So, as well as transport, the blood
is also involved in immune defense and blood clotting.
The carriage of oxygen to the body
cells is extremely important as it is needed for aerobic respiration, a type of
cellular respiration. Aerobic respiration is a process in
which carbon-containing compounds, usually glucose, are broken down using oxygen to
release energy. Carbon dioxide and water are
released as waste products. The oxygen is delivered to the
cells by the red blood cells, which make up about 45 percent of the blood
volume.
It is important that oxygen and
nutrients are delivered rapidly enough for the cells’ needs. So the heart has a special
structure to carry out its role as efficiently as possible.
Let’s now look at the heart and its
role in the circulatory system. The circulatory system carries the
blood around the body in one direction. The blood leaves the heart through
arteries and returns via veins. We have a double circulatory
system, which means that the blood passes through the heart twice for each complete
circuit of the body. The double circulatory system means
that oxygenated blood and deoxygenated blood are separated, so they do not mix and
reduce the oxygen getting to the cells. It also maintains the blood
pressure required to get the blood around the body, including all the way to your
big toe. But how does it do this?
Let’s look at this diagram of the
heart. Have you noticed that the left and
right labels seem to be on the wrong side? This often confuses people as we
cannot use our own rights and lefts when studying the heart. Instead, we need to treat the heart
as if it were in someone’s chest, facing us.
Now let’s take a closer look. The heart is divided down the
middle, by the septum, into the left and right sides. The left side pumps oxygenated
blood which has come from the lungs to the body. This is the systemic
circulation. The right side pumps deoxygenated
blood which has returned from the body to the lungs to be reoxygenated. This is the pulmonary circulation,
pulmonary referring to the lungs. Both sides of the heart pump at the
same time, in the same rhythm, meaning that the two circulations are
synchronized.
We can now look at the movement of
the blood through the heart. Let’s start with the left-hand
side. The oxygenated blood from the lungs
enters the heart from the pulmonary vein. As mentioned earlier, pulmonary
refers to the lungs, and veins lead to the heart.
The blood first enters the top
chamber of the heart. This is the left atrium; the word
atrium refers to an entrance hall. The atrium then pumps this
oxygenated blood into the lower muscular chamber, the left ventricle, the word
ventricle referring to a cavity in an organ. The left ventricle then contracts
and pushes the blood out of the heart via the main artery, the aorta. The left ventricle has to pump the
blood with enough force to get it all around the body, so it has a thick, muscular
wall, much thicker than the right-hand side.
Once the blood has gone around the
body, providing oxygen to the cells and collecting carbon dioxide, it returns to the
heart via the vena cava, the largest vein of the body. The now deoxygenated blood enters
the right atrium. It is then pumped into the right
ventricle. This contracts and pushes the blood
out of the heart through the pulmonary arteries, which lead to the left and right
lungs. Remember both left and right atria
and then left and right ventricles contract together. So the blood is pushed out of the
heart on both sides at the same time.
You can see here that the right
ventricle wall is much thinner than the left as it only has to pump the blood a
short distance. And the blood needs to be under
lower pressure to prevent damage to the many capillaries in the lungs.
Now that we have learnt about the
cardiovascular system as a whole, let’s take another look at our question. We know that deoxygenated blood
will enter the right atrium first. This is designated by the letter D
in our diagram. Because the right atrium sits on
top of the right ventricle, this must be the chamber labeled A. Once blood pumped by the right
ventricle is oxygenated, it is returned to the left atrium. So, C must correspond to the left
atrium. This blood travels to B, the left
ventricle, before being pumped to the entire body, delivering oxygen again.
This means the correct answer must
be that A is the right ventricle, B is the left ventricle, C is the left atrium, and
D is the right atrium.
