Video Transcript
The diagram provided shows a basic
outline of the heart, with the major blood vessels indicated. State the blood vessels indicated
by each of the letters A, B, C, and D.
This question presents a diagram of
the human heart and asks us to identify some major blood vessels. In order to answer this question
correctly, let’s look at the structure and function of the heart and then track a
red blood cell as it moves through the circulatory system.
All of the cells in the body
require oxygen to survive. The oxygen 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. Red blood cells carry the oxygen
from the lungs to the body cells. They then carry about 75 percent of
the carbon dioxide waste back to the lungs to excrete it. The rest is carried in the plasma
of the blood.
The blood is pumped around the body
by the heart, a muscular organ about the size of your fist. Arteries carry the blood away from
the heart, “a” for away, and veins carry the blood back to the heart. If you look at this diagram, you
can see that the heart is divided into two distinct sides, the left and right, by
the septum. This is to increase the efficiency
of the system by separating the oxygenated blood in the left-hand side from the
deoxygenated blood in the right-hand side.
Have you noticed that the left and
right sides in this diagram 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.
Looking more closely at the
diagram, you can see there are two small chambers at the top, one on each side. These are called atria, which is a
name for an ancient entrance hall, an apt name seeming this is where the blood
enters the heart. Below the atria are the larger,
more muscular, left and right ventricles, which pump the blood out of the heart.
We can begin tracking our red blood
cell here in the lungs, where the oxygen has entered the cell by diffusion. The red blood cell is then carried
to the heart via the pulmonary vein. Pulmonary refers to the lungs. The blood cell enters the left
atrium, where it is then pumped into the left ventricle. The left ventricle pumps the blood
out of the heart through the main artery of the body, the aorta. The left ventricle has a thick
muscular wall, so it can pump this oxygenated blood at high pressure all around the
body.
The red blood cell then delivers
its oxygen and collects the carbon dioxide. It then returns to the heart via
the vena cava, the largest vein in the body. It enters the right atrium, which
then pumps the blood into the right ventricle. This has a much thinner muscular
wall than the left ventricle, 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. The right ventricle finally pumps
the red blood cell through the pulmonary artery to the lungs.
Most arteries carry oxygenated
blood, but the pulmonary artery is an exception. Once the blood reaches the lungs,
it undergoes oxygenation. This is the process of exchanging
carbon dioxide for oxygen molecules. Once our red blood cell contains
oxygen again, it can start its journey all over again.
Now that we have reviewed some of
the key facts about the circulatory system, let’s take another look at our question
and its diagram.
We know that the vessel carrying
deoxygenated blood from the body cells to the heart is called the vena cava. This is labeled A since it connects
with the right atrium. The vessel labeled B is carrying
blood away from the right ventricle of the heart. This must be the pulmonary
artery. Label C must be the pulmonary vein
as it returns oxygenated blood to the left atrium. Finally, blood is pumped from the
left ventricle via the aorta, labeled D.
Therefore, the correct answer to
the question is A is the vena cava, B is the pulmonary artery, C is the pulmonary
vein, and D is the aorta.
