Pulmonary arteries and the aorta
are major blood vessels that carry blood away from the heart. There are valves at the bases of
these vessels to prevent the backflow of blood into the ventricles. What is the name of these
valves? (A) Semilunar valves, (B) bicuspid
valves, (C) atrioventricular valves, or (D) ileocecal valves.
To answer this question, let’s have
a look at the structures of the heart and some key facts about the circulatory
system in general. The heart is a muscular organ that
is responsible for pumping blood all around the body. One of the jobs of the blood is to
deliver oxygen and nutrients to the cells, and it is vital these are delivered
rapidly enough to supply the needs of the cells. The heart and the rest of the
circulatory system are therefore designed to move the blood around the body as
efficiently as possible. The blood flows around the body in
one direction: from the heart, through arteries and capillaries, and then back to
the heart through veins.
If you look at the diagram, you can
see the labels numbered one and two. These refer to the right and left
atria, respectively. Atria is the plural. Atrium is the singular. These are chambers at the top of
the heart that receive blood coming back to the heart via the veins. The left atrium receives oxygenated
blood from the lungs, and the right atrium receives deoxygenated blood from the
body. Blood is then pumped from the atria
into the ventricles. The right ventricle is labeled as
three, and the left ventricle is labeled as four in this diagram. As explained in the question, the
blood will then leave the heart through the pulmonary arteries, which carry blood
from the right ventricle to the lungs, and the aorta, which carries the blood from
the left ventricle to the body.
We mentioned earlier that the blood
flows in one direction. The heart has structures to make
sure this happens efficiently. So, when the heart contracts, the
blood should flow out of the arteries only and not back into the atria. And when the heart relaxes, the
blood which is in the arteries should not flow back into the heart. This prevention of backflow of the
blood happens thanks to structures called valves. The semilunar valves are
moon-shaped valves found at the bottom of the arteries leaving the heart. Semi- means half, and lunar means
moon. These prevent the backflow of blood
from the pulmonary arteries and aorta into the heart.
Then there is the bicuspid valve,
situated between the left atrium and ventricle. Bi- means two, and cuspid refers to
a pointed tooth. So this valve has two pointed
flaps. The tricuspid valve is located
between the right atrium and ventricle, tri- meaning three, so this has three
flaps. Both the bicuspid and tricuspid
valves can also be called atrioventricular valves as they separate the atria and
ventricles. The flaps of the bicuspid and
tricuspid valves attach to tendons. This is to make sure they only open
downwards to the ventricles and they cannot turn inside out by mistake. Therefore, the blood always flows
from the atria to the ventricles.
We can now answer the question. The structures within the heart
that control blood flow from the pulmonary arteries and the aorta into the
ventricles are named in answer choice (A), the semilunar valves.