Video Transcript
The diagram provided shows a
simplified cross section of the human heart, with some major blood vessels
removed. Which of the following best
describes the function of the structure indicated by X? Option (A) it transmits electrical
signals to the atria of the heart. Option (B) it transmits electrical
signals to the heart valves, causing them to close. Option (C) it transmits electrical
signals to the heart valves, causing them to open. Or option (D) it generates regular
electrical signals, regulating heart rate.
The diagram depicts the basic
structures of the heart. We can see the atria, the
ventricles, and the electrical conduction system, which is shown in dark red. X points to one of these dark red
portions that represent the electrical system. So what element of the heart’s
electrical conduction system is this? And what is its function?
This structure is called the
sinoatrial node. The sinoatrial node is located, as
seen in the diagram, in the wall of the right atrium. The sinoatrial node is called the
heart’s pacemaker because it is responsible for generating an electrical signal at
regular intervals. The signal is passed on by other
elements of the heart’s conduction system, eventually reaching the ventricles. This causes the ventricles to
contract, forcing blood out of the heart and to the rest of the body.
Now that we know that X is the
sinoatrial node and we have learnt a little about its function, let’s take a look
through our answer choices.
We can eliminate answer (A) because
we know that the signal starts in the atrium rather than being transmitted to the
atria. Now let’s take a look at answers
(B) and (C). The valves of the heart are not
controlled by electrical signals, but rather by differentials in blood pressure. As we have learnt, X is the
sinoatrial node, which is part of the heart’s electrical conduction system. This means that X will not have any
direct effect on the opening or closing of the valves of the heart. We can eliminate these two options
as well.
Finally, let’s discuss answer (D),
which says that the structure indicated by X generates regular electrical signals,
regulating the heart rate. This is true. As we have learnt, the sinoatrial
node is the heart’s pacemaker, which generates electrical signals and therefore
regulates the heart rate. The correct answer is therefore
(D). It generates regular electrical
signals, regulating the heart rate.
