Video Transcript
What is the result of the decrease
in air pressure in the lungs? (A) The volume of the lungs
decreases. (B) There is no overall movement of
air. (C) Air is pulled in. Or (D) air is forced out.
This question asks us about air
pressure in the lungs. Let’s review how the lungs work to
work out what happens when this air pressure decreases.
The lungs are a part of the human
respiratory system responsible for inhaling oxygen and exhaling carbon dioxide. Almost every cell in the human body
requires oxygen for aerobic respiration to release energy and need to get rid of the
waste product carbon dioxide that is produced in this process. So we can tell that the lungs are
vitally important organs.
During the process of inhalation,
the intercostal muscles between the ribs contract, lifting the ribs upward. And a muscle called the diaphragm
below the lungs contracts as well, moving downward, which causes the chest cavity to
expand, allowing the lungs to also expand and stretch, filling up this extra
space. As the lungs expand, their volume
increases. As the lung volume increases, the
pressure within them decreases.
To visualize this, think of five
particles in a small box. The pressure inside the box is the
force exerted on the walls by those five particles, or in simpler terms how
frequently those particles will hit against the walls. The particles in gases like carbon
dioxide and oxygen move fairly quickly. So you can imagine these five
particles will exert quite a high pressure upon the walls of this small box. If you put the same five particles
in a container with a larger volume, they will collide with the walls less
frequently. And so the pressure is
comparatively lower than in the smaller box, just like the pressure in the lungs
decreases when they have a larger volume.
Gases tend to flow from areas of
high pressure to areas of low pressure. When the pressure in the lungs
decreases due to the increase in volume, lung pressure becomes lower than
atmospheric pressure, which causes atmospheric air containing oxygen to flow into
the lungs. So what do you think will happen in
the lungs during exhalation? Let’s find out.
During exhalation, the intercostal
muscles and diaphragm relax, causing the chest cavity to become smaller and the
volume of the lungs to decrease. As volume and pressure have an
inverse relationship, this will cause pressure in the lungs to increase. When the pressure in the lungs
increases above atmospheric pressure, the air inside the lungs and the carbon
dioxide it contains will flow from a high pressure in the lungs to a lower pressure
in the atmosphere.
If we take a look back at the
question, we can see that we are asked to determine the effect of a decrease in air
pressure in the lungs. As we now know, this occurs during
inhalation. And the low pressure in the lungs
causes air to be pulled into the lungs as the lung air pressure is lower than
atmospheric air pressure. So the correct answer to this
question is (C). Air is pulled in.
