The Mechanics of the Lung Model

You probably noticed that pushing the large balloon in towards the smaller balloons caused the smaller balloons to deflate and flatten. Pulling it out caused the smaller balloons to inflate slightly. And, all of this occurred without ever blowing air into the straw… or so it seems! Before we get into the mechanics of the system, let’s take a look at what each part of the model represents.

Each part of the model represents a different part of the respiratory system.

The diaphragm, represented by the large balloon, is a key component of the system. Often, we think of the lungs as being responsible for our breathing, and while they definitely are important, it is the diaphragm that brings the air into the system and pushes it back out.

Let’s think about the mechanics of our model first…

When the large balloon is pulled away from the cup, it opens up more space in the chamber. This means that there is room available for air molecules from outside the system to move in- and air molecules love empty space! Air molecules will always move towards areas of less pressure. When air molecules are packed together, this creates pressure. (Think about how you might feel if you were stuck in a small room with a lot of people and no open doors. You probably would not like it, and neither do the air molecules!) When air molecules are given a chance to move into an area of less pressure, they take it! We create an area of less pressure in our model by pulling the large balloon away from the cup. The air molecules in the cup move towards the extra space, which takes pressure off the small balloons. And, since the small balloons are connected by a tube to the air outside, this means air molecules from outside the system can move in! The new molecules fill the small balloons, inflating them to take up the extra space created in the cup.

In our model, pulling on the large balloon represents inhaling.

When the large balloon is pushed back in towards the smaller balloons, the reverse takes place. The large balloon pushes the air molecules in the cup closer together. They do not like being shoved together, so they in turn push against the outside of the small balloons. This puts pressure on the small balloons, which pushes the air molecules inside the small balloons, causing them to rush back up the tube and out of the system, into an area of less pressure (outside the cup). The small balloons deflate once the air molecules have been pushed out.

In our model, pushing on the large balloon represents exhaling.

Now that we understand our model, we can use our model’s relationship to the respiratory system to better understand how that system works. The diaphragm stretches across the bottom of our rib cage, just like the big balloon does. It’s a muscle and like all muscles, it has the ability to expand and contract on its own. When the diaphragm expands, it opens up space in the rib cage chamber (or chest cavity), just like our model did. This creates an area of less pressure that allows air molecules from outside our bodies to come swarming in through our nose and down our trachea (the tube connecting our nose and mouth to our lungs). The lungs fill with the air from outside our body. This is when the rest of the respiratory system gets to work, separating out all the things we need from the things we don’t! The diaphragm muscle then contracts, pushing the air back out of the lungs and out of our bodies through our nose. All of this happens, every minute of every day, without us even thinking about!