Once the air has entered through our nose or mouth it travels down our wind- pipe which is also known as the trachea. It then transports either into the left or right bronchi where it travels into the thousands of bronchioles that are present inside the lungs. Gas exchange then takes place in the alveoli, which are the ends of the bronchioles.
Here is a diagram from Compton’s interactive encyclopaedia showing the vertical section through the thorax:
I know from studying GCSE Biology what happens to the muscles and organs of our bodies when we breathe. When we breathe IN the intercostal muscles CONTRACT. These muscles move the ribcage UPWARDS increasing the volume o f Oxygen present in the lungs. The diaphragm moves DOWNWARDS, which makes it flatten out this
therefore making the chest larger. My tutor gave me these diagrams from the “Biology for you” teachers handbook.
When we breathe OUT the intercostal muscles RELAX. The ribcage LOWERS and the chest decreases in volume. The diaphragm relaxes and moves UPWARDS back into its original position. The exhaled air is then forced out of our lungs and into the outside world.
A simple and quick way to show how the lungs operate is to use the Bell jar model. The bell jar itself represents the ribcage, which protects the lungs. The glass tube represents the trachea and the bronchi. The balloons represent the lungs and the rubber sheet represents the diaphragm. Here I have shown a diagram of the bell jar model, which I have taken from the Co-ordinated Science Biology by Brian Beckett and Rose Marie Gallagher.
How does the model of the bell jar work?
When you pull the rubber sheet, which represents the diaphragm downwards the air rushes into the balloons, which represent the lungs, and causes them inflate. They fill up with air just like our lungs when we breathe in Oxygen. Then when you put the rubber sheet to its original position the balloons deflate and the volume in the jar decreases and the air comes rushing out.
Is this model a perfect model of the lungs?
Although this is the most suitable model of the lungs that I could find there are reasons why this is not a good representation.
- Firstly the bell jar that represents the rib cage does not move. I know that when I breathe the ribcage moves up and down and in and out but the model does not show this.
- The rubber sheet would not lie flat across, it should lie in a concave shape just like the actual diaphragm does.
- There would not be as much space in the lungs as there is in the jar. I know that when I breathe in the lungs take up the whole space of the ribcage but the balloons do not demonstrate this.
