The Bell Jar Model

• The Bell Jar Model is a practical depiction of the human respiratory system. It uses simple materials to represent the major parts and illustrates how they function.

• Items in the model: A bell jar stands for the thorax (chest cavity), a balloon inside it acts as the lung, and a sheet of rubber on the bottom of the jar works as the diaphragm.

• The model illustrates how the process of breathing works in the human body. When the rubber sheet (diaphragm) is pulled down, it increases the space inside the jar (thorax). This reduces air pressure inside, causing the balloon (lung) to inflate as air rushes in to fill the space.

• Pushing the rubber sheet (diaphragm) upwards decreases the space inside the jar (thorax), increasing air pressure which forces air out of the balloon (lung). This represents exhalation.

• The model demonstrates that the diaphragm’s movement is what primarily drives inhalation and exhalation. During inhalation or breathing in, the diaphragm contracts and moves downwards, making more space for the lungs to expand.

• During exhalation or breathing out, the diaphragm relaxes and moves upwards, reducing the amount of space for the lungs and forcing air out.

• However, note that the Bell Jar Model is a simplification. In reality, the human respiratory system is far more complex. For example, it has two lungs rather than one, and air enters and exits through a system of tubes (trachea and bronchi).

• The Bell Jar Model doesn’t show the partition between the two lungs, or the details of how oxygen gets into the blood (via the alveoli) and CO2 is released.

• Despite the simplifications, the Bell Jar Model is useful for understanding the basic mechanics of breathing and the role of the diaphragm in this process.