The Bell Jar Model
- The process of ventilation can be modelled using a bell jar to illustrate inspiration and expiration
- The different parts of the model represent different parts of the respiratory system
The bell jar model diagram
Parts of the bell jar model represent different parts of the human respiratory system
- The model is airtight and air is only able to enter via the glass tube, which represents the trachea
- As the rubber sheet, representing the diaphragm, is pulled down the volume of the jar increases, so the pressure therefore decreases
- Air is drawn in through the glass tube inflating the balloons, which represent the lungs
- This models the process of inspiration
- When the rubber sheet is released the volume of the jar decreases so the pressure increases and the air is drawn out of the balloons deflating them
- This models expiration
Limitations of this model
- The glass tube, representing the trachea, is rigid unlike the flexible cartilage rings of the trachea
- The bell jar, representing the thorax, is unable to move unlike the chest cavity and ribs which can move up and down
- The balloon, representing the lungs, are hollow and air-filled, whereas the lungs are filled with millions of individual alveoli
- The rubber sheet, representing the diaphragm, is pulled down whereas the diaphragm only flattens out
