The Bell Jar Model

• The Bell Jar Model is a simple representation of human lungs and their functions.
• The model consists of a bell jar (representing the thoracic cavity), a balloon (acting as the lung), and a sheet of rubber (simulating the diaphragm).
• When the rubber sheet is pulled downward, it creates a larger volume inside the bell jar, reducing the pressure. This corresponds to the diaphragm contracting and moving downwards during inhalation.
• The decrease in pressure in the jar causes air to rush into the balloon, inflating it. This mimics the lungs filling with air as we breathe in.
• Conversely, when the rubber sheet is relaxed or pushed upward, the volume inside the bell jar decreases, causing an increase in pressure. This represents the diaphragm relaxing and moving upwards during exhalation.
• The increase in pressure pushes air out of the balloon, deflating it. This is akin to when our lungs expel air as we breathe out.
• Therefore, the Bell Jar Model demonstrates that breathing is a result of changes in pressure within the chest caused by the movements of the diaphragm and rib muscles.
• It is important to note that the Bell Jar Model is a simplified representation, and does not include details such as the two lungs in the human body, the bronchi, bronchioles, alveoli, and blood vessels involved in gas exchange.
• This model does effectively illustrate the principle of breathing mechanism and can be used to explain pressure changes in the thoracic cavity and how they lead to inhalation and exhalation.
• Understanding the Bell Jar Model helps in comprehending how respiratory diseases like lung disease or emphysema, which impact the lungs’ ability to expand and contract, can affect a person’s ability to breathe.