Working Model of Lungs:
This simple Bell jar model lung can be used to demonstrate the basic principles of breathing. The model should be assembled as in the diagram. A swimming cap makes a suitable diaphragm. The cap can be attached to the bottom of the bell jar, and the balloons can be attached to the Y-shaped tube with elastic bands or plastic-coated wire.
The cavity inside the bell jar is airtight. As the diaphragm is pulled down, the volume of the cavity increases. This causes the pressure rises and the air rushes out of the balloons causing them to deflate. The act of breathing has two stages:
Inhalation: The intake of air into the lungs through expansion of chest volume.
Exhalation: The expulsion of air from the lungs through contraction of chest volume.
Inhalation and Exhalation involve muscles:
1. Rib muscles or Intercostal Muscle – The muscles between the ribs in the chest.
2. Diaphragm Muscle – The diaphragm and rib muscles are constantly contracting and relaxing approx 16 times/min, thus causing the chest cavity to increase and decrease.