Question

8. Explain why the balloons of the lung demonstration model inflate and deflate as the does this relate to what occurs in the plastic sheeting is moved up and down. How human thoracic cavity during inspiration and expiration?

Answer 1

There is a pressure present in the thoracic cavity. The manipulation of this pressure is what causes inspiration and expiration. Air flows from higher pressure areas to lower pressure areas.

Coming to the balloon lung model, let's establish the analogues of the model to the human lungs.

The balloons are the lungs and the plastic sheet is the diaphragm. When the plastic sheet is pulled, the volume of the thoracic cavity increases thus causing a drop in pressure (This is in accordance with Boyle's law of gases which states that at a constant temperature, pressure and volume have an inverse relation). This drop in pressure creates a pressure difference between the surroundings and the balloons, this leads to the air moving into the model and causing an inflation in the balloons. When the plastic sheet is moved up, the volume reduces and hence the pressure increases, which creates a difference and air flows out of the balloons.

In the lungs, during inspiration, our diaphragm expands increasing the volume and so on.

During expiration, the diaphragm relaxes. Note: it is a common mistake for people to think that the diaphragm relaxes during inspiration and contracts during expiration. This is not true. This statement implies that during inspiration no work is done. But work is done during expiration. This is wrong. YOu can try this yourself. Take a deep breath and release it and you can check for yourself which one requires more effort