Question

compare and contrast volume and pressure in the respiratory system....

Answer 1

I'll explain this simply in the context of breathing. If something isn't clear please let me know!

INHALATION: When you breathe in, your diaphragm contracts, increasing the volume of your thoracic cavity. This results in expansion of your lungs, increasing their volume. However, this decreases the pressure within the lungs (by Boyle's Law) such that the external atmospheric pressure is now greater than the pressure within your lungs. Air moves along this pressure gradient to fill your lungs and equalize their pressure with the external pressure.

EXHALATION: When you breathe out, your diaphragm relaxes and expands, decreasing the volume of your thoracic cavity and reducing the volume the lungs occupy. However, this increases the pressure within the lungs (by Boyle's Law) such that the pressure within the lungs is now greater than the external atmospheric pressure. Air moves along this pressure gradient, exiting the lungs and dispersing into the external environment, in order so that pressure may be equalized once more.

What it comes down to is this: breathing is a consequence of the inverse relationship between pressure and volume. Your ability to breathe relies on physics!