How do humans breathe?

How do humans breathe?

Richard Sheldon (Medical Advisor to the CA State Respiratory Care Board) gives expert video advice on: How is a pulmonologist different from other doctors?; What is the difference between the nasal cavity and the sinuses? and more...

Humans breathe by using muscles of inspiration. The diaphragm, which is dome shaped, will contract, flatten out, and then essentially invert itself, and in the process will suck air into the lungs. There are no muscles of expiration, so the lung, being an elastic organ will much like a balloon that's been blown up, will just let go of the neck of the balloon and it will empty. That's pretty much how the lung empties. There are some people who believe that when you breathe, the right nostril is a direct tube going to the right lung, and the left nostril is directly connected to the left lung, so that if you were to obstruct the right nostril, you would eliminate your ability to breathe through the right lung, and vice versa, with the left nostril. That's not the case. It is a matter of both nostrils empty into a large area behind the tongue, it goes down through the vocal cords, and it isn't until it gets to the end of the trachea, right and left, that you then have a split between the airflow.