How We Breathe

It’s as easy as breathing, right?

Air goes in, air goes out, what could be simpler?

Well, it is rather simple; but there are lots of moving parts and some amazing science
that occurs just to make this happen. Who likes respiratory equations?

Not everyone likes to do the math.
So let’s go through a simplified explanation.

Let’s begin with INHALATION, or inspiration.

Mental note: Inhalation is active, and exhalation is passive.

1st, a pressure gradient must occur!!!
The diaphragm muscle then contracts, and moves down.
Then, our intercostal muscles (between the ribs) must contract to expand the rib cage.
Your thoracic volume increases, and thoracic pressure drops becoming more negative.
Last, outside air that is warmed and
humidified through the nose and sinuses is drawn down through the conducting airways
into the lungs; which expand.
Gas exchange then occurs at the alveolar capillary level.
Oxygen is absorbed, then carbon dioxide is then produced as a waste product.
Finally, inspiration stops.

At the Alveoli: oxygen and carbon dioxide exchange between alveoli and capillaries

Next, we have EXPIRATION, or expiration.

Remember: Inhalation is active, and exhalation is passive.

The diaphragm relaxes and moves up in a dome shape.
Then, our intercostal muscles (between the ribs) relax.
Your thoracic volume decreases, and thoracic pressure rises becoming more positive.
Last, the lungs squeeze out the remaining air (filled with carbon dioxide)
and expel it in reverse through the conducting airways until it leaves the body.
Expiration stops.
Another pressure gradient is created…..
Then the process repeats itself.


Note: The number of times we breathe in 60 seconds (1 minute) is known as your respiratory rate,
Normal rate is 12 to 10 breaths per minute.


Article: Understanding How We Breathe