The Physiology of Breathing
We need energy to live (no duh). But how do we get that energy? I’m glad you asked! Our body gets the energy to live from the chemical reactions that occur within our body and we get those chemicals from the food we eat, the water we drink, and, yes, the air we breathe.
When we breathe air gets pulled into our lungs into tiny little sacs called alveoli. This air consists of about 78% nitrogen, 21 % oxygen (O2), and 1% other gases including carbon dioxide (CO2). The oxygen crosses from our alveoli into capillaries where it will bind to hemoglobin in our blood. This oxygenated blood will then travel to our heart where it will then be pumped through our circulatory system to be delivered to the tissues in our body.
The oxygen then will be used by our tissues in a process called aerobic respiration. This process takes place in mitochondria within our cells to create energy via the breakdown of Adenosine Triphosphate (ATP). The primary byproducts of this process are water and CO2. The CO2 will then cross from the tissue into our blood, and some will bind onto hemoglobin, while most of it will dissolve in our blood. This will then travel back to our heart, then lungs where it will cross into our alveoli, and be exhaled. Vuala!
All of that is simple enough, but there are a couple of nuances that I missed during this process. The first is that pressure is how oxygen essentially gets “pushed” into our bloodstream and onto hemoglobin. Because the pressure of oxygen in the atmosphere is greater than the pressure of oxygen within our blood, O2 will be pushed in that direction (This is also why we get winded at elevation, where the pressure of O2 is less, so less O2 is pushed into our blood). The same goes for oxygen being delivered to our tissues. Because the pressure of oxygen within our blood is greater than within our tissues, especially as those tissues work, it moves in the desired direction. Same thing occurs, but in reverse, for CO2.
The second nuance is the importance of CO2. Although it is a byproduct of respiration, it is essential for a multitude of factors, including creating the proper pH balance within our body and giving our body the signal to breathe. This is important to understand. It is the concentration of CO2 in our blood that tells our body that we need to increase or decrease the rate and depth of our breathing, not a lack of O2. We can have plenty of O2 in our body, but an accumulation of CO2 will tell us that we need to increase our rate of breathing. Conversely, we can have little CO2 which will not give our body the signal to breathe even if we don’t have enough O2. This is part of the reason why divers do not hyperventilate prior to diving underwater. Their body will not get the signal that they have to breathe even though they don’t have enough oxygen, and they experience a shallow water blackout.
Anatomy: done. Mechanics: done. Physiology: done. Well… kind of. In the next post we are going to dive deeper into physiology to see what happens if we breathe too much, and the implications that happen after.