Defined Words: lungs, alveoli, vocal cords, glottis, gullet, epiglottis
Take a deep breath. Feel your diaphragm lower as your chest rises. Take another breath. Feel the air as it moves past the back of your throat. Right now you’re meditating, that’s all it is. Just focusing on the breath and letting other thoughts fade. The breath plays an important role in our lives even though it often takes a backseat to other thoughts. Well not today! I guarantee you’ll be thinking about your breathing while discovering how and why we breathe in the first place.
Let’s start by looking back at our evolutionary grandparents, the fish. Living in water means you can move in all three dimensions. Fish can adjust their buoyancy (ability to float) by pulling in or letting out gas from their swim bladder. We know that mutations are random which means there were a few individuals who developed multiple swim bladders. Now let’s say a drought hits and some fish living in rivers are stranded in shallow pools. Less water with the same amount of fish means that there is less oxygen for each fish. Those individuals that could gulp air into their extra swim bladders had a better chance of absorbing more oxygen.
Those swim bladders would eventually adapt into what we call lungs. Some of the gulping fish continued life underwater, using a mix of gills and lungs to breathe. Others wandered out of their aquatic environment and onto the land to find more sources of food; those individuals would become the first amphibians.
Over time, muscles developed to surround the lungs to aid in the gulping of air. Think about a balloon being pulled open. Surrounding air will rush in to equalize the pressure caused by the increase in volume. This is what is happening with your intercostal muscles (between the ribs) and your diaphragm. They contract to pull your lungs open and relax to let the surrounding bones push the air out. Luckily, you have a pair of holes that always stay open to let air flow into and out of your lungs, your nostrils!
While it’s easy to think of your lungs as hollow balloons that allow for vital gas exchange, it’s important to realize the exchange would never happen without the blood there to make the swap.
You wouldn’t want liquid blood just sloshing around in your lungs. Instead we have adapted a structure to hold the air and they actually look like bundles of grapes. Our “lung grapes” are called alveoli and each is surrounded a web of capillaries. The membranes of the capillary and alveolus are thin enough for the gas exchange to take place, but keep the liquid blood enclosed in the circulatory system. The balloon part of your lungs is just the outer membrane around the alveoli clusters, filling with oxygen rich gas.
Let’s follow the path of a carbon dioxide molecule leaving the lungs. We first enter a tube connecting our five gas bladders (three on the right, two on the left) and heads up toward the throat. We’ll pass through a narrow slit formed by two pairs of antagonistic muscles. These muscles can contract or relax to change the shape of the hole that the gas passes through. We call these muscles your vocal cords and the shape controls the frequency of the sound you make.
We’ve made it to the throat. If we were to take a look behind us, we would see a pair of holes with a flap above them. The hole we just came from is called your glottis, or your “air pipe.” The other hole is called your gullet, or your “food tube.” The flap is called the epiglottis and it covers the glottis when you swallow to prevent food and water from entering the lungs. You’re probably already aware of this flap since every time you burp, releasing gas from your gullet, you can feel and even hear the vibrations made by your epiglottis flapping.
Let’s now think about how your brain factors in. The reason you breathe is not because your communication system has signaled that you need more oxygen. In fact, the reason you breathe is because a group of neurons detect a change in pH of your blood, caused by increased carbon dioxide concentration. This causes you to breathe out. I think that’s pretty cool: we only know to exhale and inhaling is just a rebound effect.
Your blood pH detection is automated by the time you’re born but it isn’t the only way you can affect your breathing. Your vocal cords are connected to neurons that you learn to use over time. With training, you can solidify the neural paths to contract the muscles a specific amount to achieve a specific pitch. Similarly, you learn to use the muscles of your tongue (the only muscle not connected to a bone) and lips with your vocal cords to create more unique sounds that you can eventually hone into words. With enough practice, you can even memorize the exact shape to contract your vocal cords to give a middle C or a high A.
How much time did you spend thinking about your own breath while reading this section? It’s one of the most vital processes that you don’t even have to pay attention to. Your body is so incredible, it’s nice to take a moment and reflect on that every once and awhile. Focus on your breathing and never forget how far we’ve come. The lungs that you’re filling with air right now used to be used for movement in the vast oceans.