Humans breathe through something called the respiratory system. This system is made up primarily of our lungs and windpipe.
Why do we have to breathe?
Our body is a very complex system. One of the main things it needs is energy. When we eat our body digests the food to get complex molecules like glucose, which it can use for energy. However, food alone isn't enough. The cells also need oxygen to react with the glucose to create the energy. We get the oxygen to our cells with the respiratory system and by breathing.
We breathe in using a muscle called the diaphragm. It flattens out making our lungs expand and fill with air. When we breathe in, air gets forced through our nose or mouth, down our windpipe, and into bronchi tubes in our lungs. These bronchi tubes branch out and get smaller and smaller, like the roots or branches of a tree.
No, these aren't a kind of pasta! At the end of the smallest branches of the bronchi are tiny air sacs called alveoli. These air sacs have a very thin, one cell thick wall that allows oxygen to be passed to red blood cells as they are passing by. There are hundreds of millions of these tiny guys in our lungs.
The alveoli don't just pass oxygen to our blood, they also help to clean out waste gas from our blood cells. This waste gas is carbon dioxide. When we need to breathe the carbon dioxide out of our lungs, the diaphragm bows up and pushes the air back out, getting rid of the carbon dioxide. This makes room for fresh air with new oxygen to come back in on our next breath.
Diagram of the Respiratory System
The nose does more for breathing than just providing a place for air to enter our body. It also helps to filter the air of dust and other stuff. It does this by using lots of hairs and mucus. It also helps warm up the air prior to getting to our lungs.
Why do we get out of breath?
When we run or do strenuous activity, our muscles burn energy and use up the oxygen in our red blood cells. To try and get more energy and oxygen to these cells, our heart will pump faster to get more blood through the lungs. At the same time our lungs will try to breathe harder and faster to get more oxygen. We end up feeling out of breath and have to take a rest so our bodies can recover.
The respiratory system also helps with talking. We couldn't talk without air. By forcing air through our vocal chords, the respiratory system helps them to vibrate and create sound like talking, singing, or shouting.