Medical Central: The Respiratory System

Today, we cover a subject full of air... the Respiratory System!

The Respiratory System
There are a couple of things we need to keep going. One is food, the other is air... primarily, oxygen. Oxygen is needed for the chemical reactions in our cells that give said cells energy.
The Respiratory System's primary purpose is to pull in air with oxygen, and expel air that has wastes out. It's the system behind breathing. Most of the time, the brain controls our breathing without our knowledge. We even forget we're doing it! All the same, we're doing it, and we need to... or we'll die.
It starts with either our nose or mouth. These are the ways air gets into the body. The nose, in fact, has mucus and hair that "cleans" the air coming in by trapping dirt and germs.
Then the air travels down the throat, past the larnyx (sp?), through the windpipe (called the trachea), into the bronchial tree. The bronchia (sp?) are the two big pipes that go into our lungs.
The lungs is where the next step takes place. These spongy bags are the primary part of the Respiratory System... also the most well-known. The lungs also big. They need to be, since they hold a ton of air-sacks called alveoli (sp?). And by "ton", I mean six million! If you spread these alveoli out, they would take up half of a tennis court!
But back to following the air through the Respiratory System. Air flows into the bronchial tree inside the lungs, until it reaches the bronchioles (sp?). These are tiny air-pipes inside our lungs. Each pipe ends in a bunch of sacks called alveoli (sp?), which are covered in tiny blood cells. These blood cells are so tiny, only one blood cell can pass through at a time! Through tiny holes in the alveolus (sp?; singular of alveoli [sp?]), blood cells give up the waste gas that is made in the cells' energy-making chemical process, carbon dioxide. Oxygen is taken out of the air, and then placed into the blood cells. The blood cells then travel back to the heart, and into the circulatory system (the energy/oxygen transport system in the body, along with the bloodstream), which is connected in this way to the Respiratory System.
Then we start the exit procedure. Basically, we go backwards through the whole system. There is sometimes an extra step, though. At the top of the trachea is the larnyx... AKA the voice-box. This is the area that contains the vocal cords. When air passes through these cords, it can make noise. When we use the vocal cords, our tongue, and mouth in sync, we can different noises and talk! And the vocal cords can adjust themselves to make higher or lower tones.
Of course, it goes much faster than what reading all that may make it seem like. And it needs to! The human body needs about a gallon of air a minute! That means we breathe over a couple thousand times a day... especially since our body isn't the greatest air-storage-device!
We have two lungs, as you may know. But did you know that one lung is smaller than the other? It's true! The left lung is smaller than the right lung. Why? Simple... the other must-have organ for life takes up some space, so the left lung has a "dent" in which this organ fits perfectly. Which organ am I speaking of? Why, the heart of course! They have to be close to work together anyway (since the heart is the part of circulatory system, and sends the blood through the lungs), and the left lung has a perfect-sized dent where the heart can lie as close as it can to its "business partners"!
The lung, being so important, needs protection. As well as the hairs and mucus in the nose, the trachea has many microscopic hair-like structures called cilia that helps to protect the lung. They catch dirt and dust, and keep them from getting into the lung, and causing problems.
In fact, this comes to the part about smoking. We all know smoking's bad. But how? Simple... the smoke kills the cilia. Then dirt and junk fill up the lungs, turning them from a healthy pink to more of a dirty black, since there's no cilia to protect them. Then cigeratte (sp?) tar (yep, there's tar there) starts blocking up the bronchioles (sp?) and parts of the bronchial tree. That causes trouble on its own, since it stops air from reaching its destination, and oxygen getting around the body! But smoking can cause lung cancer, in which lung cells go out of whack, and start growing out of control... literally growing out of control. I mean they started growing and multiplying, and, well... hello, lung cancer!
How do the lungs get air in and out? There's a muscle called the diaphragm which does this. It pulls and relaxes, making the lungs bigger and smaller. When the lungs are bigger, air rushes in. When smaller, air is pushed out. Some other muscles help, but the diaphragm is the primary one (as well as the most well-known).