 Tracee! Hey everybody, Dr. O. In this video we're going to talk about the trachea and then we're going to talk about the bronchial tree and you can see why it's called a tree. If you flip this over, it would look like a tree. The trachea, its basic function is to always stay open. The pressure changes involved in inhaling versus exhaling are only a couple millimeters of mercury. So if the trachea doesn't stay open, you have a very serious problem getting rid of air but mainly inhaling it as well. This is why, you know, if someone's trachea is crushed, it's a medical emergency because the breathing is going to be extremely difficult if not impossible. So the structure of the trachea begets that function. So the trachea, as you can see here, is formed by 15 or 16 to 20, I used to say 20, C-shaped cartilage rings. So it's a C-shaped because there's not a ring in the back. It's not a complete ring. So these rings are made of hyaline cartilage. There's dense connective tissue between them and their job is to hold this open. Now, so why isn't the ring a complete circle instead of a C? Well, because right behind the trachea is the esophagus and imagine if every time you swallowed your food had to bump down these rings kind of like, you know, you sliding down the stairs when you were a kid. The other reason is because this allows the back of the trachea, since there isn't a ring there, is what's called the fibroelastic membrane. It's primarily a muscle called the trachealus muscle and then some elastic tissue. This allows your body to control the diameter of the trachea. You can make it smaller or bigger depending on how much air you need to move. All right, that's the trachea. There at the bottom of the trachea, we would have a structure called the carina or the carina. That's where it actually branches into the two primary bronchi. The carina has a bundle of nervous tissue there where if something goes down the wrong pipe and gets into your, this far down into your trachea, it'll lead to violent coughing to help get rid of us. That's good news. As far as the bronchi, so I'll give you some numbers and explain where they come from. You have the two primary bronchi, the one for each lung, the left lung and the right lung. So you can see there are different in size because the lungs are different in size. We'll cover that in a separate video about the lungs. So there's two primary bronchi, one for each lung. There are five secondary bronchi, one for each lobe. The right lung has three lobes, superior, middle and inferior. The left lung only has two, a superior and an inferior lobe. The reason there's not a third lobe in the left lung is because the heart is there. That's where the heart sits. Then as far as tertiary bronchi, there's going to be 18 or 19 of them. So each tertiary bronchus goes to a bronchopulmonary segment and there are 18 or 19 of those. There are 10 in the right lung and there are eight or nine in the left lung. So two primary bronchi, one for each lung, five secondary bronchi, one for each lobe, 18 or 19 tertiary bronchi, one for each bronchopulmonary segment. Then these bronchi continue to branch into bronchioles or little bronchi and they're going to continue to branch until you reach what's called a terminal bronchial. So you don't see them here. I'll cover that part of it, the respiratory zone in a separate video. But each of these lungs would have over 1,000 terminal bronchioles, little tiny structures that actually lead to the gas exchange surfaces. These little bronchioles are going to have a lot of smooth muscle, which is what determines the diameter and how much air moves into and out of your lungs. But I think that's about it. All right. So that is the trachea and the bronchial tree we'll pick up and cover from terminal bronchioles on in a separate video. I hope this helps. Have a wonderful day. Be blessed.