The throat at the back of the mouth is known as the pharynx, and it's a shared passageway for food, air, and water, which is why I'm sure we've all had the nasty experience of having some food or maybe some water go down our windpipe. And the windpipe is the trachea. This is what brings air from the pharynx to the lungs, and it's actually supported by these rings of cartilage that are kind of C-shaped. Basically, if you have the tube, the ring of cartilage kinda runs around it like such. Now the beginning of the trachea is called the larynx, and this is sometimes called, like, the voice box or the vocal cords, because it contains what are known as the vocal folds, which is how I'm talking to you right now. Now the trachea is going to branch when it gets to the lungs, and these two branches are known as the primary bronchi. Now bronchi are branches from the primary bronchi, so those primary bronchi are going to branch off into many, smaller bronchi that will diffuse throughout the lungs, and they're going to be supported by cartilage, similarly to the trachea. Now the thing about these bronchi is they're going to be getting smaller and smaller. Think of it like a tree. There's going to be thick branches, and then smaller and smaller branches will come off of that. The smallest branches of these bronchi are called bronchioles, kind of like arteries and arterioles or veins and venules. Got bronchi and bronchioles. So these are the smallest branches, and these guys are not supported by cartilage, they're supported by smooth muscle, and this means they can collapse, which is a bad thing. Now the lungs are the organs of respiration in humans and mammals, So their job is going to be to inhale air, and absorb that oxygen, and exhale the waste carbon dioxide. Now, the ends of these bronchioles are known as alveoli. They kind of look like bunches of grapes, and this is where the gas exchange between air and blood is going to occur. This is the thin layer of respiratory tissue that's going to act as the transfer surface. And not only is this a thin layer, it's also aqueous. And it's going to be that aqueous interface between the air and the tissue that is going to be the surface that the gases pass through, and they're going to make their way to these capillary beds that surround the alveoli. So here, you can see the alveoli, these little pink sacs that kinda look like bunches of grapes, and they're surrounded by capillary beds, as you can see in this particular image right here. And I said that they have an aqueous layer. Now remember that water has surface tension, so in order to avoid these alveoli collapsing—right, remember bronchioles can collapse—these alveoli are even more prone to collapsing, or they would be, except they have this stuff called surfactant, which is a mix of phospholipids and proteins that are produced by some alveoli, and what they do is reduce surface tension, so they're going to help prevent the alveoli from collapsing. And we need the alveoli not to collapse, so that gas exchange can keep occurring, at that surface of the respiratory tissue. So that is the basic anatomy of the respiratory system. However, there's one important piece to the puzzle here, and it's this muscle called the diaphragm. It's kind of like a sheet of muscle that runs through the middle of your chest, and it separates the top half of your torso from the bottom half, and we call that top half the thoracic cavity, like the area in there is the thoracic cavity. You know, that's where your lungs and heart are going to be located, for example, And the bottom half underneath the diaphragm is called the abdominal cavity, and that's, like, where your guts are. Right? Your intestines and that sort of stuff. So the diaphragm runs across, and it's this sheet of muscle, and it's going to be what's responsible for pulling air into the lungs. It's going to contract and pull down, and this is going to create negative pressure that pulls air into the lungs. We'll talk about the physiology of this, later in a different lesson, but those are the main components of the respiratory system. The trachea, the bronchi, the lungs, and the alveoli are that important place where gas exchange is going to happen.
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40. Circulatory System
Circulatory and Respiratory Anatomy
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