 Dr. O. Hey everybody, Dr. O. So we've done lots of videos where we covered the conducting zone or conducting portion of your respiratory system. We started with the nose and the mouth, into the pharynx, the larynx, the trachea and down the bronchial tree. Now we're actually at the respiratory zone, which is where gases are exchanged. So the respiratory zone begins where a terminal bronchial, which we left off in the last video, where it actually attaches to a respiratory bronchial. Now we're at the part of the respiratory system that trades oxygen for carbon dioxide. So as you can see here, we have what's called an alveolar duct. So each of these respiratory bronchioles is going to attach to an alveolar duct that is going to connect, attach to the alveolar sac, which is a cluster of individual alveoli, also known as an alveolus. So the alveolus is the elastic, simple squamous epithelium that is going to stretch as you inhale to increase the surface area to make sure that you're trading as much oxygen for carbon dioxide as possible. Alveolar pores there. So we talked about the sac being a cluster of individual alveoli. It looks like a cluster of grapes if you look at them. The alveolar pore is actually how individual alveoli and alveolar sacs are connected to one another. This just makes sure that the pressure in the lungs is equalized across the lungs. You don't want one part of the lung to have more pressure than the other, because that could lead to at least parts of the lung deflating over inflating these types of things. All right, so that is, so you see the terminal bronchial there, leading to those respiratory bronchals. You also see the smooth muscle. That's going to determine how much air enters and exits these individual airways. So just remember, the alveoli, an alveolus is the primary gas exchange surface of the lungs, but the respiratory bronchials do trade a little bit of oxygen for carbon dioxide as well. One more image to talk about the cell types that you see here. There are going to be three major cell types. One, the type one alveolar cell, that's going to be like 97% of these cells. That's going to be the cells, the simple squamous epithelium that actually is real thin and allows for the diffusion of gases, trading oxygen for carbon dioxide. Type two alveolar cells, they're going to produce surfactant. So surfactant is very important because it reduces the surface tension in the alveolin keeps them from deflating. You wouldn't, if you don't have enough surfactant, your lungs could collapse because of that change in tension. The third type of cell that you're going to see here is just going to be the alveolar macrophages. Part of your immune system, they're looking for things to engulf and destroy. Lastly here, looking at this image, you do see the respiratory membrane. We'll cover that more in a different video, but the respiratory membrane is going to be the alveoli, the cells on the lung side that diffuse gases, plus a capillary with a little tiny bit of connective tissue between them. This is the respiratory membrane is actually where the diffusion of oxygen occurs from your lungs into your bloodstream and the diffusion of carbon dioxide occurs from your blood back into your lungs so you can exhale it. Okay, so that is the respiratory zone of your respiratory system. I hope this helps. Have a wonderful day. Be blessed.