Crosstalk signaling between alveoli and capillaries
Pulmonary capillaries stem from the pulmonary artery. The pulmonary capillaries are tiny blood vessels that are found within the walls the alveoli of the lungs. the collarbone to the diaphragm (the muscular wall between the chest cavity The alveoli and capillaries both have very thin walls, which allow the oxygen to. Each bronchiole ends in a cluster of microscopic air sacs called alveoli The exchange of gases occurs between the alveoli and blood in the capillaries.
Inhaled oxygen enters the lungs and reaches the alveoli. The layers of cells lining the alveoli and the surrounding capillaries are each only one cell thick and are in very close contact with each other.
Crosstalk signaling between alveoli and capillaries
Oxygen passes quickly through this air-blood barrier into the blood in the capillaries. Similarly, carbon dioxide passes from the blood into the alveoli and is then exhaled. Oxygenated blood travels from the lungs through the pulmonary veins and into the left side of the heart, which pumps the blood to the rest of the body see Biology of the Heart: Function of the Heart. Oxygen-deficient, carbon dioxide-rich blood returns to the right side of the heart through two large veins, the superior vena cava and the inferior vena cava.
The crosstalk can occur in a forward direction, as from alveolus to capillary, or in a reverse direction, as from capillary to alveolus. The crosstalk direction likely depends on the site at which pathogens first initiate signaling. Thus, forward crosstalk may occur when inhaled pathogens encounter the alveolar epithelium, while reverse crosstalk may result from interactions of blood-borne pathogens with the endothelium.Mechanism of exchange of gases/very simplified lecture.
Here, we review the factors that regulate these two directions of signaling. To develop the response, proinflammatory signals must pass between the alveolar gas and blood compartments across the alveolar—capillary barrier, which is formed by juxtaposed epithelial and endothelial membranes in the alveolar wall.
However, the barrier, formed by tight and adherens junctions of the epithelial—endothelial double membrane, highly restricts liquid fluxes between the compartments. This restriction maintains, at a minimum, metabolically required liquid fluxes that if unfettered could lead to edema, impeding gas exchange. Hence, the question we consider here relates to how proinflammatory signals negotiate the flux-restrictive alveolar—capillary barrier to induce an effective immune defense.
Then the molecule of oxygen is going to go through the epithelial cells. Those are the cells that kind of make the walls of the alveolus look the way it does. Those are kind of the flat, pancake-shaped cells. And it's going to go to the base membrane. This base membrane, remember, is kind of a foundation. It offers a lot of structural support to the lungs.
And below the base membrane, it has this layer of connective tissue that this molecule of oxygen has to get through, enters another layer of base membrane. And then it goes down into the endothelial cells. These are the cells that are also kind of pancake shaped. And these are going to make the walls of the capillary.
From there, the oxygen molecule goes into the plasma and then finally gets into the red blood cell. And of course, the red blood cells are packed full of hemoglobin. So this is a little hemoglobin protein here. And this hemoglobin has four spots on it. It's going to allow four molecules of oxygen to bind it. And so once our oxygen gets there, it's going to hope to find some hemoglobin that it's got a little free spot. And once it binds to the hemoglobin, the red blood cell is going to now carry that oxygen out to the rest of the body, wherever it's needed.
So that's kind of how oxygen gets from the alveolus out to the body. Now, let me make a little bit of space. I'm going to show you what I want to do. I want to do kind of an interesting thing here.
Hopefully, it'll help you understand this journey that the oxygen molecule is taking a little bit better. So let's imagine something like this, where you've got a nice little rectangle. I'm going to try to draw this rectangle out on the side for you, in kind of the same way I'm drawing it here. So just keep your eye on the colors, because I'm not going to relabel anything, just to kind of keep it nice and easy. What I'm going to do is just imagine that the oxygen is starting at the top of this rectangular three-dimensional square-like object I'm drawing, I guess, a three-dimensional cube, rectangular cubed.
And then it's got to get to the bottom of this rectangular cube. So at the bottom, we've got the red blood cell and the hemoglobin. That's the last layer down here. And the top layer was the alveolus or the gas.
So I actually sketched that in as well. And so that would be the very top layer.
The Circulatory System
And it has to get through all these layers. This blue layer, for example, this is that liquid that's lining the inside of the alveolus. And let me draw a molecule of oxygen starting its journey up here.
That's the gas phase, right. So it has to actually get from the gas stage through the liquid layer, into the next layer, which is the epithelial cell. That's this guy right here.
That's the second layer. Third layer, we said was the base membrane. I'm just kind of going through them one by one. And this is also kind of a nice way of a review, I suppose, as well. Then you have all that connective tissue, a nice, thick layer of connective tissue.
And remember, the base membrane and the connective tissue, they're both chock full of proteins, different types of proteins. But both are there for structural support. Got some more base membrane here on this side, and this is going to be right before you get to the endothelial cells.
That was the endothelial layer.