 So, of course, there are different, you know, in the last lecture we talked about capillary structure and oh, it's just the endothelial layer with a basement membrane and that's it. And yeah, that is it, but we have different variations of that pattern because we have different functional needs in different places in your body. So, we have three different levels of capillary leakiness. The continuous capillary is your quintessential capillary that we were talking about in the last lecture. That's the one that has a simple squamous endothelium. It's got its basement membrane. Everything's kind of continuous, nice. And there is exchange possible. Things that can diffuse through cell membranes can definitely get through continuous capillaries quite easily. Oxygen, carbon dioxide, these things go through easily. Other things are going to require transporters to get through and so certainly fluids are going to have a little bit of a harder time getting through although we will see in the next section that it's not entirely true. We do get some fluids in and out of continuous capillaries. Our next two flavors of capillaries are leakier and the middle leakiness is the fenestrated capillary. Fenestrated capillaries have literally, they're more like sieves and they have holes in them that allow bigger things to get through. So a little something to anticipate, if you let stuff, bigger items like proteins, for example, through a fenestrated capillary, you're going to have osmotic consequences for that. If you let a bunch of particles out through fenestrations, water is going to follow most likely to maintain osmotic equilibrium between your blood plasma, intercellular fluid compartment, and the interstitial fluid or the intracellular fluid compartment. So there's consequences of leakiness that lead to what we're going to look at in the next couple of sections in this lecture. We also have sinusoidal capillaries and these guys are by far the leakiest. They actually are, they're holy, they're holy capillaries and so holy in some places that they even allow entire cells to go through. Now places that you're going to see that level of leakiness in the bone marrow where you're actually producing blood cells, you got to get the blood cells from the site of production into the bloodstream. And so you need a place that's leaky to make it happen. So you have sinusoidal capillaries in those places. In the spleen, you do filtering, you actually filter out damaged blood cells and so there you need to be able to take the blood cells out of circulation and so you have sinusoidal capillaries there. The liver, the liver has sinusoidal capillaries because it's actually, well, there's lots of reasons why, but one of its functions is to produce plasma proteins. There are big old proteins that are hanging out in the blood plasma that are required for all sorts of stuff we're going to talk about today, but if you don't have super leaky capillaries, you can't build those big, huge proteins and then get them into the bloodstream. The fenestrated capillaries, you're going to find, I think I already said that you're going to find them in the kidneys, did I say that in the glomerulus? Oh crikes, I can't remember if I said it or not. I'm going to assume that I did because I feel like I did. If I didn't, you can ask me about it and I will fix it. The fenestrated capillaries for the most part don't allow proteins through, which is why you don't end up with protein in your urine, thankfully, or if you do, there's a problem. Did you know that if you have protein in your urine, it makes your urine frothy? Okay. All right, so we have different structures of capillaries. Now let's look at all the different ways that we can get stuff in and out.