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Current time:0:00Total duration:9:17

Video transcript

let's talk about capillaries are actually three major different types of capillaries I'm going to just kind of sketch out all three I started with the continuous one I just drew it out to save us a little bit of time and the continuous Kapler is actually the one that you see most commonly throughout the body so that's why I wanted to start with this one a couple of things you'll notice you'll see that there are four nuclei so four cells here making up the part of the capillary we're looking at and there's a red blood cell moving through it right and I actually have the cross section on the right side so you can actually see if we were to cut along that face that I've cut this is what you'd actually see now there are two specific things I want to point out one is that there's a little gap here between these two cells I'm sketching it in yellow just to really point it out and that gap is called an intercellular because it's between cells intercellular cleft so the intercellular cleft is that yellow streak that I just drew and if I was to point it out on this cross section it would be right there you can see little hole between the two where they don't really meet up now there are two more spots I want to point out one right there and one right there in yellow and they correspond to this spot and this spot and there there is actually really nice joining between the two cells and we call them tight junctions kind of a good name for it I suppose you can kind of see why they would call it that and these tight junctions are right there labeled with my yellow arrows now the one thing I haven't drawn I'm going to just sketch out right here is in green and this kind of is a layer beneath all these cells so these cells are making up the wall of my capillary but behind them so that the blood actually doesn't see this layer except for at the intercellular cleft is a layer called the basement membrane so this green stuff that I'm drawing for you this is our basement membrane and this basement membrane is basically like a foundation for a house it's going to keep our cells kind of grounded and keep them in place and that layer is largely made of protein let me now show you a second drawing that I did this is our second type of capillary this is a Fenne straighted capillary you can see the major difference between this one in the first one is that the second one has little holes or we call them fence trations fence durations or so this is a fenced rated capillary and these pours I'm going to just label them you can also call them pores or holes these pores are all over the capillary right so we still have just as before four cells four nuclei and one little red blood cell poking his way through and you still have the intercellular cleft so just to show you where it is on this one it's right there where the two cells really don't meet up so nicely there's a little gap there and as before there's going to be a basement membrane so let me just kind of sketch out the basement membrane all the way around and on this cross-section you can see now how I've tried to draw it as best I can to show you the pores but you have to kind of now get a little creative and see where that intercellular cleft is versus where the pores are so whenever you're looking in cross-section is a little tricky because you have to almost imagine in three dimensions now the one thing that does help us is the fact that on the inside of these endothelial cells there's I'm going to draw in blue a little layer of almost like a slime and this slime layer is called glycocalyx glyco calyx and what glycocalyx is is basically sugars that are attached to proteins and this kind of sugary protein mix is all over the inside layer of these endothelial cells and so what it does is actually gets across these pores so even though there's a pore there you might get a little bit of glycocalyx spanning the pore and it'll come across and look like that the one place where you won't see it is in the intercellular cleft because that's actually a real spot between cells so if you have an intercellular cleft like you do here let me just draw the arrow down here right there you won't see any glycocalyx there so we call that little bit of glycocalyx that's bridging the the pore we call that the diaphragm diaphragm so these sells or these are fenestrated capillaries actually have diaphragms over their pores but I'm going to put a little star next to that because sometimes you can find fenestrated capillaries that do not have this glycocalyx that's covering the inside and they therefore do not have diaphragms so this is something that is generally true but not always true so let me show you the third type of capillary then let me just show you this last drawing and this is actually the largest of the capillaries this one we call this a discontinuous discontinuous capillary and another name for discontinuous capillaries sometimes they call them sinusoids so I'm just going to write that up here as well sinusoidal liver that's kind of the the most popular place or sometimes the spleen as well or bone marrow these ones are actually a few things are the largest ones and just make a little list over here they're very large and they have a lot more of this intracellular cleft space look at all these gaps between the cells right and just sketching it in yellow just to highlight it but there's a lot of gap here between the cells meaning that these capillaries end up being very leaky so in addition to being large they're very leaky and a final thing about these guys is that unlike the other two capillaries we just talked about they have a base membrane that is often incomplete so sometimes there there are whole areas that are missing base membrane just like that you might have some base membrane here and here but you can see whole chunks are missing basement membrane and maybe there's a bit of base membrane over here so let me write that as a Third Point incomplete I'm going to write BM for basement membrane incomplete basement membrane so if this is the case it'll be easier for things to kind of escape even if you have little glycocalyx here I'm just drawing a layer of glycocalyx on our a discontinuous sinusoidal but if you even if you have this glycocalyx because of the fact that you have so much of that intercellular cleft space you don't have many of the tight junctions it's going to be easier for things to get out so moving down these three different types you're getting more and more leaky as you go down so just keep that in mind is that the leakiness of the of the vessel is increasing in fact the the most leaky is this guy down here the discontinuous type so think with me for a second let's say you're a molecule in here in the capillary and you want to get out here into the tissue what are the ways you can get there one way would be if you actually just diffused across right so one way could be diffusion and that would work really well if you're a molecule of oxygen or carbon dioxide diffusion works well for those molecules but let's say you're not one of those molecules let's say you're a larger molecule or a charged molecule how would you get across so the second way then to get across could be through a vesicle maybe you could get into a vesicle here in this cell and the vesicle could transport you from being on the inside which is where this X is to where it can actually get deposited on the other side and then of course you would still have to make its way through the base membrane but that's a at least a way of getting past the cell and so this is a second approach maybe a vesicle could carry the molecule through a third way could be through this intercellular cleft again you still have to get across that basement membrane but at least you can get across the cell by simply going around this cell so maybe that intercellular cleft could be another ticket to freedom so if you want to get around you can go that way that's a third way so what's a fourth way well now we have to kind of go down to our second drawing the fence traded one and here I would suggest maybe just going through if you're that little X maybe just going through that pore and you have to plow your way through the glycocalyx if there is some there but maybe that's another way is going through the fence tration that could be another way across right so these are four ways for things on the inside to get to the outside and as you look at this list that we made these four options you can see then that our our idea around leakiness makes sense you know because now especially when you get down to the discontent Lluis vessels at the bottom you've got large gaps you know between the cells lots of intracellular clefts you've got vesicles that can you know apply anywhere diffusion can apply anywhere and you've got the fenestration so really every opportunity for things to get out of the capillaries is available in those discontinuous or sinusoidal Ares