Cell Junctions

Voiceover: In this video we're gonna talk a little bit about cell junctions. Cell junctions are basically things that connect cells to other cells. And they often occur in epithelial tissue. We're gonna talk about three major types of cell junctions today. The first, tight junctions, the second desmosomes, and the third, gap junctions. So starting off with tight junctions. Let's say we have two cells like this. So tight junctions basically connect the two cells together. And it's kinda like a glue that connects them together really tightly like that. I think of it like a watertight seal. It's a complete fluid barrier, which means that if there's water or ions or other molecules trying to get through between the two cells, they would not be able to. So it blocks out pretty much everything, from both sides of the cells, so water and ions cannot go through that gap between the two cells. This tight junction, this watertight seal tends to occur in things like the bladder, for example. Or sometimes intestines and the kidney. They occur in places where water really cannot go to other places. For example, our bladder holds urine, which is waste, and it would be really bad for our body if our bladder was unable to be watertight, to hold that urine just within the bladder. The next type that we're gonna talk about are desmosomes. Now let's say we have again, two cells like this. What desmosomes do, is I'm exaggerating the gap between these a little bit, but they're kinda like connections that hold two cells together. And these connections actually attach inside the cytoskeleton. And again, this gap is exaggerated. Usually the cells are a little closer. But in desmosomes, if there is water or ions, they can actually flow between these cells. So ions like sodium or potassium or water, or other small molecules can actually come through in this gap. I like to think about desmosomes kinda like spot welds They kinda hold the two cells together, but it's not like a complete glued seal like the tight junctions. They're kind of spotted throughout the cell so that things can actually flow in between the cells. Desomosomes tend to occur in tissues that experience a lot of stress. They offer a little bit of space for stress relief. So these spot welds, these desmosomes can be found in our skin and in our intestines. Now you notice that our intestines actually have both desmosomes and tight junctions. These cell junctions can be scattered throughout the even the same type of cell. So intestinal tissue can have both tight junctions and desmosomes. The last one we're gonna talk about are gap junctions. So let's say we have, again, our two cells like this. Gap junctions, and again I'm exaggerating the size of our gap junction. But, they're kinda like a tunnel that actually exists between the cells. So they're like a tunnel. And what they do is they actually let water and ions and so on, flow through this gap between the two cells. So they're kinda like a tunnel. These are often found in cells or tissue that spread action potential, or cells that use electrical coupling. For example, they can be found in cardiac muscle. This allows our cardiac muscle to actually spread action potential by using these ions. This allows our heart to continue beating. It can also be found in neurons. So in summary, we have three main types of cell junctions. The first are tight junctions. These are a watertight seal which prevents water or ions from flowing in between cells. We have desmosomes which are spot welds. And these spot welds generally occur in areas of stress, and they also allow water, ions, and other small molecules to flow between cells. And lastly are gap junctions. And gap junctions are tunnels that kind of connect two cells. And these tend to occur in cells that require propagation of electrical signal.