Overview of Cellular Junctions

In this video, we are going to be talking about all of the different types of cellular junctions. This is brought to you by Dirty Medicine. Do you guys like what I'm doing on my channel? Do you want to support my channel and my quest to provide free quality medical education so that you don't need to fork up hundreds if not thousands of dollars on crappy clickbait resources in order to do well on USMLE and Comlex? If so, please consider clicking the join button. You can find that join button on my channel homepage on the bottom of every video and also as the first link in the description of any video. When you click that join link, you're going to be what's known as a Dirty Medicine member, which means that in exchange for providing secure monthly support of the channel, $4.99 a month, you will become a Dirty Medicine member. It comes with some really awesome perks. First, anytime you comment anywhere on the channel, the Dirty Medicine logo will appear after your username, so everybody will know publicly when they see your comment that you support my channel. and my mission. Additionally, you'll gain access to the locked community tab on my channel. So right now I am polling, meaning I'm asking Dirty Medicine members, hey, what do you want the topic of the next video to be? And I'm taking all of their feedback into consideration. But in the future, these perks might extend into some other cool things like unique access to members only videos or downloads, etc. Now in today's video, we are talking about cellular junctions. And for anybody that wants some practice material on this topic, I actually just released question number 32 just the other day. And question number 32 will actually take all of this information and apply it with a practice question. So I would recommend that you watch this video, learn this material, and then test your knowledge by doing practice question number 32 on my channel. So today we're talking about the different types of cellular junctions. And in order to understand... the different types of cellular junctions we have to look at the cell so here is a very simplified drawing of two adjacent cells and we're going to go through the different types of cellular junctions one at a time i'll tell you the important things that you need to know for usmle and comlex which will mostly include the function of that type of connection as well as what it is comprised of so what structures make up that junction and then for each of these different types of junctions i have a one sentence mnemonic which is super easy to memorize and apply so basically at the end of this video you'll not only understand all of the junctions because we're going to talk about them individually but you'll have four or five sentences that you can put in your pocket and use when you take usmle or complex to simplify all of this complex information into four or five simple phrases right so i like to keep it stupid and simple Let's get started by talking about tight junctions. So tight junctions, as the name implies, are very tight junctions. And because they're tight junctions, they keep cells locked tightly together. They prevent the movement of small solutes between cells. So with two cells being so close to each other microscopically, there are solutes that can pass between them. And it's the job of the tight junction to form that very secure connection. and prevent that from happening because as you might imagine if you're passing solutes between cells inappropriately that can cause cellular damage now tight junctions are composed of two structures one is occludens and one is called clotins so you've got occludens and you've got clotins now my mnemonic to memorize all this information in one simple sentence is that tight junctions occlude and claudicate so if you think about the name of the junction it's a tight junction and again its core function is to block the movement of small solutes. So what is it trying to do? Occlude and claudicate. Occlude means to block. And claudicate, if you think about like vascular claudication, claud, C-L-A-U-D, is a prefix which kind of means to like plug up and block. So again, you think about vascular claudication, blood is blocked from getting into the area it needs to go. So claudication fits into this phrase. So. tight junctions occlude and claudicate. That's the one sentence that you need to memorize. And when you think about that sentence, what does it tell you? It tells you we're talking about tight junctions. It tells you the role of the tight junctions to block things. And then occlude and claudicate should remind you of occludens and claudens, which are the two structures found in tight junctions. Now let's talk about adherens junctions. So the adherens junctions anchor adjacent cells together using cytoskeletons. So think about the name. adherens, it adheres the cells together. Now this is composed of two things interacting. One is E-cadherin, the other is actin. And E-cadherin is pretty easy to remember because the name of the junction is adherens. So some people just refer to this as the E-adherens junction. But in any event, my single sentence to memorize this, my mnemonic is adherence junctions act to cather cells together. So what does this tell you? It tells you we're talking about adherence junctions. They act to cather cells together. Act for actin and cather for e-catherin. And you definitely want to know this mnemonic because on test day, if you see e-catherin or you see actin, the test writer is trying to tell you that they are focusing on adherence junctions. So very, very high yield. So those are your adherence junctions. Next, let's talk about two very similarly related junctions. We've got both desmosomes and hemidesmosomes. So both of these structures provide structural support via intermediate filaments. Now, desmosomes specifically are composed mostly of interactions between cytokeratin and desmoplakin, whereas the hemidesmosomes connect keratin to the basement membrane. Now clinically, these are really relevant when it comes to differentiating two very high yield dermatologic conditions. So those conditions are Bullis pemphigoid, which I'll depict on the left part of this slide shown in blue, and pemphigus vulgaris, which I will depict on the right side of this slide shown in red. Now let's go through these two diseases very superficially and very briefly. and explain why there is a significant clinical difference between hemidesmosomes and desmosomes. So starting with bullous pemphigoid, this affects hemidesmosomes. This is a type 2 hypersensitivity reaction which causes IgG against hemidesmosomes. So you have dysfunction or damage of the hemidesmosomes. Now both of these diseases, just to be clear, have the sort of blistering or bullae formation. But the subtle differences between them is what you'll be tested on on USMLE or Comlex. So Bullis pemphigoid has a negative Nikolsky sign. What's Nikolsky sign you ask? If somebody has either Bullis pemphigoid or pemphigus vulgaris and you're trying to figure out which one they have because they have those blisters or those bullae, you run your fingers over the skin and with tensile force if the skin sloughs off that would be a positive Nikolsky sign. But you don't see that in bolus pemphigoid. You do see that, however, in pemphigus vulgaris. So pemphigus vulgaris, the pathophysiology is that this is also a type 2 hypersensitivity reaction. But this time it's IgG directed at desmoglian. Now that is a substance that makes up the desmosome. And therefore, the problem in pemphigus vulgaris is the desmosome. Now. This does cause a positive Nikolsky sign. So if you have a patient with pemphigus vulgaris and you rub your finger across the affected skin, that skin will slough off and it looks pretty disgusting. You can Google it to see an image. But if you think about this, how do you know the difference? How do you memorize the difference between bullis and pemphigus? Well, because pemphigus vulgaris has vulgar in its name, it's the more vulgar or the more serious disease. So it's the one with the positive Nikolsky sign. And because it's the more vulgar one, it is the disease that affects the desmosomes. Because hemidesmosomes, I sort of think of as the sort of desmosomes. And therefore, the more benign disease is directed against the sort of desmosomes. But the serious disease is directed at the full-blown desmosomes. So the vulgar one, the bad one, is desmosomes with the positive Nikolsky sign. And... Bullis is the benign one. B for Bullis, B for benign. It's not as serious and it has a negative Nikolsky sign because it's directed its pathology at the sort of desmosome. Now, again, if you were to come back to my picture here, it should make a little bit of sense why you see a positive Nikolsky or acantholysis at the intercellular junctions when the problem is the desmosomes. Because the desmosomes connect the cells intercellularly, whereas the hemidesmosomes really provide that structural... basement membrane connection. So you're going to see that sloughing intercellularly, that acantholysis intercellularly. So just remember that your desmosomes are the vulgar one. So pemphigus vulgaris is the one that acts on desmosomes. It's the one with the positive Nikolsky sign. Now the mnemonic that you see at the top of this slide is that I need some intermediate support, which tells you that for both your desmosomes and your hemidesmosomes, You need sum for desmosum or hemidesmosum. Intermediate support reminds you that these both involve intermediate filaments. So we've got a mnemonic to remember that they're involved with the intermediate filaments. The sum tells us we're talking about desmosums or hemidesmosums. But again, And just know the difference between pemphigus vulgaris and bullous pemphigoid for USMLE and COMLEX. So that's it for our desmosomes and our hemidesmosomes. The last intercellular junction that we need to talk about are the gap junctions. Gap junctions permit both chemical and electrical communication between adjacent cells. And these are composed of structures called connexons, C-O-N-N-E-X-O-N. Now, Perhaps obviously my mnemonic here is a chemical connexon between the gap. So you've got this gap between cells and there is a chemical connexon or chemical connection, if you will, between the gap. What does this tell us? Well, this tells us that we're talking about gap junctions since the mnemonic ends with the word gap. It tells us that it permits chemical communication and by extension electrical communication because of chemical and connection or connexon, if you will. just reminds us of the structure that composes the gap junctions. So with that said, this is really all you need to know when it comes to intercellular or intracellular communication and junctions. And for your studying pleasure, I'm going to fill out this table for you. So you see the five type of junctions, and we'll fill in the role of these junctions, the core components, and then my one sentence mnemonic. So if you're looking, and by the way, I'm not going to go through and read this table to you, but... The takeaway here is that if your brain is stuck and you feel like you only can fit so much more information in there for USMLE or COMLEX, and you want to take your shot on these questions with just my single sentence mnemonics, it's really only five sentences that you need to know. Tight junctions occlude and claudicate. Adherence junctions act to cadher cells together. I need some intermediate support for both desmosomes and hemidesmosomes and a chemical connection between the gap. So if you know those five sentences, you're already in pretty good shape to tackle most of the questions that you'll get about this. But just remember the very, very high yield part of today's video is the difference between pemphigus vulgaris and bullous pemphigoid, understanding which one affects the desmosome, which one affects the hemidesmosome, and whether or not there is a positive Nikolsky sign.

You can find that join button on my channel homepage on the bottom of every video and also as the first link in the description of any video. When you click that join link, you're going to be what's known as a Dirty Medicine member, which means that in exchange for providing secure monthly support of the channel, $4.99 a month, you will become a Dirty Medicine member. It comes with some really awesome perks. First, anytime you comment anywhere on the channel, the Dirty Medicine logo will appear after your username, so everybody will know publicly when they see your comment that you support my channel.

and my mission. Additionally, you'll gain access to the locked community tab on my channel. So right now I am polling, meaning I'm asking Dirty Medicine members, hey, what do you want the topic of the next video to be? And I'm taking all of their feedback into consideration.

But in the future, these perks might extend into some other cool things like unique access to members only videos or downloads, etc. Now in today's video, we are talking about cellular junctions. And for anybody that wants some practice material on this topic, I actually just released question number 32 just the other day.

And question number 32 will actually take all of this information and apply it with a practice question. So I would recommend that you watch this video, learn this material, and then test your knowledge by doing practice question number 32 on my channel. So today we're talking about the different types of cellular junctions. And in order to understand... the different types of cellular junctions we have to look at the cell so here is a very simplified drawing of two adjacent cells and we're going to go through the different types of cellular junctions one at a time i'll tell you the important things that you need to know for usmle and comlex which will mostly include the function of that type of connection as well as what it is comprised of so what structures make up that junction and then for each of these different types of junctions i have a one sentence mnemonic which is super easy to memorize and apply so basically at the end of this video you'll not only understand all of the junctions because we're going to talk about them individually but you'll have four or five sentences that you can put in your pocket and use when you take usmle or complex to simplify all of this complex information into four or five simple phrases right so i like to keep it stupid and simple Let's get started by talking about tight junctions.

So tight junctions, as the name implies, are very tight junctions. And because they're tight junctions, they keep cells locked tightly together. They prevent the movement of small solutes between cells. So with two cells being so close to each other microscopically, there are solutes that can pass between them.

And it's the job of the tight junction to form that very secure connection. and prevent that from happening because as you might imagine if you're passing solutes between cells inappropriately that can cause cellular damage now tight junctions are composed of two structures one is occludens and one is called clotins so you've got occludens and you've got clotins now my mnemonic to memorize all this information in one simple sentence is that tight junctions occlude and claudicate so if you think about the name of the junction it's a tight junction and again its core function is to block the movement of small solutes. So what is it trying to do?

Occlude and claudicate. Occlude means to block. And claudicate, if you think about like vascular claudication, claud, C-L-A-U-D, is a prefix which kind of means to like plug up and block.

So again, you think about vascular claudication, blood is blocked from getting into the area it needs to go. So claudication fits into this phrase. So. tight junctions occlude and claudicate. That's the one sentence that you need to memorize.

And when you think about that sentence, what does it tell you? It tells you we're talking about tight junctions. It tells you the role of the tight junctions to block things. And then occlude and claudicate should remind you of occludens and claudens, which are the two structures found in tight junctions.

Now let's talk about adherens junctions. So the adherens junctions anchor adjacent cells together using cytoskeletons. So think about the name.

adherens, it adheres the cells together. Now this is composed of two things interacting. One is E-cadherin, the other is actin. And E-cadherin is pretty easy to remember because the name of the junction is adherens. So some people just refer to this as the E-adherens junction.

But in any event, my single sentence to memorize this, my mnemonic is adherence junctions act to cather cells together. So what does this tell you? It tells you we're talking about adherence junctions.

They act to cather cells together. Act for actin and cather for e-catherin. And you definitely want to know this mnemonic because on test day, if you see e-catherin or you see actin, the test writer is trying to tell you that they are focusing on adherence junctions. So very, very high yield.

So those are your adherence junctions. Next, let's talk about two very similarly related junctions. We've got both desmosomes and hemidesmosomes.

So both of these structures provide structural support via intermediate filaments. Now, desmosomes specifically are composed mostly of interactions between cytokeratin and desmoplakin, whereas the hemidesmosomes connect keratin to the basement membrane. Now clinically, these are really relevant when it comes to differentiating two very high yield dermatologic conditions.

So those conditions are Bullis pemphigoid, which I'll depict on the left part of this slide shown in blue, and pemphigus vulgaris, which I will depict on the right side of this slide shown in red. Now let's go through these two diseases very superficially and very briefly. and explain why there is a significant clinical difference between hemidesmosomes and desmosomes. So starting with bullous pemphigoid, this affects hemidesmosomes.

This is a type 2 hypersensitivity reaction which causes IgG against hemidesmosomes. So you have dysfunction or damage of the hemidesmosomes. Now both of these diseases, just to be clear, have the sort of blistering or bullae formation.

But the subtle differences between them is what you'll be tested on on USMLE or Comlex. So Bullis pemphigoid has a negative Nikolsky sign. What's Nikolsky sign you ask?

If somebody has either Bullis pemphigoid or pemphigus vulgaris and you're trying to figure out which one they have because they have those blisters or those bullae, you run your fingers over the skin and with tensile force if the skin sloughs off that would be a positive Nikolsky sign. But you don't see that in bolus pemphigoid. You do see that, however, in pemphigus vulgaris. So pemphigus vulgaris, the pathophysiology is that this is also a type 2 hypersensitivity reaction. But this time it's IgG directed at desmoglian.

Now that is a substance that makes up the desmosome. And therefore, the problem in pemphigus vulgaris is the desmosome. Now.

This does cause a positive Nikolsky sign. So if you have a patient with pemphigus vulgaris and you rub your finger across the affected skin, that skin will slough off and it looks pretty disgusting. You can Google it to see an image.

But if you think about this, how do you know the difference? How do you memorize the difference between bullis and pemphigus? Well, because pemphigus vulgaris has vulgar in its name, it's the more vulgar or the more serious disease.

So it's the one with the positive Nikolsky sign. And because it's the more vulgar one, it is the disease that affects the desmosomes. Because hemidesmosomes, I sort of think of as the sort of desmosomes. And therefore, the more benign disease is directed against the sort of desmosomes. But the serious disease is directed at the full-blown desmosomes.

So the vulgar one, the bad one, is desmosomes with the positive Nikolsky sign. And... Bullis is the benign one.

B for Bullis, B for benign. It's not as serious and it has a negative Nikolsky sign because it's directed its pathology at the sort of desmosome. Now, again, if you were to come back to my picture here, it should make a little bit of sense why you see a positive Nikolsky or acantholysis at the intercellular junctions when the problem is the desmosomes.

Because the desmosomes connect the cells intercellularly, whereas the hemidesmosomes really provide that structural... basement membrane connection. So you're going to see that sloughing intercellularly, that acantholysis intercellularly.

So just remember that your desmosomes are the vulgar one. So pemphigus vulgaris is the one that acts on desmosomes. It's the one with the positive Nikolsky sign.

Now the mnemonic that you see at the top of this slide is that I need some intermediate support, which tells you that for both your desmosomes and your hemidesmosomes, You need sum for desmosum or hemidesmosum. Intermediate support reminds you that these both involve intermediate filaments. So we've got a mnemonic to remember that they're involved with the intermediate filaments. The sum tells us we're talking about desmosums or hemidesmosums. But again, And just know the difference between pemphigus vulgaris and bullous pemphigoid for USMLE and COMLEX.

So that's it for our desmosomes and our hemidesmosomes. The last intercellular junction that we need to talk about are the gap junctions. Gap junctions permit both chemical and electrical communication between adjacent cells. And these are composed of structures called connexons, C-O-N-N-E-X-O-N. Now, Perhaps obviously my mnemonic here is a chemical connexon between the gap.

So you've got this gap between cells and there is a chemical connexon or chemical connection, if you will, between the gap. What does this tell us? Well, this tells us that we're talking about gap junctions since the mnemonic ends with the word gap. It tells us that it permits chemical communication and by extension electrical communication because of chemical and connection or connexon, if you will. just reminds us of the structure that composes the gap junctions.

So with that said, this is really all you need to know when it comes to intercellular or intracellular communication and junctions. And for your studying pleasure, I'm going to fill out this table for you. So you see the five type of junctions, and we'll fill in the role of these junctions, the core components, and then my one sentence mnemonic.

So if you're looking, and by the way, I'm not going to go through and read this table to you, but... The takeaway here is that if your brain is stuck and you feel like you only can fit so much more information in there for USMLE or COMLEX, and you want to take your shot on these questions with just my single sentence mnemonics, it's really only five sentences that you need to know. Tight junctions occlude and claudicate.

Adherence junctions act to cadher cells together. I need some intermediate support for both desmosomes and hemidesmosomes and a chemical connection between the gap. So if you know those five sentences, you're already in pretty good shape to tackle most of the questions that you'll get about this.

But just remember the very, very high yield part of today's video is the difference between pemphigus vulgaris and bullous pemphigoid, understanding which one affects the desmosome, which one affects the hemidesmosome, and whether or not there is a positive Nikolsky sign.

Transcript for:Overview of Cellular Junctions

Transcript for:
Overview of Cellular Junctions