Understanding Cell Junctions: The Key to Cell Communication and Structure

what's up ninja nerds in this video today we're going to be talking about cell junctions but before we get started

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let's get into this video all right ninjas let's talk about cell to cell junctions really it's not that hard

right it's basically just little adhesions that are forming between cells and there's many different functions of

these cell to cell junctions obviously if you had one cell here in one cell here and we had just certain proteins

that were anchored between these maybe it's to hold them together so that way if there's any kind of shearing forces

or stretching or abrasive forces it can resist the separation of those cells or if you have ions that are trying to move

between the cells and you don't want those certain things to move through it can block that it can act as like a

diffusion barrier or maybe you have little channels that exist between these two cells and you

want the cells to communicate with one another or last but not least you know there's a structure here we have a cell

here we have a cell there's a structure underneath these cells called a basal lamina

and a basal lamina is actually a little bit of connective tissue and we also have a heat adhesion molecules that not

just connect cell to cell but connect the cell to the extracellular matrix or the basal lamina

and this is what makes up what's called your basement membrane in order for us to truly understand

cell-to-cell's junctions though we have to really zoom in look at their structure know the names of those

structures the significance of it what these things are actually functionally for

and know what happens if these things are damaged or what clinical things are important

so what i want us to do is actually want to really zoom in on this connection between the cells

blow that up and look at these cells in a more zoomed in fashion and this is what we're going to be pretty much

focusing on for the rest of this video there is a couple different types of cell to cell junctions and then cell

extracellular matrix or basal lamina junction the first one that we'll discuss is

called tight junctions and there's proteins called occludings and claddins and zone occludens all of these things

that we'll get into that that's the first one the second one that we'll talk about is

called the adherence junctions and the third one that we'll talk about is called your desmosomes

now what you guys will understand is that tie junctions big thing to take away from it is they're more of like a

diffusion barrier they block things from moving between cells and help to hold cells tightly together

adherence junctions are much stronger than type junctions and they're really good for shearing forces and abrasive

forces but you know desmosomes are the most tough and really really high tensile against high shearing forces a

lot of abrasive stretch next thing is gap junctions and these are good for cell to cell communication

and last but not least is what's called your hemidesmosomes and these are what connect cells

to the basal lamina or the extracellular matrix so we have tight junctions at hearings junctions desmosomes gap

junctions and hemidesmosomes let's talk about each one of these individually understand their structure understand

their function and understand the clinical significance all right so the first solid cell junction that we have

to talk about is called tight junctions now tight junctions what i need you guys to know i need to know the structure the

function and the clinical significance okay so first thing about the structure when we talk about these here's cell

number one let's actually let's call this cell number one and this is cell number two

and again we're just looking at the cell membranes of cell number one and cell number two and how these cell membranes

are actually joined together okay because that's the point of the junction that we have here this tight junction

there's two particular proteins that come out from the cell membrane and interact with one another in between the

space between these cells and this per this pink protein up here there's two types one is called clawdens

so you have what's called clawdens and then the other one down here in this purple color here is called occludens

so you have two particular proteins that are basically spanning through the extracellular

space and actually anchored into the cell membrane of cell one and cell two and again these proteins are called

claudines and occludens now on the inner cytosolic so this would be

on the cytosol side right so this is the cell membrane this would be on the cytosol this would be the extracellular

space on the cytosolic side there's these black proteins these black circular

proteins these black circular proteins are called zona

occludins they're called zona occludings and there's different types there's zo1

zo203 okay so again you have spanning through the

cell membrane out into the extracellular spaces the claudines and occludens they connect with one another from cell one

to cell two on the cytosolic side you have the zona occludens and they're bound to that actual cludens and

claudin's proteins okay then the last protein here on the inner cytosolic side that are bound to the

zone occludens these kind of navy blue ones here these are called actin

filaments they're called actin filaments so there is again

knowing these proteins this is a very important thing because if they ask you on the test high

junctions the actual part of the protein that spans through the cell membrane out to

the extracellular component and attaches cell to cell those are called clawdens and occludens

the proteins on the cytosolic side that is bound to those actual transmembrane proteins the occludings and claudians is

called zona occludens and then the proteins that are bound on

the most inner cytosolic side to the zona occludens are called the actin filaments

now why is this important the significance of the tight junctions

is really within the name they tightly hold the cells together and the main focus of that is imagine

you have some type of like sodium molecule or potassium molecule or maybe you have some type of like protein

molecule that you don't want to be able to move

between these cells you want to block that process that is the function of these actual

tight junctions so their design is to act as a diffusion barrier and pretty much block

the transport of ions and different types of large molecules between the cells okay that's really it

what i really want to add on though is imagine that we have two parts of the cell right

so you have this part of the cell all right let's imagine here i have this blue

tissue here this remember this was called the basal lamina it was just underneath it's called the

it basically makes up whenever you have the cell and then this basal lamina makes up what's called the basement

membrane this is the basal surface of the cell this is the apical surface of the cell

tight junctions are mainly connecting cell to cell at the apical surface that's a very

important thing so another thing i need you guys to remember is that they're connected at what surface

the apical surface so they connect cell to cell at the

apical surface and they're primarily a diffusion barrier for things like ions and large molecules that's really it

now what kind of locations would you want these diffusion barriers where you want

to really kind of hold cells tightly together and maybe block certain things that you want to be able to move

not to be able to actually move between the cells and get into a particular area well i would think that one really

important one that you'd really really want to be careful of is your brain right you don't want just

proteins just moving wherever they want in and out of the blood and into your actual neural tissues so the blood-brain

barrier is definitely riddled with lots of tight junctions so the blood brain barrier would definitely be one

big one so you know within the blood-brain barrier you have these cells here this

is a capillary here this is a blood vessel and then this blue stuff is called the

basal lamina and then this third thing is called your astrocytes right so these three things are what make up

your blood-brain barrier well these uh kind of red cells are called

endothelial cells and in between the endothelial cells you see these these actual pink and purple

proteins those are called your tight junctions so whenever you have molecules that are running through here maybe you

have some type of like amino acid or some type of protein molecule that you don't want to be able

to get out into this area where the neurons are at these actual proteins will block that so that's their function

of it as a diffusion barrier so think about blood-brain barrier another one

is you know actually within our gi tract our git is a really important one that i want you guys to remember so two big

ones if you don't remember the other ones please don't forget this one blood brain barrier and git

the git we also have lots of these little tight junctions near the apical surface

because we also want to be able to again prevent certain types of pathogens certain types of molecules

that are in our gi tract from getting in to the actual blood where things are supposed to be absorbed

so we want to have tight junctions here that control the movement of certain types of molecules

from the actual lumen and into the bloodstream you know what else

is that especially in the stomach you know the cells are tightly bound to one another

if you have these cells that are tightly bound to one another in the stomach what's the stomach make a lot of

hydrochloric acid we want those cells to be really tightly close to one because if we have some separation between them

what can happen that hydrochloric acid can seep in between those cells and cause necrosive damage so it's also

really important to think about this whenever you have these two cells within the stomach you definitely want a really

tight connection because imagine if that nasty hydrochloric acid was able to seep between these it would cause destructive

lesions so that's another thing so again it's trying to prevent nasty molecules and

nasty proteins or pathogens from being able to move from the lumen and into the tissues or the blood around that actual

gi tract other areas to think about is your respiratory system obviously

within the respiratory tract there's definitely going to be these beautiful tight junctions

and there's actually a specialized tight junctions we actually have to mention this this might come up in your usmle is

that in the kidneys there's what's called leaky i know it's weird but we call them leaky junctions they're a sub

of tight junctions and in the actual proximal convoluted tubule is the specific place that i want

you guys to remember there's what's called leaky junctions so if you imagine you take kind of an uh a cell here and a

cell here and let's imagine this is a part of the kidney tubules these cells have these little leaky

junctions between them they're like tight junctions but they allow for certain types of ions to be able to pass

through things like potassium things like chloride things like sodium and water okay so that's a specialized tight

junction they're called leaky junctions and they're found in the proximal convoluted tubule of the kidneys so to

recap occludants claudines zona occludens actin again apical surfaces where these tight junctions are

connecting they're a diffusion barrier big ones to remember is blood-brain barrier

git respiratory tract and again there's this modified type called leaky junctions in

the kidney tubules why is all this important why do we need to know this here's why here's the clinical relevance

to it you know there's a nasty pathogen okay two of them one is called helicobacter

pylori you guys know this pathogen and there's another one called clostridium

difficile these pathogens they release nasty types of toxins you know what these toxins do

they cause destruction of these tight junctions if you destroy the tight junctions and

you form kind of a little space between these okay so now i can form like actual space

between these cells i can now easily allow for certain types of

things molecules whatever it may be to be able to go in between these cells a lot easier

in the stomach where h pylori likes to stay what would that do

if you actually got rid of the tight junctions in this area you would allow hydrochloric acid to

start eroding its way through and then imagine what can happen if you start having like that kind of process

happening where you start forming these nasty little things called

ulcers so then the actual helicobacter pylori again it can actually invade into these

areas and what can this cause what is this disease called this is called peptic

ulcer disease so peptic ulcer disease is the result of the h

pylori separating the tight junctions within the stomach and allowing for the acid to infiltrate in between causing

ulcers c diff you guys know this one it's going to infiltrate in between these actual

cells start separating them and when you separate them what's going to be able to leak out different things

like water and different ions and that's going to cause lots of diarrhea

and as a result if you get all of this intense diarrhea this is a infectious process called

clostridium difficile associated diarrhea and that is due to the c diff because again you're forming separation

between those cells and allowing for things to now easily be able to get pulled into the lumen of the gi tract

and plus more inflammatory molecules like more pathogens can actually leak into the bloodstream that way as well

so you get the significance of type junctions now

let's now move on to the next one which is called the adherence junctions all right so let's talk about the second

junction the adherence junctions the adherence junctions are really cool so when we talk about in comparison tight

junctions versus adherence junctions these are more specifically what we're going to talk about for more shearing

forces stretch being able to resist a lot of high tensile types of abrasive forces really

but in order to do that we have to know the particular proteins that are involved to help in that process so the

first component here is these blue proteins and this is actually a really important component here so these

proteins here are called cadherins but we give them a special you know number a little letter before we

call it e cad adherence so it's the extracellular component of

the catherine okay because the catherine actually anchors into the cell membrane and then you have the component of it

that actually is going to bulge out from the cell membrane into the extracellular space so this is an e-cad here and this

is an e-cad here and it actually it's interesting is that they're both kind of like homologous to one another they both

are pretty much the same type of structure now when we have this e-cad hearing and

this e-cad here and actually binding with one another we have to have some special molecule between them that

actually helps to really anchor them together you know what that beautiful molecule is that actually sits right in

this space here good old calcium so once you have once you remember here is cad hearings

anytime you see that word cad hearings these are calcium dependent proteins that's a big thing for your test cad

herons are calcium dependent proteins so usually calcium acts as the bridge between anchoring these two cadherins

together okay so that e-cadherins coming from the cell membrane outwards into the extracellular space binding with one

another via the process of calcium the next protein which is actually going to be on that inner cytosolic side of

the cell membrane is this purple protein this purple protein here is called vinculin

and then there's another one which is this maroon color protein which is again on the inner cytosolic side

and usually it's kind of like coupled right next to the vein killing just for simplicity's sake we put it right after

it but usually they're kind of like around the same proximity with one another and these are called the katinin

proteins and there's different types of ketene and proteins okay so you have the e-cadherins then you have the vinculin

and catenan proteins and then the last part which is on the most inner cytosolic side

is what's called your actin filaments these are called your actin filaments

so when someone says hey which types of junctions contain actin filaments on their most inner cytosolic side you can

say tight junctions and adherence junctions and you'll see later that even other

proteins as well but that is the basic structure so from extracellular side e-cadherins with

calcium then vinculin and katanan and then actin filaments on the almost inner part now because these have all of these

really important anchoring proteins they're more for resisting a lot of stretch

okay so when we talk about their function if we have cell one here and cell two

these are if you actually look compared this is the apical surface so if i had kind of that basal lamina again

this is the basal lamina here this is the apical surface this is the basal surface

these are usually a little bit more basil so if we had to compare let's say here's your tight junctions

it's going to be more basal in comparison to the tight junctions so if we were to put here for their actual

position of where they are they're more basal in comparison

two tight junctions okay beautiful that's one thing the

second thing that i really want you to remember is tight junctions are more as a diffusion barrier right they block

ions molecules large proteins things from being able to move past them between the cells

adherence junctions are more for shearing or abrasive forces

so any type of like thing where there's a lot of stretching there's a lot of rubbing

anything that's trying to separate cells apart from one another this is their design they're more designed to be able

to resist those shearing and abrasive forces that is their design they're not really a diffusion barrier they're more

resistant allowing for stretch okay keeping those cells together so

with that being said what type of tissues would you really want to have these kinds of junctions really anywhere

where there's tight junctions we have adherence junctions they give a little bit more of that ability to prevent the

cells from separating from one another from intense types of stretch or abrasion

what kind of things would that be well your stomach and your gastrointestinal tract have to accommodate

to food and fluids so they're going to have to stretch they have to accommodate to that so they'd be found within your

gastrointestinal tract so that'd be one your git the other thing is your epithelial

tissue your epithelial tissue within your respiratory tract your respiratory tract

may have to also undergo particular dilation and constriction within your bronchioles and so because that they

also have to not only have that process but you know whenever your alveoli are inflating they have to be able to

accommodate maybe a certain amount of stretch or distensibility our lungs are naturally compliant so we want the lungs

to be able to have some compliance and ability to stretch whenever they're being inflated versus whenever they're

actually exhaling and they're collapsing so lungs would be another tissue that you want to allow for them to stretch

but not separate from one another whenever they're actually expanding so the lungs

or any part of your respiratory tract really also

your urogenital system which part of these would actually be the bigger one though

your bladder right your bladder has to be able to stretch and accommodate urine so your urinary tract would be a very

important one so whenever your your bladder is getting filled up with all that urine and you're like oh baby i

gotta go these cells help to be able to prevent those these uh adherence junctions

prevent these cells from wanting to separate from one another they allow for more of that stretch

and again shearing type of abrasive forces all right so not just these areas but also think about blood vessels blood

vessels have to be able to stretch right particularly it have to undergo what's called vasodilation

so they have to be able to expand but they also have to be able to constrict so because of that they're going to

undergo particular you know stretching shearing abrasive forces also blood flow is hitting against these so there's also

that type of force there so we want to be able to have nice junctions there to allow for again the vasodilation aspect

which prevents the cells from separating during that process but also if blood is flowing through here and hitting against

these vessels with high pressure they have to be able to accommodate that high shearing forces all right what's another

type of tissue that undergoes a lot of you know abrasive and kind of like shearing forces the skin right

yeah so the skins are definitely a big one that one's going to take on a lot of stretching abrasive types of forces a

lot of like anything that's really going to be involving a lot of excessive rubbing against the skin so that would

be a big thing to think about as well so we got git respiratory tract urinary tract blood vessels and skin this is a

big big one though don't forget that one and that's one of the things that really differentiates tight junctions from the

adherence junctions as well now here's what's really cool clinical significance wise you know uh these

adherence junctions especially those eek adherents you know whenever people develop cancer

unfortunately cancer certain types of genes

may be mutated i guess is the best way of saying it and whenever these genes are

mutated it can alter the structure of some of these proteins and what it can do is it can alter the structure of

those cadherin proteins and what can happen is if those cadherin proteins aren't actually present are the

cells going to be able to stick with one another very well no

and so what happens is these cadherin proteins maybe become mutated in a particular way where they aren't

allowing for these cells to stick with one another think about why that could be a problem let's say that you have

somebody who develops a cancer right and these cells are basically kind of glob together you have this mass now

and it undergoes a particular mutation and that mutation allows for maybe a

clump of these cells to separate off from one another so let's say that these cells just kind of clumped off and

separate because these actual proteins got mutated now i can have a clump

of these cells that can spread from this primary location to a secondary location of some other portion of the body

what does that call whenever you have a solitary cancer where some of the cancer cells can break off and spread to other

areas of the body this is called metastasis and so having that process there

can be due to mutations that involve these catherine proteins so you see why that's actually

somewhat significant to think about okay now let's talk about desmosomes all right so let's talk about desmosomes the

desmosomes are actually a really cool i want you to compare these similar to the adherence junctions so they're really

good for shearing forces again a lot of you know pretty much keeping cells tightly together

a lot of abrasive forces they provide resistance to that you know again shearing and abrasive forces but they're

stronger than the adherence junctions so when you're comparing you have tight junctions adherence junctions and

desmosomes the strength actually of the adhesion between the cells is stronger as you're going in tight junctions to

adherence junctions to desmosomes okay now what are the proteins that make up the desmosome structure when you're

looking at it again you have these proteins they're called cadherins so cadherins again these are the

components of these proteins the red ones that are from the cell membrane they span outwards into the

extracellular space so these cadherins here they're really cool and there's these

proteins that kind of like connect together almost like a zipper really and they're really interesting there's two

types here one is called desmoglian and the other one is called desmocolon

so you have desmoglian and desmocolon these are two types of cadherins that are interlocking with one another in the

extracellular space now remember what i told you cad hearings

what does that mean they're calcium dependent proteins so what are you gonna have interlocking

these proteins together you're gonna have calcium out here interlocking these proteins together it's a very important

thing so from the extracellular side spanning through the cell membrane into the extracellular space you have

cadherins called desmoglian and desmocolin and their calcium dependent connection

then you have this big fat plaque that actually is going to be anchoring these down to the cytosolic part of the

cell membrane and this is called desmo plaquen so this is pretty much what's called the

plaque protein and the main component of that is called the desmoplaquen okay so this is kind of anchoring the

actual desmoglean and desmocolon to that structure which is going to be again more towards the actual in part like the

cytosolic membrane of that component right so you have the cytosolic component of the cell membrane that's

where the desmoplacken is primarily anchored and then coming from that out into the extracellular space is the

desmoclean and desmocolon proteins which are calcium dependent connection okay the next part which is actually

going to be on the inner side here which really helps to hold these cells tightly together this purple component here is

called your intermediate intermediate filaments and the main component here that's

really really important is called keratin so it's keratin that's the main

intermediate filament so if i were to ask you again

the components of the desmosomes from the extracellular space you have the cadherins desmoglia and desmocol which

are calcium dependent then on the inner cytosolic component of the cell membrane of cell one cell two is the plaque

protein which is mainly desmoplacan and then all the way in the cytosol spanning into it is the intermediate filaments

which is primarily keratin now we already said a little bit here is that these particular desmosomes are

really good for high tensile

stress and stretch right so anything that's going to be involving a lot of stretch

anything for a lot of your abrasive anything with high abrasive and kind of shearing forces is what these things are

really good at so any abrasive shearing forces these are extremely extremely good at

okay now there's

two particular types of tissues that i want you to remember okay there's a lot of them but there's two particular types

that i really don't want you guys to forget desmosomes are highly populated within

your cardiac tissue so they're highly populated within the cardiac tissue

and there is a special name for these desmosomes that are located in the cardiac tissue

and we'll talk about them when you have these cardiac myocytes and they're connecting from one another

we you know heart tissue has to be able to stretch accommodate blood coming into it

so what you want is you don't want those cardiac myocytes to separate from one another so they have to be able to

accommodate a decent amount of stretch so what happens is there is a very specific name

for this thing and when we have these they're called inter

collated disks and basically what these things are is

there are two components there's the desmosomes which is what we're talking about now and there's one more thing and

that is called gap junctions and we're going to talk about that in a little bit

but these are the two components that make them up in the cardiac tissue and again very very high yield don't forget

this intercalated discs so we have cardiac tissue the other one is the skin very very important

especially for the clinical significance so i don't want you guys that it's also know that it's important for your skin

tissue especially the epidermis so it helps to connect the epidermal cells to one another

why is this important well you know there's a disease it's a very interesting one it's called

pemphigus vulgaris you're like what pemphigus vulgaris

this is an autoimmune disease and what happens is your actual immune

system cells your plasma cells they make auto antibodies against their own tissues but guess what

those proteins are that it's attacking these antibodies love to attack the desmosomes specifically the desmoglian

and when you actually separate the desmoglin when you destroy that then these two cells aren't able to connect

well with one another and they start separating and when the epidermal cells start separating from

one another guess what you get you get a nasty blistering ulcerative type of disease and that's what this

disease is it's an autoimmune kind of skin condition it's a blistering disease that's due to the destruction of the

desmoglin proteins which is basically the desmosomes and these can cause nasty blisters

and ulcers and one of the biggest things that differentiate from the other one we're

going to talk about is this usually involves the oral mucosa whereas the other one does not involve the oral

mucosa okay that's the desmosomes now let's talk about hemidesmosomes all right

let's talk about the next type of cell junction now this one's actually kind of a tricky one because it's not

technically a cell to cell junction it's actually a cell to extracellular matrix junction or cell to basal lamina

junction but that's actually nice because it's an easy one to remember because it's not a cell true cell to

cell junction so what are the components of the hemidesmosomes all right there's a

couple different proteins so remember this is not a cell to sell so let's call let's let's actually label this this is

cell right we can sell one doesn't really matter but it's a cell and then this blue component here is what's

called the basal lamina and there's a bunch of different proteins of the basal lamina right if

you were to list some of them you'll have things like fibronectin i'll list a couple of them fibronectin

is a good one can't go wrong with laminin and another one that's always a big one

is collagen so these are some of the proteins that are involved in the extracellular matrix of the basal lamina

right this is the connection the hemidesmondosome is the connection to

the basal lamina made up of these different types of proteins to the actual cell membrane okay

now what are the components of it all right so the basal lamina i'm just having these

blue things the proteins like the fibronectin the lamina and the collagen it's coming up and connecting to this

purple component that is connected to this cell what is this purple component here that's really the big thing and

this purple component here is called integrins they're called integrins

okay that's really the biggest thing that you guys need to remember out of the hemi now is desmond is that the

integrins are the protein that spans through the entire cell membrane of this cell and

connects the cell here to the extracellular matrix which is the basal lamina consisting of

fibronectin laminin collagen all of these different types of extracellular proteins

what's the proteins on the inner cytosolic side of the cell membrane that is helping to anchor that

actual transmembrane protein or the integrins down this orange proteins are basically the

same thing as the desmosomes they're intermediate filaments and this could include

keratin okay so this would include keratin that is the basic thing of this

structure so when we're talking about the components of the hemidesmosomes the basal lamina which has fibronectin

lamina and collagen it's connected to the integrins which are the protein that is actually spanning through the cell

membrane coming out and connecting to the basal lamina and on the inner cytosolic side of that cell membrane

there's the intermediate filaments are keratin proteins okay what is the different

basic functions really it's super simple because when we talk about these hemidesmosomes they're basically helping

to form what's called your basement membrane okay it's basically helping to form the

basement membrane which is just this connection of the basal lamina to the epithelial cells of different tissues

that's all it is it maintains that connection between the basal lamina and the epithelial tissue above it that

forms the basement membrane that's it nothing crazy so could you imagine there's a nasty

disease because really the big places that i really want you guys to think about this is the skin it's the easiest

one that makes the most clinical relevance so the skin is a big one right but any other type of epithelial tissue

your epithelial tissue the respiratory tract epithelial tissue of the gi tract epithelial tissue the urogenital tract

any of those epithelial tissues are going to have this i think the skin is the easiest one to remember though

but again remember it's any of the epithelial tissues that are lining your gi tract respiratory tract and

neurogenital tract with the skin there's a very interesting part process here so you know here this

is the epithelial tissue we call that like the stratum basale and then that anchors it down to the

dermis below it right well the anchoring connection here if i were to really draw it in this kind of like bluish color

right here this is really where your basal lamina is so

what if i had a disease where my body has these plasma cells and they make these auto antibodies that are

directed against the proteins the entegrins that connect the basal lamina to the

epithelial cells and my antibodies go and destroy that connection so what would the antibodies do they would

destroy this connection right here i would no longer have integrins anchoring the cells to the base membrane and these

cells would separate so imagine me forming a separation between those two that's going to form blisters and nasty

ulcers okay what is that disease called it's called bolus pemphigoid

bolus pemphigus so these are basically what's called sub epidermal

blisters that can actually ulcerate whenever you kind of rub them they call it the

positive nikolsky sign we'll talk about it more with derm but these usually spare the oral mucosa and they involve

like the axilla they involve like the anal genital area and the different inguinal areas and sometimes even the

trunk as well but this is the clinical significance is

that these anchor the actual epithelial cells to the basement or to the basal lamina forming the basement membrane if

you have an auto antibodies that are destroying that it can separate them from these sub-epidermal blisters and

the condition is called bolus pemphigoid we finished talking about the hemidesmosomes let's hit it home with

the gap junctions all right instead of the last cell junction that we got to talk about here is gap junctions these

are really cool junctions now the biggest thing to remember is that these aren't really for

blocking the movement they're not really a diffusion barrier like tight junctions they're not really designed to be able

to resist kind of abrasive and shearing forces like the adherence junctions and like the desmosomes and they're not

really anything that's connecting another cell to a connective tissue these are primarily allowing for cell to

cell communication which is so cool now what are the different components in the structures and proteins involved here so

this whole thing here is called a gap junction but a gap junction is actually made up of two particular types of

proteins so when we take a gap junction it's actually made up of what's called conexons

connexons and there's two of them basically so two connexons make up a gap junction so imagine here this whole

thing here this whole component so here's cell one and here's cell two if you look right

here this right here is one connexon so this is one connexon and then right

here to this component right here this is a another connexon these two together are what make up a

gap junction now what's really interesting about this

is that when you actually zoom in on a connexon a connexon just one of these connexons

is made up of six this is so annoying right two three four five six connexins so when we talk about what a connexin is

so here we have what's called a connexin it's made up of what's called connects ends and how many six of them so let's

kind of recap this a gap junction is connexons two of them and a connexon

is actually what six connexins together that make this big protein so if you want to think about how many

total connections would make up a gap junction 12 right because you need one connexon another connexon and each one

of them is six so what is the whole purpose to know out of this

well these gap junctions which are made up of two connexons and one connexon is made of six connexins

is allowing for cell to cell communication and that is what's so cool about these

so if you have for example you have a cation like sodium or calcium these ions can move from this

cell to the next cell and allow for that ion transfer and that can be important in

certain types of cells that are excitable so what kind of cells would this be really really important in where

it's going to be cells where i want them to be really excitable right and i want them to be able to propagate those

electrical potentials onto other cells nearby so that would be a big deal in cardiac

tissue in smooth muscle tissue or even in certain types of neurons those are

excitable cells and we need that propagation of electrical activity which can be made via these gap junctions or

cell to cell communications so tissues where this can be important in is going to be your cardiac tissue

lots of gap junctions there but again what do we call those because remember cardiac tissue actually has what's

called intercollated discs which are desmosomes and gap junctions the other tissue would be your smooth

muscle tissue so you know smooth muscle tissue obviously a good example of this is your

gastrointestinal tract but you also have smooth muscle within the respiratory tract

and you also have smooth muscle within the euro genital tract so any type of smooth muscle even in

your blood vessels you actually have again smooth muscle so again all of these would be

particular is cardiac muscle smooth muscle what else neurons

certain types of neurons is also going to be a big one so some specific types of neurons actually do communicate via

gap junctions now not only does it allow for ions to move from cell to cell but it can also allow

for certain types of proteins or second messenger molecules to move from cell to cell you notice uh there's other things

you know it's called cyclic amp you guys have heard that right cyclic amp it activates things like protein kinase a

there's another molecule called ip3 all of these different types of molecules these are like cell signaling

molecules right and basically if they're let's say that you have some type of stimulus let's say here's some type of

molecule and it acts on a receptor on this cell so here's a receptor on this cell

when this molecule stimulates this it can activate these particular molecules exciting this cell

well maybe this cell would want to let the other cell know and so not only can ions move from cell to cell but we can

also have certain types of signaling molecules like cyclic amp ip3 other types of cytokines

which can alert the cells nearby why would that be important let's say for example

let's say you had a cell here and let's say here's a pathogen here's a pathogen

and this actual cell gets infected by this pathogen alright so now this cell is infected

what this cell could do is it could do a couple things it could tell the cell nearby hey go ahead and

make some specific anti-microbial proteins against this pathogen and it very well could do that

but it also could say to the nearby cell hey man there's a virus nearby there's a pathogen nearby you just need to go

ahead and kill yourself and it may actually trigger that cell to undergo a programmed cell death to

prevent it from being infected by that pathogen and so what it can do is it can signal

certain types of molecules nearby maybe certain types of cytokines and tell them hey

time to trigger what's called apoptosis

which is that programmed cell death process to be able to protect that cell and say hey we don't want this cell to

have another reservoir for this virus to continue to keep populating and making more and more viruses just go ahead and

die so that we can prevent that actual virus from being able to have cells as a reservoir to continue to keep making

viruses and that may be a process that occurs and that can happen not only

by certain types of molecules being released extracellularly things like interferons and letting

these cells know but it can happen via these gap junctions communicating with the nearby cells saying hey some stuff's

going on go ahead and prepare yourself for that and so not only is the function of gap

junctions allowing for ions to move from cell to cell allowing for electrical communication

but also it's important for being able to allow for cell to cell communication to trigger apoptosis to trigger maybe

certain cellular adaptive processes to undergo hypertrophy atrophy maybe whatever it may be but allows for that

cell to cell communication and it's a very cool protective response and that my friends finishes our lecture on cell

junctions i hope it made sense i hope that you guys enjoyed it and as always ninja nerds until next time

[Music] you