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Video transcript

to help us understand how cell-to-cell communication works I want you to think back to your good old elementary school days and in particular I want you to think about the things you'd have to do in order to secretly talk to your friends during class so here you are sitting in your classroom and you desperately want to tell your friend here something so you write a little note and you pass it to them from your hand directly to their hand so they see the note but no one else sees it it's just for them but let's say you want to tell your friend across the room something I don't know about you but when I was in elementary school I used to write notes on pieces of paper folded up into a paper airplane and I had pretty good aim back then so I'd throw my paper airplane over to my friend across some distance and they'd get my message and again they'd be the only one who got the message no one else got my little paper airplane message and if I wanted to tell a few friends something I might call a little huddle and actually say a few things just to this group of friends here so my voice would cross this small distance between us now let's kick things up a notch I was kind of a rebel in elementary school and sometimes I'd go to the Secretary's desk and take over the intercom to say funny things to my friends maybe to tell them to meet me at the flagpole or on the playground at recess or something and so this intercom message that I send out that would go to everyone it would be broadcasted to the whole school and so those who wanted to come meet me would do that and those who wouldn't wouldn't and we can think of cells as little people that do really similar things because you might not always think about it but it's really really important that cells are able to talk to each other and evolutionarily cells being able to communicate with each other are a major reason why we're as complex as we are as human beings and I'll give you examples of when cells might talk to each other as we go along here so how two cells pass notes to each other how do they directly communicate with each other well one way is by actual direct contact so cells have lots of proteins stuck in there are plasma membranes here that that serve a lot of functions and the most important one is for communication so let's look at a macrophage here this is a type of white blood cell that's a part of your immune system so when these macrophages see a foreign invader maybe a little bacteria or a virus they can ingest it they can ingest it then they break it down and then they display a little piece of it which is now called an antigen on their surface so they show it off on their surface with one of these cell surface proteins here and this one in particular is called an MHC 2 protein so now this little antigen here has become the note that they want to pass on this antigen is the message and so another white blood cell maybe maybe a helper t-cell might come along and then grab hold of this antigen here with one of its cell membrane proteins in this case a t-cell receptor so just by doing this the macrophage here managed to pass a message on to the helper T cell here and now based on which antigen this is the T cell can decide whether to start a full-blown immune response maybe it'll go off and ring more alarm bells by activating other antibody cells which are called b-cells or not maybe they'll just do nothing it just depends on what type of note this is so when cells directly touch to communicate sort of unsurprisingly this is called direct cell cell communication or just direct binding now what about our other methods of communication cells can also communicate over short distances this is our paper airplane here so for example let's look at two neurons so they're in close approximation but one end of a neuron doesn't quite touch the start of the next neuron here there's a little gap there called the synaptic cleft so what neurons do is they release little signals called neurotransmitters to communicate with each other so neurotransmitters get released from the end of this neuron and they'll diffuse across this little distance here until they bind onto one of the dendrites of this next neuron and that effectively is the message on from this neuron to this next neuron the paper airplane is thrown from here to here and and this is called neural communication and over here just like calling a huddle one cell can talk to a small group of cells locally as well so for example just underneath our skin let's say the the skin inside our nose we have these immune cells called mast cells and they're really important in mediating allergic reactions that's why I purposely pick the nose here so let's say you're allergic to certain pollens and one day in the spring you found yourself walking through the park inevitably you'd breathe in some pollen and then the pollen would go on to attach to these antibodies stuck to our mast cells and what happens as a response to this is that the mast cells release little chemical signals called histamine so histamine acts as our short-range message it travels around two cells in the area to let them know that an allergen has been found and let's some notice start preparing for an allergic reaction to take place and this type of communication is called paracrine signaling paracrine meaning nearby finally the intercom take over how do ourselves talk to huge groups of cells at once well they do that by endocrine signaling so for example cells in our pituitary gland in our brain make a lot of the important hormones in our bodies so let's say that they're making growth hormone gh to send around to to all the cells in the body sending this hormone is their form of communication here so they'll create the growth hormone inside their cell bodies and they'll release them into the bloodstream and now our growth hormone can travel through the bloodstream and get to literally any place in the body so every cell of your body has the opportunity to get this growth hormone message it doesn't mean that every cell will necessarily respond to the message some cells just don't have the right proteins to bind certain hormones but either way you can see that this is a long distance form of communication
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