okay i want to take some time and talk about the other type of cell that you find in the stratum based sole which is this little guy right here and here's another one they are called melanocytes and they with a couple of friends are responsible primarily for skin color and it's really interesting to talk about these and of course skin color has had a lot of undeserved cultural significance so i want to talk about what's actually going on with skin color so what these cells actually do is let me show you them a little closer up so this is a closer up picture of this little guy called a melanocyte and then this figure is stained so that you can see the melanin what these guys are going to do i'll draw a bad picture for you is they are really responsible for protecting um the nuclei of your cells from uv damage okay so uv radiation you may or may not know is um a dna mutagen it causes dna mutations and so what happens is mutations this is my bad picture of a melanocyte dna mutations make cancers more likely so what these melanocytes actually do is um they make and secrete a pigment called melanin which there are different forms of melanin and some of them are brown some of them are yellow brown some of them are black and so what they are going to do is they're going to go through protein synthesis and they're going to make the melanin okay and these are little vesicles of melanin and whether what they're going to do is they are going to dump the melanin wherever uv radiation whichever side uv radiation is going to go so they're going to secrete the melanin out here and keratinocytes are actually going to take it up as well and it kind of works like wearing a dark shirt on a sunny day because this will actually bounce off uv radiation and the big objective here is to protect our friends the nuclei and not just my own nuclei but all the nuclei and all of the other cells i want to try to protect these so these are maybe a whole bunch of keratinocytes and i want to protect all of these nuclei so not only do i protect myself but i also protect it and then they take in some of the melanin that i have made and the more melanin you make and secrete the better protection your nuclei have so it's a brown yellow brown or black pigment and it's responsible in part for the color of the skin the color of the hair and the color of the eyes that's not the only pigment i'll get to the other ones in just a second so i always think that melanocytes look kind of like oogie boogie right remember oogie boogie from nightmare before christmas i think they look kind of like that especially some of these guys right here they look kind of like oogie boogie okay so um i want to talk a little bit more about them and about skin color variation and then what happens when you tan first off of course we know that people are not black or white there's a tremendous amount of tonal variation in skins in skin color and they're it that is both related to the amount of melanin you have in your skin and also to two other pigments so what is true is that we all have the same relative number of melanocytes differences in skin color are due to the location of the melanocytes do they stay close to the bottom or they go close to the top and also how persistent melanin is in people with inherently genetically darker skin meaning not related to tanning which we'll get to in just a second the melanin goes into more of the keratinocytes and ends up being closer to the surface and therefore is more protective in addition with darker skin colors you have more persistent melanin which stays around longer after protein synthesis but there are also two other pigments that are present that are responsible for skin tone variation because skin is not just dark versus light it's also different tones depending on how much pink you have in your skin so if you look at this man right here he's got a decent amount of pink in his skin simply because the hemoglobin in his capillaries is very close to the surface so you get that pinkish hue whereas this gentleman and this gentleman and actually this gentleman they all have some more yellow tones to their skin or greenish tones to their skin and my skin has that tone in it as well and that is because of another pigment in the skin called carotene you have greater and lesser amounts of carotene based on your genetics so for those of us and he's also got kind of got olive skin you can have light olive you can have dark olive it has to do with the amount of carotene so really it's the combination of the three of these the type of melanin that you have is it brown yellow brown or black the amount of melanin that you have the amount of carotene that you have the amount of hemoglobin how close it is to your the surface of your skin and that's all just a genetic variability before you start tanning and what does this have to do with the genetics of humans historically well it's kind of interesting if you look at the genetics of humans historically before we were super mobile like we are now i mean not maybe this year but typically speaking if you looked at human evolution what tended to occur is that along the equatorial region where you got the most uv exposure you had the greatest survivability and the greatest reproductive success if you had much darker skin so this is um from nasa this is a uv exposure map showing where the greatest to the less you the least uv and this if you overlay it is historically a skin color map so you see the darkest pigments closest to the equator and then if you move away from the equator you get first more variability and then as you get up closer to the poles you get [Music] lighter skin colors so uv is sort of the driving factor around the equator does anybody know what it is as you get closer to the poles it's actually vitamin d production so you have less uv radiation and when darker skin colors exist closer to the poles you have a hard time getting enough uv in to do vitamin d production so typically speaking before we were all moving around everywhere darker skin closer to the equator lighter skin closer to the poles so sort of the historical basis now of course now everybody goes everywhere except this year and there's a lot of variability a lot of variability okay so that's a little bit about skin color and now let's talk about some skin color differences and some skin color disorders first one would be albinism and um when you have a a genetic mutation that causes problem in problems in the biochemical pathway for melanin production you will not produce melanin adequately and that can occur in the skin um this little boy has genetic predisposition to darker skin but then a melanin mutation that makes him not produce the melanin in his skin this little boy has um albinism of the skin the hair and the eyes so you can get a loss of pigmentation in the hair a loss of pigmentation in the skin and if you have a loss of pigmentation in the eyes what you will see is the capillaries so your your eyes can actually look pink and you can have albinism of the skin the hair the eyes are all three and here's another child with albinism of all three now um people with albinism do not have much inherent protection from uv radiation so it becomes a problem of course skin damage and skin cancers are more likely but in addition your pigment in your eyes helps to protect your eyes from uv damage and so people with albinism of the eyes have vision problems earlier in their life and they can lose their vision this child has partial albinism not completely in its eyes so he has little protection in his eyes still okay so that's albinism that is inherited it tends to be genetic most forms of albinism are autosomal recessive vitiligo is the next one and this one is autoimmune in which for some reason your immune system starts making a mistake and attacking melanocytes it thinks maybe that they are pathogens or invaders and starts attacking melanocytes and then you lose the ability to produce the pigment in those locations and it's autoimmune so there's no cure for it it usually hits relatively symmetrically and of course it's more noticeable if the person has genetically the predisposition to darker skin so you're going to notice it more in dark-skinned individuals but it exists in everyone it can't exist in everyone this is winnie harlow she's a really famous beautiful model and she's got vitiligo notice that it's relatively symmetrical which i have no idea why that is and then here's another child with vitiligo again more noticeable in people with darker skin okay so what's going on with the suntan okay so what's going on with a suntan a suntan is your body's response to uv radiation so if you hit your cells with uv radiation like we were talking about here if you hit yourselves with uv radiation what will happen is this cell right here this melanocyte will start to produce more melanin and dump it out here to try to protect you so this suntan is really a protective response and it's increased production of melanin in response to uv radiation it's really an attempt to protect your cell dna from damage and so what you're doing is you are giving exposure and saying uv radiation might cause damage and you're trying to keep up with that uv radiation and trying to make enough melanin so that damage does not occur to your nuclei so you're making your melanocytes cry little vacuoles of melanin and so what happens if you get a sunburn what happens if you get a sunburn is you know that you have overwhelmed your melanocytes ability to protect the deeper tissues because it actually causes redness and all of the blood vessels are deep in the dermis so you've irritated your epidermis enough and maybe your dermis enough so that you actually know that you have gotten the uv radiation in there okay now how about a pigmented mole a pigmented mole like i have right here is just in one area i actually have a whole bunch of melanocytes and those melanocytes in that area over produce melanin not problematic but when we get to the next thing which is melanoma which is cancer of melanocytes if you've got more melanocytes that area is more likely to have a melanoma so you want to watch your moles so let's talk about melanoma which is cancer that occurs in your melanocytes and this is a serious i mean all cancers are not are a big deal but this one is a heck of a big deal okay so this is a malignant melanoma this is the most deadly type of skin cancer it is the most likely to metastasize and move into other tissues it only accounts for about five percent of skin cancers but the majority of skin cancer deaths compared to the other two types we're learning the survival rate is relatively low it metastasizes really quickly and aggressively and there is sort of a way so i'm not asking you to do diagnostics on yourself because you actually do want to go to a doctor if you think you've got melanoma and by the way um the predisposition to all three of these types of skin cancers um there is a genetic predisposition you don't inherit them but if you've got people in your family who have these types of skin cancers then you want to keep an eye on your skin and also keep an eye on sun exposure because sun exposure increases the likelihood of all three types of skin cancer we're going to learn about so melanoma recognition always go to the doctor if you think it is but there is the abcde rule typically speaking and i'll show you some pictures in just a second melanomas are asymmetrical in shape their borders are irregular they have color variation within the melanoma the diameter is greater than six millimeters so basically bigger is more likely and then they change over time a b c d e for evolve so look at let's look at that with these in mind so these are some pictures of melanomas that were actually diagnosed by dermatologists so a are these asymmetrical yeah they are asymmetrical b do they have irregular borders meaning not smooth borders they do c do they have color variation within them they do this one's not quite as dramatic but notice that this right here is actually lighter color darker much darker here um diameter you can't tell from here but if they were bigger they'd be more likely to be a concern um and then e again you can't tell from the picture but if a person had been watching these and they changed over time that would be a decent indicator so if you have anything that looks anything like these or if you have a mole that looks like it's changing you definitely want to get it checked sooner rather than later because um you can of course survive a melanoma typically the treatment is very very aggressive because these cancers are really aggressive but catching them early is way better than catching them late okay and that is it for the stratum based only