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How are you seeing this video? How are you hearing? Why are you touching the pencil that

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you have in your hand? Because of a very special organs that you have in our body.

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We are going to study the five most important organs. Point number two, sense organs.

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the first sense organ that we are going to study is our skin the sense of touch 2.1 touch

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what are the different parts of our touch how can we feel heat cold pressure harm how do we

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feel all this. Let's cut our skin and see inside. As you can see it's not an easy

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drawing to do but I know you will do the best. Let's see, the skin is made up of

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three different layers. On the upper part we have the epithermis, this upper part

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here. This upper part is special because it's compound of different layers but

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but the only one who is dividing is this one here, I made an arrow in this line here,

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is where all the divisions of the different cells are done.

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The cells divide, but as you can see, the blood capillaries do not reach the epidermis.

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So how do they get the nutrients? How do they get the oxygen?

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They cannot. So after a few days of living, they die.

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them but luckily to us even though they die they perform a very special function which is to

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protect us these layers will be coming up and up and up higher up until they make the outer part

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of our skin so basically our skin is made up of that cells that's why if we cut our cell but it's

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a superficial cut we don't get hurt or we don't get blood out of it why because in the epithermis

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there is no blood capillaries the middle part is the dermis and it's the place where all the

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receptors that we have in our skin are we have different types of receptors but remember receptors

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are neurons yes the same neurons that we have seen in unit number seven these neurons with their

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axon their cell body the dendrites are here in specific places which are receptors and they are

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going to transmit the information from the skin up to our brain to the cortex to the cerebral cortex

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in order to perform a response to that touch as you can see there are different structures

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which goes from the epidermis to the dermis like for example like for example the hairs

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that we have all around our body we have certain areas where we have more hair than other like

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our head but usually in all our body we are full of hair which have the function of protecting us

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as you can see the hair comes from the epidermis and it's inserted in the dermis by the

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hair follicle there are also some detectors of pain there some receptors for the pain that's why

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if we try to push our hair and get it out we are hurt there are also some sebaceous gland

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that i represent here here like this which secrete some fats that are going to lubricate and make

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our skin more flexible it's very they are very very important for our skin

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they can also cause troubles for example in puberty your hormones are really high or really

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low so with these hormones disorder what happens is that the sebaceous glands start secreting a lot

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of fat that's why you can have green on your face or have acne that's a problem with the skin at

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your age. Also, there are some sebaceous glands which have special function for mammals. Remember

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that we are mammals, so we feed our babies with milk, with the women's milk. Our mammary glands

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are sebaceous glands that are modified to secrete milk instead of secreting fat.

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But let's go with the receptors that we have in our skin. We do not have only one type of receptor,

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depending on the sensation that we have we have one receptor or another let's

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start with the thermoreceptors those who are related with temperature it's not

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the same to feel cold or to feel hot we have different receptors the Krause

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corpuscles these corpuscles are related to cold temperatures but instead

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related to warm temperatures we have the Ruffini endings. In these endings we have

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the sensation of heat or warm temperatures. If we talk about pressure, we

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feel pressure on our skin, we can have a superficial touch, in this case the

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The masonry corpuscles are activated, but if it's a deeper pressure, we have the patini's corpuscle working here,

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depending on the superficial or internal.

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And what happens with the sensation of pain?

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Imagine that we cut or we burn, we have different sensations.

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First, if we cut, we have the pressure and then we have the pain.

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Then, the pain, they are responsible, the nerve endings.

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We have nerve endings here all around our skin and when we get hurt they transmit the information to the brain and the rest of our body.

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And the last layer of them is the hypothermia, is the lower one of them.

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In this layer we have a connective tissue, we have an adipose tissue.

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and if you remember from the unit number to the tissues you will remember that the adipose tissue

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is the one related with fats so we have cells which inside have a lot of fats

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and its duty is to protect the skin and to make contact with the organs that we have under our

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skin do we have the same sensation of touching every part of our body well as you can see in

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the picture that does not happen why because in our hand we need to get a really really concrete

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and specific touch to grab things or to carry things to us on our lips we need to have special

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receptors to get food inside our mouth so the areas where there is a special need of touch we

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have more receptors of them so there is different for each area of our body what about the color of

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our skin why there are different races and the different races have different colors well it's

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not the same to live in the equator than living on the poles people who live near the equator

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they have more insulation from the sun direct insulation so their skin needs to be protected

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so they have more of these cells called melanocytes melanocytes are going to dark the skin

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and protect the people who live in those locations whereas people that live on the northern areas

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they have very few hours of sunlight during the day especially during winter even in summer the

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the sun is really low. What they need is to get as much light as possible. That's why they need

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to synthesize more vitamin D with the skin. There is a problem for people who move from

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northern areas to the equator because they need to put a lot of sun tan so they don't get burned

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and also from people who live near the equator and go to northern countries because they need

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supplements of vitamin d because if not their body doesn't work correctly and you can see skin

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has a lot of interesting facts a lot of different things to learn about a lot of different receptors

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so i hope you enjoyed this class tomorrow we'll talk about the senses of smell and taste