Skin Color Study Materials

‭Skin color‬ ‭ This color is linked to the presence of melanocytes and melanin but he told us that the number of‬ ✪ ‭melanocytes, if it varied according to the location in a given individual, there is no variation‬ ‭according to sex or race and in fact the number global melanocyte count is approximately constant‬ ‭in all individuals of the human race. What differs is the quantity, the size of the melanosomes and it‬ ‭is the nature of the pigment, the quality and the quantity of pigment.‬ ‭ For example, melanosomes in a black subject are more numerous, denser therefore the quantity of‬ ✪ ‭melanins they contain is greater and they are also less easily destroyed in keratinocytes; actually the‬ ‭melanosomes are produced by the melanocytes and are then discharged into the neighboring‬ ‭keratinocytes and then as these keratinocytes rise into the different layers of the epidermis, and the‬ ‭melanocytes are gradually destroyed by keratohyalin so there are melanocytes at the level of the‬ ‭most basal layers of keratinocytes and then as we go up, in the superficial layers, the melanosomes‬ ‭and melanin disappear. And on a black subject, this disappearance is slower.‬ ‭ We were able to calculate that there are 10 times more melanosomes in black people than in black‬ ✪ ‭people and twice as much as among Asian subjects. Sun exposure causes stimulation of‬ ‭melanogenesis: an increase in the number of melanocytes. In fact there will be a differentiation of‬ ‭precursors which will enter the cell cycle and divide and this stimulation results from the increase in‬ ‭alpha MSH receptors, increase in the synthesis of melanins by the activation of tyrosinase and there‬ ‭is also under the effect from solar radiation a chemical modification of melanin which darkens these‬ ‭melanin grains.‬ ‭ So all this will transform the color of the skin: we can distinguish in solar radiation the UV A‬ ✪ ‭which have a wavelength 300 /400 nm and these have an immediate action on the melanogenesis‬ ‭therefore immediately modifies the alpha MSH receptors, the activity of tyrosinase... UV B which‬ ‭has a lower wavelength (300), they have an action shifted in time compared to the first. Hair‬ ‭coloring is linked to the presence of this melanin but is also due to the incorporation by the‬ ‭keratinocytes which will be at the origin of the production of hair and therefore incorporation by‬ ‭these keratinocytes of melanosomes containing melanin.‬ ‭ Depending on the proportion of the two types of melanins (eu or phéo), we have different colors‬ ✪ ‭at the level of the epithelial cells which form the hair: we describe three colors of black, brown and‬ ‭yellow hair which depend on the proportion of eumelanin or pheomelanin. During aging, the‬ ‭coloring of the integuments changes and the hair turns white, and this is due to two things:the‬ ‭decrease in the number of alpha MSH receptors in the melanocytes which are responsible for the‬ ‭production of melanin at the level of hair keratinocytes and then the second explanation is a‬ ‭reduction, a premature destruction by apoptosis of the number of these melanocytes. That's the‬ ‭mechanism but it seems that there is, regardless of aging genetic susceptibilities and sometimes‬ ‭there are people with white hair at 30, well before the normal age.‬ ‭ There are anomalies of coloring and appendages, pathologies: the l'albinism is impressive:This‬ ✪ ‭are individuals who do not have skin and hair coloring, albinos are whites and this is linked to a‬ ‭deficiency in tyrosinase so there is either absence of the production of tyrosinase (genetic) or a total‬ ‭functional deficiency of this enzymatic activity therefore no possibility of producing melanin‬ ‭because tyrosinase is essential for both first stages of the production of this melanin.‬ ‭ What is important is that they do not have more protection against ultraviolet radiation, solar‬ ✪ ‭exposure and the core of skin cells, these keratinocytes are no longer protected and this explains the‬ ‭significant proportion of skin cancer among them. Another anomaly: at the level of this coloring is‬ ‭Victivigo which is a pigmentation disorder so there are areas which are depigmented and this‬ ‭vitivigo is linked to the disappearance of melanocytes in certain skin areas. Addison's disease is an‬ ‭endocrine disease enne, a disease of the adrenal cortex which results in a deficiency of a‬ ‭hormone:cortisol and it is accompanied by hyper pigmentation therefore activation of melanocytes‬ ‭linked to this cortisol deficiency.‬