12/17/2023 0 Comments Brown blood after membrane sweepMelanocytes produce two types of melanin. Differences in skin color are also attributed to differences in size and distribution of melanosomes in the skin. The genetic mechanism behind human skin color is mainly regulated by the enzyme tyrosinase, which creates the color of the skin, eyes, and hair shades. People have different skin colors mainly because their melanocytes produce different amount and kinds of melanin. They also regulate melanin production and replication of melanocytes. One melanocyte supplies melanin to thirty-six keratinocytes according to signals from the keratinocytes. Under normal conditions, melanosomes cover the upper part of the keratinocytes and protect them from genetic damage. As they become full of melanin, they move into the slender arms of melanocytes, from where they are transferred to the keratinocytes. Melanin is made within small membrane–bound packages called melanosomes. Melanin is produced by cells called melanocytes in a process called melanogenesis. The social significance of differences in skin color has varied across cultures and over time, as demonstrated with regard to social status and discrimination. Females evolved to have lighter skin so their bodies absorb more calcium. The body synthesizes vitamin D from sunlight, which helps it absorb calcium. Females need more calcium during pregnancy and lactation. In addition, it has been observed that females on average are significantly lighter in skin pigmentation than males. The leading theory is that skin color adapts to intense sunlight irradiation to provide partial protection against the ultraviolet fraction that produces damage and thus mutations in the DNA of the skin cells. Natural skin color can also darken as a result of tanning due to exposure to sunlight. Some researchers suggest that human populations over the past 50,000 years have changed from dark-skinned to light-skinned and vice versa as they migrated to different UV zones, and that such major changes in pigmentation may have happened in as little as 100 generations (≈2,500 years) through selective sweeps. Areas that are far from the tropics and closer to the poles have lower intensity of UVR, which is reflected in lighter-skinned populations. Areas that receive higher amounts of UVR, generally located closer to the equator, tend to have darker-skinned populations. There is a direct correlation between the geographic distribution of ultraviolet radiation (UVR) and the distribution of indigenous skin pigmentation around the world. Color is not entirely uniform across an individual's skin for example, the skin of the palm and the sole is lighter than most other skin, and this is especially noticeable in darker-skinned people. The red color underlying the skin becomes more visible, especially in the face, when, as consequence of physical exercise or sexual arousal, or the stimulation of the nervous system ( anger, embarrassment), arterioles dilate. The skin color of people with light skin is determined mainly by the bluish-white connective tissue under the dermis and by the hemoglobin circulating in the veins of the dermis. Melanin is produced within the skin in cells called melanocytes and it is the main determinant of the skin color of darker-skin humans. The actual skin color of different humans is affected by many substances, although the single most important substance is the pigment melanin. Differences across populations evolved through natural selection or sexual selection, because of social norms and differences in environment, as well as regulations of the biochemical effects of ultraviolet radiation penetrating the skin. Differences in skin color among individuals is caused by variation in pigmentation, which is the result of genetics (inherited from one's biological parents), exposure to the sun, disorders, or all of these. Human skin color ranges from the darkest brown to the lightest hues. For animal skin pigmentation, see Biological pigment.Įxtended Coloured ( Afrikaans: Kleurlinge or Bruinmense) family from South Africa showing some spectrum of human skin coloration
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