On pages 53-54, Dr. Moalem describes skin color and its connection to the role of the skin in the body. The skin is part of many different biological systems such as the immune system, nervous system, circulatory system, and metabolism. It's also very important for both creating vitamin D and protecting the folate within the body. This relates to big idea 4: biological systems interact, and these systems and their interactions possess complex properties. Explain the biological process that occurs that determines and changes skin color. How did skin color evolve in different areas of the world? How does this connect to other biological systems within the body to help or hinder them?
Tanning is a process that occurs in response to the body's exposure to the sun to protect the body from excessive sun exposure. This response is triggered by the pituitary gland. However, this process can be blocked easily. Explain how this process of tanning can be disrupted. Connect your response to big idea 4.
Response Part 1:
ReplyDeleteSkin color is determined by a pigment called melanin that human bodies produced. Melanin absorbs light and is produced by specific cells called melanocytes. Though every human has the same number of melanocytes, differences in skin color happen based on how efficient the melanocytes are and also what type of melanin they produce. The two types of melanin are red/yellow pheomelanin, which absorbs less light and leads to lighter skin, and black/brown eumelanin, which absorbs more light and leads to darker skin (pg. 53). When melanin is produced in the melanocyte, it is bound to a protein matrix and contained inside a structure called a melanosome. It is then transferred to a keratinocyte cell; from here, it moves through the epidermis layers and affects skin color (http://www.examiner.com/article/what-determines-skin-color).
Within this skin color, there are two ways skin color is affected and changed. Constitutive skin color is the initial melanin in the skin; this is the skin color people are born with and it is generally not affected by the environment. Facultative skin color occurs because of environmental factors such as sunlight (http://www.examiner.com/article/what-determines-skin-color).
Skin color evolved in different parts of the world by natural selection based on the environmental pressures of how much sunlight was present. The skin needs to absorb enough sunlight to produce vitamin D but also needs to protect the folate stores from the damaging sun. Both of these are essential to health: vitamin D balances blood levels of certain minerals and is also necessary for a working heart, nervous system, and immune system; folate helps the body replicate DNA and produce red blood cells and is also critical during pregnancy. Based on these two factors, in hot and sunny Africa, dark skin was selected for because it better protects folate stores, which are essential to health. Since there was already so much sun, those with darker skin still absorbed enough sunlight to create vitamin D while protecting folate. However, as certain populations moved north, due to geographic isolation and different environments, lighter skin was selected for. Because of the weaker and less frequent sunlight in the north, dark skin now blocked out too much sunlight and not enough vitamin D was produced. Therefore, lighter skin was the variation selected for because lighter skin absorbed enough sunlight for sufficient vitamin D production. Because the sunlight was weak and not as frequent, folate stores were still protected enough (pg. 55). Another possible correlation has been found between children’s exposure to sunlight and whether they will develop multiple sclerosis in their adult life. This seems to occur in places where the sunlight is not usually intense. Though research is ongoing about how skin color affects this, it may be a factor in determining the likelihood of contracting this disease (http://anthro.palomar.edu/adapt/adapt_4.htm).
(Sanika Bhargaw, sbharga4@students.d125.org)
Response Part 2
ReplyDeleteThe pituitary gland triggers melanocytes to produce more melanin when the body is exposed to sun—this is why, after extended sun exposure, people tan. When the body is exposed to sun, the pituitary gland produces certain hormones that boost the melanocytes and produce increased melanin (pg. 54). Specifically, the hormone is called MSH (Melanocyte-Stimulating Hormone) and is secreted by the anterior pituitary (https://www.pituitary.org/faq/faq.aspx). The anterior pituitary is one of the two different glands that make up the pituitary gland (http://www.siumed.edu/~dking2/erg/pituit.htm#adeno).
This process (of tanning or producing more melanin) can be blocked or disturbed by disrupting the trigger that signals the pituitary gland to secrete the hormone MSH. The pituitary gland gets signals from the optic nerve (pg. 54) so when the optic nerve senses sunlight, the pituitary gland will respond and secrete MSH. However, this can be disrupted by something as simple as wearing sunglasses; because the optic nerve senses far less sunlight than there actually is, the pituitary gland secretes much less MSH so melanin production is not boosted very much (pg. 54).
(Sanika Bhargaw, sbharga4@students.d125.org)