September 30 Lecture

September 30 Lecture - September 30, 2008 Hair One of the...

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September 30, 2008 Hair One of the accessory structures of the integumentary system Does hair grow indefinitely? - Hair has a growth cycle - scalp hair has a growth cycle of 3-5 years - hair in the eyelash grows for 2-3 months - As the growth cycle continues, the cells that are found in the hair matrix (bottom of hair follicle), become inactive and die - The root of the hair becomes keratinised and detaches from the base of the follicle and is shed - While it is becoming keratinised and being shed, the cells in the matrix begin dividing, resulting in new cells and eventually replacing the hair shaft - We lose about 70-80 hairs/day from the scalp Colour of Hair - The colour of the hair is due to the presence and activity of melanocytes at the root. Activity of these cells is genetically pre-determined. - With age, the production of pigments from melanocytes decreases - Air bubbles begin to become trapped in the medulla of the hair shaft - Both of these processes result in a loss of colour. - This process can be accelerated by hormones, stress - Hair colour can be altered chemically - The chemical configuration of the proteins in the cuticle can be disrupted by harsh chemicals - These cuticular cells become leaky, after which pigments/dyes can penetrate into the hair shaft - Thus, the cortex and the medulla of the hair shaft absorb the dye Application of the hair shaft - During the process of shaft development, the cells of the hair follicle are constantly absorbing nutrients from the circulatory system, thus chemicals in circulation can become part of the hair shaft - Because of this, hair can be used to diagnose conditions such as lead poisoning (lead finds its way into the hair shaft) - The time of exposure to a contaminant can be calculated by determining the growth rate of the hair shaft and the location on the hair shaft where the contaminate is found - There is a hypothesis and circumstantial evidence that Adolf Hitler was exposed to elevated lead levels about 4 months before his death Application of Bird Feathers - The breeding grounds of many bird species can be determined by feathers (feathers are the bird equivalent of hair and are very chemically similar to hair) based on the fact that breeding and moulting occur at the same place - The chemical profile of the feather is matched with a geological profile of an estimated breeding site. -
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This note was uploaded on 10/23/2011 for the course BIOL 2125 taught by Professor Dr.park during the Winter '02 term at A.T. Still University.

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September 30 Lecture - September 30, 2008 Hair One of the...

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