September 30 Lecture (Jen)

September 30 Lecture (Jen) - September 30, 2008 Hair:...

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September 30, 2008 Hair: Accessory Structure of the Integumentary System - Hair has a nonuniform growth cycle across body o Scalp hair has a growth cycle of 3-5 years o Hair in the eyelash grows for about 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 root is becoming keratinised and is shed, the cells in the matrix begin dividing, resulting in new cells that eventually replacing the hair shaft - We lose about 70-80 hairs/day from the scalp - Hair Colour o Colour of hair is due to the presence and activity of melanocytes at the root o Activity of these cells in genetically pre-determined o With age, the production of pigments from melanocytes decreases and air bubbles begin to become trapped in the medulla of the hair shaft. Both of these processes result in a loss of hair pigmentation (colour) o Process of loss of hair pigmentation can be accelerated by hormones, stress o 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 - During the process of shaft development, the cells of the hair follicle are constrantly absorbing nutrients from the circulatory system, causing the chemicals in circulation to become part of the hair shaft o Because of this, hair can be used to diagnose conditions such as lead poisoning (lead finds its way into the hair shaft) o 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 o 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: o 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 o The chemical profile of the feather is matched with a geological profile of an estimated breeding site. o
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September 30 Lecture (Jen) - September 30, 2008 Hair:...

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