| MadSci Network: Development |
Hair is produced by the skin, which consists of two distinct layers, the epidermis and the dermis; these are separated by a layer of connective tissue - the basal lamina. Molecular (inductive) signals between the cells of the dermis and the epidermis lead to the formation of a specialized cellular tissue, the hair follicle, which produces hair. |
Different regions of your skin differ -- the skin on the soles of your feet is different from the skin on the top of your head, or on your back. These differences are determined in part by which specific genes are expressed in specific skin regions. For example, different keratins – the major structural proteins of the skin – are expressed in different regions. |
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The regional differences between regions of the skin are under genetic control - the same type of control that determines where arms and legs emerge from your body. It leads to differences in the thickness of the skin, the number of sweat glands (per unit area), and the types of hair follicles formed. |
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It is the type and behavior of hair follicles that determines the quality and length of the hair produced in various regions of the body. Hair follicles have a distinctive cycle. They go through a cycle in which they grow (anagen), regress (catagen), become dormant (telogen), and then grow again (anagen). It is the relative length of the growth and the regression phases, that appears to control hair length. A number of recent papers indicate that changes in signals mediated by various "growth factor" proteins plays an important role in the regulation of the hair growth cycle. |
So a combination of the type of hair follicle formed in various parts of the body, and the regulation of the follicle cycle determines the length of hair formed. |
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