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Biology of Hair
By peace | March 2, 2006
Structure and Function of Hair Follicles
Hair is much more complicated than it appears. It helps transmit sensory information and creates gender identity. Hair is important to the appearance of men and women. There is hair on all the major visible surfaces of the body. It is also the only body structure that is completely renewable without scarring. This article explains what exactly hair is and how it works.
Hair Origin
A developing fetus has all of it’s hair follicles formed by week 22. At this time there are 5 million follicles on the body. One million of those are on the head, and 100,000 are on the scalp. This is the largest number of follicles we will ever have – follicles are never added during life. As the size of the body increases as we grow older, the density of the hair follicles on the skin decreases.
Hair Basics
Our hair is made of a type of protein called keratin. A single hair consists of a hair shaft (the part that shows), a root below the skin, and a follicle, from which the hair root grows. At the lower end of the follicle is the hair bulb, where the hair’s color pigment, or melanin, is produced.
Most people lose about 50 to 100 head hairs a day. These hairs are replaced – they grow back in the same follicle on your head. This amount of hair loss is totally normal and no cause for worry. If you’re losing more than that, though, something may be wrong. The medical term for hair loss – losing enough hair that a person has visibly thin or balding patches – is alopecia (pronounced: ah-luh-pee-shuh).
If you have unusual hair loss and don’t know what’s causing it, it’s a good idea to see your doctor. A doctor can determine why the hair is falling out and suggest a treatment that will correct the underlying problem, if necessary.
At the base of the hair follicle are sensory nerve fibers that wrap around each hair bulb. Bending the hair stimulates the nerve endings allowing a person to feel that the hair has been moved. One of the main functions of hair is to act as a sensitive touch receptor. Sebaceous glands are also associated with each hair follicle that produce an oily secretion to help condition the hair and surrounding skin.
Hair Shape
The amount of natural curl a hair has is determined by it’s cross-sectional shape. Hair that is most similar to a circle is straight and hair that is flattened and elliptical is curly or kinky. The more circular the shaft is, the straighter it is. The more elliptical the shaft is, the curlier or kinkier the hair. The cross-sectional shape also determines the amount of shine the hair has. Straighter hair is shinier because sebum from the sebaceous gland can travel down the hair more easily. The kinkier the hair, the more difficulty the sebum has traveling down the hair, therefore the more dry or dull the hair looks.
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