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Hair

Hair is found on most skin surfaces and its main purpose is to protect the body in several ways. This organ extends from the visible tip of the hair strand to the outside of the dermis (skin) then beneath the top layer of skin to the hair follicle’s root.

Formation and Orientation

There are three phases in the growth of human hair. Anagen phase; this takes place as the hair’s roots divide causing the growth and expansion of the hair shaft. The length of the anagen phase is genetically determined and once it ends, the catagen phase begins.

The catagen phase is the overall process of the restriction of blood flow to the hair shaft. This phase converts the hair follicles to “club hair” which is where the hair shaft connects with the lower section of the hair.

Lastly, the telogen phase. This is the phase of “rest” which can lead to the loss of hair. Stressors can cause the telogen phase to begin prematurely causing the “club” hair to become fully keratinized (keratin is the main source of protein in hair), die and detach from the scalp.

Each part of the body that has a large amount of visible hair such as the scalp or eyebrows has different phase lengths.

Function

Hair protects the sensory organs from being disturbed by day to day situations such as dust, dirt, and sweat. For example, the eyebrows and eyelashes work together to protect the eyes from harsh forces of nature. Because the roots of the hair follicles are connected to nerves, we are able to feel the movement of hair shafts.

Hair can also be seen as a way to prevent body heat from escaping what would be uncovered areas such as the head as well as a way to cool the body. Hair also protects the head from ultraviolet light, protecting it from sunburns and other toxins.

Image Caption: Cross section of a hair. Credit: Wikipedia

Hair


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