Hairs Hair Follicles And Sensory Receptors

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Tissue 6

Tissue 6

Perhaps the most noticeable of all the accessory structures in the skin is the thick forest of hairs that rise up from the surface of the epidermis. Each hair is basically a flexible rod of tightly packed, keratinized squamae (keratin-stuffed scales). The hair shaft is the portion of the hair that extends beyond the skin surface, while the hair root is the bottom portion embedded within a hair follicle (FAHL-uh-kul). (Review Figure 6.1.)

A hair follicle is a ''little bag'' lined by a membrane, and containing a hair. The base of the hair follicle lies within the dermis. But, like the epithelial cells of the epidermis, the flattened squamae of the hair are usually colored by melanin granules. There are melanocytes at the base of the hair follicle, and these normally add pigment to the squamae and color each hair as it grows.

The hairs on our bodies periodically loosen, and they are shed from their hair follicles. This periodic hair-shedding process is completely normal, and it seems to follow a definite pattern of Biological Order. Hairs in the eyebrows, for instance, are of very short duration - only 3-5 months, and then they are shed and re-grown! The hairs on our scalp, in marked contrast, often last ten times longer - 2-to-5 years - before they are shed.

''I'm worried about going bald!'' some of you might complain. ''My dad was bald by the time he was 40!'' ''Oh, I'm sorry!'' Professor Joe may respond to your understandable dismay. ''I can see why you are worried about suffering from fox mange (MAYNJ).'' Although it seems strange, humans who go bald are, much like foxes who lose much of their hair, suffering from alopecia (al-oh-PEA-she-ah), which is Greek for ''fox mange''!

The problem with alopecia (baldness or ''fox mange'') appears to be a Breaking of the Normal Pattern of Biological Order involved in hair shedding and re-growth on the scalp. This pattern can be broken for a variety of reasons, but most important are inherited genetic (jeh-NET-ik) factors that ''pertain to'' (-ic) the ''genes'' (genet) involved in the hair growth cycle. These hair growth genes apparently turn off or inhibit the re-growth of normal-sized hairs within the follicles, after they are shed. Instead, the affected person re-grows slender ''peach fuzz'' hairs within the follicles. From a distance, therefore, the person whose head carries such light ''peach fuzz'' does, indeed, look completely bald!

''What are the major functions of hairs?'' the bald or non-bald reader may inquire. [Study suggestion: Gently run your fingertips over the hairs on one arm, without touching the skin surface. Do you feel an annoying tickling or tingling sensation?] The major function of hair is sensory reception: specifically, the feeling of touch. There is a sensory nerve basket around the base of each hair follicle (see Figure 6.1). When the flexible hair is bent, it agitates the nerve basket, and a sensation of touch is experienced. Overall, the dermis is absolutely loaded with sensory receptors of various kinds. This makes the skin the body's major organ of sensory reception. (When you kiss someone on the lips, you are pressing into their sensory receptor-rich dermis, giving you and them a thrill!)

Tissue 1

Tissue 1

Tissue 1

Tissue 1

Organ 1

Organ 1

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