We could define the hair as an attribute of mammals. Cylindrical filament, thin, of corneous nature that animals used to maintain the level of body temperature and as a defense (camouflage).
In humans the functions of hair are merely ornamental, though, there are studies linking this ornament with sexual attraction.
STRUCTURE OF HAIR
The hair is divided into two basic parts: root and shaft.
The root is the part where takes place a high metabolic and mitotic activity.
Root ends in the bulb, this, in a central hole accommodates the dermal papilla carrying the blood supply to the hair.
Shaft is called to the part of hair, consisting of three concentric layers of cells called: medulla, cortex and cuticle. Its diameter is approximately 70 to 100 microns and its breaking load is 40 to 60 grams.
MEDULLA, has 21% of the total surface of the hair. Is located in the central part, is formed like an irregular honeycomb and composed by cornified rounded cells, without core and devoid of pigmentation.
It has no influence on the physicochemical behavior of the hair. There are hairs that may have medulla continuous, discontinuous or even lack of it. Nonexistent in the lanugo of the fetus.
THE CORTEX has a total area in the hair of 70%. It consists of cell layers that extend between the cuticle and the medulla. Is responsible of its strength, elasticity, flexibility, size, shape and texture, in short, is responsible for the mechanical properties of hair.
CUTICLE represents 9% of the total area of hair; is the outermost layer composed of flattened cells extending along the shaft surface, overlapping like a roof tile is treated. These cells are transparent and form the protective layer resistant to the forces of chemistry and physical (side pulling, etc..). If this layer is damaged, cells cease to be members, the hair becomes too porous, it loses its transparency and becomes opaque.
LIFE IN THE HAIR
The life cycle of hair starts in the bulb, then DERMAL PAPILLA produces keratin layers of cells that determine the hairline.
Hair grows between an inch and inch and a half per month, and life cycle varies from 3 to 5 years, after which, the hair is completely blocked and gives a new germinative papilla, there comes another new hair. A regular hair is composed of a variable number of hairs, between 100,000 and 150,000.
CHEMICAL COMPOSITION OF THE HAIR
The hair itself is composed by: a 28% protein, about 2% lipid and 70% water.
The most abundant protein is keratin, a protein consisting of polypeptide chains rich in cysteine.
The main elements are: carbon (C) with 45%, oxygen (O) with a 30%, nitrogen (N) with a 15%, hydrogen (H) with 6% and sulfur (S) with 5%, lesser extent we can locate: calcium (Ca), copper (Cu), cadmium (Cd), mercury (Hg), zinc (Zn), lead (Pb), iron (Fe), arsenic (As), silicon (Si) , magnesium (Mg), uranium (U), vanadium (V), sodium (Na) and potassium (K).
Primary and lower phase. Growth of a cell is a new hair.
This phase can not be observed because the process during which the hair has not yet emerged out of the skin.
The hair, from leaving the skin to the outside, can be removed and performing a trichogram in microscope, the bulb took shape like an elephant foot or fist invested, and generally, is shown less transparent, due a very intense cellular activity.
Phase in which the bulb becomes irregularly shaped, the base becomes rounded and, yet existing, the link with the papilla is minimal.
The bulb is moved to the implementation of the erector muscle and stops the growing season.
This phase has a duration ranging from 2 to 3 weeks, rare to observe and easily confused with anagen bulbs.
The bulb at this stage, is shaped similar to a match or almond, lacks keratogenous area and its size is approximately 1/3 the size of a bulb in the anagen phase.
They are easy to differentiate and exist in a ratio of: 12% women and 14% in men with in a normal hair.
Is the phase that determines the death of hair, this is approximately 3 months