The hair follicle is divided into four anatomical regions: infundibulum, isthmus, soprabulbare Region (or area of the bulge) and bulb.
On average, in the scalp hair it is about 100,000 (up to 150,000 in women) and their number is predetermined at birth.
Hair follicles are derived fetal epidermis, which is in the vagina in the dermis and nell'ipoderma and incorporates at its base an accumulation of mesenchymal cells of the dermis, highly specialized, which give rise to the dermal papilla (DP).
The origin of the development of hair follicle thickens locally a group of basal cells of the epidermis, to form the primitive hair germ. The organization and development of the primitive germ leading to the formation of an oblique cell structure, which becomes deeper in the dermis slant.
Normally, each germ appears on the skin surface, singly or in groups of 2-4 seeds at a defined distance of 270 to 350 u. All follicles originate during fetal development and birth their number is final.
The hair follicle develops into the follicle, including the sebaceous gland and the erector muscle of hair.
Infundibulum soprabulbare Isthmus Region (or the bulge area) The bulb contains the hair bulb, dermal papilla, an area of spindle cells embedded in an environment rich muscopolisaccaridi: The dermal papilla is the key area of the bulb, with a crucial link between activity of fibroblasts of the papilla and hair matrix cheratinocidi.
The area of the dermal papilla is surrounded by a dense vascular network and nervous: the nutrient supply to the bulb comes from the capillaries of the subdermal arterial plexus and is developed mainly at the level of insertion of the bulb and sebaceous duct, and even the hair bulb is surrounded by numerous myelinated nerve endings that surround it throughout its length. Part of the nerve fibers also innervate the erector muscles of hair.
For the purposes of hair transplantation is crucial to point out some essential elements:
The rich fabric of muscopolisaccaridi under the dermal papilla is the area where stem cells are essential for its stimulation and its maintenance. The hair follicles are not only individually placed in the dermis of the scalp. The actual distribution is in follicular units: clusters of 2,3,4 bulbs (sometimes 5 or 6, especially in people with particularly rich foliage) are in fact the most natural "islands" and is easy to see, in people with very thick hair with epiluminescence technique and densitometry, these small islands that contribute to the density of the foliage. With a provision for the more geometric, it is usually easier to identify the alternation of single follicular units bulbs of various sizes. Each follicular unit also comprises a level or 2 follicles. In terms dermatological unit represents the set of follicle bulb, erector muscle of hair and sebaceous gland. In terms of hair restoration, follicular unit is defined (UF) any group of follicles.
Histological evidence has showed that the erector muscle of hair has adequated organization structure follicular unit: Jimenez studies show that the erector muscle of hair has a complex shape, with beams that radiate from the central body, attached to each bulb components of the follicular unit. This organization is the functional structure of each bulb and contribute to the mechanism of leakage of sebum by the sebaceous duct.
Stem cells, can stimulate the formation of a new bulb after the telogen phase, are located in the area of the bulge, just below the insertion of the erector muscle of hair. It is assumed that the bulb in telogen, missed the accession with the dermis, epidermis scroll through the orifice, can stimulate stem cells that migrate down to the area of the dermal papilla and would create the sketch of the new phone bulb.
A complex cellular mechanism (growth factors, interleukins, and certain amino acids or poliamone specific receptors, such as spermidine) regulate the formation of new anagen cycle.
The presence in the area of the bulge and its integrity is essential to ensure the growth of regular bulb after transplantation. The knowledge of the bulb provides the possibility of reducing the risk of damage to the bulb during surgery with handling. The structure of epithelial ducts (internal and external) and the trunk full anatomy of the hair bulb and the shaft. The basic structure of the stem is keratin: keratin are different expressions of the various sections of stem. The epithelial sheath of keratin expressing different markers, because this area of epidermal origin, while the inner sheath, the medulla, cortex and cuticle express only one type of keratin, the matrix showing the origin of the bulb . The variations in the cycle of the hair bulb not play a role in hair transplantation. From the skin of the donor area are obtained, of course, bulbs in all cyclical: there are proportionately more hairs in anagen and telogen less.
Hair follicles at different stages of the life cycle can be planted:
bulbs in the anagen phase may maintain initial metabolic activity, continue in this phase and give rise to the growth of the hair shaft - bulbs in the anagen phase or late mature stage can move in catagen and subsequently telogen, the hair will fall and will develop the new frame after the resumption dell'anagen (6-9 months) bulbs catagen phase (1 to 2 percent of the total) and those in telogen (13 - 15 percent of the total) will be the dormant metabolic and will start the new anagen after at least 3 months.