Hair, the hair follicle physiology

1. Shape and color

form of hair because of race have some differences in the different, the most obvious is the hair, yellow hair, straight and thick, very curly hair, black people, and sometimes form a "pepper" kind of fat knot, white hair, ranged between the former two. Cross-sectional view from the hair, yellow hair and round, black people's hair is sometimes flat oval, which is mainly determined by the shape of the hair follicle. Black spiral of human hair follicle, yellow hair follicles completely vertical, and white hair follicles ranged between the former two. Hair color can be black, brown, golden yellow, red, white, mainly by the hair follicle melanocytes at the matrix synthesis of melanin many decisions.

2. Density

hair about 10 million, the vellus hair Zeyi forehead highest density per square centimeter 400-450 root, chest and back only 50-100 per square centimeter of root. Hair follicles during embryonic development the formation of the first 9 weeks, to 22 weeks to complete the development, in adult hair follicles are no longer increase, and with age, hair follicles gradually reduced to the scalp, for example, 20 to 30 years old per square centimeter 615-50 at the age of 30 to reduce the hair follicles 485 to 435 only 80-90 years old.

3. Hair growth rate key with the following factors

(1) site: hair the fastest, the daily growth of 0.35-0.37mm, head office of up to 0.5mm, chin daily 0.38mm, thigh daily is 0.21mm, while the forehead was 0.03mm.

(2) Gender: Female hair grow faster than men, prepubertal boys hair faster growth rate than girls; but in general, men's hair grow faster than average Women fast.

(3) Age: Failure to consider gender ,15-30-year-old hair grows the fastest.

(4) Season: The hair, for example, growing up to the peak in March every year, September was the lowest. And the beard and legs have a similar seasonal variation.

4. The growth cycle

hair growth showed some periodicity, and the hair follicle itself, the main growth cycle. Hair growth cycle for the three phases:

① growth phase (anagen)

② catagen (catagen)

③ resting (telogen)

in the growth period, a series of degenerative changes in the hair bulb, with the beginning of catagen, dermal papilla loss of metachromasia, hair matrix cells to stop proliferation, the hair bulb melanocytes stop producing and transfer to keratinocytes melanocytes, but deposited in the dermal macrophages, and epithelial outer root sheath keratinization back into the bladder, surrounding the hair shaft of the spherical lower end, forming a dilated clubbed ends, said Mao (clubhair). pouch on the liner overlying epithelium morphologically normal hair follicle isthmus epithelium similar to a thin columnar epithelial cells instead of the hair follicles under the section, and surrounding the dermal papilla and hair keratin rod connected to the bladder. Expressed in epithelial cells characteristic cable (stalk) is a thick, glass-like folds surrounded by basement membrane zone. In the stationary phase, reduced epithelial cell column, move up, followed by dermal papilla is also moving up, and a connective tissue trailing behind in the back of the epithelial column, and finally, when the hair stick up to establish the level of gross muscle attachment points, the epithelial cell column undifferentiated form a spherical cell mass, hair stick stuck in the bottom of the skins. As part of the dermal papilla and around it the reconstruction of undifferentiated epithelial cells, hair cycle starts the growing season, the formation of new epithelial hair matrix, and expand, growth, and the dermal papilla remnants of the fibrous sheath along with the move down, with the it down, the bottom column epithelial invagination, which broke into the dermal papilla to form a new hair bulb. Hair bulb melanocytes within the normal function of hair matrix cells to produce new outer root sheath, inner root sheath and hair shaft, the newly formed hair shaft extends upward to expel mao rods.

hair follicle beneath the hair follicle isthmus part is temporary, that it disappeared in catagen, and in the growing season and regeneration; In contrast, the stable part of the hair follicle (isthmus and infundibulum) nothing in the hair follicle cycle.

general, the hair growth period of about 3 years, about 3 weeks catagen, telogen about 3 months. Was asynchronous in different parts of the hair follicle growth cycle has its own table. Various parts of the hair is not the same time or seasonal growth or loss, but at different times, scattered off and regeneration. About 85% of normal hair follicles in the growing season the head, off 70-100 hairs daily, also have the same amount of hair regeneration. Duration of different parts of the hair growth cycle at different times related to the eyebrows and eyelashes of the growing season is only about 2 months, so shorter.

different parts of the hair follicle growth cycle

site	resting (%)	Growing (%)	resting time (months)	hair follicle density (a/cm 2 )	hair follicle depth (mm)
scalp	13	85	3-4	350	3-5
beard	30	70	2-3	500	2-4
upper lip	35	65	1.5	500	1-2.5
armpit	70	30	3	65	3.5-4.5
trunk	70	30	2.5	70	2-4.5
perineum	70	30	2-3	70	3.5-4.5
arm	80	20	2-4	80
leg	80	20	3-6	80	2.5-4

5. Endocrine regulation of hair growth the main regulator of thyroid hormones, sex hormones and corticosteroids and so on.

(1) thyroid hormone: one in patients with hypothyroidism may be associated with hair removal , the serum protein binding reduction in the level of iodine , while the average diameter of the hair also reduced, to 0.04-0.06mm (normal to 0.08mm), hair removal to the occipital, the head of the most obvious, given thyroxine return to normal after treatment.

(2) Estrogen: its role mainly in women after childbirth, postpartum hormone levels because of dramatic changes in estrogen levels drop rapidly, this time with the resting stage of hair growth period ratio is low, 15% telogen hair, it appeared 4-6 months after giving birth, hair loss.

(3) androgens: male face, trunk and extremities with the men and women of the pubic hair, armpit hair growth are subject to the control of androgens, it can be anti-androgen agents - - methylene chloride ene progesterone acetate to treat hirsutism; and for the hair, the role of androgen is not the same, it is mainly the scalp hair follicles, "down" effect. Immunogenicity hair loss in androgen levels in patients with high androgen, androgen receptor subunit as the aggregation of changes, combined with 5 ɑ - reductase activity increased, so the increased sensitivity in patients with androgen, causing hair loss.

6. The composition and energy metabolism of hair

hair mainly composed of hair keratin, hair, eyebrows are keratin intermediate filament family of 4 in case of a molecular weight of 60,000, in addition to There are many sulfur protein (molecular weight 9 000-2.5 million), including Gan acid/protein tyrosine more, including citrulline δ-γ glutamic acid lysine cross-linking proteins, disulfide bonds between the more so that the hair has a certain shape and texture.

hair follicles in the energy is provided by the glucose, there are three pathways: glycolysis, pentose phosphate pathway and citric acid cycle. Compared with muscle, hair follicles and rapid glycolysis, pentose phosphate pathway activity strong, in addition, growth period and the energy of telogen hair follicles are quite different, compared with the telogen hair follicle, hair follicle growth phase on glucose utilization rate increased 200%, 200% increase in glycolysis, pentose phosphate pathway increased by 800%, respiratory chain ATP produced an increase of 270%.