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Dermatology Textbooks Guide Hair Cycle Phases
1. Source :Rooks text book of dermatology 9th edition
Bolognia text book of dermatology
IADVL text book of dermatology 4th edition
Fitzpatrick text book of dermatology 8th edition
levers histopathology of skin 11th edition
2. Hair Cycle
follicle passes through 3 phases
Anagen hair
Catagen
hair,
Telogen hair
New
Anagen hair
• histologic appearance of hair follicles changes in hair
cycle,
3. IN ADULT HAIR CYCLE
Anagen -- phase of active
growth—lasts 3 yrs;
Catagen--phase of
regression—lasts 3 wks
Telogen-- resting period—
lasts 3 months
4. Hair Follicle stem cells
Hair follicle stem cells govern the cyclical
regeneration
Initially thought- “secondary germ” is located at the
base of the telogen hair follicle.
Secondary germ is a transient structure that forms at
the end of catagen from cells in the lower bulge
SC Permanently located in the bulge
5. bulge cells give rise to all epithelial layers of the hair
follicle, confirmed by using lineage analysis
Lgr5- exclusive marker of secondary germ cells(marks
bulge cells)
Lgr6, a gene related to lgr5, is expressed in an area
above the bulge in the upper isthmus.
6.
7. Anagen
Anagen can be divided into 7
different stages:
Stage I—growth of the dermal
papilla and onset of mitotic
activity in the germ-like
overlying epithelium
Stage II—bulb matrix cells
envelop the dermal papilla and
begin differentiation, evolving
bulb begins descent along the
fibrous streamer
8. Stage III—bulb matrix cells
show differentiation into all
follicular components
stage IV—matrix melanocytes
reactivate
stage V—hair shaft emerges
and dislodges telogen hair
stage VI—new hair shaft
emerges from skin Surface
stage VII—stable growth
9. During proliferation and migration of keratinocytes
into the dermis to reform the new lower follicle,
proteases and collagenases appear at the leading
edge of the downgrowth
Growth factors and their receptors are upregulated
similar to an epithelial wound
10. •Expression of keratin 6
•Dermal papilla moves
downward
•Neurocutaneous and vascular
networks are remodelled
•Melanocytes proliferate and
repopulate
11. Catagen
2-3 weeks
1% of follicles in this stage
Cessation of the mitotic activity of the matrix cells
Apoptosis in the cyclic portion of the hair follicle
Pigment production by melanocytes ceases
leading to a nonpigmented proximal end in the
telogen club hair
Melanin engulfed by macrophages
12. Perifollicular sheath
collapses,vitreous or glassy
membrane thickens.
Lower follicle retracts upward
with the dermal papilla.
Perifollicular sheath forms a
fibrous layer comprised of
fibroblasts, small blood vessels,
and collagen.
Dermal papilla becomes situated
immediately below the bulge at
the lower portion of the isthmus
13. Dermal papilla, protected from the
surrounding apoptosis and
destruction (perhaps because it
expresses bcl- 2, an antiapoptotic
factor12) condenses and begins to
move upward to come to rest below
the bulge during telogen.
FGF-5 and EGF, neurotrophins and
TGF-β1 induce premature catagen -
shortening of hair length by 15 %
14. Telogen
• Period of complete inactivity
lasting about 100 days
(3 months) in the scalp.
• 5-10% of follicles
Shedding is an active
process.
15. •Scalp loses 100-150
telogen hairs a day
•Club Hair either falls
out during telogen or
is pushed out by new
hair growth during the
next anagen phase.
16. Exogen
Milner et al proposed distinguishing hair shedding as a
separate phase called exogen.
Exogen is a highly controlled
and timed event ,shed on a
seasonal basis.
17. Exogen is an active stage is supported by
Headington’s description of one type of telogen
effluvium he termed immediate telogen release.
• Hair shedding might involve release by
desmoglein 3 which is believed to anchor the club
hair during telogen.
18. Kenogen
Usually whenever a telogen hair is shed, an anagen
hair is already present in the follicle to replace it.
At times the follicle stays empty after telogen
sheds, this is known as kenogen.
May last from weeks to months, seen in patients
of androgenetic alopecia, prepubertal children.
19. Control of Hair growth cycle
Androgens- Act through receptors in the dermal
papilla.
Increases length of anagen, diameter, and growth
rate in susceptible follicles.
Paradoxically cause shorter anagen time,
miniaturization, and slower growth in areas such as
the scalp
Axillary & Pubic hair respond to testosterone, rest of
body hair only responds to DHT made by 5-alpha
reductase type2
20. Estrogens
Prolongs anagen but decreases the growth rate.
Responsible for the post-partum telogen effluvium.
Thyroxine
Advances onset of anagen
increases growth rate.
Excesses can be stressful and lead to telogen
effluvium.
Deficiency results in slowing growth rate.