Hirsutism pathophysiology: Difference between revisions
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__NOTOC__ | __NOTOC__ | ||
{{Hirsutism}} | {{Hirsutism}} | ||
{{CMG}} {{AE}} | {{CMG}} {{AE}}; {{Ochuko}} {{RHN}} | ||
==Overview== | ==Overview== | ||
The growth of [[hair]] on sex-specific areas of the body occurs due to [[androgens]]. [[Androgens]] induce [[Vellus hair|vellus]] follicles in sex-specific areas to develop into terminal [[hairs]], which are larger and more heavily pigmented. | |||
==Pathophysiology== | ==Pathophysiology== | ||
The growth of [[hair]] on sex-specific areas of the body occurs due to [[androgens]]. [[Androgens]] stimulate the growth of vellus follicles in sex-specific areas to develop into terminal hairs, which are larger and have increased pigmentation (darker).<ref name="pmid10950157">{{cite journal |vauthors=Deplewski D, Rosenfield RL |title=Role of hormones in pilosebaceous unit development |journal=Endocr. Rev. |volume=21 |issue=4 |pages=363–92 |year=2000 |pmid=10950157 |doi=10.1210/edrv.21.4.0404 |url=}}</ref><ref name="pmid8326154">{{cite journal |vauthors=Messenger AG |title=The control of hair growth: an overview |journal=J. Invest. Dermatol. |volume=101 |issue=1 Suppl |pages=4S–9S |year=1993 |pmid=8326154 |doi= |url=}}</ref><ref name="pmid7258262">{{cite journal |vauthors=Hatch R, Rosenfield RL, Kim MH, Tredway D |title=Hirsutism: implications, etiology, and management |journal=Am. J. Obstet. Gynecol. |volume=140 |issue=7 |pages=815–30 |year=1981 |pmid=7258262 |doi= |url=}}</ref><ref name="pmid1838082">{{cite journal |vauthors=Labrie F |title=Intracrinology |journal=Mol. Cell. Endocrinol. |volume=78 |issue=3 |pages=C113–8 |year=1991 |pmid=1838082 |doi= |url=}}</ref> | |||
===Types of hair=== | |||
*There are approximately 5 million [[hair follicle]]<nowiki/>s at birth in humans with about 80,000 to 150,000 of them on the [[scalp]]. | |||
*The quality of hair is determined by hormones and other intrinsic characteristics of the [[hair follicle]]. | |||
*There are various types of hair which include: | |||
** '''Lanugo hair''': The soft hair which covers the fetal skin and it disappears within the first three months after the fetus delivery. | |||
** '''[[Vellus hair]]''': This is fine, soft hair that is not pigmented. It covers most of the body before the pubertal period. | |||
** '''[[Terminal hair]]''': This is long, coarse and pigmented. Pubertal [[androgens]]<nowiki/> for example [[dihydrotestosterone]] (DHT) convert vellus hair to terminal hair. | |||
===Phases of Hair Growth Cycle=== | |||
*There are 3 phases of hair growth cycle: | |||
**'''The hair growth phase''' (termed [[Anagen]] phase): This phase varies, depending on the body area affected. It is approximately 4 months for facial hair. | |||
**'''The involutional phase''' ([[Catagen]] phase): This phase is approximately 2-3 weeks. | |||
**'''The resting phase''' (Telogen phase): The hair shaft separates from the dermal papillae at the base of the [[Hair follicle|follicle]], which terminates growth. | |||
===Pathogenesis=== | |||
*The growth of sexual hair is dependent on the presence of [[androgens]]. | |||
*[[Androgens]] induce vellus follicles in sex-specific areas to develop into terminal hairs, which are larger and more heavily pigmented. | |||
*Hirsutism is caused by increased androgen production and/or an increased sensitivity of the hair follicles to [[androgens]]. | |||
*[[Hyperandrogenism]], resulting from any factors, prolongs the anagen(growth) phase of androgen-sensitive hairs, resulting in their conversion from fine, light, vellus hairs to coarse, dark, terminal hairs. | |||
*The response of hair follicle to [[androgens]] and other factors such as local 5 alpha-reductase activity determines the level of conversion of hair from the vellus type to terminal hair.<ref name="pmid10950157">{{cite journal |vauthors=Deplewski D, Rosenfield RL |title=Role of hormones in pilosebaceous unit development |journal=Endocr. Rev. |volume=21 |issue=4 |pages=363–92 |year=2000 |pmid=10950157 |doi=10.1210/edrv.21.4.0404 |url=}}</ref> | |||
[[image:hairf.png|thumb|center|200px| Hair Follicle<ref name="urlCategory:Hair follicle - Wikimedia Commons">{{cite web |url=https://commons.wikimedia.org/wiki/Category:Hair_follicle#/media/File:Blausen_0437_HairFollicleAnatomy.png |title=Category:Hair follicle - Wikimedia Commons |format= |work= |accessdate=}}</ref> <br> Courtesy to WikiMedia]] | |||
*Growth recommences with the formation of new hair shaft by the reactivation of the [[dermal papillae]], thereby replacing the old hair. | |||
*The hair growth cycle takes months to years to be completed, causing a delay in hair growth response to changes from effects of [[androgens]]. | |||
*[[DHT]] is a hormone that acts on the hair follicle to produce terminal hair. | |||
*Differences in the activity of [[DHT]] explains why women with the same plasma level [[testosterone]], have different degrees of hirsutism. | |||
*It is speculated that [[insulin]], at high enough concentration, stimulates the [[ovarian]] [[Thecal cells|theca]] cells to produce [[androgens]]. | |||
*There may also be an effect of high levels of [[insulin]] to activate the [[insulin-like growth factor-I|insulin-like growth factor-I (IGF-1)]] receptor in those same cells resulting in increased [[androgen]] production. | |||
==Associated Conditions== | |||
Common conditions associated with hirsutism include: | |||
*[[Diabetes]] (in [[PCOS]] ) | |||
*[[Acne]] | |||
*[[Fertility]] problems | |||
==References== | ==References== | ||
Latest revision as of 14:57, 7 November 2017
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: ; Ogheneochuko Ajari, MB.BS, MS [2] Rasam Hajiannasab M.D.[3]
Overview
The growth of hair on sex-specific areas of the body occurs due to androgens. Androgens induce vellus follicles in sex-specific areas to develop into terminal hairs, which are larger and more heavily pigmented.
Pathophysiology
The growth of hair on sex-specific areas of the body occurs due to androgens. Androgens stimulate the growth of vellus follicles in sex-specific areas to develop into terminal hairs, which are larger and have increased pigmentation (darker).[1][2][3][4]
Types of hair
- There are approximately 5 million hair follicles at birth in humans with about 80,000 to 150,000 of them on the scalp.
- The quality of hair is determined by hormones and other intrinsic characteristics of the hair follicle.
- There are various types of hair which include:
- Lanugo hair: The soft hair which covers the fetal skin and it disappears within the first three months after the fetus delivery.
- Vellus hair: This is fine, soft hair that is not pigmented. It covers most of the body before the pubertal period.
- Terminal hair: This is long, coarse and pigmented. Pubertal androgens for example dihydrotestosterone (DHT) convert vellus hair to terminal hair.
Phases of Hair Growth Cycle
- There are 3 phases of hair growth cycle:
- The hair growth phase (termed Anagen phase): This phase varies, depending on the body area affected. It is approximately 4 months for facial hair.
- The involutional phase (Catagen phase): This phase is approximately 2-3 weeks.
- The resting phase (Telogen phase): The hair shaft separates from the dermal papillae at the base of the follicle, which terminates growth.
Pathogenesis
- The growth of sexual hair is dependent on the presence of androgens.
- Androgens induce vellus follicles in sex-specific areas to develop into terminal hairs, which are larger and more heavily pigmented.
- Hirsutism is caused by increased androgen production and/or an increased sensitivity of the hair follicles to androgens.
- Hyperandrogenism, resulting from any factors, prolongs the anagen(growth) phase of androgen-sensitive hairs, resulting in their conversion from fine, light, vellus hairs to coarse, dark, terminal hairs.
- The response of hair follicle to androgens and other factors such as local 5 alpha-reductase activity determines the level of conversion of hair from the vellus type to terminal hair.[1]
Courtesy to WikiMedia
- Growth recommences with the formation of new hair shaft by the reactivation of the dermal papillae, thereby replacing the old hair.
- The hair growth cycle takes months to years to be completed, causing a delay in hair growth response to changes from effects of androgens.
- DHT is a hormone that acts on the hair follicle to produce terminal hair.
- Differences in the activity of DHT explains why women with the same plasma level testosterone, have different degrees of hirsutism.
- It is speculated that insulin, at high enough concentration, stimulates the ovarian theca cells to produce androgens.
- There may also be an effect of high levels of insulin to activate the insulin-like growth factor-I (IGF-1) receptor in those same cells resulting in increased androgen production.
Associated Conditions
Common conditions associated with hirsutism include:
References
- ↑ 1.0 1.1 Deplewski D, Rosenfield RL (2000). "Role of hormones in pilosebaceous unit development". Endocr. Rev. 21 (4): 363–92. doi:10.1210/edrv.21.4.0404. PMID 10950157.
- ↑ Messenger AG (1993). "The control of hair growth: an overview". J. Invest. Dermatol. 101 (1 Suppl): 4S–9S. PMID 8326154.
- ↑ Hatch R, Rosenfield RL, Kim MH, Tredway D (1981). "Hirsutism: implications, etiology, and management". Am. J. Obstet. Gynecol. 140 (7): 815–30. PMID 7258262.
- ↑ Labrie F (1991). "Intracrinology". Mol. Cell. Endocrinol. 78 (3): C113–8. PMID 1838082.
- ↑ "Category:Hair follicle - Wikimedia Commons".
