Hirsutism pathophysiology: Difference between revisions
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[[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]] | [[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. | *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]]. | *The hair growth cycle takes months to years to be completed, causing a delay in hair growth response to changes from effects of [[androgens]]. | ||
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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
Androgens are essential for sexual hair and sebaceous gland development. Pilosebaceous unit (PSU) growth and differentiation require the interaction of androgen with numerous other biological factors. In the embryo the pattern of PSU responsiveness to androgen is determined. Hair follicle growth involves close reciprocal epithelial-stromal interactions that recapitulate ontogeny; these interactions are necessary for optimal hair growth in culture.[1] Androgens are responsible for hair follicle size, hair fiber diameter, and the proportion of time terminal hairs spend in the anagen phase.[2] Almost all hirsute women have an increased production rate of androgens specially testosterone. [3]In some women, an increased conversion of testosterone to dihydrotestosterone (DHT) by the enzyme 5-alpha-reductase, is responsible for hirsutism.[4]
Pathophysiology
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.
- Vellus hair is transformed irreversibly to terminal hair in androgen-sensitive areas of the skin.
- 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.
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".
