| 词条 | Vellus hair |
| 释义 |
| Name= Vellus hair | Greek= | Image = Huid.jpg | Caption = Vellus hay hair | Image2= VellushaarTerminalhaar-translation.JPG | Caption2 = Comparison of the vellus hair (left) to the terminal hair (right) in humans. | Width = | Origin = | Insertion = | Blood = | Nerve = | Action = | Antagonist= }}Vellus hair is short, thin, slight-colored, and barely noticeable thin hair that develops on most of a person's body during childhood. Exceptions include the lips, the back of the ear, the palm of the hand, the sole of the foot, some external genital areas, the navel, and scar tissue. The density of hair – the number of hair follicles per area of skin – varies from person to person. Each strand of vellus hair is usually less than 2 mm (1/13 inch) long and the follicle is not connected to a sebaceous gland.[1] Vellus hair is most easily observed on children and adult women, who generally have less terminal hair to obscure it. Vellus hair is not lanugo hair. Lanugo hair is a much thicker type of hair that normally grows only on fetuses. Vellus hair is differentiated from the more visible terminal or androgenic hair, which develops only during and after puberty, usually to a greater extent on men than it does on women. The Latin language uses the word vellus to designate "a fleece" or "wool." Vellus hair is sometimes colloquially referred to as peach fuzz, due to its resemblance to the downy epidermic growths on the peach fruit. DevelopmentVellus hair replaces lanugo hair on a human fetus at 36 to 40 weeks of gestation.[2] The growth cycle of vellus hair is different from the growth cycle of terminal hair. At puberty, androgen hormones cause much of the vellus hair to turn into terminal hair and stimulate the growth of new hair in the armpit and the pubic area. In men, this change in vellus hair occurs on the face and the body. FunctionVellus hair provides both thermal insulation and cooling for the body. This insulation regulates body temperature: the vellus hair functions like a wick for sweat. While a skin pore is open, sweat wets a strand of vellus hair. The sweat on the external part of the strand evaporates. More sweat wets the external part of the vellus strand and then evaporates. This process is called perspiration. Clinical significanceThe unusual growth of vellus hair can be a side effect of some types of disease. An abundance of vellus hair can develop from an increase in the production of the cortisol hormone in a person with Cushing's syndrome. Anorexia nervosa increases vellus hair. Vellus hair can also be found in men with male pattern baldness or with hirsutism. Hormonal fluctuations in pregnant women cause foetal vellus hair to change to terminal hair. The terminal hair is usually shed after the birth of the baby upon the return of the hormones to the normal levels.[3]
Footnotes1. ^{{cite book|author=Marks, James G|author2=Miller, Jeffery |year=2006|title=Lookingbill and Marks' Principles of Dermatology|edition=4th|publisher=Elsevier Inc.|page=11|ISBN=1-4160-3185-5}} {{Human hair}}2. ^{{cite web |url=http://dermatology.about.com/od/glossaryv/g/vellus.htm |title=Vellus Hair - Peach Fuzz & Puberty Hair Growth |website=About.com |author=Heather Brannon}} 3. ^{{cite book|author=Godfrey, Sheila|url=https://books.google.com/books?id=3tPEkSn3DckC|title=The Principle and Practice of Electrical Epilation|publisher=Butterworth-Heinemann|edition=3rd|isbn=0-7506-5226-8|year=2001}} 4. ^{{cite journal|last=Gündüz|first=Özge|author2=Aytekin, Asli |title=Trichostasis Spinulosa Confirmed by Standard Skin Surface Biopsy|journal=International Journal of Trichology|date=1 January 2012|volume=4|issue=4|pages=273–4|doi=10.4103/0974-7753.111201|pmid=23766613|pmc=3681110}} 5. ^{{cite journal|last=Lacarrubba|first=F|author2=Micali, G |author3=Tosti, A |title=Absence Of Vellus Hair In The Hairline: A Videodermatoscopic Feature Of Frontal Fibrosing Alopecia.|journal=The British Journal of Dermatology|date=Mar 18, 2013|doi=10.1111/bjd.12316|pmid=23496000|volume=169|issue=2|pages=473–4}} 6. ^{{cite journal|last=Patel|first=U|author2=Terushkin, V |author3=Fischer, M |author4=Kamino, H |author5= Patel, R |title=Eruptive vellus hair cysts.|journal=Dermatology Online Journal|date=Dec 15, 2012|volume=18|issue=12|pages=7|pmid=23286797}} 1 : Hair anatomy |
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