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Lanugo is very thin, soft, usually unpigmentedhair that is sometimes found on the body of a fetus ornewborn. It is the first hair to be produced by the fetal hair follicles, and it usually appears around sixteen weeks of gestation and is abundant by week twenty. It is normally shed before birth, around seven or eight months of gestation, but is sometimes present at birth. It disappears on its own within a few weeks.[3]
It is replaced by hair covering the same surfaces, which is calledvellus hair. This hair is thinner and more difficult to see. The more visible hair that persists intoadulthood is calledterminal hair. It forms in specific areas and ishormone-dependent.[4] The term is from theLatinlana, meaning "wool."
During human development, the lanugo grows onfetuses as a normal part ofgestation, but it is usually shed and replaced byvellus hair at about thirty-three to thirty-six weeks ofgestational age. As the lanugo is shed from the skin, it is normal for the hair to be consumed by the developing fetus, since it drinks from theamniotic fluid and urinates into its environment. As a result, lanugo contributes to the newborn baby'smeconium. The presence of lanugo on newborns is not necessarily a sign ofpremature birth, as it is also seen on infants born at thirty-nine weeks of gestation (full term).
Lanugo functions as an anchor to hold thevernix caseosa on the skin. Together they protect the delicate fetal skin from being damaged by the amniotic fluid.[5] The vernix caseosa also helps to prepare the fetus for life outside the womb. It provides lubrication for birth and contributes to thermoregulation, prevention of water loss, and innate immunity. Without the lanugo to anchor the vernix caseosa, these functions would be compromised.[6]
In the absence offat, lanugo grows to serve as a replacementinsulator, and thus can be observed in malnourished patients, including those with eating disorders. When found along with other physical symptoms, for example, lanugo can help a physician make a diagnosis ofanorexia nervosa orbulimia nervosa.[7]
It is often found interatomas (congenital tumours).[citation needed]
Lanugo is also common on othermammals. For example, seals[8] and elephants[9][10][11] are often born with a covering of lanugo. Some species of fetal whales and dolphins also have lanugo.[12][13]
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Definitions from Wiktionary
Data from Wikidata