Lanugo (/, /; from Latin lana "wool") is very fine, soft, and usually unpigmented, downy hair as can be found on the body of a fetus or newborn baby. It is the first hair to be produced by the fetal hair follicles, and it usually appears on the fetus at about 5 months of gestation. It is normally shed before birth, around 7 or 8 months of gestation but is sometimes present at birth and disappears on its own within a few days or weeks.
It is replaced by hair covering the same surfaces called vellus hair, but this hair is finer and more difficult to see. The more visible hair that continues into adulthood is called terminal hair. This forms in specific areas and is hormone dependent.
During human development, the lanugo grows on fetuses as a normal part of gestation, but is usually shed and replaced by vellus hair at about 33 to 36 weeks of gestational age. As the lanugo is shed from the skin, it is normal for the developing fetus to consume the hair with the fluid, since it drinks from the amniotic fluid and urinates it back into its environment. Subsequently, the lanugo contributes to the newborn baby's meconium. Some believe the presence of lanugo in newborns is a sign of premature birth but that's not always true. It has been seen on infants born at 39 weeks gestation.
Lanugo functions as an anchor to hold the vernix caseosa on the skin. This combination with vernix caseosa protects the delicate fetal skin from damage from the amniotic fluid. The vernix caseosa also helps to transition the fetus to life outside the womb. It is thought to provide lubrication for birth and it is shown to affect thermoregulation, water loss, and innate immunity. Without the lanugo to anchor the vernix caseosa these functions would be lost.
Lanugo 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 of anorexia nervosa or bulimia nervosa.
It is often found in teratomas (congenital tumours).
Fetal whales, like humans and all other primates, also have lanugo.
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- "lanugo". Random House Webster's Unabridged Dictionary.
- "Definition of Lanugo". MedicineNet: medterms medical dictionary. Retrieved 17 February 2013.
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- Moore, Keith L (Dec 19, 2011). The Developing Human: Clinically Oriented Embryology. Elsevier. p. 98. ISBN 1437720021.
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- "Treating Eating Disorders in Primary Care", P.M. Williams, et al, American Family Physician, Vol 77 (2): January 15, 2008
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- Ecology of the Asian Elephant in Lowland Dry Zone Habitats of the Mahaweli River Basin, Sri Lanka Natarajan Ishwaran Journal of Tropical Ecology, Vol. 9, No. 2 (May, 1993), pp. 169-182
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