9/7/2023 0 Comments Downy hairIn the absence of an SHH signal, the actions of the Patched-1 (PTC1) SHH receptor inhibit the activity of the smoothened (SMO) protein. This complex then activates the transcription of various target genes. There it forms a transcription complex with DNA binding factors of the lymphoid enhancer-binding factor/T cell factor family. In the presence of an antagonistic Wnt signal, there is inhibition of the degradation complex, and β-catenin moves to the nucleus. This complex includes axin, adenomatous polyposis coli tumor suppressor protein (APC), and glycogen synthase 3-β (GSK3-β). In the absence of a Wnt signal, cytoplasmic β-catenin is phosphorylated and targeted for destruction by a protein complex. In either case, molecular messages initiating the process of hair development begin in the dermis. While other mediators are necessary for the eventual production of lanugo, these two are the most important. Antagonists of Wnt and its effectors are also crucial. The Sonic Hedgehog (SHH) pathway and its effectors are key to lanugo development and the development of other hair types. When present in an adult, lanugo can be a sign of serious underlying disease states. These include, most notably, anorexia nervosa, bulimia nervosa, various forms of malnutrition, and the presence of a teratoma. Its presence can, however, indicate premature birth in a minority of cases. Lanugo can thus be present on the neonate for the first few weeks of life. Lanugo often remains present on 30% of newborns this is a normal finding.Īfter removal of the vernix, small amounts of lanugo can temporarily remain on the neonate. Lanugo is ultimately replaced by vellus (fine, thin hair) and terminal hair (thicker hairs found on the scalp, axilla, and genitalia). It is shed at about 33 to 36 weeks gestation, when it becomes subsequently incorporated into the amniotic fluid, eventually contributing to the composition of the meconium. Hair growth starts on the scalp around the eyebrow, nose, and forehead area and proceeds in a cephalocaudal direction from head to toe. Lanugo arises about three months into development. The interaction of lanugo with the vernix is also important in controlling the tempo of the fetal developmental rate during various times in the gestation cycle. Lanugo is the first type of hair to develop in humans. It protects the fetus from damaging substances found in amniotic fluid, most notably urea and electrolytes. Vernix caseosa is the viscous white covering on newborns that protects their skin, prevents water loss, plays an important role in thermoregulation, and contributes to innate immunity. Lanugo plays an essential role in binding the vernix caseosa to the skin of fetuses.
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