limb and digit development
- Upper limb bud forms at ~ day 24. Lower limb bud at ~ day 28.
- Core of mesenchyme, surrounded by ectoderm.
- AER (apical ectodermal ridge) forms a thickening at the distal end.
Limb disorders
- Amelia - absence of a limb.
- Meromelia - absence of a part of a limb.
digit disorders
- Syndactyly - webbing (fusion) of digits.
- Polydactyly - presence of extra digits.
- Brachydactyly - shortening of digits.
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Limb Development & Developmental Disorders (eg, Polydactyly)
limb and digit development
- The upper limb bud forms at ~ day 24, followed shortly thereafter by the lower limb bud (at ~ day 28).
- The limb bud comprises a core of mesenchyme, surrounded by ectoderm.
- The AER (apical ectodermal ridge) forms a thickening at the distal end of the limb bud.
- The distal upper limb bud forms a digital plate, distally (for the fingers) and a carpal plate (for the hand). Then, via programmed cell death, digital rays form.
common limb disorders: terminology
- Amelia is absence of a limb.
- Meromelia is absence of a part of a limb.
digit disorders
- Syndactyly is webbing (fusion) of digits.
- Polydactyly is presence of extra digits.
- Brachydactyly is shortening of digits.
Known Teratogens that cause limb and digit malformations, include
Pharmaceuticals
- Valproate
- Phenytoin
- Warfarin
Toxins
- Cocaine
- Alcohol (fetal alcohol syndrome)
Metabolic conditions
- Hyperglycemia (gestational diabetes)
Infections
- Varicella Zoster