Flashcards on Human Limb Development and Congenital Anomalies
Human Limb Development & Congenital Anomalies Explained
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Upper limb embryology
21 cards
Card 1
Question: What are the two mesodermal sources for limb tissues and what does each form in the developing upper limb?
Answer: Lateral plate mesoderm forms bone, cartilage, and tendon; somatic (paraxial) mesoderm forms muscle, nerve, and vascular elements.
Card 2
Question: What is the apical ectodermal ridge (AER) and what role does it play in limb development?
Answer: The AER is a distal ectodermal signaling center that secretes fibroblast growth factors to direct proximal-to-distal limb development and prevent inte
Card 3
Question: What is the developmental consequence of removing the AER from the developing limb bud?
Answer: Removal of the AER results in limb truncation (transverse deficiency).
Card 4
Question: How can the effects of AER removal be experimentally overcome?
Answer: Application of fibroblast growth factors can overcome the effects of AER removal.
Card 5
Question: What types of limb defects are associated with deficiency of fibroblast growth factors in mice?
Answer: Deficiency of various fibroblast growth factors in mice leads to complete transverse limb defects.
Card 6
Question: In humans, are transverse limb deficiencies typically inheritable or sporadic, and when should teratogen exposure be suspected?
Answer: Transverse deficiencies are usually sporadic and not inheritable. Concern for teratogen exposure is raised when multiple limbs are involved, suggestin
Card 7
Question: What is the zone of polarizing activity (ZPA) and which axis of limb development does it pattern?
Answer: The ZPA is a posterior limb-bud signaling center that patterns the anterior–posterior (radioulnar, preaxial–postaxial) axis of the limb via secreted f
Card 8
Question: Which signaling molecule is produced by the ZPA and what anomaly can its disruption cause?
Answer: The ZPA produces sonic hedgehog protein; disruption can affect radioulnar limb formation and is associated with mirror hand anomalies.
Card 9
Question: What is the Wnt pathway's role in limb development and which axis does it influence?
Answer: The Wnt pathway (through transcription factor Lmx-1) specifies the ventral–dorsal limb axis.
Card 10
Question: Which human syndrome is linked to abnormal function of the Wnt/Lmx-1 dorsal–ventral pathway and what features does it affect?
Answer: Nail–patella syndrome is linked to abnormalities in this pathway and affects nail and pulp arrangement (dorsal–ventral limb features).