week

• What is the primary function of the dermatome in limb development?

  Connective tissue of the dermis
• The myotome gives rise to muscles of the limbs and the body wall, while sensory nerve elements are derived from the neural crest
• Lower limb buds appear in the lumbar region between days 27-28 of development.

  True
• The position of limbs along the craniocaudal axis is determined by HOX genes.
• How much later does lower limb development lag behind upper limb development?

  1-2 days
• The apical ectodermal ridge (AER) is responsible for signalling and limb patterning.

  True
• Elongation of limb buds is driven by the proliferation of mesenchyme
• What is the origin of the mesenchymal core of limb buds?

  Lateral plate mesoderm
• Match the molecular factor with its role in limb development:

  FGF10 ↔️ Induction of AER formation

  Homeobox gene MSX2 ↔️ Maintenance of undifferentiated zone

  Retinoic acid ↔️ Stylopod patterning

  HOXA11 ↔️ Zeugopod patterning
• What is the role of FGF8 and FGF4 in limb development?

  Maintenance of undifferentiated zone
• Steps in the separation of digits during limb development:

  1️⃣ Cell death in the AER creates separate ridges

  2️⃣ Cell death occurs in the interdigital spaces

  3️⃣ Digit separation is complete
• The formation of hand- and footplates occurs during the late stage of limb development.
• The zone of polarizing activity (ZPA) is located at the posterior border of the limb near the AER.

  True
• Polydactyly is often caused by disruption of the SHH pathway.
• What is the result of early loss of FGF signalling in limb development?

  Amelia
• Steps in the development of limb bones:

  1️⃣ Condensation of mesenchyme

  2️⃣ Differentiation into chondrocytes

  3️⃣ Development of hyaline cartilage models

  4️⃣ Endochondral ossification

  5️⃣ Appearance of primary ossification centers
• Match the joint component with its cellular origin:

  Capsule and ligaments ↔️ Peripheral cells of interzonal mesenchyme

  Joint cavity ↔️ Apoptosis of central cells

  Synovial membrane ↔️ Lining cells of interzonal mesenchyme
• What is the origin of limb myoblasts?

  Somites dermomyotome
• The upper limb rotates 90 degrees laterally during development.

  True
• The dorsal muscle mass in limbs gives rise to extensors
• What is the orientation of the elbows and thumbs after upper limb rotation?

  Elbows caudally, thumbs laterally
• Match the limb region with its corresponding dermatome level:

  Upper limb ↔️ C4-T2 myotomes

  Lower limb ↔️ L4-S2 myotomes
• What is the result of limb dermatomes dragging their nerve supply during rotation?

  Brachial and lumbosacral plexuses