Limb development is a complex process involving multiple signaling centers and molecular pathways. It starts with and progresses through stages of growth, patterning, and tissue differentiation along three axes.
Key players in limb development include the (AER) and (ZPA). These signaling centers coordinate growth and patterning through molecules like FGFs and , shaping the final limb structure.
Limb Development Stages
Limb Bud Formation and Elongation
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Top images from around the web for Limb Bud Formation and Elongation
Bone Growth and Development | Biology for Majors II View original
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Frontiers | Niches for Skeletal Stem Cells of Mesenchymal Origin View original
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Module 5: Cartilage and Bone – Anatomy 337 eReader View original
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Bone Growth and Development | Biology for Majors II View original
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Frontiers | Niches for Skeletal Stem Cells of Mesenchymal Origin View original
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Limb development initiates with formation of limb buds, outgrowths of mesenchymal cells covered by ectoderm
Limb bud elongates along proximal-distal axis, proximal region develops first followed by distal region
Cartilage condensation occurs within limb bud, forming initial skeletal elements that later ossify into bones
Limb undergoes patterning along three axes
Proximal-distal axis (shoulder to fingertips)
Anterior-posterior axis (thumb to pinky)
Dorsal-ventral axis (back of hand to palm)
Tissue Differentiation and Morphogenesis
Interdigital apoptosis separates developing digits and shapes final limb structure
Muscle precursor cells migrate into limb bud from somites and differentiate into specific muscle groups (biceps, triceps)
Vascularization and innervation of developing limb occur concurrently with skeletal and muscular development
Blood vessels form to supply nutrients and oxygen
Nerves grow into limb to provide motor control and sensory input
AER and ZPA Roles in Patterning
Apical Ectodermal Ridge (AER) Function
AER forms as thickened region of ectoderm at distal tip of limb bud, directing proximal-distal outgrowth
Secretes fibroblast growth factors (FGFs) maintaining underlying mesenchyme in proliferative state
and are key signaling molecules
AER removal results in truncated limbs (chicken wing experiments)