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Questions and Answers
What is the initial part of limb differentiation during development?
What is the initial part of limb differentiation during development?
What process removes the interdigital tissue to create separate digits?
What process removes the interdigital tissue to create separate digits?
Which spinal segment levels contribute to the formation of the upper limb musculature?
Which spinal segment levels contribute to the formation of the upper limb musculature?
What structure do nails develop from during limb development?
What structure do nails develop from during limb development?
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What is the role of spinal nerves during limb bud development?
What is the role of spinal nerves during limb bud development?
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What initiates limb outgrowth during development?
What initiates limb outgrowth during development?
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Which transcription factor is specifically responsible for the specification of the forelimb?
Which transcription factor is specifically responsible for the specification of the forelimb?
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At what stage of development do limb buds first become visible?
At what stage of development do limb buds first become visible?
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Which area is covered by a layer of ectoderm during limb bud formation?
Which area is covered by a layer of ectoderm during limb bud formation?
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What type of cells give rise to the mesenchymal core of the limb buds?
What type of cells give rise to the mesenchymal core of the limb buds?
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What is the shape of the upper limb buds at 32 days of development?
What is the shape of the upper limb buds at 32 days of development?
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Which genes regulate the positioning of the limbs along the craniocaudal axis?
Which genes regulate the positioning of the limbs along the craniocaudal axis?
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Where do the upper limb buds develop in relation to the embryo?
Where do the upper limb buds develop in relation to the embryo?
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What regulates the anteroposterior axis of limb development?
What regulates the anteroposterior axis of limb development?
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Which structure is essential for the proximodistal axis during limb bud development?
Which structure is essential for the proximodistal axis during limb bud development?
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What occurs when there is misexpression of ZPA or SHH in limb development?
What occurs when there is misexpression of ZPA or SHH in limb development?
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What component of the limb do the terms stylopod, zeugopod, and autopod refer to?
What component of the limb do the terms stylopod, zeugopod, and autopod refer to?
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In the dorsoventral axis, which genes are involved in the differential patterning of bones and muscles?
In the dorsoventral axis, which genes are involved in the differential patterning of bones and muscles?
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How does the Apical Ectodermal Ridge (AER) influence limb bud growth?
How does the Apical Ectodermal Ridge (AER) influence limb bud growth?
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What is the function of Fibroblast Growth Factors (FGFs) in the limb development?
What is the function of Fibroblast Growth Factors (FGFs) in the limb development?
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Which of the following does not relate to the limb growth along the proximodistal axis?
Which of the following does not relate to the limb growth along the proximodistal axis?
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Study Notes
Limb Development
- Limb development begins with mesenchymal cells activating from the lateral plate mesoderm.
- Limb buds appear as elevations on the ventrolateral body wall around week 4 (28 days).
- Limb buds are covered in ectoderm.
- Upper limb buds appear around day 26/27, and lower limb buds appear a day or two later.
- Limb buds grow larger through mesenchyme proliferation.
- Upper limb buds develop opposite the caudal cervical segments, and lower limb buds opposite the lumbar and upper sacral segments.
- Upper limb buds are paddle-shaped and lower limb buds are flipper-like by day 32.
Limb Buds
- Limb buds are formed of a mesenchymal core derived from the parietal (somatic) layer of the lateral plate mesoderm. This forms bones and connective tissue.
- The mesenchymal core is covered in cuboidal ectoderm.
- Upper limb buds appear opposite the lower cervical segments, and lower limb buds appear opposite the lumbar and sacral segments.
Molecular Regulation of Limb Development
- Limb positioning along the craniocaudal axis in the flank regions is regulated by HOX genes (HOXB8).
- HOX genes play a critical role in patterning limb bones.
- Forelimb specification is regulated by the transcription factor TBX5.
- Hindlimb specification is regulated by the transcription factor TBX4.
- Limb outgrowth is initiated by fibroblast growth factor (FGF) 10.
- FGF10 is secreted by the lateral plate mesoderm.
Proximodistal Axis
- The Apical Ectodermal Ridge (AER) is crucial for limb bud development from proximal to distal.
- AER is a thickening of ectoderm at the tip of the limb bud.
- AER induces proliferation in underlying mesenchyme.
- Limb buds grow distally as cells proliferate.
- Earliest mesenchyme forms the base/proximal cells, differentiating into cartilage.
- FGFs keep cells in the progress zone proliferating.
- Preventing their differentiation.
- Cells move away from FGF influence as the limb grows.
- Decreased FGF concentration causes mesenchyme condensation and cartilage formation.
Anteroposterior Axis
- Anteroposterior axis is controlled by the zone of polarizing activity (ZPA).
- Sonic hedgehog (SHH) is the master gene regulating ZPA.
- SHH secreted by ZPA controls digit number and pattern.
- Digits develop in a specific order (thumb on radial side).
- Misexpression of ZPA or SHH can lead to duplication of limb structures (polydactyly).
Dorsoventral Axis
- Dorsoventral axis (back vs. palm) is regulated by overlapping HOX gene expression and BMP/WNT7 genes.
- Genes control muscle pattern, orientation of joints, and epidermal differentiation.
Limb Segmentation
- Proximal part of the limb differentiates first, followed by the distal part.
- Distal end flattens into a paddle-like structure (hand/foot plate).
- Separated by proximal segments through circular constriction.
- Second constriction divides proximal part into two segments.
Limb Muscle
- Limb musculature originates from somite myotomes.
- Specific segmental levels supply muscle cells to upper and lower limbs (C5-T2 and L2-S2, respectively).
- Muscles arranged into ventral and dorsal masses.
- Ventral muscles become flexors and pronators in upper limbs, flexors and adductors in lower limbs.
- Dorsal muscles become extensors.
Limb Innervation
- Upper limb buds develop opposite the caudal cervical spinal segments.
- Lower limb buds develop opposite the lumbar and sacral spinal segments.
- Spinal nerves enter limb buds early in development.
Congenital Limb Malformations
- Amelia: Complete absence of a limb.
- Meromelia: Partial absence of a limb.
- Phocomelia: A type of meromelia where long bones are absent (hands and feet attached directly to the trunk).
- Micromelia: Limb is abnormally short, but all segments are present.
- Brachydactyly: Short digits.
- Syndactyly: Fused digits or toes.
- Cleft hand/foot: A cleft between certain metacarpal/metatarsal bones; phalangeal bones may be absent.
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Description
Explore the fascinating process of limb development during embryonic growth. This quiz covers the stages of limb bud formation, the specific timing of upper and lower limb bud appearances, and the molecular regulation involved in limb development. Test your knowledge on the mesenchymal and ectoderm components crucial for limb formation.
