MSK 1 - Development Of Limbs Flashcards Preview

CJ: UoL Medicine Semester Two (ESA2) > MSK 1 - Development Of Limbs > Flashcards

Flashcards in MSK 1 - Development Of Limbs Deck (21)
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What are the three different types of grasp with the hand?

Cylindrical, hook/snap, spherical


What are the three different types of precision grip with the hand?

Tip, palmar, lateral


When do the limb buds develop?

Towards the end of the 4th week


Which develops first - the upper or lower limb?

Lower limb development lags around two days behind the upper limb


What are the limb buds composed of?

Core of proliferating mesenchymal cells with an ectoderm covering


How does elongation of the limb bud occur?

Through proliferation of mesenchymal core. There is a thickened ectoderm at the apex of the limb bud.


What are the three spatial axes in limb development?

- proximal-distal axis (shoulder to fingertips)
- dorsal-ventral axis (palmar surface to dorsal surface)
- anterior-posterior axis (side to side)


What does the 'zone of polarising activity' (ZPA) control?

Specification of anterior-posterior axis


What does the 'apical ectodermal ridge' (AER) control?

Specification of apical-ectodermal ridge


What controls the specification of the dorsal-ventral axis?

The ectoderm


What does AER stimulate?

- Induces immediately underlying mesenchyme, which begins to differentiate.
- causes appearance of 'paddles' which form digits.
- AER regresses after this.


Where is the ZPA found? What does it do?

It is a signalling centre located at the posterior base of the limb bud, where it controls patterning and maintains AER, generating asymmetry in the limbs


How do hand and foot plates form fingers and toes?

- mesenchyme condensations within plates lead to cartilaginous models of the digital bones
- apoptosis of tissue between digits leads to interdigital spaces.


What is syndactyly?

Fusion of digits, may be just connective tissue or may also affect bones


What is polydactyly?

Extra digits, a recessive genetic trait


What is 'amelia'?

Complete absence of a limb


What is 'meromelia'?

Partial absence of one or more limb structures


Give some examples of the underlying problem in behind a limb defect

- malformation (intrinsic error in coordination of morphogenesis)
- deformation (constriction bands)
- disruption via an external agent eg thalidomide


What are the TORCH infections?

- Toxoplasmosis
- Other
- Rubella
- Cytomegalovirus
- Herpes

These can be passed from mother to child and cause congenital anomalies


How do muscles form within the limb bud?

- myogenic precursors migrate into limbs from somites (body segments)
- coalesce into two common muscle masses around skeletal elements
- individual muscles split from common masses


How do the limbs rotate as they are formed?

They extend ventrally at first, but as they elongate they rotate. The upper limb rotates laterally and the lower limb rotates medially.

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