Session 3 - Development of the Limbs Flashcards
What appears at fourth week of development?
Limb buds
What are the limb buds in embryonic development made up of?
Core of proliferating mesenchymal cells with an ectoderm covering
What are A and B?
A - Anterior B - Posterior
What are C and D?
C - Dorsal D - Ventral
What are E and F?
E - Distal F - Proximal
Give two examples of a dorsal location on the body
Back of the hand and top of the foot
Give two examples of a ventral position on a foetus
Palm of the hand and sole of the foot
What is the proximo-distl axis?
Base of the limb to the tips of the digits
What is the antero-posterior axis
From 1st digit to 5th
Where do limb buds first appear?
On the ventro-lateral body wall
What order to limb buds appear in?
Upper limb first, lower limb second
In which direction do limb buds at first extend?
Ventrally at first
What does limb development begin with?
Activation of mesenchyme within lateral mesoderm
Where are limb buds derived from?
The somatic layer of lateral plate mesoderm
What does somatic mesoderm contribute to?
Limb skeleton
What do somites contribute to?
Musculature
What is mesenchyme?
Flexible mesoderm
How does limb bud elongate?
Through proliferation of mesenchyme core
Give a feature of the apex of a limb bud
Thickened ectoderm
Give the three degrees of asymmetry of limb development
Top and bottom (Shoulder to fingertips) Front and back (No hairy palms) Side to side (Left and right hands mirror images)
What is the AER?
The apical ectodermal ridge
What is the AER critical for?
Limb bud outgrowth
What does the AER facillitate?
Limb development, proximal to distal
What is the final appearance of the AER before it regressed?
Appearance of paddles
What is the arrow pointing to?
The Apical Ectodermal Ridge
What are the anatomical effects of the AER?
Causes differentiation of underlying tissue, before finally inducing development of the digits within the hand/foot plates
What is the ZPA?
Zone of polarising activity
What are the three functions of the zone of polarising activity?
Generation of assymetry in the limbs
Asignalling centra located at the posterior base of the limb bud
Controls both patterning and maintains the AER
What does the AER mark the boundary between?
The dorsal and ventral ectoderm
Label A, B and C
A - Dorsal ectoderm B - Ventral ectoderm C - AER
What does AER mark the boundary between?
What do preaxial and postaxial refer to?
Preaxial - Medial - Thumb and Big to
Postaxial - Lateral - Little finger and little toe
What controls anterior/posterior development?
ZPA
What controls proximal - distal development?
AER
What controls dorsal/ventral development?
Ectoderm
What occurs in hand and foot plates to convert them from buds to appendages?
Digital rays
Mesenchyme condensations within plates
Cartaliginous models of the digital bone
Apoptosis
Of the tissues between the digits
What is syndactyly?
Fusion of digits, may involve just CT or bones may be fused
Polydactyly
Extra digits, genetic recessive trait
What happens to lateral plate mesoderm?
What is Amelia?
Condenses and diffentiates, undergoes endochondral ossification.
Amelia - Complete abcense of a limb
How do long bones extend?
What is Meromelia?
Secondar ossification centres appear in epiphyses. Bone growth maintained by cartilage forming regions (epiphyseal growth plates)
Partial abcesnse of one or more limb structures
How is musculature formed?
Myogenic precursors migratre into limbs from somites. Form two muscles msses - Vental (flexors) and dorsal (extensors)
What is the difference in comparments between upper and lower limb?
U limb - flexor anterior
L limb - flexor posterior
How do the reveresed compartments formed in upper limbs and legs?
Both limbs extend ventrally
However
- Upper limb: rotates laterally
- Lower limb: rotates medially
Why do limbs have the innervation they do?
Upper limb bud appears opposite the caudal cervical spinal segments
Why is innervation vital to limb development?
Without it development stalls
Describe formation of brachial plexus
Anterior divisions for anterior compartments - Regroup to form lateral and medial cords.
Posterior compartments supplied by posterior divisions
Why do nails have different innervation to rest of dorsal surface of hand?
Nails develop from nail fields on the tips of the fingers
What is a dermatome?
A single strip f skin supplied by a single spinal nerve?
What is a myotome?
Myotome is a muscle/group of muscles supplied by a single spinal nerve
What occurs in hand and foot plates to convert them from buds to appendages?
Digital rays
Mesenchyme condensations within plates
Cartaliginous models of the digital bone
Apoptosis
Of the tissues between the digits
