Embryology Flashcards
When do the early stages of development of the musculoskeletal system start and what initiates this process?
The end of the fourth week due to activation of the mesenchymal cells in the somatic lateral mesoderm
What genes regulate patterning of the musculoskeletal development?
Homeobox genes
When do the upper and lower limb buds appear?
Upper limb bud appears at day 26
Lower limb bud follows 1/2 days later
Through what process do the limb buds elongate?
Proliferation of the mesenchyme
Where do the limb buds originate?
The upper limb buds develop opposite the caudal cervical segments
The lower limb buds develop opposite the lumbar and sacral segments
What is the AER, where does it develop and what does it develop from?
Apical ectodermal ridge
Forms at the apex of each bud due to ectodermal thickening
What kind of cells are found proximal and adjacent to the AER?
Proximal mesenchyme- differentiates into blood vessels and cartilage bone models
Adjacent mesenchyme- undifferentiated, rapidly proliferating cells
How do the hands and feet develop?
The distal ends of the limb buds flatten into paddle-like hand plates and flipper-like foot plates
Digital rays are formed through condensation of mesenchymal tissues in week six in the hands and the seventh week in the feet
How is the tissue in the interdigital regions broken down?
Apoptosis mediated by bone morphogenic proteins
How are cartilaginous precursors of the limb bones developed?
Chondrification of the mesoderm in the sixth week
Primary centres of ossification appear in weeks 8-12 in response to growth factors
When are dermatomes formed?
During the fifth week, when peripheral nerves grow from the developing limb plexus into the mesenchyme of the limbs
What bones go under endochondral ossification?
All limb bones except the clavicle
How do the upper and lower limbs rotate?
They both rotate by 90 degrees
The upper limbs do so laterally
The lower limbs do so medially
What is amelia?
Total absence of a limb
What is meromelia?
Partial absence of a limb
What is phocomelia?
Some long bone absence
What is micromelia?
All parts are present except small bones
What is polydactyly?
The presence of more than five digits on the hands or feet
The extra digit is incompletely formed and lacks muscular development
It can be inherited or teratogenic
What is syndactyly?
Common birth defect of the hand or foot
What is the difference between cutaneous and osseous syndactyly?
Cutaneous syndactyly- simple webbing between the digits, more common in feet than hands
Osseous syndactyly- fusion of the bones occurs when notches between the digital rays fail to develop
What birth defects are associated with thalidomide?
Absence or deformity of long bones and intestinal and cardiac abnormalities
Describe the characteristics of congenital clubfoot
Relatively common birth defect
Sole of the foot inverted so foot is turned medially
What are the possible causes of congenital clubfoot?
Can be multifactorial (genetic and environmental factors)
Abnormal positioning of the foetus causing restricted movement
What are the causes of developmental dysplasia of the hip?
Abnormal development of the acetabulum, which is common after breech deliveries
General joint laxity
