Development: upper limb Flashcards
from bilaminar to trilaminar embryonic disc, what are the 3 germ layers:
- ectoderm
- mesoderm
- endoderm
how do limb buds first appear?
- condensation of mesenchyme
- ventrolateral on embryo
- end of wk 4
eg. syndactyly
- fusion of fingers and toes
- from just skin, soft tissue and even bone
- not proper apoptosis
eg. cleft hand or lobster claw
- embryonic absence of central digital rays
eg. polydactyly
- dominant trait
- supernumerary digit usually underdeveloped, useless, lateral vs central
eg. meromelia and amelia
absence of part of the limbs, or limbs
- amelia: absence of limb or limbs
causes: congenital limb defects
- thalidomide (antiemetic and sedative in 60s used for pregnancy sickness)
- loss of blood supply of limb
- defect in innervation at spinal/ cerebral level
two types of bone formation:
- intramembranous (skull and clavicle)
- endochondral ossification (most of rest of skeleton)
brief intramembranous ossification:
- ossification centre in ct
- bone matrix forms
- periosteum forms
- bone collar of compact bone and red marrow appears
brief endochondral ossification:
- cartilage template
- primary centre in diaphysis
- secondary centre at epiphysis
eg. achondroplasia
autosomal dominant disorder/ new mutation (1:15 000)
- limbs bowed, trunk is long, head enlarged, bulging forehead
- long bones dont grow
eg. cleidocranial dysplasia/ dysostosis:
- cranial bones dont fuse
- small maxilla
- mandibular protrusion
- clavicle under/not developed
eg. osteogensis impefecta
- impaired collagen maturation
- extreme porous / fragility of bone
- blue sclera
- spine deformities
- tendency to bleed
when do joints begin to develop?
during 6th week, 8th week resemble adult joints
- interzonal mesenchyme differentiate
eg. congenital hip dislocation:
- more common in females
- instable joint
- dislocates from muscle pull
- abnormal development of acetabulum
