Development: upper limb

Question 1

from bilaminar to trilaminar embryonic disc, what are the 3 germ layers:

Answer 1

• ectoderm
• mesoderm
• endoderm

Question 2

how do limb buds first appear?

Answer 2

• condensation of mesenchyme
• ventrolateral on embryo
• end of wk 4

Question 3

eg. syndactyly

Answer 3

• fusion of fingers and toes
• from just skin, soft tissue and even bone
• not proper apoptosis

Question 4

eg. cleft hand or lobster claw

Answer 4

• embryonic absence of central digital rays

Question 5

eg. polydactyly

Answer 5

• dominant trait

- supernumerary digit usually underdeveloped, useless, lateral vs central

Question 6

eg. meromelia and amelia

Answer 6

absence of part of the limbs, or limbs

- amelia: absence of limb or limbs

Question 7

causes: congenital limb defects

Answer 7

• thalidomide (antiemetic and sedative in 60s used for pregnancy sickness)
• loss of blood supply of limb
• defect in innervation at spinal/ cerebral level

Question 8

two types of bone formation:

Answer 8

• intramembranous (skull and clavicle)

- endochondral ossification (most of rest of skeleton)

Question 9

brief intramembranous ossification:

Answer 9

• ossification centre in ct
• bone matrix forms
• periosteum forms
• bone collar of compact bone and red marrow appears

Question 10

brief endochondral ossification:

Answer 10

• cartilage template
• primary centre in diaphysis
• secondary centre at epiphysis

Question 11

eg. achondroplasia

Answer 11

autosomal dominant disorder/ new mutation (1:15 000)

• limbs bowed, trunk is long, head enlarged, bulging forehead
• long bones dont grow

Question 12

eg. cleidocranial dysplasia/ dysostosis:

Answer 12

• cranial bones dont fuse
• small maxilla
• mandibular protrusion
• clavicle under/not developed

Question 13

eg. osteogensis impefecta

Answer 13

• impaired collagen maturation
• extreme porous / fragility of bone
• blue sclera
• spine deformities
• tendency to bleed

Question 14

when do joints begin to develop?

Answer 14

during 6th week, 8th week resemble adult joints

- interzonal mesenchyme differentiate

Question 15

eg. congenital hip dislocation:

Answer 15

• more common in females
• instable joint
• dislocates from muscle pull
• abnormal development of acetabulum

Question 16

eg. congenital clubfoot/ talipes

Answer 16

• common 1:1000 births
• multifactorial pattern
• abnormal position of foot prevents normal weight bearing

Question 17

somites differentiate into :

Answer 17

• myotome
• dermatome
• sclerotome

Question 18

myotome differentiate into:

Answer 18

skeletal muscles of neck, trunk, limbs

Question 19

dermatome differentiate into:

Answer 19

connective tissue, including dermis of the skin

Question 20

limb rotation: when and how

Answer 20

• upper limbs rotate dorsally

- lower limbs rotate ventrally