Embryology Limb Development
What are the embryonic tissues and structures that give rise to the limbs?
When does gastrulation occur?
When do limb buds start to appear?
When do limbs start to rotate and have positional changes?
What are the three parts of mesoderm?
What forms the motor axon and which embryonic layer is it from?
Neural tube, from ectoderm
What forms sensory nerves and which embryonic layer is it from?
Neural crest, from ectoderm
Which part of embryonic tissue is most important for limb development?
When does major change in morphology occur?
Week 4 body folding
What happens during embryo folding?
Lateral folding and craniocaudal folding
Describe lateral folding:
Lateral aspects fold ventrally toward the midline
What becomes the space between the layers of mesoderm?
Future body cavities
Which embryonic layer forms the inner gut tube?
Describe cranial caudal folding:
Head and tail region of embryo bend towards each other
Where did somitomeres come from?
Organized segments of paraxial mesoderm
When do somites appear?
Between the third and fifth week of development
What are somitomeres?
Loose condensations or “swirls” of mesoderm
How do somitomeres proceed?
Cephalo-caudal development (head first) and turn into somites
What are somites
Formed from somitomeres
What do somites eventually become?
Tissues and structures like dermis and skeletal muscle and vertebrae
When do the first pair of somites appear?
Around day 20 post-fertilization
What are the breakdowns of somite pairs in each region?
4 pairs in occipital region
12 in thoracic
8-10 coccygeal paired somites
Whath are sclertome?
Sub-division of somite which contribute to future vertebral segments
Which appears first, forelimbs or hindlimbs?
Where do limbs differentiate from/ which germ layer?
What is the most distal aspect of the limb bud called?
Apical ectodermal ridge
Where can you find the progress zone of undifferentiated rapidly dividing cells?
Adjacent to the apical ectodermal ridge
When do cell death occurs after the initial appearance of future digits?
Around 54 days
What happens to the embryo at about six weeks?
Terminal portion of limb buds becomes flattened into hand/ footplate.
When does limb rotation occur?
How do limbs rotate, which way do upper and lower extremities rotate?
Where are extensor musculatures located in upper and lower extremities?
Upper- posterior laterally
When do we start to see cartilage models/ bone formation?’
Around week 6
What is it called when the process of bone formation involves putting down a precursor template made of cartilage?
When do ossification begin?
By the end of embryonic period
True/False: By birth, the diaphysis of long bones is completely ossified
When do epiphyses (ends of long bone) start ossification?
At time of birth
True/False: it is possible to over-stimulate bone growth in a child as a result of growth plate fracture
What is amelia?
Complete absence of one or more limbs
What is tetra-amelia?
Absence of all four limbs
What is phocomelia?
Upper portion of a limb is absent or poor developed
What is micromelia?
Segments of the extremities are present but are abnormally short
What is macrodactyly?
There is enlargement of one or more digits likely due to abnormal nerve or blood supply
What is ectrodactyly?
Fewer than normal digits
What is another name of ectrodactyly?
Lobster claw deformity
What is clubfoot?
Excessively plantar felxed with the forefoot swung medially and sole facing inward
What is the likely cause of clubfoot?
Oligohydramnios; restrictive uterine environment
Embryology Limb Development
NMSK Exam 2 limb development embryology