Limb Development Flashcards
What is the middle limb bud structure? What does it become?
Zeugopod
becomes radius and ulna
tibia and fibula
What is meromelia? When does it occur?
shortened limbs
week 3-5 messed up; can be due to thalidomide
What is the development of upper limb arteries?
dorsal aorta –> intersegmental arteries –> primary axial artery –> brachial artery –> remodeling to adult vasculature
What maintains the dorsal surface of developing limbs?
Wnt7
What happens if you upregulate the ZPA?
additional posterior elements (polydactyly)
What is the posterior side of a developing limb?
pinky side
What myotomes do leg musculature come from?
lumbar myotomes
What is the most proximal limb bud structure? What does it become?
stylopod
becomes humerus and femur
What germ cells do cartilage and connective tissue of the limbs come from?
somatic lateral plate mesoderm
What sex is more likely to have club foot?
males
What happens in the 5th week of development?
hand and foot plates form
chondrification centers appear
What is developmental hip dysplasia?
underdevelopment of the acetabulum of the hip bone
generalized joint laxity
Which direction do lower limb buds turn?
90 degrees medially
What is the development of lower limb arteries?
dorsal aorta –> intersegmental arteries –> primary axial artery –> deep artery of thigh –> remodeling to normal vasculature
What is FGF-10?
What does it do?
signal released by limb-forming mesoderm
stimulates overlying ectoderm to become Apical-ectodermal ridge
What is the anterior side of a developing limb?
thumb side
What myotomes are upper limb muscles from?
cervical myotomes
What is syndactyly? What causes it?
webbed fingers/toes
not enough BMPs in week 8
What signal tells embryo to selectively apoptose cells to create separate digits?
BMPs
When does the first ossification occur?
12th week
what genes control positioning of limbs along the craniocaudal axis?
Hox genes
What do sensory axons follow to innervate limbs?
What sensory axons derive from?
follow motor axons
derived from neural crest cells
What happens if you duplicate the ZPA?
duplication of posterior elemnts
When do motor axons from the spinal cord enter the limb buds?
5th week
What is club foot? What is it caused by?
all anatomical structures are present, but sole of foot turned medially and dorsiflexed
caused by limb rotation problem or too little amniotic fluid
What is arthrogryposis? What is it caused by?
congenital joint contractures –> diminished range of motion in joints
causes are unclear but thought to be due to:
neuro defects, muscular abnormalities, joint tissue problems, fetal crowding
What sets up dorso-ventral patterning signals (BMps and Wnt7)?
AER (apical ectodermal ridge)
What happens in the 8th week?
separate digits formed
apoptosis mediated by BMPs to separate digits
When do the limb buds form?
4th week
What happens if you lose the ZPA?
loss of posterior limb elements
Are anterior or posterior elements formed first? Why is that important?
Posterior formed first
If you lose P elements, can screw up whole A-P patterning and lose anterior elements too
What signals does the Apical-Ectodermal Ridge release? What do they do?
FGF-8 and FGF-4
stimulate limb-bud mesoderm to grow; pattern it on proximo-distal axis
Which direction do upper limb buds turn?
90 degrees laterally
What sets up anterior-posterior pattering of limb (pinky to thumb)?
Where is it?
Zone of Polarizing Activity (ZPA)
On posterior side (little finger side)
What happens in the 7th week?
digital rays of FEET
osteogenesis of long bones begins
rotation of limbs
What sex is more likely to have developmental hip dysplasia?
females
what happens in the 6th week?
digital rays of HANDS
entire limb skeleton is cartilaginous
What is the most distal limb bud structure? What does it become?
autopod
becomes carpals, metacarpals, digits
tarsals, metatarsals, digits
What is amelia?
no upper limbs at all
What is ectrodactyly? What causes it?
lobster claw or split hand/foot
genetic: center of AER is not active/doesn’t exist –> middle digits don’t form = 4th week?
What genes helps pattern mesoderm to become bones of upper extremity limbs?
Hox genes
When does polydactyly occur?
week 6-7
What maintains the ventral surface of limb development?
BMPs
What signals does the ZPA release? What do those signal do?
Shh and retinoic acid
signal posterior elements (pinky)
When do limb buds rotate?
week 7
what is brachydactyly? What causes it?
Shortened digits
decreased FGF 4, 8, and 10 signaling in week 7 and 8
