Limb Development Flashcards by Sophia Barber

What is the middle limb bud structure? What does it become?

Zeugopod
becomes radius and ulna
tibia and fibula

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What is meromelia? When does it occur?

shortened limbs

week 3-5 messed up; can be due to thalidomide

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What is the development of upper limb arteries?

dorsal aorta –> intersegmental arteries –> primary axial artery –> brachial artery –> remodeling to adult vasculature

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What maintains the dorsal surface of developing limbs?

Wnt7

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What happens if you upregulate the ZPA?

additional posterior elements (polydactyly)

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What is the posterior side of a developing limb?

pinky side

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What myotomes do leg musculature come from?

lumbar myotomes

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What is the most proximal limb bud structure? What does it become?

stylopod

becomes humerus and femur

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What germ cells do cartilage and connective tissue of the limbs come from?

somatic lateral plate mesoderm

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What sex is more likely to have club foot?

males

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What happens in the 5th week of development?

hand and foot plates form

chondrification centers appear

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What is developmental hip dysplasia?

underdevelopment of the acetabulum of the hip bone

generalized joint laxity

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Which direction do lower limb buds turn?

90 degrees medially

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What is the development of lower limb arteries?

dorsal aorta –> intersegmental arteries –> primary axial artery –> deep artery of thigh –> remodeling to normal vasculature

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What is FGF-10?

What does it do?

signal released by limb-forming mesoderm

stimulates overlying ectoderm to become Apical-ectodermal ridge

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What is the anterior side of a developing limb?

thumb side

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What myotomes are upper limb muscles from?

cervical myotomes

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What is syndactyly? What causes it?

webbed fingers/toes

not enough BMPs in week 8

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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