Help
Options
Didn't know it?
click below
click below
Knew it?
click below
click below
Don't Know
Remaining cards (0)
Know
retry
shuffle
restart
0:00
Embed Code - If you would like this activity on your web page, copy the script below and paste it into your web page.
Normal Size Small Size show me how
Normal Size Small Size show me how
WEEK 24:
Embryology of limbs and clinical relevance:
| Question | Answer |
|---|---|
| initial growth and patterning of the limbs occurs when | during weeks 4-8 |
| appearance of limb buds | outpocketings at the end of week 4 (forelimb then hindlimb) |
| limb buds | mesenchymal core derived from lateral plate mesoderm (bones and connective tissue) with an ectodermal outer layer |
| ectodermal layer development | thickens distally and forms the apical ectodermal ridge (AER) |
| apical ectodermal ridge (AER) | has inductive influence that regulates the undifferentiation and differentiation of cells |
| cells closer to the AER | remain undifferentiated but rapidly proliferate |
| cells father away from AER | begin to differentiate into cartilage and muscle |
| how do limbs grow | proximo-distally |
| hand and footplates are formed as a result of what | limb bud flattening (WEEK 6) |
| first circular constriction | week 6- separates hand and foot plates from proximal segment |
| second circular constriction | week 8- separates proximal segments into two |
| where does apoptosis occur | at AER |
| further formation of digit formation depends on (3) | continued outgrowth of AER (inductive influence), core of mesenchyme turning into cartilage, and death of intervening tissues between digits |
| digits | fingers and toes (phalanges) |
| digits are initially interconnected by | tissue which then regresses via apoptosis to produce separate digits |
| apoptosis of interdigital tissue is dependent on | BMP signaling within the interdigital tissue under the influence of Shh from the zone of polarising activity (ZPA) |
| disruption of apoptosis of interdigital tissue can result in | syndactyly (which often affects digits 3,4, and/or 5) |
| cartilage formation involves | mesenchyme condenses and differentiates into chondrocytes where chondrocytes form the first hyaline cartilage models (week 6) needed for bone formation |
| what happens in the interzone | chondrogenesis ceased and becomes joint |
| endochondral ossification occurs when | starts by the end of week 8 |
| endochondral ossification process | mesenchyme condenses and differentiates into chondrocytes where chondrocytes form the first hyaline cartilage models and blood vessels invade the centre of diaphysis forming primary ossification centre (week 12) - bringing together osteoblast |
| secondary ossification centres are formed where and when | epiphyses after birth (growth continues as chondrocytes proliferate) |
| how many growth plates in long bones | 2 |
| how many growth plates in smaller bones (phalanges) | 1 - at the tip |
| primary ossification | occurs at week 12 where they bring together osteoblast (bone forming cells) and shove proliferating chondrocytes to epiphyseal ends |
| body musculature derived from | paraxial mesoderm (somites) |
| sclerotome | develops into vertebral and rib bones |
| myotome | develops into muscle |
| dermatome | develops into dermal connective tissue |
| myotome can further be divided into | primaxial (dorsomedial) and abaxial (ventrolateral) myotome |
| primaxial myotome (dorsomedial) | somite-derived cells only - affected by signaling factors from the neural tube to generate muscle precursors with limited migratory potential |
| abaxial myotome (ventrolateral) | respond to signals from adjacent lateral plate mesoderm to give rise to migratory population |
| limb bud elongation with migration of muscle cells includes | splitting into flexors and extensors, back muscles innervated by dorsal ramus, and body wall and limb muscles innervated by ventral ramus |
| limb rotation involves | dividing trunks and movement in both the upper and lower limb |
| trunk is divided into | segments that receive innervation from spinal nerves |
| distal ends of limbs flatten into | paddles- with the thumb and great toe most anterior and after flexure the elbow and knee lateral |
| limbs by week 7 | undergo torsion in opposite directions, upper limb rotates 90* laterally while lower limb rotates 90* medially |
| limb rotation in the lower limb | permanent pronation - which twists leg so that the foot faces downwards with great toe medial |
| dermatome | area of skin supplied by single spinal nerve which is evenly spaced horizontally in thorax and abdomen but more complex in upper and lower limbs |
| regulation of limb bud identity establishment involves (3) | paired like homeodomain transcription factor 1 (Pitx1), hindlimb-specific enhancer A/B (HLEA/B), and fibroblast growth factor 10 (Fgf10) |
| mechanism of regulation of limb bud identity establishment | |
| sonic hedgehod (SHH) and noggin found in | sclerotome |
| genes responsible for dermatome LOCATION ** | PAX3 regulated by NT-3 |
| genes responsible for DM muscle cells -> primaxial muscles | MYF5 regulated by WNT |
| genes responsible for VL muscles -> abaxial muscles | BMP4 and WNT regulates MyoD |
| PAX3 regulates | NT-3 |
| WNT regulates | MYF5 |
| BMP4 and WNT regulates | MyoD |
| patterning, growth, and maturation of the limbs occurs along | |
| proximo-distal growth and patterning S22 | |
| proximo-distal growth and patterning (S23) | |
| antero-posterior patterning (A-P patterning)^^ | established by zone of polarizing activity (ZPA) on the posterior side of limb (little finger side). SHH signaling from ZPA specifically signals formation of posterior elements |
| upregulation of ZPA signals results in | additional posterior elements (polydactyly on hypothenar side of hand) |
| duplication of ZPA results in | duplication of posterior elements (eg little fingers on both sides of thumb) |
| loss of ZPA results in | loss of posterior elements |
| dorso-ventral patterning | specifies dorsal surface (Extensors) vs ventral surface (flexors, palm/sole) of limbs |
| dorsal and ventral signaling factors | |
| SLIDE 25 | |
| limb defects - amelia | |
| limb defects - phocomelia | |
| limb defects - amniotic bonds | |
| limb defects - polydactyly | |
| limb defects - syndactyly | |
| limb defects - cleft foot | |
| transverse limb deficiencies | limb defects in which proximal structures are intact but structures distal to a transverse plane are partially or completely absent due to disruption of AER |
| osteogenesis imperfecta (brittle bones) |
Created by:
kablooey
Popular Medical sets