Limbs 2 Flashcards
congenital limb malformations defects:
Grieg Syndrome:
syndactyly and polydactyly
Apert syndrome:
syndactyly
Holt-Oram syndrome:
phocomelia (short limbs)
The three limb malformation syndromes are caused by autosomal recessive. true or false?
true
ratio of limb malformations:
1:500 to 1:1000
Phocomelia might be caused by environmental factorssuch as drugs. one example of this drug would be:
thalidomide
Formation of limb buds:
24th and 28th day
- loose mesenchyme enclosed in epidermal jacket derived from lateral plate mesoderm
- The mesenchyme forms most of the
tissues in the limb, including bone, tendons, ligaments, dermis, muscle sheaths, and blood vessels.
- A ridge, known as the
apical ectodermal ridge (AER), forms at the distal end of the limb bud.
what signal is transcribed in forelimb?
Tbx5
what signal is transcribed in hindlimb?
Tbx4
limb muscles are formed by epaxial myotome. true or false?
false. formed by hypaxial myotome
Which muscle, dorsal or ventral, forms the supinators and extensor muscle of forelimbs, and flexor and abduction muscles of hindlimb?
dorsal muscles
which digit differentiate first? then? last?
4;
3 and 2
1 and 5
What is AER?
source of mitogen needed for limb outgrowth
This protein
diffuses into limb bud mesenchyme and stimulates cell proliferation, thereby promoting limb
outgrowth:
FGF
FGF is highly concentrated at which part of the limb?
phalanges
At the proximal side, humerus, there is low FGF and high mitosis, stimulated by retinoic acid. True or false
true
The posterior margin is an organizing centre for patterning the anterior-posterior axis of the limb
bud and is known as the
zone polarizing activity
The ZPA at high concentrations specify digits at what region?
posterior
SHH is expressed in the ZPA, and has concentration dependent manner. what is its role?
mimics function of ZPA when expressed in anterior mesenchyme
in mice, Gli3 mutations enhance shh expression and cause:
polydactyly
what is Acheiropodia?
absence of distal elements in the limbs. mutation caused by deletion of DNA that controls shh in the ZPA
How does limb outgrowth cease?
- FGF activates shh
- shh in ZPA stimulates gremlin
- gremlin inhibits BMP (BMP inhibits FGF)
- limb outgrowth
- ZPA descendent cells cannot express gremlin
- go in between shh and gremlin domains
- stimulation of gremlin stops
- BMP is increased
- inhibition of FGF and outgrowth stops
How do flaps of tissue between digits disappear?
Apoptosis occurs.
BMP signalling molecules present in interdigital regions
intensive cell death–> apoptosis
incidence of syndactyly is most rare between which digits? and most common btw which digits?
1 and 2
3 and 4
