Embryology Of Limbs Flashcards
When do the limbs first start appearing?
Towards end of 4 th week! Akhr il shahar!
Lana it doesnt really need it bl bdaya aham shay il galb wl ashya2 il 6’rooreeya
What is the limb bud?
Small projections at the lateral body wall, consists of mass of mesenchyme covered with layer of ectoderm
What is the AER? What axis is it involved in forming?
Apical ectodermal ridge,
At the tip (apex) of the limb bud, the ectodermal cells divide to form the thickened AER.
The proximal distal axis!
stimulates outgrowth of limb
How does limb elongate?
Via mitotic divisions (proliferation of mesenchyme)
The AER sends signals to the underlying mesenchyme to stay UNDIFFERENTIATED, and just divide to make more of it, this extends the limb bud . Proximal mesenchyme is now far away from the AER and will start ti differentiate into other tissues.
What is ZPA
A clump of cells sitting at the posterior base of the limb bud, provides maintance to the AER and henerates asymtery in the anterior posterior axis
What is syndactly? Polydactly? Ameila? meromelia?
Syndactly»Fusion of digits (may be bone or tissue) more common in foot
Polydactly»Extra digits
Amelia»complete absence of a limb
Meromelia» partial absence of one or more limb structures
How do u develop fingers?
AER breaks up and is maintained only at tip of the digital rays,they regress and interdigital spaces appear due to apoptosis
What happens if AER gets disrupted, give one mechanism causing its disruption
Elongation of limb buds hault.
Due to external agents, infections and drugs (thalidomide)
Which forms first? Upper or lower limb?
Upper, lower lags 2 days later
What is the structural difference between cutaneous syndactyly and osseous syndactyly?
In cutaneous syndactyly there is just a skin web between the digits, whereas in osseous syndactyly there is bony fusion.
What is the structural defect underlying congenital dislocation of the hip (CHD)?
Underdevelopment of acetabulum and head of femur.
CHD is associated with breech presentation (i.e. the buttocks of the fetus are inferior and would be delivered first, rather than the head). Speculate on why this might be so.
Breech presentation may place undue pressure on the developing hip joint: fails to complete normal development.
