Manual 126-129: Embryology Flashcards
when precisely do limb buds start to develop?
during the later part of the 4th week (as soon as teh trilaminar embryo completes its lateral foldin)
where on the embryo do limb buds form?
along the ventrolateral side of the cylindrical embryonic body
which appears first upper or lower limb buds?
upper (day 26-27) – lower about 2 days later
seen at the inferior segment of the developing cervical region (C5-T1)
The ________ limb buds originate from a slightly larger segment than the _______ limb buds.
lower limbs originate from slightly larger segment than the upper limb buds
L2- S2 (6) compared with C5-T1 (4)
what is the mesenchymal core of the limb bud derived from?
somatic component of the lateral mesoderm layer of embryo
Further development and enlargement of the limb buds initially begins by a very fast division of the mesenchymal cells. Evidence has shown that this cell division is under direct control of _________ gene.
HOX homeobox-containing
also responsible for patterning of the limbs (distal ends of buds flatten into paddle-like hands and ffet)
At the distal segment of the limb bud (apex) the ectodermal cells undergo cell proliferation and show consideral thickening known as the _______
apical ectodermal ridge AER
responsible for proximal to distal limb bud growth
AER (inductive influence is a result of expression of fibroblast growth factor)
limbs will not develop in absence of AER
moving location of AER will move location of limb
by the end of the ___ week, the hand paddles show presence of digital rays which will eventually gice rise to fingers
6th week
during early part of ______ week, toe rays can be seen in the foot plates
7th week
Separation of individual digits takes place during the ___ week by the process of apoptosis in the __________ tissue between digital rays
8th week; mesenchymal tissue
the mesenchyme of limb buds gives rise to following components of the limbs:
bones joints cartilage fascial layers blood vessels lymphatic vessels
the cells of the cartilage models are derived from the original mesenchymal cells of the embryo begining by the ___ week of development
5th week
by the 6th week the entire cartilaginous skeleton is complete
during the 7th week, the cartilage models start to undergo endochondral ossification whereby the chondrocytes are replaced by bone producing cells
endochondral bone formation begins where?
diaphysis of long bones as the primary center of ossifications
long bones also develop secondary ossification centers in the epiphysis
each long bone has _____________ ossification centers
3 total
one primary and two secondary