Flashcards in Embryology Deck (36):
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
during early part of ______ week, toe rays can be seen in the foot plates
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
cervical myotomes give rise to _______ muscles. lumbosacral myotomes provide precursor cells for the _______.
pectoral girdle pelvic girdle
these cells derived from the somites provide cells tat stay deep to the ectoderm and gice rise to dermis of skin
eventually become established as nerves of limbs
the supporting cells of the nervous system ( schwann cells) are derived from the ____________.
neural crest cells
name the migrant cells
myogenic dermatomal axonal neural crest cells there is evidence which indicates that the mesenchymal cells of the limbs organize the migrant cells and control their expression
regarding limb rotation ... the area of the limb superior (cranial) to the axial line is the _____ compartment. the area inferior (caudal) to the axial line is the _________ compartment.
the superior border of the preaxial compartment is the preaxial border and the inferior border of the postaxial compartment is the postaxial border. preaxial border is along the same line as _____. postaxial border corresponds to the location of the __________.
preaxial border = same line as the thumb or the great toe postaxial border = location of the 5th toe or the little finger
preaxial compartments contain _____ muscles and the postaxial compartments contain the __________ muscles.
pre - flexor post - extensor
when do the limbs undergo a rotation along their __________ axis?
7th week long axis
upper limbs rotate _____; lower rotate _______
the flexor compartment/ preaxial of the upper limb faces _______ in the anatomical position
anteriorly the extensor compartment is located posterior to the longitudinal axis
limb defects appear in how many births?
early 60s birth defects were traced back to what drug
most susceptible time for producing limb defects
between day 24-36
extra digits resulting from having extra digital rays
attached digits. malformation in the act of apoptosis will result in two or more digits that remain attached
absence of limbs
absence of a part of a limb
failure of development of one or more digital rays. the hand or the foot appears to be split down the middle.