Embryology Flashcards
what can cause multiple extra toes?
duplicated ZPA zone of polarizing activity
limb development rotations
• Upper limbs rotate 90 degrees laterally so that thumb will point laterally, palms up • Lower limbs rotate medially so that the big toes are medial and knees are pointed anteriorly
complex syndactyly
involves bone and soft tissue - fuses digits in both layers
skeleton of the face?
splanchnocranium
dermatome
area of skin innervated by a single spinal segment
intramembranous bone ossification
no cartilage present mesenchye condenses, osteoblasts differentiate, secrete matrix, osteoblasts deposit bone and osteocytes are present
where do somites form? how?
on either side of neural groove in pairs, cranially to caudally
endochondral bone formation
long bones cartilage present grow in length by chondrocyte division and secretion of ECM primary ossification center is in shaft and secondary in bone heads
holoprosensecephaly
forebrain of embryo fails to develop into two hemispheres *possibly due to EtOH intake
cloverleaf skull
early close of multiple sutures and secondary excessive growth at the cranial base –> irregular expansion
how to fix skull deformities?
bicoronal incision
what does distruption or loss of HOX genes do?
loss or abnormal limb elements
gastrulation
single layer blastula becomes three layer gastrula
what gene specifies position of limb bud?
HOX
what directs limb bud to form along ANTERIOR-POSTERIOR axis?
ZPA zone of polarizing activity
protective case around brain?
neurocranium
what does somite differentiate into?
sclerotome (vertebra/rib only) dermatome (dermis) myotome (muscle)
lateral plate mesoderm forms what?
limb bones
what three layers does gastrulation form?
ectoderm, mesoderm, endoderm
what does the intermediate strip become?
dermis of the neck, back, and trunk
three steps of gastrulation
- embryo becomes asymmetric along both axes 2. primitive streak forms . cells from epiblast undergo mesenchymal transformation and travel inwards at streak to form germ layers via FGF sugnaling
scrococcygeal teratoma
teratoma at base of coccy - ectopic fragments of the primitive streak
direction of appendicular skeletal development?
proximal to distal and cranial to caudal
what does a bicoronal incision do?
release pressure on brain and allows resuturing of skull
two types of bone formation
endochondral - cartilage present intramembranous - cartilage not present
soft membranous sutures in skull
fontanel
myotome
group of muscles innervated by a single spinal nerve root motor equivalent of a dermotome
epimere
dorsal portion of somite or mesoderm forms muscles innervated by dorsal ramus of spinal nerve
when do somites develop?
3rd week
where does bone diameter growth occur?
diaphysis (shaft)
syndactyly
digits connected by soft tissue
what is the major signaling center for proper limb development?
apical epidermal ridge AER
ZPA
zone of polarizing activity area of undifferentiated mesenchyme at posterior of limb bud
what does the zygote emit at 3-5 hrs?
Ovum Factor - signals mother immune system NOT to attack it - permits implantation
sclerotome
forms bones
what does each gastrulation layer form?
ecotoderm –> epidermis, neural crest, nervous system mesoderm –> somites, muscle, cartilage, bones, dermis, blood endoderm –> organs and GI/resp systems
AER
apical epidermal ridge thick epithelium at distal limb bud
what axis does the ZPA direct limb bud growth?
anterior-posterior
caudal dysgenesis
impaired development of lower half of body
which myotome form limbs: abaxial or primaxial
abaxial
each somite forms what three things?
sclerotome, myotome, and dermatome
primaxial vs abaxial
p - adjacent to neural tube, closer to axis and less migratory, dorsal muscles of back, body wall and girdles a - myoblasts further from neural tube, respond to lateral signals to form limbs
AER is consistently supplied by what?
single large blood vessel
how are embryos staged?
according to number of somites
How are toes and fingers split?
apoptosis of cells
