Gross Anatomy L21

at the end of week 3/beginning week 4, what does paraxial mesoderm on either side of neural tube condense into segmentally?

somites

what are the things somites differentiate into

sclerotome, dermatome, myotome

sclerotome

cartilage and bone of most of the axial skeleton (ribs, vertebrae)

dermatome

dermis of the back

myotome

skeletal muscles of the back, body walls, and limbs with 2 populations

two populations of myotomes

dorsomedial group, ventrolateral group

dorsomedial group

intrinsic/deep/epaxial muscles of the back innervated by dorsal rami

ventrolateral group

extrinsic/superficial/hypaxial muscles of the back, muscles of the body wall, limbs innervated by ventral rami

what forms the dermis, bones and cartilage of limbs

somatic lateral plate mesoderm

where are the myoblast cells from and where do they migrate

they are from the ventrolateral myotome, and migrate to the somatic lateral plate mesoderm

endochondral ossification

mesenchyme cells to chondroblasts to form cartilaginous bone model to primary ossification center along the diaphysis, to secondary ossification center at epiphysis

what are epiphysial plates

hyaline cartilage plates between epiphysis and diaphysis allowing for longitudinal growth (forms epiphyseal line)

when do limbs begin to form as outpocketings

week 4, around day 24

what forms via somatic lateral plate mesoderm and myoblasts from ventrolateral myotome proliferation under a sheet of ectoderm

limbs

how much later than upper limbs do lower limbs begin to develop

1-2 days

what happens during weeks 5-6

limb buds are formed

apical ectodermal ridge (AER)

signals rapidly proliferating cells closest to it to remain undifferentiated while those farther away begin to develop, defines proximal distal axis

3 segments of the limb

proximal segment (stylopod), intermediate segment (zeugopod), distal segment (autopod)

proximal segment

1 long bone (humerus/femur)

intermediate segment

2 parallel long bones (radius/ulna or tibia/fibula)

distal segment

carpals, metacarpals, digits, tarsals, metatarsals, digits

zone of polarizing activity

signaling from mesenchyme located near caudal border of AER, defines cranial caudal axis

cranial axis

pollex/hallux

caudal axis

pinky

dorsal and ventral ectoderm defines what

dorsal ventral axis

selective apoptosis occurs to do what

separate hand and foot plates into five individual digits

what happens during week 7-8

repositioning of the limbs

which direction does upper limb rotate to put flexor compartment anteriorly

laterally

which direction does lower limb rotate to put flexor compartment posteriorly

medially

when is the most sensitive period for teratogen induced limb malformations

24-36 days after fertilization

absence of limb due to early limb bud developmental disruption

amelia

partial absence of a limb

meromelia

absence of long bones, rudimentary hands/feet attached to trunk by small irregularly shaped bones

phocomelia

shortened radius/ulna and or tibia/fibula (zeugopod)

mesomelia

presence of extra digits

polydactyly

fusion of two or more digits due to failure of normal interdigital apoptosis

syndactyly

shortened digits

brachydactyly

absence of all digits

adactyly

most common cause of dwarfism inherited as an autosomal dominant disorder that results in shortened, bowed limbs due to disruption of endochondral ossification

achondroplasia

rupturing or tearing of the amnion can cause pieces to detach and wrap around limbs and restrict blood flow/development

amnionic band syndrome