embryo-limb development Flashcards by ted pham

two layers of a developing embryo

embryoblast

trophoblast

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embryoblast forms

epiblast

hypoblast

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trophoblast forms

syncytiotrophoblast

cytotrophoblast

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what happens on day 16 of development?

gastrulation occurs

from bilaminar to trilaminar

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three layers that result from gastrulation

endoderm
mesoderm (layer that forms due to gastrulation)
ectoderm

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what occurs during neurulation

formation of neural tube

mesoderm forms paraxial, intermediate and lateral plate on either side of neural tube

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paraxial mesoderm organizes into what

somitomeres that become somites

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how many somites by day 35

42-44 somites

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somitomeres in the head form

neuromeres not somites

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somites from from which somitomeres

occipital region to caudal region

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what are the regions of somites

4 occipital
8 cervical
12 thoracic
5 lumbar
5 sacral
8-10 coccygeal

1st occipital and last 7 coccygeal disappear

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what two layers do somites differentiate into

sclerotome

dermomyotome

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what does the sclerotome give rise to

vertebrae and most of skull
axial skeleton
rib
cartilage 
bones of the trunk

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what do bones first appear as

condensations of mesenchyme cells

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what are the two methods of bone development

intramembranous

endochondral

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intramembranous

mesenchyme cells are just replaced by bone cells or osteocytes

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endochondral

mesenchyme become chondrocytes then form bone cells or osteocytes

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lateral plate mesoderm forms

sternum and limb bones

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neural crest forms

bones of the skull

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head somitomers form

forms the cranial vault and base of skull

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what two layers does the dermomyotome give rise to

dermatome

myotome

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dermatome gives rise to

dermis and subcutaneous tissue

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myotome gives rise to

muscle

myoblasts fuse to form myotubes which fuse to form muscle fibers

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abaxial muscle cell precursors form what

ventrolateral muscle cells
limb muscles
abdominal muscles
infrahyoid muscles

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pimaxial muscle cell precursors from what

dorsomedial muscle cells muscles of the back shoulder girdle intercostal muscles

muscle cells from the limbs are derived from

somites from specific segmental levels

epaxial

intrinsic back muscles | from primaxial

hypaxial

body wall and limb muscles | from abaxial

how do vertebral column forms from sclerotomes

caudal portion of each sclerotome proliferates and fuses with cranial portion of inferior sclerotome intersegmental

notochord forms

nucleus pulposus

mesenchyme forms

annulus fibrosus

congenital scholiosis

asymmetric fusion of vertebra appears that half of the vertebra is missing abnormal curvature of the vertebral column

accessory ribs due to

extra vertebral body

fused ribs due to

missing a vertebral body

klippel-feil anomaly (brevicollis)

short neck because of the absence or fusion of cervical vertebra at craniovertebral junction 1% of new borns

how do limb buds appear

as outpocketings from ventrolateral body wall

limb buds consist of

core of mesenchyme surrounded by surface ectoderm

upper limb buds appear by day

day 26

lower limb buds appear by day

day 28

mesenchyme is

somatic layer of lateral plate mesoderm

mesenchyme contributes to

``` bones tendons ligaments cartilage fascia joints vessels dermis ```

homeobox (hox) gene does

regulates axes and patterning

AER is essential for

the proximal-distal axis of limbs

AER stands for

apical ectodermal ridge

what forms AER

apex of each limb bud thickens to form, mutilayered

AER induces

proliferation of underlying mesenchyme

AER causes which mesenchyme to remain undifferentiated

adjacent mesenchyme

ZPA is responsible for

patterning of the anterior-posterior axis of limbs

how does ZPA form

mesenchymal cells aggregate at the posterior margin of the limb bud forming a zone of polarized activity

retinoic acid

should not be taken during pregnancy. can cause duplication of limbs normally cells in ZPA release it already

hand and foot pads form

distal ends of the limb buds flatten

what does mesenchyme do in hands and feet

mesenchyme condenses to form digital rays by 6th week for hands and 7th weeks for feet

what causes formation of separate digits

apoptosis between digits | each finger still has AER to continue distal growth

when does mesenchyme form cartilaginous models of the limb

6th week | mesenchyme to chondrocytes to cartilage

when doe endochondral ossification begin to form limb bones from lateral plate mesoderm

8th week

by what week have all bones form

12th week

when does secondary ossification center form

at birth

how do limbs rotate to each anatomical position

upper limbs rotate laterally through 90 | lower limbs rotate medially almost 90

how does dermatome start

segmentally then changes

initial blood supply to upper limb

dorsal intersegmental arteries from aorta

primordial vascular pattern consists of

primary axial arteries

what does the axial artery become

brachial and then common interosseous

what are the secondary branches from the brachial

radial and ulnar arteries

which artery degenerates

median artery

what does the axial artery begin as

ischiadic atery

primary axial artery is represented by

profunda femoris popliteal posterior tibial

minor limb anomalies are how common

fairly common

what is critical period for limb anomalies

4th-5th weeks

how often do major limb anomalies occure

1/500 | usually genetics

major cause of limb defects from 1957-1961

thalidomide

bone malformations

failure to develop formation of extra bones fusion of adjacent digits

achondroplasia

cause of dwarfism 1/15000 bowed limbs and short disturbance of endchondral ossification at epiphyseal plates

thanatophoric dysplasia

lethal skeletal dysplasia 1/20,000 respiratory failure fibroblast growth factor receptor deficiency

osteogenesis imperfecta

deficient in type 1 collagen | early hearing loss, protrusion of eyes, bowing of legs, fractures. blue-gray sclera.

amelia

absence of entire limb

meromelia

absence of part of limb

cleft hand or foot (extrodactyly)

lobster claw deformity absence of central digit failure of digital rays to form

brachydactyly

shortness of digits | associated with short stature

polydactyly

supernumery digits extra digits usually useless extra digits is medial or lateral toes not in center, useless

syndactyly-two types

1/2200 webbed digits cutaneous (webbing of digits) osseous (fusion of bone)

congenital clubfoot

generally any defect with talus 1/1000 abnormal orientation of the foot that prevents normal weight bearing inconclusive evidence for restriction movement in utero as cause environmental factors

congenital dislocation of hip

1/1500 | results from laxity of the joint capsule or underdevelopment of the acetabulum

embryo-limb development Flashcards

(82 cards)