Embryology Flashcards
How do limbs develop ?
Begins with limb buds
When do the limb buds for the upper limb appear?
Day 26
When do limb buds for lower limbs appear?
Day 28
What stimulates the somatic layer of lateral plate mesoderm to evaginate?
Somites
What forms a core of mesenchyme covered by surface ectoderm?
Somatic layer of lateral plate mesoderm
The mesenchyme directs the organization of myotomes to form structures
Bones Tendons Ligaments Cartilage Fascia Joints vessels Dermis
What structures contribute to the formation of limbs?
Epidermis
Muscles
Nerves
Melanocytes
What embryonic structures are associated with epidermis, muscles, nerves, and melanocytes?
Aer Somites Neuroectoderm Neural crest Respectively
The limb buds grow mainly by what process?
Proliferation of mesenchyme
What genes regulate axes and patterning?
Hox genes
What forms at the apex of limb bud?
It thickens and forms apical ectodermal ridge
What does the Aer signal for?
Proliferation of the underlying mesenchyme
What is formed when mesenchymal cells aggregate at the posterior margin of the limb bud?
Zone of polarizing activity (ZPA)
What is the zone of polarizing activity responsible for?
Patterning of anterior/posterior axis
Retinoic acid
Shown to disrupt the development of limbs
When do the mesenchyme in the hand and foot plates condense to form digital rays?
6th and 7th week respectively
What induces the mesenchyme to form bones at the tips of digital rays?
Aer
When does chondrification centers appear ?
5th week
When do cartilaginous models of all limb bones appear?
6th week
When does osteogenesis begin?
8th week
When do the ossification of limb bones occur?
Begins toward the end of the embryonic period (week 8)
What is the composition of epiphyses at the time of birth?
Shafts of the long bones are ossified but epiphyses are still cartilage
How do the embryonic limbs obtain anatomical position?
Rotation of limbs
The upper limbs rotate laterally through 90 degrees on their long axis- extensors on the dorsal aspect of upper limb
The lower limb rotates medically almost 90 degrees - extensors on anterior aspect of lower limb
How do the limbs get innervated?
Motor axons from spinal cord each the dorsal and ventral muscle masses during 5th week
Motor neurons grow first
Dermatomes
Refer to segmental bands of skin innervated by spinal cord segment
As limbs elongate, the cutaneous distribution migrates along the limbs
There is a significant OVERLAP b/n dermatomes
What is the blood supply to the limbs?
Dorsal intersegmental arteries that arise from dorsal aorta
Primordial vascular pattern consists of primary axial arteries and its branches
What do the axial artery of the upper limb become!?
Brachial and continues as the common interosseous
The radial and ulnar arteries as secondary branches of the brachial
What artery typical degenerates?
Median artery
What becomes of the Axial artery of the lower limb?
Profunda femoris
Popliteal
Posterior tibial
Which weeks are the most critical for limb development?
4th and 5th weeks
What did thalidomide cause?
Many limb defects
The drug was used to tx morning sickness
What usually causes limb defects?
Genetic factors
Achondroplasia
Cause of dwarfism
Limbs are bowed and short
Disturbance of endochondral ossification at epiphyseal plates
Thanatophoric dysplasia
Lethal skeletal dysplasia
Infants die soon after birth because of respiratory failure (muscles?ribs?)
Attributed to fibroblast growth factor receptor deficiency
What is Amelia?
Absence of an entire limb
Meromelia
Absence of a part of a limb
What is cleft hand or foot?
Lobster claw deformity - fusion of digital rays
Absence of central digits - fusion of digital rays
Failure of digital rays to form-absence of digits
Floating thumb
Absence of the metacarpal bone in the thumb
Congenital absence of the radius
Radius failed to for,
Hand deviates laterally
Brachydactyly
The digits are relatively short
Associated with short stature
Polydactyly
Supernumery digits
Extra division of digital rays
Extra digit Usually useless
Syndactyly
Defect is characterized by the fusion of the digital rays
Can be cutaneous (webbing of the digits) or Osseous (fusion of the bones)
Congenital club foot
Talipes
Any defect involving the talus
results from abnormal orientation of the foot that prevents normal weight bearing
May be caused by environmental factor
Congenital dislocation of the hip
Defect results from laxity of the joint capsule or underdevelopment of the acetabulum
Genuine recurvatum
Congenital hyper extension of the knee
Returns to normal alignment without intervention
