Exam 3 embryology Flashcards
What layer does the skull and face bones come from?
Neuroectoderm
What layer does the base of the skull, vertebrae and ribs come from?
paraxial mesoderm
What layer does the appendicular skeleton come from?
lateral plate mesoderm
What week does the skeleton begin forming?
Week 4
What is the immature form of somites?
somitomeres
What induces the formation of somites?
Neural tube
How does development of somites progress (direction)?
Rostral to caudal
What genes induce the formation of somites?
Hox (homeobox)
What is mesenchyme?
Loosely organized embryonic connective tissue derived from mesoderm
What is intramembranous ossification? What kind of bones?
Mesenchymal cells differentiate directly into osteoblasts to form flat bones
What is endochondral ossification? What kind of bones?
Mesenchymal cells transform into chondroblasts, lay down hyaline cartilage. Osteoblasts come in and continue laying down bone. Long bones (femur, phalanges, sternum, vertebrae)
What is bone growth complete?
when epiphyseal plate disappears
What is marfan syndrome?
autosomal dominant disorder due to mutation for fibrilin that affects connective tissue; results in long thin limps and CV/lung problems
What layer does skeletal muscle form from?
paraxial mesoderm > somites > dermomyotome > myotome
What layer does smooth and cardiac muscle form from?
Lateral plate mesoderm–> splanchnic mesoderm
Explain steps of myogenesis
mesoderm >mesenchyme >myoblasts >myotubes >multinucleated muscle fibers > striated skeletal muscle
What gives rise to myoepithelial cells of mammary and sweat glands and iris muscle?
ectoderm
What is unique about the formation of vertebrae?
They are intersegmental, formed by caudal part of one and the rostral part of another somite
What forms the nucleus pulposis?
The notochord
What forms the annulus fibrosis of the vertebrae?
sclerotome
How does spina bifida develop?
failure of the neural tube to close, meaning vertebral arch fails to fuse
Describe Spina bifida occulta, meningocele, meningomyelocele
Occulta: least severe, lumbosacral region, tuft of hair. Meningocele: meninges protrude through defect in spinal cord or skull. Meningomyelocele: most severe, meninges and spinal cord protrude through defect
Describe congenital dermal sinus
Neural ectoderm fails to completely separate from surface ectoderm, meaning spinal cord may be tethered/open to environment
Describe hemivertebrae; what does it cause?
failure of one ossification center on side of vertebral body. Causes congenital scoliosis.
Describe congenital brevicollis (Klippel-Feil sequence)
shortened neck due to non-segmentation of cervical vertebrae
What is pectus excavatum
concave chest due to defect in sternal development, can compress lungs, shift heart
Where do ribs start to form?
costal processes of thoracic vertebrae
What causes thoracic outlet syndrome?
cervical C7 rib, can compress neuromuscular structures supplying upper limb
What does the epimere develop in to?
Erector spinae/spinal muscles
What structure leaves the spinal cord to innervate the erector spinae?
Dorsal primary rami
What does the hypomere develop into?
Thoracic muscles
What structure innervates the hypomere muscles?
ventral primary rami
Describe poland syndrome
Failure in the development of the pectoralis muscles, usually unilateral
Describe prune belly syndrome
poor development of abdominal muscle wall causing skin to wrinkle, usually urinary tract abnormalities and descent of the testicles
Describe congenital torticollis
spasm or shortening of sternocleidomastoid muscles
What forms first, upper limbs or lower limbs?
Upper limbs form first
What genes control positioning of the limbs?
Homeobox (Hox) genes
Where does the upper limb bud first form?
C5-T1 somite levels
Where does the lower limb bud first form?
L2-S2 somite levels
What category does the apical ectodermal ridge (AER) fall into?
a placode
What is the apical ectodermal ridge?
thickening at the distal end of the limb bud which secretes FGFs
What polarity does the AER help the limbs form into?
Proximal and distal axis
How does the zone of polarizing activity (ZPA) form?
respond to FGFs from the AER
What genes does the ZPA express?
sonic hedgehog gene
What axis does the ZPA help to develop?
anterior-posterior axis (pinky vs thumb)
What is absence of malformation of one or more limbs called?
Amelia
What is partial absence of a limb called?
Meromelia or phocomelia
What is syndactyly?
Failure of apoptosis resulting in webbed fingers or toes
What is polydactyly?
duplication of digits
