Flashcards in Week 3 - Limb Embryology Deck (33)
What does the neural tube induce?
The formation of vertebrae
What does the notochord do first (before the neural tube is there)?
It induces the overlying ectoderm to invaginate, forming the neural groove and tube.
What is the significance of the notochord?
-Mechanical role in the folding process
-Signals: formation of neural tube/groove, somites (indirectly), musculoskeletal system (via Shh)
-Contributes to: vertebral bodies & intervertebral discs
What happens in the embryo from weeks 3-4?
The notochord induces the formation of the neural tube which then induces the formation of somites!!
What is mesenchyme?
Embryonic connective tissue - derived from mesoderm and neural crest- multipotent - turns into myoblasts, chondroblasts, osteoblasts, fibroblasts, etc.
What happens at week 4 of development?
1. Neural tube begins to close
2. Cephalo-caudal and lateral folding
3. Appearance of somites/somitomeres
4. Genesis of organ systems
5. Appearance of pharyngeal arches (face and neck)
6. Otic and optic development begins
7. Limb buds appear
How many somites are there and what do they form?
There are about 42 pairs of somites with 7 in the head region that stay somitomeres. These 7 contribute mesoderm to the head and neck regions. The lower 35 somite pairs make up the vertebral column and limbs
When do primary ossification centers appear?
Week 8 (diaphysis)
What is marfan syndrome?
-Problems with collagen everywhere in the body, can cause lens dislocation and early aneurism
-Connective tissue disorder the causes excessive long bone growth
-Long, thin limbs
-Also can affect heart, vessels, bones, eyes and lungs
What is osteogenesis imperfecta?
-Defect in type I collagen gene (most cases)
-Autosomal dominant or recessive
-Extreme bone fragility, thin, curved bones
-Frequent fractures, decreased bone density
What is acrondroplasia?
Most common form of dwarfism
-Affects long bones
-May be autosomal dominant inheritance or spont. mutation in FGFR3 gene
-Brain growth and intellect usually normal
What is gigantism?
Excess growth hormone during childhood before growth plates close. Overall large size: height and organs; normal proportions
What is acromegaly?
It is excess growth hormone after growth plates closed. Large, heavy bones especially face, hands and feet.
What is congenital hip dysplasia/dislocation?
Born with incomplete formation of acetabulum. May self correct or child can also be placed in a harness to correct the syndrome. Symptoms include: leg positions that don't match, less movement, uneven leg length
What happens to sclerotomes during resegmentation of the vertebral column?
Sclerotomes get divided in two and then recombine around the intersegmental artery, leaving room inbetween the new groups for the spinal nerve.
How many cervical nerves and vertebrae?
8 nerves, 7 vertebrae
What does the notochord become?
The nucleus pulposis of the intervertebral disc
What produces the vertebral foramen in vertebrae?
Sclerotome surrounds the notochord and neural tube. Then the sclerotome migrates and ossification centers form and the vertebral foramen, neural arch, etc are formed in the vertebrae
What is spina bifida?
It is the mildest of defects in spine. It's a type of occult spinal dysgraphia, a condition that results from failure of the neural tube to close. Vertebral arch fails to fuse, leaving the spinal cord exposed. Severity varies
What is spina bifida occulta?
Least severe form. Usually in lumbrosacral region, often marked by a tuft of hair.
What is meningocele?
Meningese protrude through defect in spinal cord or skull.
What is myelomeningocele?
It's where the meninges and spinal cord protrude through defect. Most severe
What is congenital dermal sinus?
The neural ectoderm fails to completely separate from the surface ectoderm. The patient presents with a paramedian pit which may or may not communicate with the spinal cord. Most commonly found in lumbar region. The 'pit' is very susceptible to infection. Patient can have multiple rounds of sinusitis.
What is Klipppel-feil syndrome?
congenital fusion of any cervical vertebrae, scoliosis and shortened neck is often common with this syndrome. Sometimes this condition also presents abnormalities in the heart, kidney, rib, palate abnormalities.
What is congenital scoliosis?
It results from hemivertebra. There is only one chondrification center/ossification center that forms. In some cases, you only develop part of one vertebrae and this curves the whole spine.
What is thoracic outlet syndrome?
Being borne with one extra rib in the upper cervical area. Neurovascular compression is caused and due to narrowing of passageway between neck and axilla. - Extra rib can crush cervical artery. When this happens in the lumbar region, there usually aren't as many problems.
What is pectus excavatum?
Excessive growth of connective tissue during sternum development. Can cause heart and/or lungs to be compressed. Symptoms include fatigue, rapid pulse, recurrent respiratory infections, heart murmur, chest pain.
When is the critical period for limb development?
What controls the location of the development of limb buds?
Hox - homeobox genes
What does the zone of polarizing activity do?
It secretes Shh which determines which side of the limb bud will be anterior and which side will be posterior. Limb buds start developing on the front side of the body and grow straight out.
When does bone development begin?
During late 3rd week.
What are the two types of bone formation?