HSF 1 - Unit 3 Embryology Flashcards
Development of the Skeletal System
how does skeletogenesis occur in the axial skeleton?
vertebrae form as intersegmental structures derived from adjacent sclerotomes which split into cranial and caudal sections; with the caudal portion of one sclerotome fusing with the cranial portion of the sclerotome caudal to it. spinal nn emerge between each vertebrae and grow out to contact myotomes
there are originally how many somites of the cervical vertebrae?
8 (which is why there are 8 cervical spinal nerves), but the fusion of one to the cranium results in 7 cervical vertebrae, spinal nerves of this portion of the spine exit above vertebrae of the same number while others will exit below the same-numbered vertebrae
what do sclerotomes form during development of the spinal cord?
neural arches surrounding the developing spinal cord, also form the vertebral body (centrum)
what happens to the notochord during spinal cord development?
it regresses except where it is incorporated into intervertebral discs
what happens when you get a herniated disc?
the nucleus pulposus gets pushed into the spinal canal and compressed, causes pain
what is congenital scoliosis?
abnormal lateral curvature of the spine, resulting from disruption of normal vertebral development; although many types (semisegmented, fully segmented, wedge vertebrae, block vertebrae, unsegmented bar, unsegmented bar with hemivertebrae) all result from abnormal formation and segmentation of the vertebral precursors (somites)
what do ribs arise from?
zones of condensed mesenchyme lateral to the body of the vertebrae (from sclerotome); develop from costal processes, grow into ribs in thoracic region only
cervical ribs
ribs that grow in the cervical portion of the spine; can result in thoracic outlet syndrome that can cause issues with the brachial plexus due to compression
how does the sternum develop?
from cartilaginous sternal bars in ventral body wall; fuse with one another in cranial-caudal direction and form the manubrium, body, and xiphoid process
what is pectus carinatum?
an overgrowth of cartilage causing the sternum to protrude. can be evident at birth; adolescent males during growth spurt. may occur as a solitary congenital abnormality or in association with other genetic disorders or syndromes
what is pectus excavatum?
caused by overgrowth of the costal cartilage in such a way that restricts the expansion of the ribs and pushes the sternum inward, cause is unknown
what is a sternal cleft?
an unclosed sternum that leaves this space directly over the heart vulnerable
what is a sternal foramen?
it is an ossification anomaly found in 4-10% of the population that leaves a hole in the distal portion of the body of the sternum, leaving a hold directly over the heart. This can be mistaken for a bullet wound or sternal disease by a CT scan, and is a common acupuncture point (danger danger)
how does the appendicular skeleton develop?
- with patterns of Hox gene expression and inductive interactions between the mesoderm and ectoderm (epithelia)
- there are mechanical influences (early morphogenesis-late prenatal)
- anomalies are common and highly visible, may be related to disturbances in specific cellular or molecular interactions
when is the initiation of limb development?
outgrowth from the body wall late in week 4, with the frontlimb being greater than the hindlimb
how is limb positioning regulated?
positioning along craniocaudal axis is regulated by HOX gene expression along the axis, these are expressed in overlapping patterns from head to tail
what happens once positioning along craniocaudal axis is determined?
placement along proximodistal, anteroposterior, and dorsoventral axes must be decided
what is limb growth initiated by?
TBX5 and FGF10 in the forelimb and TBX4 and FGF10 in the hindlimb, secreted by lateral plate mesoderm cells
what is Holt-Oram syndrome?
an autosomal dominant syndrome that causes a mutation in the transcription factor TBX5, which is important in the development of both the heart and upper limbs. this always causes variable upper limb abnormalities that can be either unilateral or bilateral; asymmetric may involve the radial, carpal, and thenar bones. the most prevalent findings are malformations or fusions of the carpal bones
what are the types of reduction defects?
is an arrest or failure of development, can be part (meromelia) or all (amelia) of a limb missing. phocomelia is when the feet and hands arise close to the trunk
what is mesomelia?
shortened forearm or leg elements, fetal sonography performed at week 20 can demonstrate the typical finding of mesomelic dysplasia
how does the AER form?
AER= apical ectodermal ridge
once limb outgrowth is initiated, BMPs, expressed in the ventral ectoderm, induce formation of the AER. the AER sends signals to grow out from the body wall and where to put characteristics of the limbs
directs limb bud organization along proximo-distal axis and maintains dorsal/ventral axes
what is RF? what does it do?
=radical fringe, found in the dorsal half of the limb ectoderm, and restricts the location of the AER to the distal tip of the limbs. it also induces the expression of SER2 at the border between cells that are expressing RF and those that are not. This is the border where AER is established. expression of RF is repressed by engrailed-1 in the ventral ectoderm
what is engrailed-1? what does it do?
assists in the formation of the border (AER) in ventral ectoderm cells and represses RF expression here
