Development of the Skeletal System (embryology) Flashcards
The caudal and rostral sections of the vertebral column fuse and become what?
vertebrae
What do spinal nerves grow between
vertebrae
What do growing spinal nerves innervate?
myotome
How many somites are there, and how many fuse to make cervical vertebrae?
8 original somites; 7 of them fuse.
Cervical spinal nerves exit ____ vertebrae of the same number. Others spinal nerves exit ____ vertebrae.
above; below
What do sclerotomes form around the developing spinal cord?
neural arches and the vertebral body.
As development progresses, the notchord regresses until it is only found where?
in the intervertebral discs.
What is congential scolosis?
abornmal lateral curvature of the spine caused by disruption of normal vertebral development.
Hemivertebrae (scolosis) results from what?
Failure of the vertebrae to fully form. Some vertebrae are smaller than others.
Block vertebrae/unsegmented bar (scolosis) results from what?
Failure of the vertebrae to fully segment. Some of the vertebrae are fused together.
Unsegmented bar with hemivertebrae (scolosis) results from what?
failure of formation AND segmentation; some vertebrae are fused and smaller than others.
Ribs arise from what zones?
zones of condensed mesenchyme lateral to the vertebra.
What region do ribs usually grow?
thoracic region; they can also grow in the cervical and lumbar regions.
What does the sterum develop from?
sternal bars in the ventral body wall; the sternal bars on the left and right side of the rib cage come to the midline and fuse together.
What does the sternum form?
manubrium body and xiphoid process.
what is pectus carinatum?
the overgrowth of cartilage causing th sternum to protrude.It is caused by the overgrowth of costal cartilage.
What is sternal formaen?
ossification in the sternum that looks like a bullet hole.
The positioning of the limbs is regulated by the expression of what genes?
hox genes
Limb outgrowth is initiated by what genes?
TBX5 (forelimb) and TBX4 (hindlimb)
What is meromelia? What amelia?
Partial (meromelia) or total absence (amelia) of the limbs.
What is phocomelia?
When the feet and hands arise close to the trunk
In mesomelia, which section of the arm is greatly shortened?
the forearm
What is radial club hand?
Abnormality in the position of the hand and forearm. Some muscular and neural structures may not be present.
What is the apical ectoderm ridge?
A region of the ectoderm that forms a ridge when limb outgrowth is inititaed by BMPs.
Once the AER has formed, what other two regions form and assists in limb differentiaton?
the apical ectodermal ridge and the zone of polarizing activity.
What occurs at the zone of polarizing activity?
the region tells the body where to put things, like fingers.
What occurs at the progress zone?
mitosis and limb lengthening.
What occurs at the AER?
limb bud organization and maintenance of the dorsal/ventral axes.
After AER is established, what does it express?
FGF4 and FGF8; both maintain the progress zone. FGF4 and 8 allow for the mitosis and growth of cells in the region (and hence distal growth of the limb).
The expression of what two genes at the zone of polarizing activity direct organization of the limb bud and patterning of digits?
Shh and Retinoic aid.
If Shh and retinoic acid are misexpressed in the zone of polarizing activity, what can occur?
a mirror image duplication of limb structures results.
Removal or addition of the AER to a developing limb results in what?
the absence of limbs or the duplication of a limb OR polydactyly.
Polydactyly usually results in the growth of a finger or toe on what side?
lateral (not by the thumb or big toe).
What does the zone of cell division contain?
a region of actively dividing cells.
What does the zone of differentation contain?
a region of cell specialization.
The cells closest to the AER become what structures?
distal structures; this is caused by the secretion of FGFs.
Cells far from the AER become what structures?
proximal structures.
What does thalidomide do?
Disrupts signaling from the AER to the progress zone; this causes limbs to be shortened or nonexistent.
The ___ of cells removes the webbing between fingers and toes.
apoptosis
What is syndactyly?
webbed fingers or toes due to failure of apoptosis.
What is brachydactyly?
The development of short digits; it often results in short stature.
What is cleft hand or foot?
lobster claw; it often results in the absence of one or more central digits.
As the limb develops, how does it rotate?
90 degrees laterally, then 90 degrees medially.
Many congential limb abnormalities are the result of what?
a combination of genetics and the environment.
What is sirenomelia?
mermaid syndrome.
What is achondroplasia?
dwarfism; it results form abnormalities at the epiphyseal plate and zones of proliferation. Bones do not grow correctly.
What is brittle bone disease?
Fragile bones. It also inclues blue sclera in the eye
What is talipes equinovarus (club foot)?
abnormal position of the foot caused by a lack of space in the uterus, whether by multiple fetuses or by a lack of amniotic fluid.
How is club foot treated?
braces and sometimes surgery.
A 13 year old male patient presents a depressed sternum. You determine that he has pectus carinatum. What has caused his condition?
overgrowth of cartilage in the costal region.
You encounter a patient who exhibits photocmelia. What is her condition and what is it caused by?
She has limbs close to the trunk; it is caused by an abnormality in the zone of polarizing activity.
In an embryology laboratory, you decide to study limb growth. You add an extra AER to a growing limb bud of a chick embryo. What will occur in the developing chick?
The chick will grow an additional limb.
You encounter a patient who has a very short limb caused by thalidomide. How has thalidomide caused shortening of the limb?
Signaling between the AER and progress zone has been disrupted, and the progress zone stops mitotically dividing (and hence, growing more limb).
