Embryology (Lecture 2) Flashcards
Limb bud appear in the __ week
4th
limb bud appear as
as small elevations on the ventrolateral body wall
limb buds are derived from
the somatic body wall (lateral plate mesoderm)
Mesenchyme (embryonic tissue) covered in
ectoderm
upper limb buds are visible in the
cervical region ~day 24
lower buds are visible in the
lumbar region ~day 28
limb bud contains MESENCHYME that will form ____ of the lower extremity
cartilage/bone and dermis
muscles are derived from
somites, myoblasts migrate into developing limb
where are motor units derived from?
spinal cord
schwann cells,
melanocytes,
sensory neurons
and sympathetics are derived from
neural crest cells
proximal/distal directional axes of limb
thigh,leg,foot
dorsal/ventral directional axes of limb
anterior vs posterior thigh/leg
dorsum vs plantar foot
cranial/caudal directional axes of limb
big toe (cranial,preaxial) to little toe (caudal, postaxial)
limb elongation progresses from `
proximal to distal
stylopod
thigh
zeugopod
leg
autopod
foot
in early stages of limb elongation the limbs appear as
flippers on the ventrolateral wall
ectoderm over distal tip of limb condenses to form
the apical ectoderm ridge (AER)
what represents to dorsal/ventral boundary
apical ectoderm ridge (AER)
underlying mesenchyme induces
the formation of AER
AER induces the proliferation of
the underlying mesenchyme and elongation of the limb (progress zone)
mesenchyme obtains positional information about
future proximal/distal location
studies that removed the AER showed
the formation of truncated limb
mesenchyme will differentiate into
cartilage as a cartilage precursor model to bone.
in fetal development where do the flexor and extensor compartments meet?
pre-axial (cranial) and post-axial (caudal) borders
Pre-axial (cranial) border
medial side of the limb (tibal side)
which border is demarcated by the great saphenous vein
pre axial (cranial) border
post-axial (caudal) border
lateral side (fibular side) of the limb
which border is demarcated by the small saphenous vein
the post-axial (caudal) boarder
mesenchyme differentiates into
cartilage
ossification occurs from
cartilage templates (most) or connective tissue
what develops from inter-membranous ossification
tips of distal phalanges (ungal tuberosity , tufts)
when does bone become visible on radiographs
once it begins ossification
joints form from
mesenchyme between cartilage templates of future bones
joints can differentiate into either
- collagen (fibrous)
- hyaline cartilage (synchondrosis)
- joint cavity (synovial)
Synovial Joint
development of an interzone between cartilage templates
in a synovial joint where does the cavitation develop
within interzone
limb muscles are derived from
hypaxial myogenic precursors that migrate ventrally along dorsolateral wall
when does migration of the hypaxial myogenic precursors begin
week 4/5
muscle mass increases by __ until ___
mitosis until mid fetal period
myoblasts form 2 condensations
- dorsal mass (extensor)
- ventral mass (flexor)
dorsal mass is located ___ before limb rotation
posteriorly (dorsal)
After limb rotation, dorsal mass is located
- Posterior in upper limb
- Anterior in lower limb
- Not lower limb girdle (pelvic girdle)
Ventral mass is located ___ before limb rotation
anterior/ventrally
after rotation, ventral mass is located
- Anterior in upper limb
- Posterior in lower limb
- Not lower limb girdle
__ rami from spinal cord segments migrate into developing limb
Ventral
Dorsal branches (divisions) innervate
dorsal muscle mass
Ventral branches (divisions) innervate
ventral muscle mass
axons innervate muscle mass when?
before they split into individual muscles
lumbar plexus
ventral rami of L1-4
ventral rami have __ division
ventral and dorsal
subcostal nerve
- ventral rami T12
- cutaneous supply to superior anterolateral thigh
Branches of the lumbar plexus
- Iliohypogastric
- Ilioinguinal
- Genitofemoral
- Lateral femoral cutaneous
- Nerves to psoas major muscle
- Femoral
- Obturator
- Accessory Obturator
Ventral Division of L1
Iliohypogastric and Ilioinguinal
Ventral division of L1,L2
Genitofemoral
dorsal divisions of L2,3
Lateral Femoral cutaneous
dorsal divisions of L2-4
- nerve to psoas major muscle
- Femoral, (nerve to iliacus muscle)
Ventral divisions of L2-4
Obturator
Ventral divisions of L3,4
Accessory Obturator
A part of L4 also contributes joints with L5 ventral rami to form
lumbosacral trunk
branches of the sacral plexus
Superior Gluteal Inferior Gluteal Nerve to Piriformis Perforating cutaneous nerve Sciatic Posterior cutaneous nerve to thigh Nerve to Quadratus femoris Nerve to obturator Internous Pudendal
dorsal divisions of L4-S1
Superior gluteal
dorsal divisions of L5-S2
inferior gluteal
dorsal divisions of S1,2
Nerve to piriformis
dorsal divisions of S2,3
Perforating cutaneous nerve
dorsal divisions of L4-S2 and ventral divisions of L4-S3
Sciatic
dorsal divisions of S1,2 and ventral divisions of S2,3
Posterior cutaneous nerve of thigh
ventral divisions of L4-S1
Nerve to quadratus femoris
ventral divisions of L5-S2
Nerve to obturator internus
ventral divisions of S2-4
Pudendal
Zone of polarizing activity (ZPA) is a signaing center that forms in
the dorsal mesenchyme just below AER (apical ectodermal ridge)
controls pattern formation on an anterior/posterior axis
zone of polarizing activity
the Hallux at the Cranial/anterior end is exposed to a __ amount of morphogen compared to the little toe
lesser
one of the important morphogens influencing the formation of the digits
Sonic Hedghog
Primary vessel that supplies the developing limb
axis (axial) artery
axis artery arises from
dorsal root of umbilical artery
the axis artery passes along
posterior aspect of developing limb in the plantar foot
external iliac forms from
dorsal root of umbilical artery
femoral artery forms from
exteral iliac artery
femoral artery travels to
posterior thigh where it then communicates with the axis artery
proximal to the femoral artery communicating the with axial artery
the axial artery will disappear
axis artery disappears but what arteries persist
inferior gluteal and ischiadic artery
___ eventually becomes major supplier to lower extremity through its communication with __
femoral artery; popliteal artery
Dorsal root of umbilical becomes
common iliac
Remnants of axis artery
- Inferior gluteal
- Popliteal
- Ischiadic artery (sciatic artery)
- Fibular
5th week
- Hand and foot plates develop, hands develop earlier
- Flat and paddle shaped
6th week
- Joints become more observable
- Digital rays of hand plate develop
- Limbs move to a more ventral position
7th Week
- Digital rays of the foot develop
- Limb rotation
limb rotation initially the knees and elbows are facing
laterally
upper and lower limbs rotate in
oppositie directions
upper limbs rotate ___ to face caudally
laterally/exertnall
lower limbs rotate ___ to so knees face cephalically
medially/internally
8th week
- Fetal position is attained by the end of the week
- Mesenchyme between digits degenerates (apoptosis)
Complete or partial union between 2 or more tarsal bones
tarsal coalition
developemntal fusion that results from incomplete or faulty mesenchymal segmentation
tarsalcoalation; Genetically programed to develop
in tarsal coalition, ___ and __ are most common
Calcaneonavicular and talocalcaneal
tarsl coalition is classified by the type of tissue that bridges the bones
- fibrous (syndesmosis)
- cartilaginous (Synchondrosis)
- bony (synostosis)
syndactyly
congenital malformation caused by the the failure of differentiation of digits (mesenchyme doesn’t separate)
fusion of toes in syndactyly can be either __ and can effect __
single or multiple; skin and soft tissue OR soft tissue and bone
Cutaneous Syndactyly
- Failure of mesenchyme degeneration between digits
- Causes webbing between digits
- Can be complete or partial
- More of a functional problem in the hand
Osseous Syndactyly
Failure of mesenchyme to segment in the foot
Amelia
lack of limb; absence/failure of formation of an entire limb
amelia is cause by
interruption of the limb formation process (prevented or interrupted early on
absence of all limbs
tetra-amelia
Meromelia
partial absence of a limb
where does meromelia occur
can occur at any level of the limb
phocomelia
seal limb
type of meromelia where rudimentary hands or feet are attached to trunk
amelia, meromelia, phocomelia can be cause by
vascular interuption, genetic, or caused by terogens (like thalidomide, chemicals, radiation)
congenital absence of bone example
fibula (fibular hemimelia) can be partial or complete absence
Cleft foot or hand (ectrodactyly)
- “Lobster Claw Foot (hand)”
- Rare anomaly
- Central conical defect from periphery to tarsals
- Presentation varies
- Affects central rays
- Surgically addressed early on to prevent pathological adaptation
Polydactyly (many digits) formation of extra digits that can be due to
genetic defect or part of a syndrome. can appear differently.
Polydactyly in lower limb types
pre axial
post axial
central
Pre-axial polydactyly:
extra digit towards the hallux
Post-axial:
- extra digit towards little toe
- more common
- Surgically corrected
central
extra digit involves digits 2,3, or 4
Macrodactyly
- Enlargment of digits
- Overgrowth of bone/tissue