Transcript Appendicular &limb by dr.saro0ona

APPENDICULAR &LIMB
BY
DR.SARO0ONA
‫‪ ‬هذه احملاظرة ما يه اال خدمه بس يطة دلفعيت الغالية ‪428‬‬
‫‪ ‬بأذن هللا احملاظرة اكمةل ‪,,‬ويه نسخه من الكتاب ‪,,‬وهديف الول مهنا اين أفيد أيل‬
‫ما عندمه الكتاب أو ما حيبون الكتاب‬
‫‪ ‬و أبغى منمك دعوتني بظهر الغيب الوىل لوادليت الغالية ابلشفاء العاجل ‪,‬و الثانية‬
‫يل ابلتوفيق والتيسري هبالفاينل‬
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‫وال دكتور العيال‬
‫أختمك ‪dr.saro0ona‬‬
THE
APPENDICULAR SKELETON CONSISTS
OF
Pectoral and pelvic girdles
limb bones
• The model of pectoral girdle and upper limb bones appear
slightly before those of the pelvic girdle and lower limbs
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Mesenchymal bones form in the limb buds during
the(5) fifth week
mesenchymal bone models in the limbs undergo
Chondrification to form hyaline cartilage bone
models in the (6 )sixth week.
The clavicle initially develops by
intramembranous ossification and it later forms
growth cartilages at both ends
The bone models appear in a proximodistal
sequence
Paterning in the developing limbs is regulated by
homeobox containing (hox) genes
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in the eighth week ,Ossification begins in the long
bones & Initially occurs in the diaphysis from the
primary ossification centers
By 12 weeks primary ossification centers have
appeared in nearly all bones of the limbs.
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The clavicles begin to ossify before any other bone in
the body.
The femora are the next bones to show traces of
ossification
First indication of ossification in cartilaginous model
appear in the center of the future shaft, called primary
center of ossification
PRIMARY OSSIFICATION
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Primary centers appear at different times in
different bones .But ,Most of them develop
between 7th and 12 weeks
Virtually all primary centers of ossification are
present at birth
The part of the bone ossified from a primary
center is the diaphysis
SECONDARY OSSIFICATION
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Secondary ossification centers of the bones at
knee are the first to appear in utero
The centers for the distal end of femur and proximal
end of tibia appear during 34 to 38 weeks(last month)
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Consequently they are present at birth
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Most secondary centers of ossification appear after
birth,
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The part of bone ossified from the secondary
centers called epiphysis
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The bone forms from the primary center in the
diaphysis do not fuse with that formed from the
secondary centers in the epiphysis until the bone
grows to its adult length
The delay enables lengthening of the bone to
continue until the final size is reached
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During bone growth, epiphysial plate intervenes
between the diaphysis and epiphysis
The epiphysial plate is eventually replaced by
bone development on each of its two sides,
diaphysial and epiphysial
When this occurs, growth of the bone ceases
LIMB DEVELOPMENT
 Limb
development begins with the activation
of a group of mesenchymal cells from the
somatic layer of lateral mesoderm.
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Limb buds first appear as elevations
(swelling ) of the ventrolateral body wall
toward the end of the 4th week ( 28 days).
Homeobox- containing genes ( Hox ) regulate
the limb development.
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The limb buds appear as elevations of the
ventrolateral body wall by end of 4th week
The limb buds form deep to a thick band of
ectoderm
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The upper limb buds are visible by 26 to 27 days
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Lower limb buds appear 2 days later
LIMB BUD
Limb buds elongate by the proliferation of the
mesenchyme.
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The upper limb buds appear disproportionately low on
the embryo’s trunk because of the early
development of the cranial half of the embryo.
The early stages of limb development are alike
for the upper and lower limbs
Because of their form & function, there are many
distinct differences between the development of
hand and foot
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At the apex of each limb bud the ectoderm
thickens to form and apical ectodermal ridge (AER)
The AER, a multilayered epitheleal structure , is
induced by the underlying mesenchyme
Bone morphogenic protein signaling is required 4 its
formation
AER exerts an inductive influence on the limb
mesenchyme that initiates growth of limbs in
proximal-distal axis
DIGITAL RAYS
By the end of 6th week, mesenchymal tissue in
the hand plates has condensed to form digital
rays
 These mesenchymal condensations or finger buds
outline the pattern of the digits
 During the 7th week, similar condensations of
mesenchyme form digital rays and toe buds in
the foot plates
 At the tip of each digital ray ,a part of AER
induces development of the mesenchyme into the
mesenchymal primordia of the bones(phalanges)
in the digits
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The intervals between the digital rays are occupied
by loose mesenchyme
 Soon the intervening regions of mesenchyme break
down forming notches between the digital rays
 As the tissue breakdown progresses, separate digits
are formed by the end of 8th week
 Programmed cell death (apoptosis) is responsible for
the tissue breakdown in the interdigital regions, and
is probably mediated by bone morphogenetic
proteins, signaling molecules of the transforming
growth factor B ( )‫بيتا‬
 Blocking these cellular and molecular events could
account for syndactyly, webbing or fusion of the
fingers or toes
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FINAL STAGES OF LIMB
DEVELOPMENT
As the limb elongate, mesenchymal models of the
bones are formed by cellular aggregation
 Chondrification centers appear later in the 5th
week. By the end of the 6th week, the entire limb
skeleton is cartilaginous.
 Osteogenesis of long bones begins in the 7th week
from primary ossification centers in the middle of
the cartilaginous models of long bones
 ossification centers are present in all long bones by
the 12th week
 Ossification of the carpal (wrist) bones begins
during the first year after birth
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From the dermomyotome regions of the somites,
myogenic precursor cells migrate into the limb
bud and later differentiate into myoblasts (
precursors of muscle cells ).
As the long bones form, myoblasts aggregate and
form a large muscle mass in each limb bud
In general this muscle mass separates into dorsal
(extensor) and ventral (flexor) components
 The mesenchyme in the limb bud gives rise to
bones, ligaments, and blood vessels
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The cervical and lumbosacral myotome
contribute to the muscles of the pectoral and
pelvic girdles.
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Early in the seventh week the limbs extend
ventrally
extensor aspect
of limbs
dorsal
flexor aspect of
the limbs
ventral
postaxial
border
preaxial
border
caudal
cranial
 The
developing upper limbs rotate in opposite
directions and to different degrees
 Rotations of Limbs:
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upper limbs rotate laterally through 90
degrees on their longitudinal axis
 Now
the future elbows point dorsally
 Extensor
muscles lie on the lateral and
posterior aspects of the limb
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lower limbs rotate medially through 90
degrees
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the future knees face ventrally
 Extensor
muscles lie on the anterior aspect of
the lower limb
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Developmentally, the radius and tibia are homologous
bones
Ulna and fibula , just as the thumb and great toe are
homologous digits
Synovial joints appear at the beginning of the fetal period
, conceding functional differentiation of limb muscles and
their innervations
CUTANEOUS INNERVATIONS
OF LIMBS
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There is strong relationship between the growth and
rotation of the limb and the cutaneous segmental
nerve supply of limbs.
Motor axons arising from the spinal cord enter the
limb buds during the fifth week Grow into dorsal and
ventral muscle masses.
Sensory axons enter the limb buds after the motor
axons and use them for guidance.
Neural crest cells, the precursors of schwann cells,
surround the motor and sensory nerve fibers in the
limbs Form the neurolemmal and myelin sheaths.
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During the 5th week, the peripheral nerves grow
from the developing limb plexuses into mesenchyme
of limb buds.
The spinal nerves are distributed in segmental
bands, supplying both dorsal and ventral surfaces of
the limb buds.
A dermatome is the area of skin supplied by a single
spinal nerve and its ganglion, however , cutaneous
nerve areas and dermatomes show considerable
overlapping
As the limbs elongate, the cutaneous distribution of
the spinal nerves migrates along the limbs and no
longer reaches the surface in the distal part of the
limbs
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The original dermatomal pattern changes during
growth of the limbs
An orderly sequence of distribution can still be
recognized in the adult
In the upper limb, observe that the area supplied
by C5 and C6 adjoin the areas supplied by T2, T1
and C8 but the overlap between them is minimal
at the ventral axial line.
A cutaneous nerve area is the area of skin
supplied by a peripheral nerve.
Because there is overlapping of dermatomes , a
particular area of skin is not exclusively innervated
by a single segmental nerve.
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The limb dermatomes may be traced progressively
down the lateral aspect of the upper limb and back
up its medial aspect.
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A comparable distribution of dermatosomes occur
in the lower limb , which may be traced down the
ventral aspect and then up the dorsal aspect of the
lower limbs.
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When the limbs descend they carry their nerves
with them
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This explains the oblique course of the nerves
arising from the brachial and lumbosacral plexuses
BLOOD
SUPPLY TO LIMBS
The limb buds are supplied by branches of the
intersegmental arteries which arise from the aorta
and form a fine capillary network throughout the
mesenchyme.
 The primordial vascular pattern consists of a
primary axial artery and its branches which drain
into a peripheral marginal sinus.
 Blood in the marginal sinus drain into a peripheral
vein
 The vascular pattern changes as the limbs develop,
chievly gy angiogenesis (sprouting from existing
vessels)
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new vessels coalesce with other sprouts
to form new vessels
 The primary axial artery becomes the
brachial artery in the arm and the common
interosseous artery in the forearm which has
anterior and posterior interosseous
branches.
 The ulnar and radial arteries are terminal
branches of the brachial artery.
 As the digits form, the marginal sinus breaks
up and final venous pattern is represented by
basilic and cephalic veins and their
tributaries develop.
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In the thigh, the primary axial artery is
represented by the deep artery of the thigh
( profunda femoris ).
In the leg, the primary axial artery is
represented by the anterior and posterior tibial
arteries.
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anomalies of the limbs
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