Chapter 23
Development of
the face, neck and limbs
1. Development of branchial apparatus
* branchial apparatus: including branchial
arch, branchial groove, branchial
membrane and branchial pouch
---by the 4th week,
---frontonasal
prominence:
mesenchymal
proliferation of ventral surface of brain vesicle
---heart prominence: development of heart
---primitive pharynx: cranial part of the
foregut
---branchial or pharyngeal arch:
/proliferation of mesenchyma of primitive
pharynx
/6 pairs
---branchial groove: the depressions between
branchial arch
---branchial pouch:
/outpocketings of endoderm of primitive pharynx
/opposed to branchial groove
---branchial membrane: the thin membrane
between branchial groove and branchial
pouch
2. Formation of face
---five elevations
/frontonasal prominence
/maxillary prominence:
paired,
upper
branches
of
first
branchial arch
/mandibular prominence:
paired,
lower
branches
of
first
branchial arch
---stomodeum
/the depression between five elevations
/opposed
to
primitive
pharynx
by
buccopharyngeal membrane, will break down,
then stomodeum communicates with the
foregut
---nasal placode: by the 5th week, thickening of
ectoderm of lower part of frontonasal
prominence
---nasal pit: depressions in nasal placode
---median nasal prominence and lateral nasal
prominence: proliferation of mesenchyme at
the margins of the nasal placodes
---by the 5th week, right and left mandibular
prominences fuse to form the lower jaws
and lips
---by the 6th week, medial nasal prominence
merge to give rise to median portion of
the nose, middle portion of upper lip, the
philtrum
---by the 6-7th week, maxillary prominence fuse
with median and lateral nasal prominences to
give rise to upper jaw, lateral portion of upper
lip, lateral portion of nose
---by the end of 6th week, nasal pits deepen and
fuse to form nasal sac, separate with oral
cavity by oronasal membrane, then this
membrane ruptures by the 7th week, primitive
nasal cavity opens into the oral cavity
---development of eye: appear on each
side of frontonasal prominence, grow in
a medial direction
---development of ear: appear on lower
portion of lower jaw, grow in a posterior
and upper direction
3. development of palate
---median palatine
process:
or
primary palate
/by the 6th week
/mesenchymal
proliferation
of
inner portion of
intermaxillary
segment
/to give rise to
small portion of
palate
---lateral
palatine
process:
/by 8-9th week
/mesenchymal
proliferation of inner
portion of maxillary
prominence
/fuse with each other,
then fuse with the
triangular
primary
palate
to
form
secondary palate
---incisive foramen: the midline landmark
between the primary and secondary
palates
---hard palate: ossification of anterior portion
of secondary palate
---soft palate: posterior portion of secondary
palate
---nasal septum: formed by ectoderm and
mesoderm proliferation of frontonasal
prominence and maxillary prominence,
then grows down and joins with the
cephalic aspect of palate
4. development of neck
* developed by 2nd ,3rd ,4th ,6th pairs of
branchial arches
---by 4-5th week, the 2nd branchial arch
grow to caudal direction, cover the
3,4,6th branchial arches, fuse with
epicardial ridge
---epicardial ridge:
upper ridge of
heart
prominence
---cervical sinus:
the
space
between
2nd
and
3,4,6th
branchial
arches
---the 2nd branchial arches fuse with 3,
4,6th branchial arches, cervical sinus
disappear
---become
longer:
differentiate
of
branchial arches, become longer of
esophagus and trachea, descent of
heart will help the formation of neck
5. development of limbs
---upper and lower
limb buds:
/by 4th week, formed
by the proliferation
of
somatic
or
parietal mesoderm
/mesodermal core
/ectodermal cap
---circular constriction: 2, divided the each limb
bud into 3 segments
---hand and foot plates:
/terminal portion of the buds becomes flattened
/digital ray: thickening portion in plates
/7-8th week, the tissue between digital ray
apoptosis
---somatic or parietal mesoderm of limb
buds differentiate into cartilage, then
through endochondral ossification to
form bone
---somitic mesoderm differentiate into
muscle of limb buds
6. Congenital malformations
1) cleft lip:
a. unilateral cleft lip:
results from failure of
the
maxillary
prominence to merge
with medial nasal
prominence on the
affected side
b. bilateral cleft lip : results from failure
the maxillary prominences to merge
with the medial nasal prominence on
both sides
c. median cleft lip: results from failure of
the medial nasal prominences to merge
and form the intermaxillary segments
2) oblique facial cleft:
results from failure
of
the
maxillary
prominence to fuse
with the lateral nasal
prominence
3) cleft palate
a. cleft of the primary palate
b. cleft of secondary palate
c. cleft of the primary and secondary palates
4) cervical cyst and cervical fistula:
cervical cyst results from failure of
atresia of cervical sinus, if cervical cyst
open to cavity of pharynx or body
surface, called cervical fistula
5) abnormalities of the extremities:
a.
reduction defect: meromelia,
phocomelia and amelia
b. duplication defect: polydactyly
c.
dysplasia: sirenomelus and
syndactyly