Sukumal Chongthammakun,Ph.D. Department of Anatomy
Faculty of Science, Mahidol University Email: [email protected]
http://intranet.sc.mahidol/AN/
Germ layer contribution
Chondrogenesis
• Begins week 5
• Condensation and differentiation
• Centers of chondrification
• Secretion of the extracellular matri
x
• Entrapment of chondroblast
• Formation of chondrocyte
Interstitial growth
Appositional growth
Growth of cartilage
Osteogenesis
Mechanism of bone formation
• Endochondral ossification
• Intramembranous ossification
Endochondral ossification
• 3Ossification begins at the start of fetal period (mo. )
• PPPPPPPPPPPPP PPPPPPPPPPPPPP PPPP P PPPPP PP PPPPPPPPPPPPPPP PPPPP
• P PPPPPPPPPPPPPP PPPP PPPPPPPPPPP PPP PPPPPPPPP PP P PPPPP PP PPPPPPP
• PPPPPPPPPPPPP PPP PPPP PPP P PPPP PPPPPP
• PPP PPPPPPP PPPPP PP PPP PPPPPPPPP PPPPPPPPPPP PPP , PPPPPPPPPP
• Penetration by the vascular bud
Intramembranous ossification
• Condensations of mesenchymal cells • Secretion of osteoid
• Spicules are formed
• Networks of trabeculae
• Entrapment of osteocytes
The Axial Skeleton
1 . The vertebral column 2 . The attached rib 3. The sternum 4 . The skull
PPPPPPPPP PPP PPPP PPP PPPP PP PP PPPPPPPPPPPP ossification of the sclerotome regions of somites
• PPPPPPPPP P PPPPP PPPPPPPP PPP PPPPPPPPPP PPPPPP PPPP
• PPPP P PPPPPPPPPPPP P PPPPPP PPP PPPPPPPPP( )
• Dorsal portion forms costal processes laterally - P PPP PPPPP(1 1 2 : )
• Intervertebral disks are formed
• P PPPPPPPP PPP PPPP PP PPP PPPPPPP PPPPPPPP
• The fibrocartilage is formed around N. pulposus ( )
All somites contribute to the formation of t he axial skeleton of the body and head
42 44to pairs of somites develop• 4 1occipital ( degenerates)• PPPPPPPP8• 12 thoracic• PPP PPP5• 5 sacral• - - 810 57coccygeal (last degenerate)
Development of the skull
Neurocranium
• membranous neurocranium
• cartilaginous neurocranium
Viscerocranium
• membranous viscerocranium
• cartilaginous viscerocranium
Membranous Neurocranium
Cartilaginous Neurocranium
Membranous Viscerocranium
Cartilaginous Viscerocranium
• Somatic lateral plate mesoderm forms the skelet
on of the appendages : the limb bones and appendic
ular girdles
• The appendicular skeleton is formed by endochondral ossification of cartilage models
Appendicular Skeleton
Development of the Joints
Synovial Joints
interzonal mesenchyme differenciates :
1. Peripherally: to capsular and other ligaments
2. Centrally: disappears and becomes the joint cavity
3. Where it lines the capsule and articular surfaces: PPPPP PPP PPPPPPPP PPPPPPPP
Development of the Joints
Cartilaginous Joints
Interzonal mesenchyme differenciates into:
• Hyaline cartilage eg. Costochondral joints
• Fibrocartilage eg. Symphysis pubis
Development of Joints
Fibrous Joints
Interzonal mesenchyme differenciates into:
• Dense fibrous connective tissue eg. Sutures of the skull
• Limbs form by “budding” out from the ventrolateral body surface.
• Limbs are formed by ectoderm coverin g a
solid mesoderm core, with no endoder m
contributions. There is no coelom.
Embryonic features unique to the limbs
1. Somatic lateral plate mesoderm: cartilage, bone & CNT
2. Skeletal muscle is outsider migrating in from the somites.
3. Surface ectoderm: epidermis of skin & its specialization
4. Nerves & blood vessels grow in from the body using connective as a guide.
Germ layer origins of the limbs
1. Limb mesoderm induces surface ectoderm to form “ apical ectodermal ridge (AER)”.
2. AER induces mesoderm underneath to continue proliferation then commit to specific derivatives.
-3. Limb mesoderm also induces the formation of limb specific mesoderm specializations eg. Nails.
Limb mesoderm and surface ectoderm interaction
• Directed by AER
• The first deposit is programmed to form humerus
• The last deposit is programmed to form the bone s
of phalanges
- Proximal Distal Limb Axis
• Dorsal side is continuous with the dorsal side surface of the body.
• Ventral side is continuous with the ventral side surface of the body.
- Dorsal Ventral Limb Axis
• is established by a gradient of inducing signals released from cells of the “zone of polarizing activity (ZPA)”
• The most caudal bones (eg. Little finger) form in response to exposure to a maximum of inducer.
• The most cranial bones (eg. Thumb) form in response to PP PPP PPP PPP PPPPPPPPPPPPP PP PPPPPPPP.
• Retinoic acid may be the ZPA inducer
- Cranial Caudal Limb Axis
4Limb buds appear at the end of week and t he beginning of week 5 and become externall
y constricted into regions by week 8
6Week : oo ooo ooooo ooo oooooooooo ooooooo oo(
rential constriction) - 7 8 :Week
Formation of finger and toe rays (longitudinal constriction)
8Week : Formation of 2nd circumferential constriction
Constriction and Regression
Final feature of limb development : Limbs rotate about their long axis.
90The arms rotate o dorsolaterally The legs rotate 90 o ventrolaterally
Rotation
Rotation of the limbs results in : 1. The final orientation of the joints 2. The final location of muscle groups. 3. The mature patterns of sensory innervation of the skin called “dermatome”.
• Germ layer origins : All skeletal muscle is derived from somitic myotomes
• Connective tissue directs muscle mass formation
• Formation of multinucleated skeletal muscle cells occurs by fusion of myoblasts with each other.
• Skeletal muscle cell fusion, formation of contractile machinery, and specific fiber types do not require nerve input.
Histogenesis of skeletal muscle
Distiguishing between trunk, head and limb muscles
1. Trunk muscles form directly from myoblasts remaining in the myotomes.
2. The cells that migrate form intrinsic limb muscles, and the muscles of shoulder and pelvic girdles.
3. Cells from the most cranial myotomes form head and neck muscle after they migrtae into the pharyngeal arches.
Innervation : the key to the origin of skeletal muscles
Cranial nerves : muscles of pharyngeal arches
Spinal nerves : muscles of neck, body and limbs Dorsal primary rami Ventral primary rami
Axial muscles of the trunk
Trunk (axial) muscles form directly from myotomes.
Dorsal portion : epimere epaxial muscles
Ventral portion : hypomere hypaxial muscles
Appendage muscles: limbs and appendicular girdles
Limb muscles and appendicular girdle muscle s all
originate from myotomal cells that migrate into
the limbs.
Dorsal limb bud mases extensors
supinatorsabductors
Ventral limb bud massesflexorspronatorsadductors
The intrinsic limb muscles are formed from both li mb muscle masses.
All muscles of the appendicular girdles are derive d from the dorsal limb muscle mass.
Innervation: Dorsal muscle mass :
dorsal branches of ventral 1o rami Ventral muscle mass :
ventral branches of ventral 1 o rami
Appendage muscles: limbs and appendicular girdles
Muscles of the head and neck
PPPPPPPPPP P PPPPPP PPPP PPPPPPPPPP PPPPPP PPPPPP forming muscles.
Innervation helps distinguish the origins.
Origins of the Craniofacial Muscles--------------------------------------------------------------------------------------------------------
Mesodermal Origin Muscles Innervation--------------------------------------------------------------------------------------------------------
1 2Somitomeres , PPP PPPPPPP, , recti ( ) 3Somitomere Superior oblique ( ) 4Somitomere PPP -PPPPPPP P PPPPPP Trigeminal (V) 5Somitomere PPPPPPP PPPPPP ( ) 6Somitomere - Jaw opening and other 2nd arch muscles ( ) 7Somitomere PPPPPPPPPPPPPPP ( )
1 2Somites , Intrinsic laryngeals Vagus (X) -P25 Tongue muscles ( )--------------------------------------------------------------------------------------------------------
Congenital Defects of the Skull
Caused by genetic and environmental factors and disturbing neural crest migration into/and proliferation in pharyngeal
arches
Anencephaly : failure of cranial neuropore to close in week 4.
Craniofacial synostosis : premature closure of sutures between flat bones of neurocranium
coronal suture : oxycephaly/turricephaly sagittal suture: scaphocephaly
Craniofacial dysostosis : underdevelopment of arch facial bones, including maxill and mandible
Scaphocephaly
A. Oxycephaly B. Plagiocephaly
Congenital Defects of Vertebrae and Ribs
Hemivertebra : results in scoliosis
Spina bifida : vertebral arches fail to fuse dorsally
Congenital Defects of the Limbs
Causes : genetic/environmentHyperthermia
Drugs eg. Aspirin, anticonvulsant dimethadione, excess RA
Achondroplasia (chondrodystrophy) : premature ossification in epiphyseal plate of long bones
a. Short vertebral column . Short limbs with thick diaphyses in long bones
c. Sunken midfacial region . Normal to superior mental capacity
Achondroplasia
Congenital Defects of the Limbs
Amelia : complete absence of limb(s)
PP PPP PPPP: ( ) ( )
Phocomelia : a form of meromelia in which proximal structures are small or absent
Polydactyly : extra digits (incomplete and useless)
Syndactyly : fused or web digits (lobster claw)
A. Unilateral amelia B. Meromelia
A. Syndactyly B. Lobster claw
Congenital Defects of the Skeletal Muscles
Muscular dystrophy : a family of genetic diseases in which there is postnatal degeneration of various muscle groups
-Duchenne muscular dystrophy : caused by a lack of actin binding protein called dystrophin
Absent or underdeveloped muscle groups :• associated with bone defects• unassociated with bone defects