DEVELOPMENT OF BONE.pptx and embryology to

development of bone is very important to know

1. DEVELOPMENT OF BONE BY Dr. Eva Nabawanuka Mugerwa Year 1 RADIOLOGY Resident TUTOR; DR AMEDA FAITH

2. Pathology……get into the details of the pathology, what went wrong?, is it chromosomal?, add pictures. Slides were too bulky

3. CONTENT Introduction Types of bone formation Embryology of the axial skeleton Related pathology

4. INTRODUCTION The process of bone formation is also known as osteogenesis/ ossification 2 types of bone formation 1.Intramembranous ossification 2. Endochondral ossification Skeletal system develops from para axial and lateral plate mesoderm and from the neural crest.

5. Cont’d Para axial mesoderm forms segmented series of tissue blocks on @ side of the neural tube called somitomeres in the head region and somites from the occiput caudally. At the end of the 4 th week, sclerotome cells form loosely organized tissues called mensenchyme . Mesenchymal cells migrate and differentiate into fibroblasts, chondroblasts or osteoblasts

6. Intramembranous ossification Intramembranous (within the membrane) Bone forms directly from sheet like layers of fibrous embryonic connective tissue; the mesenchyme Selected centrally located mesenchyme cells cluster and differentiate into osteoblasts forming an ossification centre Osteoblasts secrete the organic matrix (osteoid) of bone Osteoid is mineralized after a few days Occurs in flat bones of the cranium and clavicle

7. Intramambranous osssification cont,,, Bone matrix is secreted within the fibrous membrane Trapped osteoblasts become osteoclasts Bone forms between blood vessels randomly oosr 0steoblast osteiod osteoclast Newly calcified bone matrix

8. Accumulating osteoid is laid between embryonic blood vessels which form a randomized network of trabeculae to form woven bone Vascularized mesenchyme condenses on the external surface of the woven bone and becomes periosteum Trabeculae just deep to the periosteum thicken forming a woven bone collar that is later replaced by mature lamellar bone

9. Cont’d Spongy bone consisting of distinct trabeculae persists internally and the vascular tissue becomes red marrow Trabeculae thicken at periphery to form compact bone

10. ENDOCHONDRAL OSSIFICATION Endochondral (within the cartilage) Occurs in the bones of the limbs and pelvis Mesenchymal cells condense and differentiate into chondrocytes 6 th week; chondrocytes form the first hyaline cartilage models foreshadowing the bones of the limbs and pelvis

11. Cont’d Blood vessels invade the centre of the cartilage models and restricting proliferating chondrocystic cells to the ends (epiphyses) of the bones Chondrocytes towards the diaphysis undergo hypertrophy and apoptosis as they mineralise sorrounding matrix Osteoblasts bind to the mineralised matrix and deposit bone matrices

12. Cont,, Later as blood vessels invade the epiphyses secondary ossification centres form Growth of bones is maintained by proliferation of chondrocytes in the growth plates By the 12 th week, primary ossification centres are present in long bones By birth, the diaphysis is ossified, the epiphyses is still cartilagenous

13. Endochondral Articular cartilage secondary ossification centre

14. Radiological application . Ossification studies in hands and wrists of children provide information on age. Femur length is used in Prenatal ultrasonography to estimate fetal growth and gestational Age

15. THE SKULL The skull has 2 parts NEUROCRANIUM (forms protective case around the brain) VISCEROCRANIUM (forms skeleton of the face) Neural crest cells in the head region also differentiate into mesenchyme to participate in formation of the bones of the face and skull Occipital somites and somitomeres also contribute to the formation of the cranial vault and base of the skull

16. NEUROCRANIUM HAS 2 PORTIONS 1.Membranous part; made of flat bones of the skull 2.Cartilaginous part ; chondocranium forms bones of base of the skull

17. MEMBRANOUS NEUROCRANIUM Derived from neural crest cells and paraxial mesoderm Mesenchyme from these two sources invests the brain and undergoes membranous ossification hence formation of a number of flat membranous bones Flat bones of the skull include ; frontal, parietal and occipital bones

18. Flat membranous bones characterised by presence of needle like bone spicules Bone spicules progressively radiate from primary ossification centres towards the periphery Membranous bones enlarge by apposition of new layers on the outer surface and by osteoclastic reception from inside

19. CARTILAGINOUS NEUROCRANIUM (CHONDROCRANIUM) Consists of a number of separate cartilages Cartilages lying at the rostral limit of the notochord which ends at level of pituitary gland in the centre of sella turcica are derived from neural crest cells and are called prechordal cartilage Chordal cartilage ;derived from paraxial mesoderm found posterior to notochord Base of skull formed when these cartilages fuse by endochondral ossification

20. CARTILAGINOUS NEUROCRANIUM ethmoid

21. VISCEROCRANIUM Consists of bones of the face Formed mainly from 1 st 2 pharyngeal arches The 1 st arch gives rise to the dorsal portion; the maxillary process which gives rise to the maxilla bone, zygomatic bone and part of the temporal bone The ventral portion ;the mandibular contains meckel”s cartilage ; mesenchyme around merkels cartilages condenses and ossifies and gives rise to the mandible

22. Vertebral column Vertebrae form from the sclerotome portions of the somites derived from para axial mesoderm. During the 4 th week; sclerotome cells migrate around the spinal cord and notochord to merge with cells of the opposing somite on @ side of the neural tube The caudal half of @ sclerotome grows into and fuses with the cephalic half of the subjacent sclerotome; a process called resegmentation.

23. Cont’d Mesenchymal cells between the cephalic and caudal parts of the original sclerotome segment don’t proliferate but contribute to formation of the intervertebral disc. The notochord regresses in the region of the vertebral bodies but enlarges in the region of the intervertebral disc and contributes to the nucleous pulposus. The two primary curves of the spine (thoracic and sacral) are formed as the spine is established.

24. Ribs and Sternum The bony portion of @ rib develops from sclerotome cells that grow out from the coastal processes of the thoracic vertebrae. Coastal cartilages are formed by sclerotome cells that migrate across the lateral somatic frontier into the adjacent lateral plate mesoderm. The sternum develops from the parietal layer of lateral plate mesoderm in the ventral body wall. Two sternal buds are formed on either side of the midline and later fuse to form cartilaginous models of the manubrium, sternebrae and xiphoid process.

25. Related Pathology Abnormalities may be due to; Malformations; these occur during formation of structures resulting in partial or complete absence of a structure Disruptions; result in morphologic alterations of already formed structures eg amniotic bands causing toe amputations Deformations; result from mechanical forces that mold a part of a fetus Syndromes; Group of anomalies occurring together that have a specific common cause e.g …..

26. Skull dev’t defects Craniosynostosis; is due to premature closure of the sutures. The shape of the skull depends on the suture closed prematurely Early closure of the sagittal results in frontal & occipital expansion. Skull is long and narrow (SCAPHOCEPHALY) Early closure of the coronal sutures results in a short skull (BRACHCEPHALY) Closure of the coronal suture on one side results in asymmetric flattening of the skull (PLAGIOCEPHALY) Megalocephaly; large skull and small mid face Microcephaly; usually related to alcohol fetal syndrome

27. Other skeletal deformities Anchondroplasia Hypochondroplasia Cleidocranial dysostosis Scoliosis Klippel- Feil sequence; cervical vertebrae are fused together causing a short neck and reduced mobility Spina bifida (occulta and cystica ) Cervical ribs Cleft sternum Pectus carinatum Pectus excavatum

28. THANK YOU Questions? Comments?