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Building Your Bones:Osteogenesis

Building Your Bones:Osteogenesis. At 12 WEEKS: FETAL SKELETON. Pink Bones are Cartilagnous Red Bones are Ossified (Calcium) You Should Know that the Skull bones ( flat bones) were NEVER cartilage! They formed directly into bone ( de novo). How and When Do Our Bones Ossify?.

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Building Your Bones:Osteogenesis

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  1. Building Your Bones:Osteogenesis

  2. At 12 WEEKS: FETAL SKELETON • Pink Bones are Cartilagnous • Red Bones are Ossified (Calcium) • You Should Know that the Skull bones ( flat bones) were NEVER cartilage! They formed directly into bone ( de novo)

  3. How and When Do Our Bones Ossify? • Osteogenesis and Ossification are synonymous terms

  4. How and When Do Our Bones Ossify? • 1. The hyaline cartilage of fetal skeleton changes to bone during the first 3 months of life. Also, certain bones form “de novo”. • 2. Bones grow in length through early adulthood causing growth in height . Bones thicken throughout life. • 3. All through life there is REMODELING and REPAIR

  5. So.. When The Fetal Turns to Bone, It does it in Either of 2 Ways.. Depending On Which Bone We are Referring to…

  6. Direct Ossification The embryonic connective tissue ossifies directly… (intramembranous ossification) Intramembranous ossification takes place in the so-called dermal bones of the skull, clavicles and mandible.

  7. Intramembranous Ossification • Condensation of mesenchyme into trabeculae • Osteoblasts on trabeculae lay down osteoid tissue (uncalcified bone) • Calcium phosphate is deposited in the matrix forming bony trabeculae of spongy bone • Osteoclasts create marrow cavity • Osteoblasts form compact bone at surface • Surface mesenchyme produces periosteum

  8. Intramembranous Ossification 1 • Produces flat bones of skull clavicle. Mandible.

  9. Cartilage to BONE ENDOCHRONDAL OSSIFICATION: THE STEPS OF:

  10. The Hyaline Model

  11. Calcification of the Cartilage

  12. Formation of the First Ossification Center

  13. Medullary Cavity Develops

  14. Formation of the Secondary Ossification Center

  15. Formation of Compact Bone

  16. The Mature Bone

  17. Briefly Speaking… • Mesenchymal Cells form Pericondrium which then forms hyaline • Formation of Primary Ossification Center, Bony Collar and Periostium • Formation of Secondary Ossification of Center, Penetration of Blood Vessels into Bony Collar • A Secondary Marrow Cavity appears in the epiphysis . • Spongy Bone fills the epiphyses

  18. Stages of Endochondral Ossification

  19. Let’s Look at BONE GROWTH

  20. Epiphyseal Plate • This is the zone where bones elongate; It is the “growth zone” of bones. • A strip of hyaline cartilage that consists of “zones” • The transitional zone, facing the marrow cavity is called the METAPHYSIS.

  21. The Metaphysis • Zone of reserve cartilage = hyaline cartilage • Zone of proliferation • chondrocytes multiply forming columns of flat lacunae • Zone of hypertrophy = cell enlargement • Zone of calcification • mineralization of matrix • Zone of bone deposition • chondrocytes die and columns fill with osteoblasts • osteons formed and spongy bone is created

  22. Figure 7.13

  23. Figure 7.12

  24. How Does A Child Grow in Height? • Chondrocyte multiplication in zone 2 and hypertrophy in zone 3 continually push cartilage in zone 1 towards the end of the bone and the bone elongates.

  25. Intestitial Growth • Bones Grow Longer • Bone elongation is really a result of cartilage growth. Chondrocytes multiply and then there is depostion matrix in the interior. • What happens if there is an ERROR in interstitial growth in long bones???

  26. When no elongation…… • A condition called: Achondroplastic Dwarfism As a child failure of chondrocytes in zones 2 and 3 of metaphysis in long bones, fail to multiply and enlarge. Other bones are unaffected. Person is dwafted but trunk and head size normal.

  27. Dwarfism • Achondroplastic • long bones stop growing in childhood • normal torso, short limbs • spontaneous mutation during DNA replication • failure of cartilage growth • Pituitary • lack of growth hormone • normal proportions with short stature

  28. Wolf’s Law of Bone • States that the architecture of a bone is determined by the mechanical stresses placed upon it. • Bone remodeling is a collaboration of the action of osteoblasts and osteoclasts • It bone is NOT used, osteoclasts get rid of bone matrix…less bone mass. • It bone is heavily used, or stress is applied, osteoblasts deposit and thicken bone.

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