DEVLOPMENT OF BONE

1. DEVLOPMENT OF BONE PROF. DR MASOOD AHMED

2. BONES ARE SPECIAL CONNECTIVE TISSUE COVERED BY A MEMBRANE CALLED PERIOSTEUM MARROW CAVITY IS LINED BY MEMBRANE CALLED ENDOSTEUM

3. ADULT BONE • ADULT BONES ARE MADE UP OF LAYERS OF BONY TISSUE CALLED LAMELLAR BONE • CONSISTING OF COLLAGEN FIBERS AND MINERAL SALTS THAT ARE DEPOSITED IN GELATINOUS GROUND SUBSTANCE • EVEN THE SMALLEST PIECE OF BONE IS MADE UP OF SEVERAL LAMELLAE OF BONE PLACED ONE OVER THE OTHER AND CALLED LAMELLAR BONE

5. NEWLY FORMED BONE • DOES NOT HAVE LAMELLAR STRUCTURE • COLLAGEN FIBERS ARE PRESENT IN BUNDLES THAT RUN IN DIFFERENT DIRECTIONS, INTERLACING WITH EACH OTHER, THEREFORE CALLED WOVEN BONE

6. FORMATION OF BONE • THE PROCESS OF BONE FORMATION IS KNOWN AS OSSIFICATION • ALL BONES ARE MESODERMAL IN ORIGIN • FORMATION OF MOST OF THE BONES IS PRECEDED BY CARTILAGE MODEL CALLED ENDOCHONDRAL OSSIFICATION • BONE SOME TIMES DEVELOP DIRECTLY IN MESENCHYMAL MEMBRANE CALLED MEMBRANOUS OSSIFICATION

7. INTRAMEMBRANOUS OSSIFICATION • MESENCHYMAL CELLS BECOME DENSELY PACKED CALLED MESENCHYMAL CONDENSATION

8. SOME OF THE CELLS LAY DOWN BUNDLE OF COLLAGEN FIBERS IN CONDENSATION

9. SOME OF THE CELLS BECOME ENLARGED WITH BASOPHILLIC CYTOPLASM AND CALLED OSTEOBLAST • Osteoblast

10. OSTEOBLAST SECRET GELATINOUS MATRIX IN WHICH THE FIBERS GET EMBEDDED • FIBERS ALSO SWELL UP AND CAN NOT BE SEEN DISTINCTLY • THE MASS OF SWELLEN FIBERS AND MATRIX IS CALLED OSTEOID

11. Newly formed bone is always a woven bone, whether compact or cancellousLater replaced by lamellar bone

12. ENDOCHODRAL OSSIFICATION

13. AT THE SITE WHERE BONE HAS TO BE FORMED MESENCHYMAL CELLS BECOME CLOSELY PACKED • SOME MESENCHYMAL CELLS BECOME CHONDROBLAST AND LAYDOWN HYALINE CARTILAGE • MESENCHYMAL CELLS ON SURFACE BECOME PERICHODRIUM • IN THE AREA WHERE BONE FORMATION HAS TO BEGIN CARTILAGE CELLS BECOME CONSIDERABLY ENLARGED AND SECRET ALKALINE PHOSPHATE

15. UNDER INFLUENCE OF ALKL POSPH ,INTERCELLULAR SUBSTANCE BETWEEN CARTILAGE CELLS BECOME CALCIFIED

16. BECAUSE OF CALCIFICATION NUTRITION OF THE CARTILAGE CELLS IS CUT OFF AND THEY DIE , • LEAVING BEHIND EMPTY SPACES CALLED PRIMARY AREOLA

17. THESE SPACES ARE INVADED BYPERIOSTEAL BUDS (PERICHONDRIAL BLOOD VESSELS NAD OSTEOPROGENITOR CELLS) • PRIMARY AREOLA FUSE AND LARGE SPACES CALLED SECONDARY AREOLA ARE FORMED

18. OSTEO PROGENITOR CELLS LINE UP INSIDE THESE SPACES AND LAY DOWN THE OSTEOID EXACTLY IN A WAY LIKE IN INTRAMEMBRANOUS OSSIFICATION • THIS OSTEOID IS CALCIFIED AND LAMELLOUS OF BONE IS FORMED • IN THIS WAY LAMELLI ARE LAID DOWN OVER THE SURFACES OF PREVIOUS LAMELLAE • SOME OF THE OSTEOBLAST ARE CAUGHT BETWEEN TWO AND ARE CALLED OSTEOCYTE SPACE BETWEEN TWO LAMELLAE IS CALLED LACUNAE

20. SUBSEQUENTLY THE CONCENTRIC LAMELLAE ARE LAID INSIDE THE ORIGINAL RING THUS FORMING AN OSTEONTHE ORIGINAL SPACE BECOME SMALLER AND SMALLER AND BECOMES A HVERSION CANAL

21. THE OSTEON FORMED ARE CALLED PRIMARY OSTEON • SOON THEY ARE INVADED BY THE BLOOD VESSELLS AND OSTEOCLAST • WHICH CREAT NEW SPACES • THESE NEW SPACES ARE FILLED IN BY BONY LAMELLAE FORMED BY OSTEOBLAST AND CALLEDSECONDARY OSTEON • THIS PROCESS OF FORMATION AND DESTRUCTION IS CONTINUED EVEN AFTER BIRTH

22. PROCESS OF BONE FORMATION IS SAME IN TWO METHODS • CARTILAGE ONLY ACTS AS SUPPORT FOR DEVELOPING TRABECULAE AND DOES NOT CONVERT INTO BONE • THE SITE WHERE FIRST OSTEOID IS LAID DOWN IS KNOWN USUALLY LIES IN SHAFT(DIAPHYSES) OF LONG BONES AS PRIMARY CENTRE OF OSSIFICATION • ALKAINE PHOSPHATASE ENZYME IS SECRETED BY OSTEOBLAST AND IS NEEDED FOR DEPOSITION OF MINERALS (CALCIUM SALTS) IN THE GROUND SUBSTANCE..

23. HOW BONES INCREASE IN LENGTH