DEVLOPMENT OF BONE
PROF. DR MASOOD AHMED
BONES ARE SPECIAL CONNECTIVE TISSUE
COVERED BY A MEMBRANE CALLED PERIOSTEUM
MARROW CAVITY IS LINED BY MEMBRANE CALLED ENDOSTEUM
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
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
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
INTRAMEMBRANOUS OSSIFICATION
•MESENCHYMAL CELLS BECOME DENSELY PACKED CALLED MESENCHYMAL CONDENSATION
•SOME OF THE CELLS LAY DOWN BUNDLE OF COLLAGEN FIBERS IN CONDENSATION
•SOME OF THE CELLS BECOME ENLARGED WITH BASOPHILLIC CYTOPLASM AND CALLED OSTEOBLAST
• Osteoblast
•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
Newly formed bone is always a woven bone, whether compact or cancellous Later replaced by lamellar bone
ENDOCHODRAL OSSIFICATION
•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
UNDER INFLUENCE OF ALKL
POSPH ,INTERCELLULAR SUBSTANCE
BETWEEN CARTILAGE CELLS
BECOME CALCIFIED
•BECAUSE OF CALCIFICATION NUTRITION OF
THE CARTILAGE CELLS IS CUT OFF
AND THEY DIE, •LEAVING BEHIND
EMPTY SPACES CALLED PRIMARY
AREOLA
•THESE SPACES ARE INVADED BYPERIOSTEAL
BUDS (PERICHONDRIAL BLOOD VESSELS NAD
OSTEOPROGENITOR CELLS)
•PRIMARY AREOLA FUSE AND LARGE SPACES
CALLED SECONDARY AREOLA ARE FORMED
•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 OSTEOCYTESPACE BETWEEN TWO LAMELLAE IS CALLED LACUNAE
SUBSEQUENTLY THE CONCENTRIC LAMELLAE ARE LAID INSIDE THE ORIGINAL RING THUS FORMING AN OSTEON
THE ORIGINAL SPACE BECOME SMALLER AND SMALLER AND BECOMES A HVERSION CANAL
•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
•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 ..
HOW BONES INCREASE IN LENGTH