devlopment of bone

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