BONES.pdf

7/29/2019 BONES.pdf

1/21

BONES

The most highly differentiated of thesupporting tissue

A type of dense connective tissue

Lightweight yet strong and hard Has a high ability to withstand stress next to

cartilage.

Has high compressive strength of 170 MPa

Serves multiple functions

Its extracellular component are calcifiedmaking it hard and brittle.

7/29/2019 BONES.pdf

2/21

Histogenesis of Bones

Bone formation during fetal development involves twoprocesses

1. Intramembranous bone formation (ossification)

Mainly occurs during formation of flat bones of the skullbut also the mandible, maxilla and clavicles.

The bone is formed directly from messenchymal tissuerather than from cartilage.

Bones developed in this type of formation is termed asMembrane bones

2. Endochondral bone formation (ossification)

Occurs in long bones and most of the rest of the bones of

the body. It involves an initial hyaline cartilage that continues to grow.

Bones developed in this type of formation is termed asCartilage Bones

7/29/2019 BONES.pdf

3/21


Intramembranous bone formation (ossification)

1. Developement of osification center

2. Calcification3. Formation of trabeculae

1. Development of osification centerThe group of messenchaymal cells that are

interconnected by its process but withoutcytoplasmic continuity, and suspended in a semi

fluid intercellular substance forms a membrane.These cells are termed osteoprogenitor cells and thewhole membrane is termed as osification center.

7/29/2019 BONES.pdf

4/21



2. CalcificationThe messenchymal sheet or membrane become

highly vascularized and osteoblast are formed.Osteoblast secrete intercellular substances such

as collagen (type I), glycosaminoglycan and twosubstances exclusively found in bones, theosteocalcin and osteopontin which are resposible

for the calcification of the matrix. Later the matrixbecome calcifiable through osteobalstic activity;thus mineral deposits are in Place; then thelacunae and canaliculi are formed.

7/29/2019 BONES.pdf

5/21



3. Formation of trabeculae

Successive layer of matrix are added by apposition. Asgrowth continues, group of trabeculae forms thespongy or woven type of bone. Later some spongy

bones transformed into compact bone as the areabetween the trabeculae are filled concentric lamellarbones creating an inner and outer plate. Between theplates, spongy bones remains and the space within it,

the primary marrow cavities are filled with highlyvascularized connective tissue and eventually becamemyeloid or hematopoietic tissue and the connectivetissue that surrounds a mass of bones give rise to

Periosteum.

7/29/2019 BONES.pdf

6/21


Endochondral bone formation (ossification)

1. Development of cartilage model2. Growth of cartilage model

3. Development of primary ossification center

4. Development of secondary ossification center

5. Formation of articular cartilage and epiphyseal

plate

7/29/2019 BONES.pdf

7/21



1. Development of cartilage modelDuring fetal age, bones of vertebral column, pelvis,

and the extremities are first formed of hyaline

cartilage. This cartilage is known as cartilagemodel.

2. Growth of cartilage model

this cartilage model continue to grow by bothinterstitial and appositional growth. And this

cartilage must be removed before ossification

can occur.

7/29/2019 BONES.pdf

8/21



3. Development of primary ossification center

The primary ossification center mostly appear duringfetal development, though a few short bones beginstheir primary ossification after birth.

This primary ossification center is principally initiatedwithin the perichondrium surrounding the center ofdiaphysis when it becomes highly vascularized andassumes osteogenic function. With the appearance of

the bony ring which will later on turn intoperiosteumcome changes in the cartilage it self. In the center ofdiaphysis cartilage tissues reduced in amount andcalcified forming the primary marrow space.

7/29/2019 BONES.pdf

9/21



4. Development of secondary ossification centerSecondary ossification occurs after birth and forms

the epiphyses of long bones and the extremities

of irregular and flat bones. Ossification extendtoward both ends of the cartilage. The periosteal

bone collar thickend and widens, and assists the

new bone during dissolution of cartilage withinthe diaphysis. Calcification of the cartilage,

formation of cartilage column and bone

deposition causes an increase in bone length.

7/29/2019 BONES.pdf

10/21



5. Formation of articular cartilage and epiphysealplate

The diaphysis and both epiphysis are separated by

growing zone of cartilage (epiphyseal plate) whenthe child reaches skeletal maturity (18 25 y/o)

all of the cartilage is replaced by bone fusing the

diaphysis and epiphysis together (epiphysealclosure). At this stage there is no further

proliferation will happened and growth ceases.

7/29/2019 BONES.pdf

11/21

Distinguishing characteristic of bones

1. Abundant osteocytes

2. Homogenous matrix and fibers are notprominent

3. Solid, hard and brittle ground substance

4. Blood vessels are present in canals surroundedby bone matrix.

5. Can grow only by appositional mechanism

6. Bone architecture is not static

7/29/2019 BONES.pdf

12/21

Two forms of bones

1. Cancellous or spongy (Substancia spongiosa)

Distinguishing Characteristics:

Shows a simple and less organized structure

Composed of anastomosing bone trabeculae or

spicules

Show a meshwork pattern with numerous small

cavities lined by endosteum containing bone

marrow

Absence of Harvesian system.

7/29/2019 BONES.pdf

13/21

Two forms of bones

Cancellous or spongy (Substancia spongiosa)

Distributions:

Bones of skull and face

Middle or inner portion of all other bones.

It is found only as a thin portion inside the diaphysis

of long bones but constitutes a greater part of theepiphysis

The numerous small communicating marrow cavities orintertrabecular spaces vary greatly in size andshapes. They are lined by a cellular membrane calledendosteum which is composed of flattened cells thatare potential bone and blood-forming cells.

7/29/2019 BONES.pdf

14/21

Two forms of bones

2. Compact (Substancia compacta)

Distinguishg characteristics:

Composed of dense and concentrically arranged bonylamellae.

Appears more solid with fewer cavities

Shows a regular arrangement of lamellae

Presence of periosteum, a dense fibrous membranethat covers all portion of the compact bone exceptthose covered by articular cartilage.

Presence of harvesian system with both inner innerand outer circumferential lamellae.

Distributions:

Outer surface of all bones

Shaft of diaphysis

7/29/2019 BONES.pdf

15/21

Two categories of vascular channels

1. Harvesian Canals the longitudinal channels in

the center of the Harvesian system containing 1or 2 blood vessels. They are connected with oneanother and communicate with free surface andmarrow cavity through transverse and oblique

channels Volkmans Canals

2. Volkmans Canals distinguished from theharvesian canals since they are not surroundedby concentrically arranged lamellae buttransverse the bone in a direction perpendicularor oblique to the lamellae. They are often largerthan harvesian canal.

7/29/2019 BONES.pdf

16/21

Cells of bones

1. Osteoprogenitor cells undifferentiated cells having thecapacity for mitosis and for further structural andfunctional specialization.

2. Osteobalast responsible for the synthesis of collagenfibers, formation of bone matrix and found on thesurfaces of developing bones. Nucleus is round and largewith basophilic cytoplasm which indicates active protein

synthesis.3. Osteocytes the principal cells of fully formed bone

residing in the lacuna with in the calcified interstitialsubstance. Elongated in shape and less basophilic thanosteoblast.

4. Osteoclast giant multinucleated cells responsible inbone resorption. They are frequently found in the shallowconcavities in the surface of bone called lacunae ofhowship.

7/29/2019 BONES.pdf

17/21

Diagram of sector of the shaft of long bone and picture of harvesian system

7/29/2019 BONES.pdf

18/21

Molecular structure of bone matrix

Inorganic

Calcium

Magnesium

Sodium

Carbonated hydroxyapatite

Organic

Collagen (type I) Protein polysaccharides

Chondrotin sulfate

Glycosaminoglycans

Osteocalcin Osteonectin

Osteopontin

Bone sialo protein

7/29/2019 BONES.pdf

19/21

Functions

Mechanical

Protection

Structure

Movement

Sound transduction

Synthetic

Blood productionMetabolic

Mineral storage

Growth factor storage

Fat storage Acid base balance

Detoxification

Endocrene organ

7/29/2019 BONES.pdf

20/21

Bone disorders

Osteoporosis increase risk of bone fracturedue toreduce bone mineral densisty

Osteomyelitis - infection and inflammation of the boneor bone marrow.

Osteosarcoma - is an aggressive malignant neoplasm.The tumor may be localized at the end of the long

boneOsteogenesis imperfecta - a congenital bone

disorderwith defective connective tissue, or withoutthe ability to make it, usually because of a deficiency

of Type-I collagen.Osteochondritis dissecans -is a joint disorder in which

cracks form in the articular cartilage and theunderlying subchondral bone.

7/29/2019 BONES.pdf

21/21

Bone disorders

Bone metastases - is a class of cancer metastases

that results from primary tumor invasion to bone.Anencephaly absence of bone of the cranial vault.

Documents

BONES.pdf