BONE TISSUE

DEVELOPMENT and GROWTH

FUNCTIONS

• Support/Movement• Protection• Mineral reservoir• Site of blood cell

production• Storage of fat

Skeletal Cartilage

• Consists primarily of water• Contains no nerves or blood

vessels• Surrounded by perichondrium

– Dense irregular connective tissue– Maintains shape

Skeletal Cartilage

• Basic components– Chondrocytes in lacunae– Extracellular matrix with jellylike ground

substance• 3 Types

– Hyaline– Elastic– Fibrocartilage

Hyaline Cartilage

• Most abundant• Fiber not detectable• Locations

• Articular cartilage• Costal cartilage• Respiratory cartilage• Nasal cartilage

Elastic Cartilage

• Contains more elastic fibers; more flexible• Found in ear and epiglottis

Fibrocartilage

• Highly compressible• Great strength• Locations

– Knee– Vertebral disks

Cartilage Growth

• Two methods– Appositional – adds to outside– Interstitial – growth from inside

• Growth stops during adolescence

Bone Histology - Cell Types

• Osteocytes – mature bone cells – Osteoblasts – bone forming cells – Osteoclasts – bone destroyers

BONE OSSIFICATION

Process by which tissue becomes bone

Also called osteogenesis

Bone Formation

• Bone formation begins approx. 8 weeks into fetal development from a skeleton that is mostly fibrous membranes and cartilage

• Intramembranous ossification – bone forms from the fibrous membranes

• Endochondral ossification – bone forms from hyaline cartilage

Intramembranous Ossification

• Osteoprogenitor (mesenchymal) cells in fibrous C.T. develop into osteoblasts

• Osteoblasts secrete collagen matrix• Calcification occurs in ossification centers;

forming a network of bone rather than layers• Bony plates form which are later converted into

compact bone• Flat bones only; skull & clavicles• Fontanelles are areas not ossified at birth

ENDOCHONDRAL OSSIFICATION

• Forms most bones• Hyaline cartilage model in shape of the bone

initially; a pH change causes cartilage to calcify and the cells to die

• Primary ossification center forms as blood vessels from periosteum and osteoblasts invade calcified cartilage

• Matrix formed (osteoid= unmineralized bone matrix)• Ossification occurs = calcium salts deposited • Primary centers form before birth; Secondary centers

form 8th month dev.

Epiphyseal Plate

• Cartilage region between primary and secondary ossification centers

• Responsible for postnatal bone growth• Zone of resting cartilage• Growth Zone – mitosis occurs • Transformation Zone – cartilage matrix

deteriorates• Osteogenic Zone - bone salts deposited

Calcium regulation

• Calcium is most abundant mineral in the body; 99% located in the bone

• Regulated by two hormones: PTH (parathyroid hormone) and calcitonin

• PTH - raises blood calcium levels• Calcitonin - lowers blood calcium levels

Hormones and Vitamin Effect on Bone Growth

• Testosterone• Estrogen• Growth Hormone• Throxine - • Vitamin D – calcium absorption

Bone Types• Compact Bone

– also called dense bone

– hard, strong and solid bone that forms the outer layer of all bone

– provides support, protection and resists stress

• Contains osteons

• Cancellous – also called spongy

bone– found more toward

the inner portion of bone

– open lattice-work of struts and plates that serves to store bone marrow

• Trabeculae

Osteons = Haversian System

• Haversian canal • Volkmann’s

canals• Lamellae• Lacunae• Canaliculi

Bone Types

• Long – arms and legs• Short – wrist and ankle

– Sesamoid – forms within a tendon (patella)

• Flat – sternum, scapula, ribs, skull• Irregular – vertebrae & coxal bones

Structure of a Long Bone

• Diaphysis• Epiphysis• Articular cartilage• Periosteum – connective tissue covering bone• Medullary cavity• Endosteum – connective tissue; lines inside

Bone Fractures

• Open ( Compound) – penetrates skin

• Closed (Simple)• Partial/Complete - Greenstick• Comminuted – broken into 3 or

more pieces

Bone Repair

• Formation of clot ( hematoma)• Callus ( soft followed by hard) • Mineralization of callus by calcium &

phosphorus• Remodeling