Post on 11-Feb-2016
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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