6.5 BONE FORMATION
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Created by:
jessicaloveschicken on June 18, 2012
Description:
ossification or osteogenesis: process by which bone forms
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40 terms
Terms | Definitions |
|---|---|
 INITIAL BONE FORMATION IN EMBRYO AND FETUS | -cartilage formation and ossification occurs in 6th week of embryo development -intramembrous ossification: bone forms directly within mesenchyme arrange in sheetlike layers -endochondrial ossification: bone forms within hyaline cartilage that develops from mesenchyme |
| INTRAMEMBRANOUS OSSIFICATION | ... |
| development of ossification center | -chemical messages cause mesenchymal cells to form together from osteogenic cells to osteoblasts -osteoblasts secrete organic extracellular matrix until its surrounded by it |
| calcification | -secretion stops -osteocytes lie in lucanae and extend through canaliculi -calcium and other salts are deposited in extracellular matrix and hardens |
| formation of trabeculae | -form spongy bone -blood vessel differentiate into red bone marrow |
| development of periosteum | much of newly formed bone is destroyed and renewed into adult size bone |
| bones formed by intramembranous ossification | -skull and mandible |
| ENDOCHONDRAL OSSIFICATION | -replacement of cartilage to bone |
| development of cartilage model | -chemical messages cause mesenchymal cells to crowd together where bone will form and develop chondroblasts |
| growth of cartilage model | -chondroblasts turn into chondrocytes -interstitial growth: cartilage grows by continual cell division of chondrocytes and further secretion of cartilage extracellular matrix; increase in length -appositional growth: growth on outer surface and thickness |
| development of primary ossification center | -nutrient artery penetrates periochondrium and calcifying cartilage model through nutrient foramen and change cells from chondroblasts into osteoblasts -periochondrium turns into periosteum to form bone -forms spongy bone -primary ossification center: region where bone tissue replace most cartilage |
| development of medullary cavity | -as primary ossification center grow towards end of bones, osteoclasts break down spongy bone and is replaced with compact bone |
| development of secondary ossification center | -develops when epiphyseal artery enters epipyses |
| formation of articular cartilage and epiphyseal plate | -hyaline cartilage becomes articular cartilage |
| BONE GROWTH DURING INFANCY, ADOLESCENCE, ADULTHOOD | ... |
| growth in length | two stages: -interstitial growth of cartilage in epiphyseal side -replacement of cartilage on diaphyseal side of epiphyseal plate with bone by endochondral ossification -epiphyseal plate: layer of hyaline cartilage in metaphysis of growing bone that has four zones: |
| zone of resting cartilage | -nearest epiphysis -consist small scattered chondrocytes -anchor epiphyseal plate to epiphysis of bone |
| zone of proliferating cartilage | -larger chondrocytes stacked like coins -interstitial growth as they divide and secrete extracellular matrix |
| zone of hypertrophic cartilage | -large maturing chondrocytes in columns |
| zone of calcified cartilage | -dead chondrocytes because extracellular matrix around them has calcified -becomes new diaphysis -as bone grows, new chondrocytes are formed on epiphyseal side of plate, while old chondrocytes on diaphyseal side of [plate are turned into bone |
| when bone stops growing | -epiphyseal cartilage stops dividing -bone replace all cartilage -epiphyseal plate turns into epiphyseal line |
| GROWTH IN THICKNESS | -periosteum form osteoblasts which secrete extracellular matrix -osteoblast turn into osteocytes -osteoclasts in endosteum destroy bone tissue lining of the medullary cavity, therefore enlarging bone thickness |
| REMODELING OF BONE | -ongoing replacement of old bone tissue by new bone tissue -bone resorption: removal of minerals and collagen fibers from bone by osteoclasts -bone deposition: addition of minerals and collagen fibers to bone by osteoblasts -remodeling removes injured bones, make it stronger than before |
| bone resorption | -osteoclasts attach to endosteum or periosteum and release lysosomal enzyme and acids to digest collagen fibers and other organic substances while acid dissolve bone mienrals -products of bone resorption diffuse into blood capillaries |
| Pagets disease | abnormal acceleration of remodeling process -newly formed bone especially in pelvis, limb, skull, vertebrae becomes hard and brittle and fractures easily |
| FACTORS AFFECTING BONE GROWTH AND REMODELING | -minerals -vitamins; vitamin A for osteoblasts -hormones; insulin like growth factors stimulate osteoblasts -during puberty, sex hormones increase osteoblast activity and responsible for growth spurt |
| FRACTURE AND REPAIR OF A BONE | ... |
| TYPES OF FRACTURES | ... |
| open (compound) | -broken bone protrude skin -close simple fracture doesnt |
| comminuted | bone is crushed or broken to pieces and smaller bone fragments lie between two main fragments; most difficult to treat |
| greenstick | -one side of bone is broken and other side bends -occurs in children whose bones are not fully ossified yet |
| impacted | -one end of bone is driven into interior of the other |
| pott's | fracture of distal end of lateral leg bone (fibula) with serious injury of distal tibial articulation |
| colle's | -fracture of distal end of lateral radius in arm and distral fragment is displaced |
| stress fracture | -fissures in bone that has no evidence of injury to other tissues -caused by strenous activity like running and jumping |
| REPAIR OF BONE FROM FRACTURE | ... |
| formation of fracture hematoma | -fracture hematoma: mass of clotted blood formed around site of fracture where circulation of blood stops -osteoclasts and phagocytes remove dead bone cells |
| fibrocartilaginous callus formation | fibrocartilaginous callus: mass of repair tissue consisting of collagen fibers and cartilage that bridges broken ends of bone -developed by fibroblasts and periosteum |
| bony callus formation | -osteogenic cells develop into osteoblasts which begin to produce spongy bone trabeculae -bony callus: cartilage is converted to spongy bone |
| bone remodeling | -dead portions of original fragments of broken bone are resorbed by osteclasts -compact bone replace spongy bone |
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