Bone Formation Flashcards
When does osteogenesis occur?
In embryo to form bony skeleton, during adolescence for growth, during adulthood for remodeling and repair
Two processes of bone formation
Intramembranous ossification, endochondral ossification
Intramembranous ossification: when does it occur?
used in initial formation of flat bones and some irregular; mech of ossification in periosteum and endosteum; fractures heal through similar process
Process of intramembranous ossification
condensation of mesenchyme -> osteoprogenitors -> osteoblasts that secrete bone matrix around themselves -> formation of irregular, immature, primary bone -> aggregation of osteoblasts-> osteoblasts add layers of bone
Spicules
islands of developing bone during intramembranous ossification; trabeculae
Trabecular network
neighboring spicules contacting one another to form a network during bone development
osteoblast
secrete components of bone matrix
osteoid
initial non-calcified matrix material secreted by osteoblast
osteocalcin
secreted by osteoblasts during intramembranous ossification; bind calcium and alkaline phosphatase
osteonectin
binds matrix components to minerals (Ca and phosphate)
Endochondral ossification: basic definition
bone deposited on a pre-existing cartilage matrix
What bones are formed by endochondral ossification?
short and long bones
Fontanelles
flat bones of skull don’t initially meet in a baby
Steps of endochondral ossification
(1) formation of cartilage model (2) growth of cartilage model (3) formation of bone collar (4) chondrocyte hypertrophy (5) secretion of materials by hypertrophic cells (6) death of chondrocytes and disintegration of matrix (7) invasion of periosteal blood vessels and osteogenitor cells (8) osteoprogenitor cells develop into osteoblasts that secrete osteoid (9) formation of secondary ossification
Bone collar
compact bone just beneath the periosteum that forms during endochondral ossification
Where does cartilage remain after endochondral ossification?
articular and epiphyseal
What is secreted by hypertrophic cells in endochondral ossification?
type x collagen, alkaline phosphatase (nec for mineral deposition), VEGF (stim vascular invasion)
Epiphyseal growth plate zones
resting, proliferation, hypertrophy, calcification, ossification
closure of epiphyseal plate
end of growth in length of bone, ossification of epiphyseal plate, occurs at ~20 yrs
Length growth in bone
proliferation on epiphyseal side, deposition on diaphyseal side of plate; growth hormones stimulate activity
Bone growth: width
new bone established beneath periosteum by appositional growth, bone resorption from inner aspect of shaft –> increased diameter and larger marrow cavity
osteoporosis
bone resorption exceeds bone deposition
calcitonin
hormone produced by thyroid; decreases osteoclastic activity -> reduced blood Ca++
PTH
hormone produced by parathyroid;increases osteoclastic activity -> increased blood Ca++; stims GI tract to absorb Ca++; reduces excretion of Ca++ from kidney
explain calcium regulation as it applies to bone metabolism
primary ossification center
diaphysis, where endochondrial ossification originates
secondary ossification center
form in epiphyses and process is similar to endochondrial ossification in diaphysis (primary ossification centers). Exception: boney collar not formed, cartilage on end of epiphyses –> becomes articular cartilage
compaction
process of additional bone being added to fill spaces b/t trabeculae
