Bone Development Flashcards
what are the two types of bone development?
- intramembranous ossification
2. endochondral ossification
intramembranous ossification
osteoblasts develop directly from mesenchymal cells (no hyaline cartilage model)
what kind of bones develop from intramem ossification?
flat bones of skull and face
week 8
what are the steps of intramem oss?
- development of ossification center
- calcification
- woven bone and periosteum develops
- replacement of woven bone
development of ossification center
mesenchymal cells -> osteoprogenitor cells (more rounded, basophilic, more RER) -> osteoblasts -> cluster of osteoblasts (ossification center)
what secretes osteoid?
osteoblasts in ossification center
calcification
calcium and mineral salts deposited around collagen fibers, osteocytes sit in lacunae
woven bone and periosteum development
spicules increase in size by appositional growth (along surface), mesenchyme at periphery of bone condenses to form periosteum
replacement of woven bone
by lamellar bone, forming compact and spongy bone
endochondral ossification
mesenchyme is replaced by hyaline cartilage model
steps of endochondral ossification
- development of fetal cartilage model
- bone collar forms at diaphysis and shaft cartilage calcifies
- primary oss. center develops in diaphysis
- secondary oss centers develop
- hyaline cart is retained as articular cart.
- epiphyseal plate ossifies
development of fetal cartilage model
mesenchyme -> chondroblasts -> secrete matrix -> hyaline cart model -> model surrounded by periochondrium
how does hyaline cartilage model grow?
interstitial growth (chondrocytes in lacunae) appositional growth (chondrocytes at surface)
bone collar forms at diaphysis and shaft cartilage calcifies
chondroblasts at mid region -> osteoblasts, secrete osteoid, then calcified (1st bone tissue)
surrounding cart calcifies, chondrocytes die, matrix breaks down, porous (calcified) hyaline cart is created
primary oss. center develops in diaphysis
osteopro cells -> osteoblasts -> matrix deposited alongside calcified cart
capillaries and osteoprogenitor cells form periosteum, penetrate bone collar, and grow into degraded calcified cart location
2ndary ossification centers develop
in epiphysis after birth
hyaline cart is retianed as articular cart
epiphyseal plate
articular cart o nthe ends of model, epiphyseal plate between epiphysis and metaphysis
epiphyseal plate ossifies
forms epiphyseal line at end of puberty, plate is replaced with bone
what bones form from endochondral ossification?
long bones
what spaces for from BVs entering disintegrated calcified cartilage?
bone marrow
bone growth of long bones
basically endochondral ossification, and occurs in epiphyseal plate
zones of hyaline cartilage during bone growth
- zone of resting
- zone of proliferation
- zone of hypertrophy
- zone of calcified cartilage
- zone of ossification
zone of resting
closest to epiphysis, chondrocytes single or in small groups
zone of proliferation
chondrocytes in lacunae endergo mitosis and stack like coins (isogenous groups), epiphysis is puched away from diaphysis
zone of hypertrophy
chondrocytes increase in size, cytoplasm occumulates glycogen, matrix is thinned
zone of calcified cartilage
matrix calcifies by forming hydroxyapatite crystals (basophilic), chondrocytes die
zone of ossification
right by diaphysis, BVs and blood cells and osteoprog cells and psteoclasts enter, primary bone is laid down onto calcified cartilage spicules (eosinophilic)
eventually, primary bone replaced by secondary bone
bone growth (width) in long bones
appositional growth (along surface), osteoblasts secrete bone matrix to external surface just below periosteum, osteoclasts resorb bone at endosteal surface
control of bone remodeling
negative feedback for maintenance of calcium homeostasis
what happens if too much calcium in blood?
parafollicular cells in thyroid secrete calcatonin -> inhibit osteoclasts, encourages Ca deposition in bone
what happens if too little calcium in blood?
parathyroid glands secrete PTH -> stimulate osteoclasts to resorb bone
