BIOL 3100 Lecture 17: growth of lone bones
19 Oct 2019
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How Bones Grow Long
• Epiphyseal plate is area of growth in long bone.
• Its layer of hyaline cartilage where ossification occurs in immature bones
• On epiphyseal side of plate, cartilage is formed; on diaphyseal side, cartilage is ossified &
diaphysis grows in length
• When chondrocytes cease their proliferation & bone replaces cartilage, longitudinal growth
stops. All that remains of plate is a epiphysis line in mature bones
How Bones Grow in Diameter
• Growth in diameter continues after longitudinal growth ceases
• Osteoclast resorb old bone in medullary, while osteoblasts via intramembranous ossification
produce new bone tissue beneath periosteum
• This increases the diameter of diaphysis & medullary cavity
Endochondral Ossification (osteogenesis)
• Process in which boens form by replacing hyaline cartilage
• Involves primary and secondary ossification center
• Type of ossification taking place from centers arising in cartilage. Involves deposition of lime
salts in cartilage matrix, followed by absorption & replacement by true bony tissue
• Cartilage is formed first & bone is laid down replacing it
• Important in formation of long bones
Intramembranous ossification
• Bones from directly from mesenchymal tissue
• Development of osseous tissue within mesenchymal tissue w/o prior cartilage formation
• Doesn’t form an intermediate cartilage
• Important in formation of flat bones
• Takes less time to form bone
Ossification Center
• Cluster of osteoblasts found in early stages of intramembranous ossification
Osteoid
• Uncalcified bone matrix secreted by osteoblasts
Perichondrium: membrane that covered cartilage in early bone development stage before periosteum
Canaliculi: channels within bone matrix that house osteocyte’s cytoplasmic extension that it uses to
communicate & receive nutrients
Epiphyseal plate (growth plate): sheet of hyaline cartilage in metaphysis of immature bone; replaced by
bone tissue as organ grows in length
Lacunae: spaces in bone that house osteocyte
