Lecture 5 Flashcards
What are the two ways that bone develop?
Intramembranous bone formation involves development within layer of condensed mesenchyme
Endochondral bone formation occurs via a cartilage
model that is replaced by bone
Describe the process of intramembranous bone formation?
- Begins when mesenchymal cells condense to form a primary ossification center, from which osteoblasts differentiate and begin secreting osteoid
- The osteoblasts will become trapped in their own matrix
- Ossification centers expand into spicules as more
osteoblasts aggregate
(Bone trabeculae (fused spicules) is the name given to the bone developing at these sites) - The spongy bone develops as the bony trabeculae join together
- Blood vessels will invade the area
- Periosteum forms surrounding mesenchymal cells
- numerous ossification centers fuse together forming bone
What find of bones form from intramembranous bone formation?
flat bones
How does endochondral bone formation occur?
- the outline of the bone is hyaline cartilage
- Formation of periosteum and subperiosteal bone
collar for support in diaphyseal region - The cartilage matrix is calcified and blood vessels erode into that calcified cartilage
- formation of the primary ossification center (osteogenic cells and blood vessels)
- The subperiosteal collar becomes thicker and bone forms on the calcified cartilage complexes
- Secondary ossification centers (in a similar manner)
form in the epiphyses. Epiphyseal cartilage (epiphyseal
growth plate) is formed between the primary and
secondary ossification centers - Epiphyseal plate disappearance occurs at different times
- Fusion of diaphyseal and epiphyseal marrow cavities
What are the five regions of the epiphyseal plate?
- zone of reserve cartilage- stem cells
- zone of proliferation- rapid mitotic division
- zone of hypertrophy- enlargement of chrondrocytes
- zone of calcified cartilage - lacunae coalesce and the interlacunar matrices become calcified, causing apoptosis of chondrocytes
- zone of resorption - bone is beginning to be elaborated upon the calcified cartilage, and osteolytic activity begins to resorb the calcified bone-cartilage complex
How does an osteon develop?
Longitudinal ridges form along the bone and osteogenic cells in the periosteum transform into osteoblasts
Osteoblast start producing bone matrix which form ridges that close off periosteal capillaries as they meet
Periosteum lining the newly formed canal becomes the
endosteum and starts forming concentric lamellae to form the osteon
How are bones repairs?
- After bone damage, hemorrhaging is followed by
blood clotting, and macrophages remove much of
the debris via phagocytosis - Fibroblasts proliferate in the periosteum and endosteum and surround the area internally and
externally to isolate it
How is a callus formed on the bone?
A fibrocartilaginous callus is formed both internally and
externally
- chondrocytes will differentiate from connective tissue and cartilage which will be replace by bone via endochondral bone formation.
- Bony callus is eventually resorbed and replaced with
secondary bone as the repair process continues
How does vitamin D effect bone?
Vitamin D is necessary for proper ossification
How does vitamin A effect bone?
Vitamin A deficiency inhibits proper bone formation and growth
What happens if GH is lacking in childhood
short stature
What happens if GH is in excess in childhood
gigantism
What happens if GH is in excess during adulthood?
acromegaly
What is osteoporosis type I?
post-menopausal women due to estrogen levels decreasing
What is osteoporosis type II?
age related (70s +80s)
