Bone Part 2 Flashcards
Size of the Haversian System
= size of osteoclast
(200um in diameter)
Bone Remodeling
produces osteons
-removal of existing bone by osteoclast
-redeposition of new bone by osteoblast
The outer margin of the osteon is
“cement line”
Is bone remodeling continuous?
yes (bone is an active organ)
What are the 3 phases of the bone remodeling cycle?
- resorption
- reversal
- formation
resorption
osteoclast digest old bone
reversal
mononuclear cells appear on bone surface
formation
osteoblast lay down new bone (until it is replaced completely)
Bone remodeling is both
systemic (Ca) and local
The major systemic regulator of bone remodeling are
-PTH
-Calcitonin
-Growth Hormones
-Glucocorticoids
-Sex Hormones
Wolf’s Law
apply a force to a bone will respond to that force
(braces)
Pattern of bone remodeling is determined by
local mechanical stresses (force)
Endochondral ossification
-replacement of cartilage precursor with bone
-most of the body
Where would you find Endochondral ossification
long bones, vertebrae, pelvis, and base of the skull
Intramembranous ossification
-direct replacement of mesenchyme bone
Primary Ossification Center
mid-diaphysis
Secondary Ossification Center
epiphyses
Process of Endochondral ossification
- primitive mesenchyme cells differentiate into chondroblast, lay down early perichondrium
- cartilage model made
3.osteoprogenitor cells and osteoblast lay down bone, Bone Collar
4.Starts to Calcify (chondrocytes die due to lack of blood) - Blood vessel are brought in along with osteoprogenitor cells and osteoblasts
- Replace everything in diaphysis (1’)
- secondary ossification sites occur (after birth)
Bone Collar or Periosteal Cuff
first bone laid down and is under perichondrium on the shaft
Epiphseal Plate
-region of the metaphysis left open (unmineralized)
-allow conintous longitudinal growth
What is still visible on x-ray after a epiphyseal plate has closed?
epiphyseal line