Bone formation and remodeling Flashcards
Osteogensis
Intramembranous- direct, mesenchymal mass of embryo
Endochondral- indirect, from hyaline cartillage template
Intramembranous ossif
Mesenchymal cells of embryo condense and inc vascularization
OB differentiate and secrete osteoid to form spicules, eventually a synctium with cell processes touching other OB
Ca-P salts deposited trapping OB into osteocytes
IO spicules
Inner/outer aspects of membranous bone
Spongy bone core
Continue to form meshwork bw bone marrow and BV
Undergo compaction to form inner/outer tables of compact bone
Spongy core remains trabecular throughout life, constantly remodeling
Endochondral Ossif
Long bones length
Cartilagous template is established, occurs throughout life
EO process
Hyaline cartilage ossifies into shaft
Perichondrium becomes mineralized, choking cartilage, cells become bone
BV enter 1 center of oss
OC chew up cartilage, then OB cells form bone
Primary center of ossification
Forms, attacked by OC, removal forming marrow cavity
Secondary center of ossification
Cartilaginous epistles form the ends at diff times
Epiphyseal plate- growth plate, forms
Once stopped (mineralization), no bone growth occurs
Regions of long bone
Epiphysis- top
Metaphysis- contains epiphyseal plate
Diaphysis- shaft
Metaphyseal region: Reserve Proliferative zone Hypertrophic zone Calcification Zone Ossification Zoe
R- furthest from OC, little growth
PZ- chondrocytes proliferating, active growth toward RZ replacing lost cells
HZ- cell div stops, cells/lacuna enlarge (inc length)
CZ- chondrocytes enlarge greatly, surrounding matrix calcified
OZ- chondrocytes degenrate bc low O2/nutrients
matrix dissolves, lacuna digested by OC
OB surround spicules and secrete osteoid to form spongy bone
OC resorb bone and enlarge marrow cavity
Long bone Length
Occurs at Epiphyseal plate
Continued production of Hyaline cartilage is essential
Controlled by hormones
Bone width
New layers of bone added to outer aspects of diaphysis via appositional growth
Intramembranous
Spongy bone to compact
Spongy bone primordium- collagen fibers woven randomly
All bone must have inner/outer layer- cortex
Compaction Peripheral marrow spaces
BV
Peripheral marrow spaces filled with osteoid from OB in which collagen is in 1 dir (primary osteon) Parallel fibered/ non-lamellar
BV bring monocytes that form OC to remodel
Compaction OB form
Osteon forms
OB form, deposit osteoid in lamellae (some form osteocytes)
Growth in width diminishes marrow space
Osteon forms around BV
Osteon construction in …
Created in empty space- narrrowed by addition of osteoid
Remodeling Process
spongy/cmpact bone
Release Ca into ECF
Establishes bone strength via reparing microscopic damage and maintains Ca homeostasis
Osteoclastic Osteolysis-
uses osteoclasts, resp for LT maintenance of Ca level
Release acids to break down HAC of bone, breaks down collagen and proteins
Also remodel osteons, released by PTH
Osteolytic Osteolysis
Osteolysis of walls of lacunae, help to maintain short term adjustments of blood Ca
Dissolution of HAC w min deg of collagen/GS
Also stimulated by PTH
Spongy Bone remodeling
Reversal (cement) line- shows where bone resorption ceased and new osteoid deposited
Demarked by Trabecular Bone structural unit (BSU) new bone and struct/fn unti of spongy bone
Resting bone surface of spicule/trabeculae
flat BLC
Lamina lamitans
unmineralized layer of osteoid
Signals received by BLC can make them go to osteoid destructive state & secrete collagenase
BLC change shape, detach and begin osteolysis
Compact bone remodeling
Dynamic, continual progression from weak embryonic spongy bone to lamellar bone
Women becomes parallel fibered via osteons
Primary bone becomes secondary (lamellar) via continued remodeling
Behing cutting zone
devoid active cells (RZ) and osteoid/OB and CZ
Spongy vs compact remodeling
Spongy= trabecular surface
Compact- cylinder
Fn/sequence is similar
Spongy bone has higher tunrover
Remodeling cycle time
approx 196 days, 5 phases
Longest portion is mineralization phase
