Bone Formation, Growth And Repair Flashcards
What is osteogenesis and the 2 types
-bone formation
1 intramembranous
2 endochondral
What types of bone are made by intramembranous
- flat bones of the skull
- the clavicle
What type of bones are made by endochondral
-most bones in the body including long bones
Describe intramembranous ossification
- starts in condensed sheets of embryonic CT
- ossification center forms and osteoblasts secrete and calcify osteoid into woven bone
- the centers enlarge and fuse forming larger woven bone
- later remolded into lamellae enclosing cancellous bone
What is an ossification center , why due they continue growing In intramembranous and what happens to none ossification center forming bones
- areas where mesenchymal cells proliferate and differentiate into osteoblasts
- due to continuous secretion of osteoid
- become periosteum and endosteum
Endochondral ossification describe pre-natal
- begin in hyaline shaped model
- bone collar forms in perichondrium which is transitioning to periosteum which impedes diffusion of nutrients and chondrocytes swell up and eventually die
- space left is invaded by capillaries and progenitor form periosteum
- progenitor diff and make 1• ossification center at center of diaphysis
- bone later remodeled as lamellae
Endochondral ossification describe around birth
-2• ossification center develops at epiphysis
What separates ossification centers during birth and describe it
-epiphyseal plate which is cartilage not replaced by bone
Purpose of epiphyseal plate
-longitudinal bone growth
What is epiphyseal line
-remnant of plate when bone reaches full stature
Where doesn’t bone replaces cartilage
-articulate cartilage and epiphyseal plate
How do the chondroblasts die and when does 1• ossification center form
-due to lack of nutrients
/1st trimester ( 12 months of development )
The zones of epiphyseal
Zone of resting ( farther from diaphysis of 1• ossification center ) 2 proliferation zone 3 Zone or hypertrophy 4 Zone of calcified cartilage 5 zone of ossification
Describe first 2 zones of epiphyseal
1 has typical hyaline cartilage
2 cartilage cells divide and secrete collagen 2 and ground substance
-matrix now organized parallel to diaphysis
Describe the 3rd and 4th zone of epiphyseal
- chondrocytes swell up due to presence of periosteum and they secrete collagen X to stiffen matrix
- also release growth factors
-chondrocytes secrete calcium hydroxyapatite and calcify matrix then die by apoptosis
Describe the zone of ossification
- progenitor and capillaries invade space left by dead chondrocytes
- settle on calcified matrix and secrete osteoid - woven - lamellae
Function of collagen X and growth factors
- stiffens matrix
- reduces diffusion of metabolites further and caused chondrocytes to die
-promote vasculature to enter from diaphysis
Why doesn’t thickness of epiphyseal change
-rate of destruction and proliferation are equal
Describe appositional growth
- increase in thickness of bone
- cells of perichondrium of cartilage proliferate and differentiate into osteoblasts
- secrete seems at the edge of bone increasing thickness
What accompanies appositional growth
-resorption of endostenum and growth of medullary cavity
What is a hematoma
-localized bleeding outside of vessels due to trauma or disease
Describe metabolic role of bone
- calcium reservoir
- blood formation
Describe bone repair of fracture
- torn vessels release blood which clots forming a fracture hematoma
- hematoma removed by macrophages and replaced by soft fibrocartilage( soft callus )
- blood vessels invade soft callus and osteoblasts
- cells secrete osteoid which calcifies into woven bone
- woven remodeled into lamellae continuous with uninjured area. Vasculature reestablished
Where does periosteum regain continuity after fracture
-at soft callus
