Bone And Ossification Flashcards
2 ways in which bone is formed
Endochondral ossification
Intramembranous ossificatiom
Endochondral ossification
Transformation of a pre-existing cartilaginous model or proformer
Intramembranous ossification
Direct ossification of a primitive mesenchymal connective tissue
What is the first stage of long bone formation
Creation of cartilaginous models or proformers
Subsequently converted to bone
What are proformers made of
Hyaline cartilage
Hyaline cartilage of proformers synthesis
By chondroblasts
Produce a glassy amorphous looking matrix within which the cells become trapped causing them to transform into less synthetically active chondrocytes
Formation of chondroblasts
Differentiate from progenitor cells within embryonic connective tissue (mesenchyme)
What encapsulates hyaline cartilage
Fibrous perichondrium that contains both progenitor cells and differentiated chondroblasts
Major component of osteoid
Type 1 collagen
Primary bone
First type of bone to be produced in a developing bone
Structure of primary bone
Randomly woven collagen
Calcium is amorphous not crystalline
What type of bone is present at birth
Primary bone
Structure of secondary bone
Collagen organised into regularly arranged laminae
Calcium deposited as hydroxyapatite with the long axes of the crystals parallel to the collagen fibres
Characteristics of secondary bone
Light
Strong
How can secondary bone occur
Woven bone (open framework)
Compact lamellae
Osteons
Osteoclasts
Occur frequently in developing bone
Multinucleated cells
Digest bone and play a part in remodelling
Original of osteoblasts
Differentiate from precursor cells contained within capsule of the proformer or that arrive in the cavity of developing bone via the blood stream
Which cells produce bone
Osteoblasts
Osteocytes
When the osteoid is ossified osteoblasts become trapped within the matrix where they regress into a less active form
How is contact between osteocytes maintained
By minute canaliculi within the bone through which spidery processes from the osteocytes make contact with each ither
When are long bones first created
2nd trimester
How do long bones start in utero
Hyaline cartilage proformers
Which type of cartilage is particularly responsive to growth and sex hormones
Epiphyseal cartilage
Growth plates
Continue to exist beyond puberty and are largely responsible for the lengthening of bones during childhood and adolescence
1st stage of endochondral ossification
Formation of hyaline cartilage proformers
2nd stage of endochondral ossification
The shaft (diaphysis) of the proformer becomes calcified and a bony collar is established around it
3rd stage of endochondral ossification
The bony collar is penetrated by blood vessels that bring in more osteoprogenitor cells that differentiate into osteoblasts and lay down bone
4th stage of endochondral ossification
A primary centre of ossification is established- involves the erosion of the proformer cartilage and formation of primary bone
6th stage of endochondral ossification
Later secondary centres of ossification of formed in the heads (epiphyses) of the bones
7th stage of endochondral ossification
As the primary and secondary centres expand the amount of cartilage is reduced so that it becomes restructure to the epiphyseal growth plates that separate the diaphysis from the epiphyses and to the articular surfaces of the bones
Epiphyses
Heads of the bines
Diaphysis
Shaft of the proformer