Bone and Ossification Flashcards
Describe the charactaristic features of bone
Extremely rigid but living connective tissue
Supplied with nerves, blood vessels and lymphatics
Consists of cells e.g. osteoblasts, osteoclasts and osteocytes and collagenous fibres in a hard calcified matrix
Highly specialised for mechcanical strength whilst remaing lightweight
Describe the functions of bone
Support
Protection of internal organs
Reservoir of inorganic substances (calcium and phosphorous)
What are the two types of bone?
Spongy (cancellous/ trabecular)
Compact (dense)
What are the differences between compact and spongy bone?
Compact bone is hard and dense and forms the outer layer of most bones whereas pongy bone is porous and highly vascular and fouund depper within bones
Describe the function of the cells found in bone
`Osteoblasts - involved in rebuilding bone, synthesise the osteoid matrix
Osteocytes- present in mature/ resting bone. Found in lacunae cavities. Entombed osterblasts.
Osteoclasts- breakdown bone
Describe the extracellular components of bone
Contains organic salts e.g. calcium phosphate/ calcium carbonate
The interaction of salts with collagen cause hardness and rigidity
Flexibility of bone due to collagen
Calcium and phosperous in matrix is either stored or released into the blood
Describe the microstructure of compact bone
Concentric lamellae of bone arranged around a central canal (Haversian Canal) containing blood vessels and nerves
Between lamellae are lacunae of cells (either osteocytes or osteoblasts) which connect their slender cytoplasmic projections through canaliculi (tiny interconnecting tunnels between lamellae)
Canals which are not at the centre of an osteon are Volkmanns canals
The outside of bone is surrounded by a tough vascular fibrous layer called periosteum
Describe the microstructure of spongy bone
An irregular network of trabeculae exists where interconnecting spaces are filled with bone marrow.
Osteocytes lie between lamellae but there are no canals
The bone marrow cavities are lined with a thin cellular layer called endosteum
How is bone a living tissue?
It is constantly undergoing remodelling and repair through the actions of the cells which release or incorporate calcium from the matrix
What are the 4 stages of fracture repair?
Haematoma formation
Fibrocartilaginous callus formation
Bony callous formation
Bone remodelling
Describe haematoma formation in fracture repair
Blood vessels in bone and periosteum break
Mass of clotted blood forms
Bone cells at edges of break die/ become necrotic due to no blood supply
Swelling and inflammation
Phagocytic cells and osteoclasts remove dead and damaged tissue
Macrophages remove blood clot
Describe fibrocartilaginous formation in fracture repair
New blood vessels infiltrate haematoma
Procallus of granulation tissue forms (rich in fibroblasts and capillaries)
Fibroblasts produce collagen fibres to span the break
Other fibroblasts differentiate to into chondroblasts to form hyalin cartilage
Externally bulging fibrocartilaginous matrix splints the broken bone
Simultaneously in the centre of the bone osteoblasts from periosteum, endosetum and bone marrow invade fracture site and begin formation of spongy bone
Describe bony callous formation
Within a week, bone trabeculae appear in the fibrocartilaginous callus
Trabeculae develop as callus is converted to a hard bony callus of spongy bone
Endochondral ossification replaces all cartilage with cancellous bone but intramembranous ossification also produces new cancellous bone in this area
This stage lasts about 2 months
Describe bone remodelling
The callus of cancellous bone is remodelled into compact bone especially in the cortical region
This process lasts several months
Bulging material is removed by osteoclasts
Describe endchondral ossification
Replacement of pre existing hyaline cartilage template by bone
It is the way in which most bones in the body develop
Describe long boen development by enchondral ossification
Initial cartilage model
Collar of periostel bone appears in the shaft
Central cartilage calcifies and nutrient arteries penetrate to supply osterogenic cells. Primary ossification centre formed.
Medulla becomes spongy bone. Cartilage forms epiphyseal growth plates. Epiphyses form secondary centres of ossification.
Epiphyses ossify and growth plates move apart, lengthening bone.
Growth plates replaced by bone. Articular hyaline cartilage persists.
Describe intramembranous ossification
Occur within condensations of mesenchymal tissue and not by replacement of a pre existing hyaline cartilage template
Mineral deposits within the trabeculae radiate outward from a central point
Which bones develop by intramembranous ossification
Flat bones e.g. skull bones, maxilla, mandible, pelvis and clavicle
Also contribute to the thickening of long bones
