(10) TOB 4.2 BONES Flashcards
What is immature bone?
Bone with osteocytes fairly randomly arranged
What is mature bone?
Bone with osteocytes arranged in concentric lamellae of osteons
What is an osteon?
Cylindrical concentric layers of compact bone which surround haversian canal
How does bone differ from cartilage?
It’s vascular
Give three characteristics of bone
Can withstand stress, Responds to stress and strains via growth, Sensitive to pain, Contains cells, fibres and ground substance
Give four functions of bone
SupportProtectionMineral storageHaemopoieses
What are two forms of bone?
Compact and spongelike (dense and cancellous)
What is haemopoiesis?
Formation of blood cellular components
What is the structure of compact bone?
Osteons with central haversian canal, which communicate via volkmanns canals
What is a haversian canal?
A neurovascular canal
How do osteocytes connect to each other?
Caliculi
What is spongy bone? (also known as cancellous and medullar bone)
Meshwork of trabeculae filled in with marrow
Two different types of marrow?
Red - Red blood cell synthesis
Yellow - Adipose tissue
What is marrow cavity lined with?
Endosteum
What is endosteum?
Thin layer of connective tisswue which lines the medullarly cavity
Where is the epiphysis of the bone?
The head
What percentage of bone matrix is inorganic?
65%
Name two inorganic salts found in bone matrix
matrix Calcium phosphate and Calcium Carbonate
Where does bones hardness and rigidity come from?
Interaction between inorganic salts and collagen
Where does bones flexibility come from?
Collagen fibres
Where are Calcium and Phosphate stored in bone?
In the extracellular matrix
What four things are calcium required for in the body?
Muscle contraction, blood coagulation, cell membrane permeability and nerve impulse transmission
What does PTH do?
Stimulates osteoclasts to reabsorb bone matrix, releasing calcium into blood
What happens when blood calcium levels higher than normal?
Calcitonin released, which inhibits osteoclast realse and decreases bone reabsorption
What are the three bone cell types found in bone?
Osteoblasts, Osteoclasts and Osteocytes
What is the function of osteoblasts?
Synthesise organic components of cells, making bone and produce the osteoid matrix.
What are osteocytes?
What are osteocytes?
How are osteocytes formed?
When osteoblasts are entombed to produce osteocytes.
What are osteoclasts?
Large multinucleated cells from monocytes which digest bone
What is periosteum and what is it made up of?
Two layers, connected by Sharpeys fibres. One dense collagenic outer layer, the other is more loosely arranged containing osteogenic cells and is referred to as osteogenic layer.
Describe primary microstructure of bone, and give another name for it
Immature bone
First bone to appear in the development and repair, it’s then replaced by mature bone
Collagen fibres arranged in a random, interwoven fashion
More cells and less minerals
Secondary microstructure of bone
Compact dense cortical bone
Series of Haversian Systems (osteons): consisting of concentric lamellae of bone laid around a central canal containing blood vessels.
The spaces between Haversian systems are filled with bony lamellae (interstitial lamellae)
The outer surface has extended lamellae (circumferential)
Sponge-like cancellous medullary
Bone, which is always surrounded by compact bone.
It forms the meshwork of bone plates or trabeculae then the spaces are filled with marrow
Give two ways in which bone develops
endochondral ossification
intramembranous ossification.
Outline endochondral ossification
Cartilage is reabsorbed and replaced with bone (e.g. long bones)
Begins at the primary centre in the shaft (diaphysis) and later at each end (epiphysis – secondary centre)
Growth in length is at epiphyseal growth plates
Outline intramembranous ossification
The bone begins as highly vascularised loose connective tissue.
Mesenchymal cells differentiate osteoblasts surrounded by collagen fibres and ground substance.
They secrete uncalcified matrix (osteoid) and then become osteocytes
How does bone remodel?
through the actions of osteoclasts and osteoblasts releasing and incorporating calcium into and from the matrix.
Outline process of fracture repair
Break –> Haematoma –> Osteo Callus –> Primary Bone –> Secondary Bone
1.Bone breaks
2.Bone matrix is destroyed and the bone cells adjoining the fracture will die
3.Inflammatory cells invade and form a pre-callus which contains a blood clot (haematoma) and fibrous tissue
(If the periosteum is still intact a pro-callus is formed when the area is invaded by osteoclasts and macrophages which is more fibrous)
4.An osteocallus of primary bone is made which is then calcified to secondary
5.The bone is pulled and pressured to match the contours of the surrounding bone (mainly via tendons) and eventually forms mature bone
6.Bone heals without forming a scar
What are the zones in an epiphyseal growth plate?
Reserved cartilage Proliferation Hypertrophy Calcified cartilage Resorption
Outline what happens in each zone of the epiphyseal growth plate.
Reserved cartilage – no cell proliferation/matrix production
Proliferation – cells enlarge, divide to form columns and secrete matrix
Hypertrophy – enlarge greatly, matrix composed between columns
Calcified cartilage – cells degenerate, matrix calcified
Resorption – matrix in direct contact w/ marrow cavity. Small blood vessels and connective tissue invade region of dying chondrocytes which leave calcified spicules. Bone is laid down on spicules
