Bone: structure growth and repair Flashcards
Compact bone
Around the outsides of bone.
Coarse cancellous bone
Adult spongy bone
Fine Cancellous bone
Fetal bone. Cancellous means spongy.
Trabeculae
Small elements in lamaller bone (adult coarse cancellous or stingy bone)
Why is bone good under tension
It contains a lot of collagen
Why is bone good under pressure and torsion
Hydroxapatite
Components of bone
Collagen and hydoxyapatite. Very little proteoglycan
Periosteum
Fibrous layer on the surface of bone that contains osteoblasts that generate new bone
Endosteum
Surface of cancellous bone and inner surface of compact bone with similar properties to the periosteum
Cells in bone
Osteoblast (immature)
Osteocyte (mature)
Fibre(s) in bone
Collagen
Proteoglycan matrix in bone
Decorin
What does decor do
Holds the collagen fibres together
Glycoproteins in bone
Osteonectin (bind components of matrix together)
What is the mineral in bone
Hydroxyapatite. Allows the bone to withstand compression and torsion
Describe membrane bone
A kind of fine cancellous (fetal bone). Forms from osteoblasts in flat sheets creating the flat bones of the skull
Describe cartilage bone
A kind of fine cancellous bone (fetal bone) formed from cartilage creates most bones in the body.
Describe woven bone
Fetal fine cancellous bone. Called woven as the collagen fibres are not yet arranged in parallel.
How does fine cancellous bone (woven bone) turn into adult bone (lamellar bone)
Turns into coarse cancellous (spongy) and compact bone. It becomes lamellar bone when collagen fibres are laid down in alternating parallel sheets. Happens gradually.
Where are osteoblasts found
On the surfaces of bone in the osteogenic layers, either periosteum or the endosteum
How is the periosteum attached to the bone
Through collagen fibres at right angles to the bone known as sharpy’s fibres
Describe the growth of bone
Grows at the periosteal and endosteal surfaces. Osteoblasts divide and the progeny away from the bone surface remains in the periosteum or endosteum and divide again. The other progeny secretes new bone matrix. Called appositional growth
Appositional growth
Means applying something (bone) to a surface
When do osteoblasts become osteocytes
Once they divide and secrete matrix and have surrounded themselves with hydroxyapatite
What do osteoblasts secrete
Collagen fibres and hydroxyapatite and other matrix components
How do osteocytes obtain their nutrition
Osteocytes have cell processes which run in small channels called canaliculi. Each cells passes on nutrients to its neighbour which in turn passes its nutrients to its neighbour. Nutrition comes from the endosteum or periosteum
How far can nutrients be passed before the last cell in the chain suffers from deprivation
0.2 mm. Therefore maximum thickness of trabeculea is 0.4mm (pass from both surface). This is why blood supply has to exist in compact bone which is thicker than 0.4 mm
How do blood vessels get inside the bone?
- They are enclosed at the surface during appositional growth (primary)
2) They invade channels in bone formed by osteoclasts (secondary)
Two forms of osteon formation
Primary (appostional) formation where periosteum surrounds blood vessels and becomes endosteum which lays down bone in towards blood vessel.
Secondary
What is the canal in the middle of the osteon called
Havasian canal
What are the canal the run perpendicular to the osteon that hols capillaries that feed into the havarsian canals called
Volkmans canals
What are the canal the run perpendicular to the osteon that hols capillaries that feed into the havarsian canals called
Volkmans canals
How does bone remodelling occur?
Through removing bone from the inside and adding bone on the outside.
This occurs through osteoclasts derived from blood cells.
How do osteoclasts work
Osteoclast seals onto bone with ‘collar’. In the basolateral membrane of the osteoclast is a ruffled border. Within the border are vesicles holding acids and enzymes. Acids digest hyroxapatite, enzymes digest the collagen.
Hormonal control of bone removal
Parathyroid hormone- increases osteoblast and osteoclast activity, decreases bone mass.
Calcitonin- reduces osteoclast activity
Describe the interplay between RANK and RANK-L
RANK is a molecule found on primitive osteoclasts. RANK-L is found on mature osteoblast. When RANK-L binds to RANK this signals the primitive osteoclast to differentiate and become mature.
What does OPG do
OPG- osteoprotegrin. Acts to block RANK-L binding to RANK. Inhibits bone loss
Why does decreasing oestrogen levels cause osteoperosis
Oestrogen reduces the activity of osteoclasts through decreasing RANK L levels
What does HRT do
Reduces the activity of osteoclasts, less bone reabsorption
Is most adult bone composed of primary or secondary osteons?
Secondary
At what rate is bone replaces each year?
2%
What are the three molecules that control osteoclast activity
RANK, RANK-L and OPG
Where does growth in long bones occur
Epiphyseal plates
Describe the process of long bones growing in length
In youth there are epiphyseal plates which grow cartilage at one end which at the other end the cartilidge dies and blood vessels bring in osteoblasts and bone forms this occurs until closure of the epiphyseal plates during/ after puberty.
How do bone fractures heal
The periosteum and endosteum provide osteoblasts which secrete bone cells in a collar around the fracture site. Later osteoclasts dig out channels and new secondary osteons to knit together fracture
What are the stages of growth in growth in length of a long bone
From the epiphyses side of cartilage: Zone of resting Zone of proliferation Zone of maturation Zone of ossification
What is a howships lacunae
The space around the osteoclast on the surface of the bone.
