H07 & 08: Bone Flashcards
What are the functions of bone?
Protect soft tissue, support body, allow for movement, mineral storage, haematopoiesis, hormone production.
What allows bone to be involved in haematopoiesis?
The presence of bone marrow
What allows bone to protect soft tissues & support the body ?
The fact that it is made of rigid CT
What allows bone to be used for movement?
The fact that it has articular cartilage that has no perichondrium which allows for smooth movement.
What allows bone to be used for storage of mineral?
It has a lot of inorganic material.
What is the ratio of organic material to inorganic material?
1:2
What is the inorganic material that makes up bone and what are the main components of this inorganic material?
Inorganic material is hydroxyapatite crystals, composed of calcium & phosphorus.
Where are osteoprogenitors found?
Periosteum, endosteum & cells lining Harvesian systems & Volkmann’s canals
What do oesteoprogenitors come from?
Mesenchyme
What do osteoprogenitors give rise to?
Osteoblasts
Where are osteoblasts found?
Surface of bone
What do osteoblasts do?
They produce osteoid, which is the organic component of bone.
What do osteoblast differentiate to form?
Osteocytes
Where are osteocytes found?
In the lacuna of bone
What is different between osteoblasts & osteocytes?
Osteocytes are embedded in their own matrix and they are the fully matured and differentiated form of osteoblasts
How do osteocytes sense stress on bone and what is this ability used for?
Osteocytes have dendrites so they can sense the stress on bones & send signals to other bones. They use this ability to mitigate stress on bones by regulating formation & absorption of bone.
What is the role of osteocytes apart from sensing stress on bones?
Transport of metabolites & hormones between cells.
Where do osteoclasts come from?
Myeloid origin
What do osteoclasts look like?
They are giant, motile & multinucleated cells.
What is the role of osteoclasts?
They get rid of bone.
How do osteoclasts get rid of bone?
They have the enzyme collagenase that gets rid of the collagen in bone & acid that dissolves the minerals.
How is bone resorption of bone increased?
Increased by parathyroid hormone that increases release of calcium
How is bone resorption decreased?
Hormone calcitonin decreases release of calcium in blood and opposes the actions of PTH hormone
Where is intermembranous bone formed?
In the skull
Where is endochondral bone formed?
In the growth plates
How is intermembranous bone formed?
Mesenchyme lays down a bone blastema that lays down woven bone
What is intermembranous bone?
Primary bone
How is endochondral bone formed?
A cartilage model is formed by collagen type II and bone is laid down.
What are osteons?
Harvesian systems
When are primary osteons formed?
When bone is initially formed
How are osteons formed?
- B.v runs along surface of bone containing osteoblasts.
- Bone surface invaginates.
- Invagination closes with b.v in the center.
- Osteoblasts produce matrix.
- Osteoblasts are constantly laid down which creates lamellae.
What is at the centre of osteons?
Harvesian canals
What is at the centre of Harvesian canals?
Blood vessel
State the zones of a growth plate.
Resting zone
Proliferative zone
Maturation zone
Hypertrophy zone
Degenerative zone
Osteogenic zone
What is the resting zone composed of?
Chondrocytes & hyaline cartilage
What happens in the proliferative zone?
Chondrocytes undergo successive mitotic division to form columns
What happens in the maturation zone?
Chondrocytes have stopped dividing.
What happens in the hypertrophy zone?
Chondrocytes become vacuolated and matrix becomes calcified.
What happens in the degenerative zone?
Chondrocytes senesce, leaving space for osteoprogenitors to invade.
What happens in the osteogenic zone?
Osteoprogenitors differnetiate into osteoblasts & accumulate on the surface of calcified cartilage. Woven bone formation can begin.
Where is the osteogenic zone found?
In the metaphysis of the bone
Which type of collagen is found in the proliferative zone?
Collagen type II
Which type of collagen is found in the hypertrophy zone?
Collagen type X
How does bone increase in diameter?
- Osteoprogenitor cells increase in diameter.
- Bone is laid down beneath the periosteum.
- Osteoclasts in the medulla maintain the thickness of the bone cortex.
What is the difference between bone modelling and bone remodelling?
Bone modelling is most prominent during growth & development –> allows bone to adapt to stresses.
Bone remodelling involves resorption of bone & laying down new bone but the shape of the bone remains the same.
What is the basic outline of bone remodelling?
Osteoclasts resorb bone & osteoblasts lay down new bone.
What is the detailed outline of bone remodelling, with the different stages?
- Activation stage: where cytokines & growth factors stimulate differentiation of pre-osteoclasts.
- Resorption stage: where calcified bone is resorbed.
- Reversal stage: where resorption ends.
- Formation stage: where osteoblasts synthesise new bone matrix.
- Quiescence stage: where osteoblasts become resting bone-lining cells.
What are the stages of repair after a fracture & what happens in each of them?
Inflammatory stage: haematoma forms, inflammatory cells infiltrate the area. Fibroblasts form granulation tissue & osteoclasts clear bone debris. Neovascularisation occurs.
Repair stage: provisional soft callus composed of hyaline cartilage & woven bone are formed. Fracture is bridged by woven bone through endochondreal ossification.
Remodelling stage: Callus is remodelled & lamellar bone is formed in response to bone use.
How long is the inflammatory stage?
Days long
How long is the repair stage?
Weeks to months long
How long is the remodelling stage?
Length varies depending on degree of displacement, blood supply, age of patient and degree of stabilisation.
What is the function of sesamoid bones?
They are used to prevent wear and tear as tendons pass over joints.
What are splanchnic bones?
Bones that develop in soft tissue organs.
What is the function of splanchnic bones?
They provide strength to soft tissue organs.
What are pneumatic bones?
Bones with air spaces to make them lighter.
Whaat is the function of pneumatic bones?
Allows for flight as they are less dense.
