Bone Modelling and Remodelling Flashcards
What is the difference between modelling and remodelling bone?
Modelling is the growing skeleton which happens in children. There is a net bone formation increasing bone mass. Less osteoclastic resorption.
Remodelling is done in adults, there is not net change in bone mass.
Why do we need to remodel bone?
Bone maintains blood calcium levels as it is a store and release.
We also remodel to maintain bone mass so there is a steady state between bone resorption and formation.
We remodel as a lot of mechanical force is put on bone.
What are the percentages for bone mass and bone turnover in cortical and trabecular bone?
Bone Mass
Cortical - 80%
Trabecular - 20%
Bone turnover
Cortical - 20%
Trabecular - 80%
How does remodelling occur?
The lining cells in bone are originally quiescence. Osteoclasts are then activated and begin resorption of the lining cells. Osteoblasts are then activated and they begin cell formation forming osteiods.
Matrix synthesis then occurs at the reversal line and mineralisation of the new cells formed.
What is a basic multicellular unit?
The Basic Multicellular Unit (BMU) is a wandering team of cells that dissolves an area of the bone surface and then fills it with new bone.
Which cells of the bone are multinucleated?
Osteoclasts
What does a high number of reversal lines mean?
High bone turnover
For survival, what do the osteoblasts need for cartilage to be before resorption?
They need it to be calcified.
In endochondral ossification, what happens to the length and the thickness of the bone?
Length increases, the thickness remains unchanged
What are 4 factors which regulate bone remodelling?
- Systemic Hormones
- Growth factors/cytokines (makes cells mature)
- Local factors
- Nuclear Transcription factors (regulated by signalling molecules)
What percentage of bone do we lose per month?
2-3%
What is Wolffs law and how does it work?
Mechanical stress is responsible for determining the architecture of bone and that bone tissue is able to adapt its mass and 3D structure to stress bearing demands.
Bone is laid down along lines of maximal compressive or tensile stress.
Which cells are important in maintaining the structural integrity of cells and hence best suited to respond to these forces?
Osteocytes
Explain Osteoporosis
A bone disease leading to the loss of trabecular bone so the bone becomes more prone to fracture.
What disease occurs from remodelling happening too much?
What disease occurs when osteoclasts are not functioning (bone marrow fills with bone)?
Paget’s disease of bone
Osteopetrosis
