Week 5

Question 1

Functions of:
Osteoblasts
Osteoclast
Osteocytes

Answer 1

Functions of:
Osteoblasts > form new bone
Osteoclast > remove bone
Osteocytes > mechanosensors that regulate the remodeling proces

Question 2

To what 2 things are osteocytes sensitive to?

Answer 2

Mechanical load & fluid flow

Question 3

What is the mechanical signal S?

Give exampels of stress/strain parameters & physiological loadingpatameters

Answer 3

Something that can be measured by osteocytes.
Stress/strain parameters:
- peak/average strain
- strain-rate
- energy stress
- von Mises stress (geeft aan wanneer een monster plastisch vervormt onder een meerdimensionale aangebrachte spanning)

Physiological loadingpatameters:

• accumulated microdamage
• fluid flow
• cell wall shear stress

Question 4

Mechanostat theory:
How can it explain bone shape adaptation?

How can bone straightening due to load?

Answer 4

It depends on the load:

• high load > bone formation
• low load > bone resorption

More load is added to the hollow side of bone > load on the other side decreases > bone on other side will resorb > more bone is formed on the side with more load.

Question 5

Mechanostat theory:

How can it explain bone density distribution?

Answer 5

The ‘plate model’ can be used to predict distribution. Dark indicates bone and white indicates no bone. There is sometimes also a grey value, but in real life there is no grey value; there is bone or no bone.

Question 6

Mechanostat theory:

How can it explain bone microstructural morphology?

Answer 6

The functions of osteoclasts (- bone, attracted by microdamage), osteoblasts (+ bone) and osteocytes (mechanosensor, influence osteoblasts) are transformed into a computer simulation.

Question 7

Mechanostat theory:

How can it explain bone cell targeting? 3 rules

Answer 7

1. Osteoblasts and osteoclasts always go together
2. Osteoclasts do not penetrate trabeculae
3. Osteons develop in the bone longitunidal direciton (osteon is een systeem van concentrische lamellen van osteocyten die de te grote gaten van osteoclasten opvullen)

Question 8

How does the hypothesis work that strain is the coupling factor in remodeling? Explain the cycle.

Answer 8

1. Quiescence: bone lining cells are on the bone.
2. Resorption cavity: osteoclasts attach to the bone and form an resorption cavity > this leads to an increase in strain around the cavity.
3. Mechanically regulated formation: osteoblasts are attracted to the stimulus and fill the cavity with bone matrix.
4. Quiescence: cavaty is filled with osteoblasts.

Question 9

What is a bone disease?

Answer 9

A medical condition which affects the bone

Question 10

Examples of bone diseases

Answer 10

• Osteolysis: active resorption of bone by osteoclasts
• Osteomalacia: softening of bones through impaired bone metabolism
• Rickets: defective bone growth due to lack of Ca or Vit D.
• Osteosarcoma: malignant primary bone tumor.
• Fibrous dysplasia: normal bone is replaced with fibrous bone tissue.
• Paget’s disease: enlarged and misshapen bones.
• Osteogenesis imperfect: defective connective tissue
• Pycnodysostosis: enzyme Cathepsin K defect.
• Osteomyelitis: infection and inflammation of the bone (marrow).
• Acromegaly: too much growth horhome.
• Perthes’ disease: disruption of blood flow to the ball of the femoral head.