Week 1

Question 1

How does mechanical loading influence bone? (4 things)

Answer 1

It plays an important role during bone:
1. formation: primair and secondair center of ossification.
Hydrostatic pressure leads to hyaline cartilage & minerazilation of bone. While strain leads to fibrous connective tissue & woven bone.
2. growth: orientation of the (hypertrophic) cells
3. remodeling & adaptation: bone tissue is constantly renewing itself (bone turnover), micro-cracks are repaired, and enables adaptation of the strucutre.
4. functioning

Question 2

What are the rules involved in bone mechanics?

Answer 2

Wollf’s law: mass and orientation of trabecular structure are adapted to its mechanical load.

Pauwels (1957) + Carter (1985) + Prendergast (1995): mechanical loading plays an important role during growth (insufficient loading can lead to poliomyelitis or skeletal/ idiopathic deformities).

Question 3

How come we don’t identify all the osteoporotic patients?

Answer 3

WHO definition: BMD less than 2.5 SD from the average of the age of 30 (T-score). Measured with DEXA.

Risk factors: female >50y, nordic caucasian, physical inactivity, vit. D deficiency, low weight, calcium deficiency, alcohol, coffee, smoking, medication.

Problem: BMD is not an accurate predictor of bone fracture risk.
Fracture risk influenced by:
1. Bone strength: density, micro-architecture, tissue strength, force direction
2. Changes of high load to occur: impaired vision, poor balance, reduced protective response –> not taken into account!

Question 4

What are the 3 functions of osteoblasts?

Answer 4

1. Osteoblasts form bone tissue by secreting bone matrix
2. Regulation of calcium and phosphate homeostasis.
3. Regulation of hematopoiesis

Question 5

What is the function of osteocytes?

Answer 5

Osteocytes are embedded in the bone matrix where they keep the tissue alive. They are mature bone cells. Most common bone cells (95%). Function:

1. Main mechanosensor (bone deformation, fluid flow) > communication through secretion of soluble factors.
2. regulation of calcium homeostasis.

Question 6

What is the function of osteoclasts?

Answer 6

Osteoclasts: large, mutinucleated, life span 7wk.
Functions:
1. Bone resorption in lacunae (damaged or superflous bone tissue) > contribute to bone shape.
2. Regulation of hematopoietic cells’ movement from BM to blood.
3. Involved in immune response of bone and inflammation of bone.

Question 7

How can we distinguish bone cells?

Answer 7

1. Morphology
2. Function
3. Location

Question 8

What is the difference between osteoblasts and bone lining cells?

Answer 8

Osteoblasts are in contact with each other and are active. Bone lining cells are resting/inactive. Bone lining cells cover 75% of the cancellous bone surface and 95% of cortical bone surface.