Bone and Bone Turnover

Question 1

What are the functions of bone (living tissue)?

Answer 1

1) Mechanical → supports muscle attachment
2) Protective → to vital organs and bone marrow
3) Metabolic → a reserve of calcium and phosphate ions

Question 2

What are the types of bone?

Answer 2

1) Flat/long bone

2) Cortical/trabecular bone

Question 3

What factors influence bone turnover?

Answer 3

Age, peak bone mass, hormones, nutrition

Question 4

What is crucial in controlling the quality of bone?

Answer 4

Remodelling/turnover

Question 5

Describe cortical bone

Answer 5

• 85% of the skeletal mass
• Abundant in shaft of long bones
• Largely affected by primary hyperparathyroidism and post-menopausal period
• Controlled by systemic hormones and PTH

Question 6

Describe trabecular bone

Answer 6

• 15% of the skeleton
• Has a larger surface area, spongy
• Bone remodelling occur in environment of narrow cells, cytokines and growth factors

Question 7

What is bone turnover?

Answer 7

A constant process of losing and forming bone, like skin expect that it takes a v long time

Question 8

What are osteoclasts?

Answer 8

• Large, nucleated cells responsible for bone resorption

- Bone resorbing/bone losing cells responsible for the initial action

Question 9

What happens during bone turnover?

Answer 9

1) Under the influence of signals e.g. receptor activator of nuclear factors kappa B-ligand (RANKL), interleukins, PTH, cytokines osteoclasts initiate bone resorption
2) An acidified microenvironment is created between the osteoclast and cell surface causing mobilisation of mineralised content of the bone
3) After osteoclastic resorption and apoptosis, proliferation of osteoblasts (bone forming cells) occur which line these pits, and finally mineralised bone is formed

Question 10

What are markers of bone turnover?

Answer 10

This is a dynamic process, so during bone turnover products are released/excreted which are used to assess bone turnover which is constant

Question 11

What are bone resorption markers?

Answer 11

Markers obtained when the bone is actively being lost

Question 12

What are examples of urine bone resorption markers?

Answer 12

1) Hydroxyproline
2) C telopeptide of type 1 collagen (CTX)
3) N telopeptide of type 1 collagen (NTX)
- Have a reference range depending on age and gender

Question 13

Why are C/N telopeptide of type 1 collagen markers of bone resorption?

Answer 13

Type 1 collagen is the predominant protein of the bone and during bone turnover it is cleaved and excreted in urine and serum

Question 14

What are examples of serum bone resorption markers?

Answer 14

1) C telopeptide of type 1 collagen (CTX)

2) N telopeptide of type 1 collagen (NTX)

Question 15

What are bone formation markers?

Answer 15

Substances produced when osteoblasts cause bone formation

Question 16

What are examples of serum bone formation markers?

Answer 16

1) Bone specific alkaline phosphatase (BALP)
2) Osteocalcin
3) P1CP/P1NP (pro-collagen)