The Bone Remodelling Cycle

Question 1

What are the four stages of the bone remodelling cycle?

Answer 1

Quiescence
Resorption
Retraction
Formation

Question 2

Describe the resorption stage of bone remodelling.

Answer 2

Osteoclasts bind to extracellular proteins via their integrin receptors and form a resorption compartment in which the ruffled border secretes hydrogen ions and proteolytic enzymes to dissolve the mineralised bone.

Question 3

Following resorption, what happens to osteoclasts?

Answer 3

They undergo apoptosis and are replaced by osteoblasts to lay down new bone

Question 4

What are the main factors which control osteoblastic proliferation and differentiation?

Answer 4

PTH

Wnt

Question 5

The transition from mesenchymal stem cell to preosteoblast is assisted by…?

Answer 5

BMP 2

BMP 7

Question 6

The differentiation of a preosteoblast into an osteoblast follows which pathway?

Answer 6

cbfa1

Question 7

Which factors mainly regulate osteoclast formation and activity?

Answer 7

Oestrogen
Vitamin D
TNF-alpha

Question 8

Describe the role of osteoblasts in maturation of osteoclasts.

Answer 8

The binding of RANKL which is secreted by osteoblasts to its receptor RANK on the osteoclast precursor will promote differentiation into a mature osteoclast by activating the precursor cell to undergo fusion to create a multi-nucleated cell which will mature into a osteoclast

Question 9

Describe the role of OPG in osteoclast differentiate.

Answer 9

OPG can be secreted by osteoblasts upon oestrogen stimulation and is a decoy receptor for the RANKL and so will prevent RANKL binding to the precursor of the osteoclast to prevent osteoclast differentiation

Question 10

Which cells secrete sclerostin which inhibits Wnt signalling in cells on the surface of bone to inhibit bone formation by osteoblasts?

Answer 10

Osteocytes

Question 11

What is sclerostin production inhibited by?

Answer 11

PTH