Bone tissue remodelling Flashcards
Bone tissue is constantly remodelled
TRUE or FALSE
TRUE
Old bone is resorbed and new bone is deposited
What triggers constant bone tissue remodelling?
Microdamage
External mechanical cues - bone mass is controlled by mechanical forces like gravity/weight
Serum calcium-homeostasis requirements
What surface molecule do osteoblasts express?
RANKL
What does RANKL stand for?
Receptor activator of NF-kB LIgand
What are two mechanisms by which bone tissue remodelling is kept at homeostatic levels?
Coupling hypothesis
Limiting osteoclastogenesis
What is coupling hypothesis?
The coupling of the number of active osteoclasts with the number of active osteoblasts
Keeps a balance
How does limiting osteoclastogenesis work?
Osteoblasts secrete the soluble antagonist osteoprotegerin (OPG)
Masks RANKL
Blocks RANK from binding
Limits osteoclastogenesis
Which cells express RANK on their surface?
Osteoclasts
What does the RANK-RANKL binding do?
Mediates osteoclast maturation and activation
What controls the expression of RANKL and OPG in osteoblasts?
Additional signaling molecules and hormones
What are 3 hormones that inflluence the release of stored calcium
Parathyroid - increases serum calcium levels
Calcitonin - decreases serum calcium levels
Calcitrol - increase serum calcium levels
What process causes release of stored calcium?
Bone resorption
How does parathyroid hormone increase calcium release from bone?
PTH receptor in osteoblasts
Increase RANKL expression
Decrease OPG secretion
Activates osteoclastogenesis indirectly
Increases calcium concentration in blood
Characteristics of PTH
Secreted by parathyroid hormone
Short half-life
Rapid response
How does calcitonin decrease calcium release from bone?
Inhibits osteoclasts directly
Antagonises PTH effects
