Bone Remodeling

Bone Remodeling

• Bones are remodeled continually– Means that they are broken down, built back up,

change in shape, etc• Bone remodeling is in response to 2 factors:– Calcium levels in the blood– The pull of gravity and muscles

Bone Remodeling: Calcium Levels• When calcium levels drop

below homeostatic levels, your parathyroid gland releases parathyroid hormone (PTH)– This stimulates osteoclasts to

break down bone to release calcium in the blood

• When calcium levels are too high, calcium is deposited in the bone

• This is how bones are storage organs!!

Bone Remodeling: Gravity and Muscles

• The more weight-bearing exercises you do, the stronger your bones will be– This causes an increase in bone size

• Bedridden patients and astronauts suffer from bone mass/atrophy from lack of stress on their bones

Balance• There is a balance between

osteoclasts and osteoblasts• Predict:– What would happen if the

osteoblasts were too good at their job?• Melorheostosis (remember

this??)– What would happen if the

osteoclasts were too good at their job?

Gorham’s Disease

• “Vanishing Bone Disease”• Osteoclasts are overproductive and bones are

broken down faster than they are built• http://www.youtube.com/watch?v=lHN3Qwb

m86Q