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Week 47: Osteoporosis > Bone Homeostasis > Flashcards

Flashcards in Bone Homeostasis Deck (10)
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1

How long does
1. Resorption
2. Formation
take?

1. ~3 weeks to dig resorption pit
2. ~3-4 months for osteoid to fill in pit, mineralization takes years

2

2 kinds of remodelling in cortical bone

Haversian remodelling
Periosteal apposition

3

Haversian remodelling

Within cortical bone
Very slow (concentric)
Osteoclasts in the cutting cone, blasts in the closing cone
Leaves a Haversian canal (clear trace)
Mineralization increases slowly

4

Periosteal apposition

Cortical surface
No initial bone resorption
Triggered by mechanical strains (exercise)
Associated with endosteal resorption
Continues into old age

5

Sclerostin

Secreted by osteocytes
Decreases bone formation

6

When bone remodeling is increases does bone loss or formation dominate?

Bone loss
Because it is faster

7

Calcitonin

Inhibits osteoclasts
Decreases resorption and increases formation

8

Estrogen, progesterone and testosterone effects on bone

Estrogen: decreases resorption in women and men
Progesterone: increase formation in women
Testosterone: decreases resorption and increases formation in men
An acute decrease in estrogen and testosterone result in increased resorption though

9

Effects of higher than physiological levels of cortisol

Increase resorption
Decrease formation

10

PTH effect on bone

Hourly or continuous exposure (like in hyperparathyroidism): increases resorption
Intermittent dosing (as a therapy): increases formation