1. Physiology of Bone Remodeling Outcomes
Compare and contrast the function of osteoblasts and osteoclasts during bone growth, repair, and remodeling.
2. Explain the roles of calcitonin, parathyroid hormone and calcitriol in bone remodeling and blood calcium regulation.
3. Contrast the remodeling processes of a child (birth to adolescence) and an adult (middle to old age).
From: HAPS learning Outcomes Module F

2. Technical Requirements
Flash Player
Can be downloaded for free at the following URL

3. Types of Bone Cells Osteocytes Osteoclasts
Sense mechanical strain, to direct osteoclast and osteoblast activity
Derived from osteoblasts that develop into osteocytes while the bone is being formed
Are connected to each other through long fingerlike extensions
Osteoclasts
Dissolve and resorb bone
Large multi-nucleated cells
Derived from bone marrow and related to white blood cells

4. Types of Bone Cells Cont.
Osteoblasts
Refill cavity from osteoclast with secretion called osteoid
Catalyze the mineralization of osteoid
Become lining cells when finished filling a cavity
Derived from bone marrow and related to structural cells
Lining Cells
Cover bone not undergoing bone remodeling
Regulate movement of calcium into and out of bone
Removal of these cells necessary for osteoclasts to resorb bone

6. Bone Remodeling Sequence
Video courtesy of Dr Susan Ott, from website:
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7. So what does bone remodeling look like?
Photo courtesy of Dr Susan Ott, From:

8. Normal Bone Turnover
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9. Estrogen Deficient Bone Turnover
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10. Why is bone remodeling important to study?
Osteoporosis, or porous bone, is a disease characterized by low bone mass and structural deterioration of bone tissue, leading to bone fragility and an increased susceptibility to fractures especially of the hip, spine and wrist.
Normal Bone Osteoporotic bone
Reprinted from Dempster, DW et al. J Bone and Mineral Research 1986: 1:15-21

11. Risk Factors Factors you cannot change: Factors you can change: Gender
Age
Body Size
Ethnicity
Family history
Factors you can change:
Sex hormone levels
Anorexia
A diet low in calcium and vitamin D
Use of certain medicines, such as glucocorticoids or some anticonvulsants
An inactive lifestyle
Cigarette smoking
Excessive use of alcohol

12. Bone Mass Changes with Age in Females
(Wasnich RD et al.  Osteoporosis:  critique and practicum.  Honolulu:  Banyan Press; 1989: )

13. Bone Density Decreases in Men and Women
(expressed as percent control
of peak bone mass)
Gambert SR, Schultz BM, Hamdy RC.  Osteoporosis:  clinical features, prevention,
and treatment.  Endocrinol Metab Clin North Am.  1995;    24:317-71

14. Thinking Question Can men develop osteoporosis?
See webct discussion forum for help
Can men develop osteoporosis?
What approximate years of life are osteoblasts most active?

15. Hormonal Regulation of Calcium
Why is the body so concerned about blood calcium levels?
Many Reasons!
Calcium is very important for many cell signaling events
It is necessary for:
Nerve signaling
Coagulation
Secretion by neurons and glands
Cell division
Muscle contraction

16. If the blood calcium levels are low…
Parathyroid gland
(located on posterior
Of thyroid gland)
Parathyroid hormone (PTH)
Osteoclasts degrade
Bone matrix
Release Calcium into the bloodstream
Raising Calcium levels

17. If blood calcium levels are high…
Thyroid gland
Calcitonin
Stimulates Calcium deposits
In bone
Thus lowering blood calcium levels

18. Calcitrol Active form of Vitamin D
Release is stimulated by high PTH levels and low blood calcium and phosphate levels
Inhibits calcitonin release and increases absorption of calcium and phosphate in the GI tract and reabsorption of calcium in the kidneys

19. Thinking Questions
See webct discussion forum for help
One problem with extended duration space travel is that while astronauts are in space their bone density decreases. Thinking about what you have learned about bone cells, which cells could be causing this bone loss?
What hormone would you want to use to treat an osteoporotic patient?